time and travelling at light speed

Why does time change when traveling close to the speed of light? A physicist explains

Assistant Professor of Physics and Astronomy, Rochester Institute of Technology

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Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to [email protected] .

Why does time change when traveling close to the speed of light? – Timothy, age 11, Shoreview, Minnesota

Imagine you’re in a car driving across the country watching the landscape. A tree in the distance gets closer to your car, passes right by you, then moves off again in the distance behind you.

Of course, you know that tree isn’t actually getting up and walking toward or away from you. It’s you in the car who’s moving toward the tree. The tree is moving only in comparison, or relative, to you – that’s what we physicists call relativity . If you had a friend standing by the tree, they would see you moving toward them at the same speed that you see them moving toward you.

In his 1632 book “ Dialogue Concerning the Two Chief World Systems ,” the astronomer Galileo Galilei first described the principle of relativity – the idea that the universe should behave the same way at all times, even if two people experience an event differently because one is moving in respect to the other.

If you are in a car and toss a ball up in the air, the physical laws acting on it, such as the force of gravity, should be the same as the ones acting on an observer watching from the side of the road. However, while you see the ball as moving up and back down, someone on the side of the road will see it moving toward or away from them as well as up and down.

Special relativity and the speed of light

Albert Einstein much later proposed the idea of what’s now known as special relativity to explain some confusing observations that didn’t have an intuitive explanation at the time. Einstein used the work of many physicists and astronomers in the late 1800s to put together his theory in 1905, starting with two key ingredients: the principle of relativity and the strange observation that the speed of light is the same for every observer and nothing can move faster. Everyone measuring the speed of light will get the same result, no matter where they are or how fast they are moving.

Let’s say you’re in the car driving at 60 miles per hour and your friend is standing by the tree. When they throw a ball toward you at a speed of what they perceive to be 60 miles per hour, you might logically think that you would observe your friend and the tree moving toward you at 60 miles per hour and the ball moving toward you at 120 miles per hour. While that’s really close to the correct value, it’s actually slightly wrong.

This discrepancy between what you might expect by adding the two numbers and the true answer grows as one or both of you move closer to the speed of light. If you were traveling in a rocket moving at 75% of the speed of light and your friend throws the ball at the same speed, you would not see the ball moving toward you at 150% of the speed of light. This is because nothing can move faster than light – the ball would still appear to be moving toward you at less than the speed of light. While this all may seem very strange, there is lots of experimental evidence to back up these observations.

Time dilation and the twin paradox

Speed is not the only factor that changes relative to who is making the observation. Another consequence of relativity is the concept of time dilation , whereby people measure different amounts of time passing depending on how fast they move relative to one another.

Each person experiences time normally relative to themselves. But the person moving faster experiences less time passing for them than the person moving slower. It’s only when they reconnect and compare their watches that they realize that one watch says less time has passed while the other says more.

This leads to one of the strangest results of relativity – the twin paradox , which says that if one of a pair of twins makes a trip into space on a high-speed rocket, they will return to Earth to find their twin has aged faster than they have. It’s important to note that time behaves “normally” as perceived by each twin (exactly as you are experiencing time now), even if their measurements disagree.

You might be wondering: If each twin sees themselves as stationary and the other as moving toward them, wouldn’t they each measure the other as aging faster? The answer is no, because they can’t both be older relative to the other twin.

The twin on the spaceship is not only moving at a particular speed where the frame of references stay the same but also accelerating compared with the twin on Earth. Unlike speeds that are relative to the observer, accelerations are absolute. If you step on a scale, the weight you are measuring is actually your acceleration due to gravity. This measurement stays the same regardless of the speed at which the Earth is moving through the solar system, or the solar system is moving through the galaxy or the galaxy through the universe.

Neither twin experiences any strangeness with their watches as one moves closer to the speed of light – they both experience time as normally as you or I do. It’s only when they meet up and compare their observations that they will see a difference – one that is perfectly defined by the mathematics of relativity.

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Would you really age more slowly on a spaceship at close to light speed?

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Every week, the readers of our space newsletter, The Airlock , send in their questions for space reporter Neel V. Patel to answer. This week: time dilation during space travel. 

I heard that time dilation affects high-speed space travel and I am wondering the magnitude of that affect. If we were to launch a round-trip flight to a nearby exoplanet—let's say 10 or 50 light-years away––how would that affect time for humans on the spaceship versus humans on Earth? When the space travelers came back, will they be much younger or older relative to people who stayed on Earth? —Serge

Time dilation is a concept that pops up in lots of sci-fi, including Orson Scott Card’s Ender’s Game , where one character ages only eight years in space while 50 years pass on Earth. This is precisely the scenario outlined in the famous thought experiment the Twin Paradox : an astronaut with an identical twin at mission control makes a journey into space on a high-speed rocket and returns home to find that the twin has aged faster.

Time dilation goes back to Einstein’s theory of special relativity, which teaches us that motion through space actually creates alterations in the flow of time. The faster you move through the three dimensions that define physical space, the more slowly you’re moving through the fourth dimension, time––at least relative to another object. Time is measured differently for the twin who moved through space and the twin who stayed on Earth. The clock in motion will tick more slowly than the clocks we’re watching on Earth. If you’re able to travel near the speed of light, the effects are much more pronounced. 

Unlike the Twin Paradox, time dilation isn’t a thought experiment or a hypothetical concept––it’s real. The 1971 Hafele-Keating experiments proved as much, when two atomic clocks were flown on planes traveling in opposite directions. The relative motion actually had a measurable impact and created a time difference between the two clocks. This has also been confirmed in other physics experiments (e.g., fast-moving muon particles take longer to decay ). 

So in your question, an astronaut returning from a space journey at “relativistic speeds” (where the effects of relativity start to manifest—generally at least one-tenth the speed of light ) would, upon return, be younger than same-age friends and family who stayed on Earth. Exactly how much younger depends on exactly how fast the spacecraft had been moving and accelerating, so it’s not something we can readily answer. But if you’re trying to reach an exoplanet 10 to 50 light-years away and still make it home before you yourself die of old age, you’d have to be moving at close to light speed. 

There’s another wrinkle here worth mentioning: time dilation as a result of gravitational effects. You might have seen Christopher Nolan’s movie Interstellar , where the close proximity of a black hole causes time on another planet to slow down tremendously (one hour on that planet is seven Earth years).

This form of time dilation is also real, and it’s because in Einstein’s theory of general relativity, gravity can bend spacetime, and therefore time itself. The closer the clock is to the source of gravitation, the slower time passes; the farther away the clock is from gravity, the faster time will pass. (We can save the details of that explanation for a future Airlock.)

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Is Time Travel Possible?

We all travel in time! We travel one year in time between birthdays, for example. And we are all traveling in time at approximately the same speed: 1 second per second.

We typically experience time at one second per second. Credit: NASA/JPL-Caltech

NASA's space telescopes also give us a way to look back in time. Telescopes help us see stars and galaxies that are very far away . It takes a long time for the light from faraway galaxies to reach us. So, when we look into the sky with a telescope, we are seeing what those stars and galaxies looked like a very long time ago.

However, when we think of the phrase "time travel," we are usually thinking of traveling faster than 1 second per second. That kind of time travel sounds like something you'd only see in movies or science fiction books. Could it be real? Science says yes!

This image from the Hubble Space Telescope shows galaxies that are very far away as they existed a very long time ago. Credit: NASA, ESA and R. Thompson (Univ. Arizona)

How do we know that time travel is possible?

More than 100 years ago, a famous scientist named Albert Einstein came up with an idea about how time works. He called it relativity. This theory says that time and space are linked together. Einstein also said our universe has a speed limit: nothing can travel faster than the speed of light (186,000 miles per second).

Einstein's theory of relativity says that space and time are linked together. Credit: NASA/JPL-Caltech

What does this mean for time travel? Well, according to this theory, the faster you travel, the slower you experience time. Scientists have done some experiments to show that this is true.

For example, there was an experiment that used two clocks set to the exact same time. One clock stayed on Earth, while the other flew in an airplane (going in the same direction Earth rotates).

After the airplane flew around the world, scientists compared the two clocks. The clock on the fast-moving airplane was slightly behind the clock on the ground. So, the clock on the airplane was traveling slightly slower in time than 1 second per second.

Credit: NASA/JPL-Caltech

Can we use time travel in everyday life?

We can't use a time machine to travel hundreds of years into the past or future. That kind of time travel only happens in books and movies. But the math of time travel does affect the things we use every day.

For example, we use GPS satellites to help us figure out how to get to new places. (Check out our video about how GPS satellites work .) NASA scientists also use a high-accuracy version of GPS to keep track of where satellites are in space. But did you know that GPS relies on time-travel calculations to help you get around town?

GPS satellites orbit around Earth very quickly at about 8,700 miles (14,000 kilometers) per hour. This slows down GPS satellite clocks by a small fraction of a second (similar to the airplane example above).

GPS satellites orbit around Earth at about 8,700 miles (14,000 kilometers) per hour. Credit: GPS.gov

However, the satellites are also orbiting Earth about 12,550 miles (20,200 km) above the surface. This actually speeds up GPS satellite clocks by a slighter larger fraction of a second.

Here's how: Einstein's theory also says that gravity curves space and time, causing the passage of time to slow down. High up where the satellites orbit, Earth's gravity is much weaker. This causes the clocks on GPS satellites to run faster than clocks on the ground.

The combined result is that the clocks on GPS satellites experience time at a rate slightly faster than 1 second per second. Luckily, scientists can use math to correct these differences in time.

If scientists didn't correct the GPS clocks, there would be big problems. GPS satellites wouldn't be able to correctly calculate their position or yours. The errors would add up to a few miles each day, which is a big deal. GPS maps might think your home is nowhere near where it actually is!

In Summary:

Yes, time travel is indeed a real thing. But it's not quite what you've probably seen in the movies. Under certain conditions, it is possible to experience time passing at a different rate than 1 second per second. And there are important reasons why we need to understand this real-world form of time travel.

If you liked this, you may like:

Why is the speed of light the way it is?

It's just plain weird.

Paul M. Sutter is an astrophysicist at SUNY Stony Brook and the Flatiron Institute, host of Ask a Spaceman and Space Radio , and author of " How to Die in Space ." He contributed this article to Space.com's Expert Voices: Op-Ed & Insights . 

We all know and love the speed of light — 299,792,458 meters per second — but why does it have the value that it does? Why isn't it some other number? And why do we care so much about some random speed of electromagnetic waves? Why did it become such a cornerstone of physics? 

Well, it's because the speed of light is just plain weird.

Related: Constant speed of light: Einstein's special relativity survives a high-energy test

Putting light to the test

The first person to realize that light does indeed have a speed at all was an astronomer by the name of Ole Romer. In the late 1600s, he was obsessed with some strange motions of the moon Io around Jupiter. Every once in a while, the great planet would block our view of its little moon, causing an eclipse, but the timing between eclipses seemed to change over the course of the year. Either something funky was happening with the orbit of Io — which seemed suspicious — or something else was afoot.

After a couple years of observations, Romer made the connection. When we see Io get eclipsed, we're in a certain position in our own orbit around the sun. But by the next time we see another eclipse, a few days later, we're in a slightly different position, maybe closer or farther away from Jupiter than the last time. If we are farther away than the last time we saw an eclipse, then that means we have to wait a little bit of extra time to see the next one because it takes that much longer for the light to reach us, and the reverse is true if we happen to be a little bit closer to Jupiter.

The only way to explain the variations in the timing of eclipses of Io is if light has a finite speed.

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Making it mean something

Continued measurements over the course of the next few centuries solidified the measurement of the speed of light, but it wasn't until the mid-1800s when things really started to come together. That's when the physicist James Clerk Maxwell accidentally invented light.

Maxwell had been playing around with the then-poorly-understood phenomena of electricity and magnetism when he discovered a single unified picture that could explain all the disparate observations. Laying the groundwork for what we now understand to be the electromagnetic force , in those equations he discovered that changing electric fields can create magnetic fields, and vice versa. This allows waves of electricity to create waves of magnetism, which go on to make waves of electricity and back and forth and back and forth, leapfrogging over each other, capable of traveling through space.

And when he went to calculate the speed of these so-called electromagnetic waves, Maxwell got the same number that scientists had been measuring as the speed of light for centuries. Ergo, light is made of electromagnetic waves and it travels at that speed, because that is exactly how quickly waves of electricity and magnetism travel through space.

And this was all well and good until Einstein came along a few decades later and realized that the speed of light had nothing to do with light at all. With his special theory of relativity , Einstein realized the true connection between time and space, a unified fabric known as space-time. But as we all know, space is very different than time. A meter or a foot is very different than a second or a year. They appear to be two completely different things.

So how could they possibly be on the same footing?

There needed to be some sort of glue, some connection that allowed us to translate between movement in space and movement in time. In other words, we need to know how much one meter of space, for example, is worth in time. What's the exchange rate? Einstein found that there was a single constant, a certain speed, that could tell us how much space was equivalent to how much time, and vice versa.

Einstein's theories didn't say what that number was, but then he applied special relativity to the old equations of Maxwell and found that this conversion rate is exactly the speed of light.

Of course, this conversion rate, this fundamental constant that unifies space and time, doesn't know what an electromagnetic wave is, and it doesn't even really care. It's just some number, but it turns out that Maxwell had already calculated this number and discovered it without even knowing it. That's because all massless particles are able to travel at this speed, and since light is massless, it can travel at that speed. And so, the speed of light became an important cornerstone of modern physics.

But still, why that number, with that value, and not some other random number? Why did nature pick that one and no other? What's going on?

Related: The genius of Albert Einstein: his life, theories and impact on science

Making it meaningless

Well, the number doesn't really matter. It has units after all: meters per second. And in physics any number that has units attached to it can have any old value it wants, because it means you have to define what the units are. For example, in order to express the speed of light in meters per second, first you need to decide what the heck a meter is and what the heck a second is. And so the definition of the speed of light is tied up with the definitions of length and time.

In physics, we're more concerned with constants that have no units or dimensions — in other words, constants that appear in our physical theories that are just plain numbers. These appear much more fundamental, because they don't depend on any other definition. Another way of saying it is that, if we were to meet some alien civilization , we would have no way of understanding their measurement of the speed of light, but when it comes to dimensionless constants, we can all agree. They're just numbers.

One such number is known as the fine structure constant, which is a combination of the speed of light, Planck's constant , and something known as the permittivity of free space. Its value is approximately 0.007. 0.007 what? Just 0.007. Like I said, it's just a number.

So on one hand, the speed of light can be whatever it wants to be, because it has units and we need to define the units. But on the other hand, the speed of light can't be anything other than exactly what it is, because if you were to change the speed of light, you would change the fine structure constant. But our universe has chosen the fine structure constant to be approximately 0.007, and nothing else. That is simply the universe we live in, and we get no choice about it at all. And since this is fixed and universal, the speed of light has to be exactly what it is.

So why is the fine structure constant exactly the number that it is, and not something else? Good question. We don't know.

Learn more by listening to the episode "Why is the speed of light the way it is?" on the Ask A Spaceman podcast, available on iTunes and on the Web at http://www.askaspaceman.com. Thanks to Robert H, Michael E., @DesRon94, Evan W., Harry A., @twdixon, Hein P., Colin E., and Lothian53 for the questions that led to this piece! Ask your own question on Twitter using #AskASpaceman or by following Paul @PaulMattSutter and facebook.com/PaulMattSutter.

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected].

Paul M. Sutter is an astrophysicist at SUNY Stony Brook and the Flatiron Institute in New York City. Paul received his PhD in Physics from the University of Illinois at Urbana-Champaign in 2011, and spent three years at the Paris Institute of Astrophysics, followed by a research fellowship in Trieste, Italy, His research focuses on many diverse topics, from the emptiest regions of the universe to the earliest moments of the Big Bang to the hunt for the first stars. As an "Agent to the Stars," Paul has passionately engaged the public in science outreach for several years. He is the host of the popular "Ask a Spaceman!" podcast, author of "Your Place in the Universe" and "How to Die in Space" and he frequently appears on TV — including on The Weather Channel, for which he serves as Official Space Specialist.

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• voidpotentialenergy This is just my opinion but i think L speed is it's speed because the particle part of it is the fastest it can interact with the quanta distance in quantum fluctuation. Light is particle and wave so the wave happens in the void between quanta. Gravity probably travels in that void and why gravity seems instant. Reply
• rod The space.com article wraps up the discussion with, "So on one hand, the speed of light can be whatever it wants to be, because it has units and we need to define the units. But on the other hand, the speed of light can't be anything other than exactly what it is, because if you were to change the speed of light, you would change the fine structure constant. But our universe has chosen the fine structure constant to be approximately 0.007, and nothing else. That is simply the universe we live in, and we get no choice about it at all. And since this is fixed and universal, the speed of light has to be exactly what it is. So why is the fine structure constant exactly the number that it is, and not something else? Good question. We don't know." It seems that the *universe* made this decision, *But our universe has chosen the fine structure constant to be...* I did not know that the universe was capable of making decisions concerning constants used in physics. E=mc^2 is a serious constant. Look at nuclear weapons development, explosive yields, and stellar evolution burn rates for p-p chain and CNO fusion rates. The report indicates why alpha (fine structure constant) is what it is and c is what it is, *We don't know*. Reply

Admin said: We all know and love the speed of light, but why does it have the value that it does? Why isn't it some other number? And why did it become such a cornerstone of physics? Why is the speed of light the way it is? : Read more

rod said: The space.com article wraps up the discussion with, "So on one hand, the speed of light can be whatever it wants to be, because it has units and we need to define the units. But on the other hand, the speed of light can't be anything other than exactly what it is, because if you were to change the speed of light, you would change the fine structure constant. But our universe has chosen the fine structure constant to be approximately 0.007, and nothing else. That is simply the universe we live in, and we get no choice about it at all. And since this is fixed and universal, the speed of light has to be exactly what it is. So why is the fine structure constant exactly the number that it is, and not something else? Good question. We don't know." It seems that the *universe* made this decision, *But our universe has chosen the fine structure constant to be...* I did not know that the universe was capable of making decisions concerning constants used in physics. E=mc^2 is a serious constant. Look at nuclear weapons development, explosive yields, and stellar evolution burn rates for p-p chain and CNO fusion rates. The report indicates why alpha (fine structure constant) is what it is and c is what it is, *We don't know*.

• rod FYI. When someone says *the universe has chosen*, I am reminded of these five lessons from a 1982 Fed. court trial. The essential characteristics of science are: It is guided by natural law; It has to be explanatory by reference to natural law; It is testable against the empirical world; Its conclusions are tentative, i.e., are not necessarily the final word; and It is falsifiable. Five important points about science. Reply
• Gary If the universe is expanding , how can the speed of light be constant ( miles per second , if each mile is getting longer ) ? Can light's velocity be constant while the universe expands ? So, with the expansion of the universe , doesn't the speed of light need to increase in order to stay at a constant velocity in miles per second ? Or, do the miles in the universe remain the same length as the universe 'adds' miles to its diameter ? Are the miles lengthening or are they simply being added / compounded ? Reply
• Gary Lets say we're in outer space and we shoot a laser through a block of glass. What causes the speed of the laser light to return to the speed it held prior to entering the block of glass ? Is there some medium in the vacuum of space that governs the speed of light ? Do the atoms in the glass push it back up to its original speed. If so, why don't those same atoms constantly push the light while it travels through the block of glass ? Reply

Gary said: Lets say we're in outer space and we shoot a laser through a block of glass. What causes the speed of the laser light to return to the speed it held prior to entering the block of glass ? Is there some medium in the vacuum of space that governs the speed of light ? Do the atoms in the glass push it back up to its original speed. If so, why don't those same atoms constantly push the light while it travels through the block of glass ?

Gary said: If the universe is expanding , how can the speed of light be constant ( miles per second , if each mile is getting longer ) ? Can light's velocity be constant while the universe expands ? So, with the expansion of the universe , doesn't the speed of light need to increase in order to stay at a constant velocity in miles per second ? Or, do the miles in the universe remain the same length as the universe 'adds' miles to its diameter ? Are the miles lengthening or are they simply being added / compounded ?

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Here's What Actually Happens When You Travel at the Speed of Light, According to NASA

NASA created a fun video to answer all of our burning questions about near-light-speed travel.

Ever wish you could travel at the speed of light to your favorite destinations ? Once you see the reality of that speed, you may rethink everything.

"There are some important things you should probably know about approaching the speed of light," NASA's video, Guide to Near-light-speed Travel , explains. "First, a lot of weird things can happen, like time and space getting all bent out of shape."

According to the video, if you're traveling at nearly the speed of light, the clock inside your rocket would show it takes less time to travel to your destination than it would on Earth. But, since the clocks at home would be moving at a standard rate you'd return home to everyone else being quite a bit older.

"Also, because you're going so fast, what would otherwise be just a few hydrogen atoms that you'd run into quickly becomes a lot of dangerous particles. So you should probably have shields that keep them from frying your ship and also you."

Finally, the video tackles the fact that even if you were moving at the speed of light, the "universe is also a very big place, so you might be in for some surprises." For example, your rocket's clock will say it takes about nine months to get from Earth to the edge of the solar system. An Earth clock would say it took about a year and a half. Fortunately, NASA astronauts have a slew of tips for avoiding jet lag along the way.

"If you want to get to farther out vacation spots," the video explains, "you'll probably need more than a few extra snacks. A trip to the Andromeda Galaxy, our nearest large neighbor galaxy, can take over one million years. And a trip to the farthest known galaxy where it currently sits might take over 15 billion years, which is more vacation time than I think I'll ever have."

The video doesn't explain how your rocket will travel at the speed of light. Our technology just isn't there yet, but maybe the aliens will share that tech with us soon. Until then, you can track the first crew launch of Artemis II , a rocket that will fly around the moon in 2024 before making its first lunar landing in 2025.

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May 8, 2014

Does light experience time?

by Fraser Cain, Universe Today

Have you ever noticed that time flies when you're having fun? Well, not for light. In fact, photons don't experience any time at all. Here's a mind-bending concept that should shatter your brain into pieces.

As you might know, I co-host Astronomy Cast, and get to pick the brain of the brilliant astrophysicist Dr. Pamela Gay every week about whatever crazy thing I think of in the shower. We were talking about photons one week and she dropped a bombshell on my brain. Photons do not experience time . [SNARK: Are you worried they might get bored?]

Just think about that idea. From the perspective of a photon, there is no such thing as time. It's emitted, and might exist for hundreds of trillions of years, but for the photon, there's zero time elapsed between when it's emitted and when it's absorbed again. It doesn't experience distance either. [SNARK: Clearly, it didn't need to borrow my copy of GQ for the trip.]

Since photons can't think, we don't have to worry too much about their existential horror of experiencing neither time nor distance, but it tells us so much about how they're linked together. Through his Theory of Relativity, Einstein helped us understand how time and distance are connected.

Let's do a quick review. If we want to travel to some distant point in space, and we travel faster and faster, approaching the speed of light our clocks slow down relative to an observer back on Earth. And yet, we reach our destination more quickly than we would expect. Sure, our mass goes up and there are enormous amounts of energy required, but for this example, we'll just ignore all that.

If you could travel at a constant acceleration of 1 g, you could cross billions of light years in a single human generation. Of course, your friends back home would have experienced billions of years in your absence, but much like the mass increase and energy required, we won't worry about them.

The closer you get to light speed , the less time you experience and the shorter a distance you experience. You may recall that these numbers begin to approach zero. According to relativity, mass can never move through the Universe at light speed. Mass will increase to infinity, and the amount of energy required to move it any faster will also be infinite. But for light itself, which is already moving at light speed… You guessed it, the photons reach zero distance and zero time.

Photons can take hundreds of thousands of years to travel from the core of the Sun until they reach the surface and fly off into space. And yet, that final journey, that could take it billions of light years across space, was no different from jumping from atom to atom.

Source: Universe Today

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25 Questions (and Answers!) About the Great North American Eclipse

The McDonald Observatory’s guide to one of nature’s most beautiful and astounding events: What you might see, how to view it safely, how astronomers will study it, how animals might react, and some of the mythology and superstitions about the Sun’s great disappearing act.

1. What’s happening?

The Moon will cross directly between Earth and the Sun, temporarily blocking the Sun from view along a narrow path across Mexico, the United States, and Canada. Viewers across the rest of the United States will see a partial eclipse, with the Moon covering only part of the Sun’s disk.

2. When will it happen?

The eclipse takes place on April 8. It will get underway at 10:42 a.m. CDT, when the Moon’s shadow first touches Earth’s surface, creating a partial eclipse. The Big Show—totality—begins at about 11:39 a.m., over the south-central Pacific Ocean. The shadow will first touch North America an hour and a half later, on the Pacific coast of Mexico. Moving at more than 1,600 miles (2,575 km) per hour, the path of totality will enter the United States at Eagle Pass, Texas, at 1:27 p.m. CDT. The lunar shadow will exit the United States and enter the Canadian province of New Brunswick near Houlton, Maine, at 2:35 p.m. (3:35 p.m. EDT).

3. How long will totality last?

The exact timing depends on your location. The maximum length is 4 minutes, 27 seconds near Torreon, Mexico. In the United States, several towns in southwestern Texas will see 4 minutes, 24 seconds of totality. The closer a location is to the centerline of the path of totality, the longer the eclipse will last.

4. What will it look like?

Eclipse veterans say there’s nothing quite like a total solar eclipse. In the last moments before the Sun disappears behind the Moon, bits of sunlight filter through the lunar mountains and canyons, forming bright points of light known as Baily’s beads. The last of the beads provides a brief blaze known as a diamond ring effect. When it fades away, the sky turns dark and the corona comes into view— million-degree plasma expelled from the Sun’s surface. It forms silvery filaments that radiate away from the Sun. Solar prominences, which are fountains of gas from the surface, form smaller, redder streamers on the rim of the Sun’s disk.

5. What safety precautions do I need to take?

It’s perfectly safe to look at the total phase of the eclipse with your eyes alone. In fact, experts say it’s the best way to enjoy the spectacle. The corona, which surrounds the intervening Moon with silvery tendrils of light, is only about as bright as a full Moon.

During the partial phases of the eclipse, however, including the final moments before and first moments after totality, your eyes need protection from the Sun’s blinding light. Even a 99-percent-eclipsed Sun is thousands of times brighter than a full Moon, so even a tiny sliver of direct sunlight can be dangerous!

To stay safe, use commercially available eclipse viewers, which can look like eyeglasses or can be embedded in a flat sheet that you hold in front of your face. Make sure your viewer meets the proper safety standards, and inspect it before you use it to make sure there are no scratches to let in unfiltered sunlight.

You also can view the eclipse through a piece of welder’s glass (No. 14 or darker), or stand under a leafy tree and look at the ground; the gaps between leaves act as lenses, projecting a view of the eclipse on the ground. With an especially leafy tree you can see hundreds of images of the eclipse at once. (You can also use a colander or similar piece of gear to create the same effect.)

One final mode of eclipse watching is with a pinhole camera. You can make one by poking a small hole in an index card, file folder, or piece of stiff cardboard. Let the Sun shine through the hole onto the ground or a piece of paper, but don’t look at the Sun through the hole! The hole projects an image of the eclipsed Sun, allowing you to follow the entire sequence, from the moment of first contact through the Moon’s disappearance hours later.

6. Where can I see the eclipse?

In the United States, the path of totality will extend from Eagle Pass, Texas, to Houlton, Maine. It will cross 15 states: Texas, Oklahoma, Arkansas, Missouri, Illinois, Indiana, Kentucky, Ohio, Pennsylvania, New York, Vermont, New Hampshire, Maine, Tennessee, and Michigan (although it barely nicks the last two).

In Texas, the eclipse will darken the sky over Austin, Waco, and Dallas—the most populous city in the path, where totality (the period when the Sun is totally eclipsed) will last 3 minutes, 51 seconds.

Other large cities along the path include Little Rock; Indianapolis; Dayton, Toledo, and Cleveland, Ohio; Erie, Pennsylvania; Buffalo and Rochester, New York; and Burlington, Vermont.

Outside the path of totality, American skywatchers will see a partial eclipse, in which the Sun covers only part of the Sun’s disk. The sky will grow dusky and the air will get cooler, but the partially eclipsed Sun is still too bright to look at without proper eye protection. The closer to the path of totality, the greater the extent of the eclipse. From Memphis and Nashville, for example, the Moon will cover more than 95 percent of the Sun’s disk. From Denver and Phoenix, it’s about 65 percent. And for the unlucky skywatchers in Seattle, far to the northwest of the eclipse centerline, it’s a meager 20 percent.

The total eclipse path also crosses Mexico, from the Pacific coast, at Mazatlán, to the Texas border. It also crosses a small portion of Canada, barely including Hamilton, Ontario. Eclipse Details for Locations Around the United States • aa.usno.navy.mil/data/Eclipse2024 • eclipse.aas.org • GreatAmericanEclipse.com

7. What causes solar eclipses?

These awe-inspiring spectacles are the result of a pleasant celestial coincidence: The Sun and Moon appear almost exactly the same size in Earth’s sky. The Sun is actually about 400 times wider than the Moon but it’s also about 400 times farther, so when the new Moon passes directly between Earth and the Sun—an alignment known as syzygy—it can cover the Sun’s disk, blocking it from view.

8. Why don’t we see an eclipse at every new Moon?

The Moon’s orbit around Earth is tilted a bit with respect to the Sun’s path across the sky, known as the ecliptic. Because of that angle, the Moon passes north or south of the Sun most months, so there’s no eclipse. When the geometry is just right, however, the Moon casts its shadow on Earth’s surface, creating a solar eclipse. Not all eclipses are total. The Moon’s distance from Earth varies a bit, as does Earth’s distance from the Sun. If the Moon passes directly between Earth and the Sun when the Moon is at its farthest, we see an annular eclipse, in which a ring of sunlight encircles the Moon. Regardless of the distance, if the SunMoon-Earth alignment is off by a small amount, the Moon can cover only a portion of the Sun’s disk, creating a partial eclipse.

9. How often do solar eclipses happen?

Earth sees as least two solar eclipses per year, and, rarely, as many as five. Only three eclipses per two years are total. In addition, total eclipses are visible only along narrow paths. According to Belgian astronomer Jean Meuss, who specializes in calculating such things, any given place on Earth will see a total solar eclipse, on average, once every 375 years. That number is averaged over many centuries, so the exact gap varies. It might be centuries between succeeding eclipses, or it might be only a few years. A small region of Illinois, Missouri, and Kentucky, close to the southeast of St. Louis, for example, saw the total eclipse of 2017 and will experience this year’s eclipse as well. Overall, though, you don’t want to wait for a total eclipse to come to you. If you have a chance to travel to an eclipse path, take it!

10. What is the limit for the length of totality?

Astronomers have calculated the length of totality for eclipses thousands of years into the future. Their calculations show that the greatest extent of totality will come during the eclipse of July 16, 2186, at 7 minutes, 29 seconds, in the Atlantic Ocean, near the coast of South America. The eclipse will occur when the Moon is near its closest point to Earth, so it appears largest in the sky, and Earth is near its farthest point from the Sun, so the Sun appears smaller than average. That eclipse, by the way, belongs to the same Saros cycle as this year’s.

11. When will the next total eclipse be seen from the United States?

The next total eclipse visible from anywhere in the United States will take place on March 30, 2033, across Alaska. On August 22, 2044, a total eclipse will be visible across parts of Montana, North Dakota, and South Dakota. The next eclipse to cross the entire country will take place on August 12, 2045, streaking from northern California to southern Florida. Here are the other total solar eclipses visible from the contiguous U.S. this century:

March 30, 2052 Florida, Georgia, tip of South Carolina May 11, 2078 From Louisiana to North Carolina May 1, 2079 From Philadelphia up the Atlantic coast to Maine September 14, 2099 From North Dakota to the Virginia-North Carolina border

12. What is the origin of the word ‘eclipse?’

The word first appeared in English writings in the late 13th century. It traces its roots, however, to the Greek words “ecleipsis” or “ekleipein.” According to various sources, the meaning was “to leave out, fail to appear,” “a failing, forsaking,” or “abandon, cease, die.”

13. Do solar eclipses follow any kind of pattern?

The Moon goes through several cycles. The best known is its 29.5-day cycle of phases, from new through full and back again. Other cycles include its distance from Earth (which varies by about 30,000 miles (50,000 km) over 27.5 days) and its relationship to the Sun’s path across the sky, known as the ecliptic (27.2 days), among others. These three cycles overlap every 6,585.3 days, which is 18 years, 11 days, and 8 hours.

This cycle of cycles is known as a Saros (a word created by Babylonians). The circumstances for each succeeding eclipse in a Saros are similar—the Moon is about the same distance from Earth, for example, and they occur at the same time of year. Each eclipse occurs one-third of the way around Earth from the previous one, however; the next eclipse in this Saros, for example, will be visible from parts of the Pacific Ocean.

Each Saros begins with a partial eclipse. A portion of the Moon just nips the northern edge of the Sun, for example, blocking only a fraction of the Sun’s light. With each succeeding eclipse in the cycle, the Moon covers a larger fraction of the solar disk, eventually creating dozens of total eclipses. The Moon then slides out of alignment again, this time in the opposite direction, creating more partial eclipses. The series ends with a grazing partial eclipse on the opposite hemisphere (the southern tip, for example).

Several Saros cycles churn along simultaneously (40 are active now), so Earth doesn’t have to wait 18 years between eclipses. They can occur at intervals of one, five, six, or seven months.

The April 8 eclipse is the 30th of Saros 139, a series of 71 events that began with a partial eclipse, in the far north, and will end with another partial eclipse, this time in the far southern hemisphere. The next eclipse in this Saros, also total, will take place on April 20, 2042.

First eclipse May 17, 1501

First total eclipse December 21, 1843

Final total eclipse March 26, 2601

Longest total eclipse July 16, 2186,  7 minutes, 29 seconds

Final partial eclipse July 3, 2763

All eclipses 71 (43 total, 16 partial, 12 hybrid)

Source: NASA Catalog of Solar Eclipses: eclipse.gsfc.nasa.gov/SEsaros/SEsaros139.html

14. What about eclipse seasons?

Eclipses occur in “seasons,” with two or three eclipses (lunar and solar) in a period of about five weeks. Individual eclipses are separated by two weeks: a lunar eclipse at full Moon, a solar eclipse at new Moon (the sequence can occur in either order). If the first eclipse in a season occurs during the first few days of the window, then the season will have three eclipses. When one eclipse in the season is poor, the other usually is much better.

That’s certainly the case with the season that includes the April 8 eclipse. It begins with a penumbral lunar eclipse on the night of March 24, in which the Moon will pass through Earth’s outer shadow. The eclipse will cover the Americas, although the shadow is so faint that most skywatchers won’t notice it.

This article was previously published in the March/April 2024 issue of StarDate  magazine, a publication of The University of Texas at Austin’s McDonald Observatory. Catch StarDate’s daily radio program on more than 300 stations nationwide or subscribe online at  stardate.org .

15. How can astronomers forecast eclipses so accurately?

They’ve been recording eclipses and the motions of the Moon for millennia. And over the past half century they’ve been bouncing laser beams off of special reflectors carried to the Moon by Apollo astronauts and Soviet rovers. Those observations reveal the Moon’s position to within a fraction of an inch. Using a combination of the Earth-Moon distance, the Moon’s precise shape, Earth’s rotation and its distance from the Sun, and other factors, astronomers can predict the timing of an eclipse to within a fraction of a second many centuries into the future.

Edmond Halley made the first confirmed solar eclipse prediction, using the laws of gravity devised only a few decades earlier by Isaac Newton. Halley forecast that an eclipse would cross England on May 3, 1715. He missed the timing by just four minutes and the path by 20 miles, so the eclipse is known as Halley’s Eclipse.

16. What are the types of solar eclipses?

Total : the Moon completely covers the Sun.

Annular : the Moon is too far away to completely cover the Sun, leaving a bright ring of sunlight around it.

Partial : the Moon covers only part of the Sun’s disk.

Hybrid : an eclipse that is annular at its beginning and end, but total at its peak.

17. What are Baily’s beads?

During the minute or two before or after totality, bits of the Sun shine through canyons and other features on the limb of the Moon, producing “beads” of sunlight. They were first recorded and explained by Edmond Halley, in 1715. During a presentation to the Royal Academy of Sciences more than a century later, however, astronomer Frances Baily first described them as “a string of beads,” so they’ve been known as Baily’s beads ever since. Please note that Baily’s beads are too bright to look at without eye protection!

18. Will Earth always see total solar eclipses?

No, it will not. The Moon is moving away from Earth at about 1.5 inches (3.8 cm) per year. Based on that rate of recession, in about 600 million years the Moon would have moved so far from Earth that it would no longer appear large enough to cover the Sun. The speed at which the Moon separates from Earth changes over the eons, however, so scientists aren’t sure just when Earth will see its final total solar eclipse.

19. How will the eclipse affect solar power?

If your solar-powered house is in or near the path of totality, the lights truly will go out, as they do at night. For large power grids, the eclipse will temporarily reduce the total amount of electricity contributed by solar generation. During the October 14, 2023, annular eclipse, available solar power plummeted in California and Texas. At the same time, demand increased as individual Sun-powered homes and other buildings began drawing electricity from the power grid. Both networks were able to compensate with stations powered by natural gas and other sources.

The power drop during this year’s eclipse could be more dramatic because there will be less sunlight at the peak of the eclipse.

20. What are some of the myths and superstitions associated with solar eclipses?

Most ancient cultures created stories to explain the Sun’s mysterious and terrifying disappearances.

In China and elsewhere, it was thought the Sun was being devoured by a dragon. Other cultures blamed a hungry frog (Vietnam), a giant wolf loosed by the god Loki (Scandinavia), or the severed head of a monster (India). Still others saw an eclipse as a quarrel (or a reunion) between Sun and Moon. Some peoples shot flaming arrows into the sky to scare away the monster or to rekindle the solar fire. One especially intriguing story, from Transylvania, said that an eclipse occurred when the Sun covered her face in disgust at bad human behavior.

Eclipses have been seen as omens of evil deeds to come. In August 1133, King Henry I left England for Normandy one day before a lengthy solar eclipse, bringing prophesies of doom. The country later was plunged into civil war, and Henry died before he could return home, strengthening the impression that solar eclipses were bad mojo.

Ancient superstitions claimed that eclipses could cause plague and other maladies. Modern superstitions say that food prepared during an eclipse is poison and that an eclipse will damage the babies of pregnant women who look at it. None of that is true, of course. There’s nothing at all to fear from this beautiful natural event.

21. How do animals react to solar eclipses?

Scientists haven’t studied the topic very thoroughly, but they do have some general conclusions. Many daytime animals start their evening rituals, while many nighttime animals wake up when the eclipse is over, perhaps cursing their alarm clocks for letting them sleep so late!

During the 2017 total eclipse, scientists observed 17 species at Riverbanks Zoo in Columbia, South Carolina. About three-quarters of the species showed some response as the sky darkened. Some animals acted nervous, while others simply headed for bed. A species of gibbon had the most unusual reaction, moving excitedly and chattering in ways the zookeepers hadn’t seen before.

Other studies have reported that bats and owls sometimes come out during totality, hippos move toward their nighttime feeding grounds, and spiders tear down their webs, only to rebuild them when the Sun returns. Bees have been seen to return to their hives during totality and not budge until the next day, crickets begin their evening chorus, and, unfortunately, mosquitoes emerge, ready to dine on unsuspecting eclipse watchers.

A NASA project, Eclipse Soundscapes, is using volunteers around the country to learn more about how animals react to the changes. The project collected audio recordings and observations by participants during the annular eclipse last year, and will repeat the observations this year. Volunteers can sign up at eclipsesoundscapes.org

22. How will scientists study this year’s eclipse?

Astronomers don’t pay quite as much professional attention to solar eclipses as they did in decades and centuries past. However, they still schedule special observations to add to their knowledge of the Sun and especially the inner edge of the corona.

Sun-watching satellites create artificial eclipses by placing a small disk across the face of the Sun, blocking the Sun’s disk and revealing the corona, solar prominences, and big explosions of charged particles known as coronal mass ejections.

Because of the way light travels around the edges of an eclipsing disk, however, it’s difficult to observe the region just above the Sun’s visible surface, which is where much of the action takes place. The corona is heated to millions of degrees there, and the constant flow of particles known as the solar wind is accelerated to a million miles per hour or faster, so solar astronomers really want to see that region in detail. The eclipsing Moon doesn’t create the same effects around the limb of the Sun, so a solar eclipse still provides the best way to look close to the Sun’s surface.

For this year’s eclipse, some scientists will repeat a series of experiments they conducted in 2017 using a pair of highaltitude WB-57 aircraft to “tag team” through the lunar shadow, providing several extra minutes of observations.

Other scientists will use the eclipse to study Earth’s ionosphere, an electrically charged layer of the atmosphere that “bends” radio waves, allowing them to travel thousands of miles around the planet. Sunlight rips apart atoms and molecules during the day, intensifying the charge. At night, the atoms and molecules recombine, reducing the charge.

Physicists want to understand how the ionosphere reacts to the temporary loss of sunlight during an eclipse. They will do so with the help of thousands of volunteer ham radio operators, who will exchange messages with others around the planet. During last October’s annular eclipse, when the Moon covered most but not all of the Sun, the experiment showed a large and immediate change in the ionosphere as the sunlight dimmed.

NASA also will launch three small “sounding” rockets, which loft instruments into space for a few minutes, to probe the ionosphere shortly before, during, and shortly after the eclipse.

Another project will use radar to study changes in the interactions between the solar wind and Earth’s atmosphere, while yet another will use a radio telescope to map sunspots and surrounding regions as the Moon passes across them.

One project will piece together images of the eclipse snapped through more than 40 identical telescopes spaced along the path of totality to create a one-hour movie of the eclipse. The telescopes will be equipped with instruments that see the three-dimensional structure of the corona, allowing solar scientists to plot how the corona changes.

23. What have astronomers learned from eclipses?

Solar eclipses have been powerful tools for studying the Sun, the layout of the solar system, and the physics of the universe.

Until the Space Age, astronomers could see the Sun’s corona only during eclipses, so they traveled around the world to catch these brief glimpses of it.

Eclipses also offered a chance to refine the scale of the solar system. Watching an eclipse from different spots on Earth and comparing the angles of the Moon and Sun helped reveal the relative sizes and distances of both bodies, which were important steps in understanding their true distances.

During an eclipse in 1868, two astronomers discovered a new element in the corona. It was named helium, after Helios, a Greek name for the Sun. The element wasn’t discovered on Earth until a quarter of a century later.

An eclipse in 1919 helped confirm General Relativity, which was Albert Einstein’s theory of gravity. The theory predicted that the gravity of a massive body should deflect the path of light rays flying near its surface. During the eclipse, astronomers found that the positions of background stars that appeared near the Sun were shifted by a tiny amount, which was in perfect agreement with Einstein’s equations.

Today, astronomers are using records of eclipses dating back thousands of years to measure changes in Earth’s rotation rate and the distance to the Moon.

24. How did astronomers study eclipses in the past?

With great effort! From the time they could accurately predict when and where solar eclipses would be visible, they organized expeditions that took them to every continent except Antarctica, on trips that lasted months and that sometimes were spoiled by clouds or problems both technical and human.

During the American Revolution, for example, a group of Harvard scientists led by Samuel Williams received safe passage from the British army to view an eclipse from Penobscot Bay, Maine, on October 21, 1780. Williams slightly miscalculated the eclipse path, though, so the group missed totality by a few miles. (The expedition did make some useful observations, however.)

In 1860, an expedition headed by Simon Newcomb, one of America’s top astronomers, journeyed up the Saskatchewan River, hundreds of miles from the nearest city, braving rapids, mosquitoes, and bad weather. After five grueling weeks, they had to stop short of their planned viewing site, although at a location still inside the eclipse path. Clouds covered the Sun until almost the end of totality, however, so the expedition came up empty.

King Mongkut of Siam invited a French expedition and hundreds of other dignitaries to view an eclipse from present-day Thailand in 1868. He built an observatory and a large compound to house his guests at a site Mongkut himself had selected as the best viewing spot. The eclipse came off perfectly, but many visitors contracted malaria. So did Mongkut, who died a few weeks later.

An expedition in 1914, to Russia, was plagued by both clouds and the start of World War I. The team abandoned its instruments at a Russian observatory and escaped through Scandinavia.

The eclipse of July 29, 1878, offered fewer impediments. In fact, it was a scientific and social extravaganza. The eclipse path stretched from Montana Territory to Texas. Teams of astronomers from the United States and Europe spread out along the path. Thomas Edison stationed his group in Wyoming, where he used a tasimeter, a device of his own creation, to try to measure the temperature of the corona. Samuel Pierpoint Langley, a future secretary of the Smithsonian, was atop Pikes Peak in Colorado. Maria Mitchell, perhaps America’s leading female scientist, decamped to Denver. And Asaph Hall, who had discovered the moons of Mars just the year before, journeyed to the flatlands of eastern Colorado.

Thousands of average Americans joined the festivities, paying outrageous prices for some of the best viewing spots. Some things, it seems, never change.

25. What about lunar eclipses?

While solar eclipses happen during new Moon, lunar eclipses occur when the Moon is full, so it aligns opposite the Sun in our sky. The Moon passes through Earth’s shadow. In a total eclipse, the entire lunar disk turns orange or red. In a partial eclipse, Earth’s inner shadow covers only a portion of the Moon. And during a penumbral eclipse, the Moon passes through the outer portion of Earth’s shadow, darkening the Moon so little that most people don’t even notice it.

Lunar eclipses happen as often as solar eclipses—at least twice per year. This is a poor year for lunar eclipses, however. There is a penumbral eclipse on the night of March 24, with the Moon slipping through Earth’s faint outer shadow, and a partial eclipse on the night of September 17, in which the Moon barely dips into the darker inner shadow. Both eclipses will be visible from most of the United States.

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Total solar eclipse 2024: Watch video and see photos of the sky spectacle

EAGLE PASS, Texas − In a moment of cosmic alignment that was precisely predicted yet undeniably mysterious , the moon crept across the face of the sun as seen from Earth, casting its shadow onto the United States on Monday.

And then it was over: A total eclipse of the sun has come and gone.  

The partial shadow crossed into the U.S. in Texas just after noon local time, and a bit more than an hour later, the minutes of “totality” began. The total eclipse of the sun then traced a path from southern Texas to northern Maine, where it exited into Canada and the ocean beyond.

The rare event was an astronomical experience like no other. Monday's eclipse was unusually accessible to millions of people. It was widely anticipated not only for its remarkable period of darkness, but for its rare timing: No total solar eclipse would be visible from the contiguous United States again until 2044. While millions of Americans may have seen today’s eclipse, a small group in Texas was among the very first.

Edge of eclipse shadow began in south Texas

Alejandra Martinez, a seventh-grade science teacher from the south Texas border city of Eagle Pass, peered up at the gray, gauzy sky, anxiously awaiting the solar eclipse’s entrance into the USA.

Sitting with a telescope under a camping canopy in a corner of the county airport, Martinez, 42, and two other science enthusiasts had been recruited by NASA to participate in an effort called Citizen CATE 2024, where more than 30 teams perched in the eclipse’s path will record the shadowy trek across the country. 

In this spot, less than five miles from the U.S.-Mexico border, she and her team would be among the first people in the U.S. to witness the phenomenon. Eagle Pass sits near the very beginning of the eclipse’s track from southwest to northeast across the country. It also sits very near dead-center of it, where the period of “totality” will be the longest. That total shadow was still more than an hour away when the edge of the shadow began to darken the sky.

Martinez, dressed in a “This Totality Rocks” T-shirt and eclipse-themed skirt, watched as the penumbra crept across the airfield, about 10 minutes past noon local time. She put on her eclipse glasses and peered up at the sky. The gauzy clouds parted. “There it is! There it is!” she yelled. “First contact. It’s begun!”

Clouds came and went as the shadow grew for the next hour. As totality approached Eagle Pass, the sky shaded a dull gray then a heavy brown and the temperature dropped a few degrees. Only a sliver of the sun remained.

A few seconds before 1:27 p.m. CT, the crowd counted down, “3..2..1…” The sun was gone, completely covered by the moon. Darkness spread over the small airport grounds. “Oh my god,” Martinez said, a hand covering her heart. “This is so cool!”

How to tell if you have eye damage from looking at a partial eclipse?

For those who took a chance and looked at the sun without protective eyewear during the eclipse, concerns may arise if their vision starts to seem impaired. Have they suffered eclipse blindness?

Looking directly at the sun even briefly without the proper safety glasses can result in eye damage, either temporary or permanent. The body's natural squinting reaction in normal circumstances prevents people from staring directly at the sun, but that reflex may not be activated during partial eclipses, even though a partly shielded sun can still burn the retina.

The American Academy of Ophthalmology says pain won't be an indication of damaged eyes because the retina lacks pain nerves. Worrisome signs are instead blurry vision, headaches, light sensitivity, blind spots in the central vision, distorted vision and changes in color perception. Anyone experiencing those symptoms should see an ophthalmologist, the AAO says.

What was the timeline of the 2024 solar eclipse?

The total eclipse began in Mexico at about 11:07 a.m. PDT, Monday before crossing into Texas at 1:27 p.m. CDT. It ended in Maine at 3:35 p.m. EDT. Even those who weren't in the path of totality could see a percentage of the eclipse.

To find out exactly when the eclipse occurred in your area, you can search by  USA TODAY's database by ZIP code  for a viewing guide.

Students in Washington get hands-on learning

Dozens of students spilled out of Ida B. Wells Middle School in Washington, D.C., gripping cardboard solar eclipse glasses and chatting with excitement. “Why is the sun shaped as a moon?” one student asked after looking toward the sun. “Why is it not getting dark?’’ asked another.

Teacher Troy Mangum, who the students called “Mr. Mango,’’ slowly explained the science behind the experience as he cautioned others to put on their glasses. Students at the school in northwest D.C. had had lessons about the eclipse leading up the day’s teaching outside the classroom.

“Anytime we can get hands on or dynamic learning … it’s invaluable,’’ said Mangum, a social emotional learning coach. “We talked about it so much. It’s nice to see them get excited about qeeky Mr. Mango type of stuff.”

Skylar Cruel, 12, had come outside with her science class. “I just really wanted to see it,’’ she said. “You get to see it turn from light to dark.”

Steps away at Whittier Elementary School, which focuses on science, technology, engineering and math (STEM), younger students put on their glasses and tilted their heads up toward the sun behind their school.

Michael Haile joined his daughter, Markan Worku, 9, a student at Whittier, and brought along his 5-year-old son, Keab. He called it a memorable experience for his children. Markan, who had been learning about solar eclipses in her third-grade class, simply said, “This is cool!’’ 

− Deborah Berry

In Michigan, a bonding experience for a mother and her three kids

In Michigan, eclipse enthusiasts packed a watch party along the Detroit Riverwalk near Cullen Plaza. They sat on the grass, on benches and berms. For Janelle Ikonen of Waterford, it was a chance to bond with her three children − Hannah, 9; Elim, 12; and Isaac, 14 − whom she took out of school for the day.

“I wanted to experience a unique event with them,” said Ikonen, 47. “It’s one of my big deals to me, to experience things with my kids. … I hope they’ll remember spending time with me.”

In Grand Rapids, where 94% coverage of the sun was expected, viewers gathered on the city's “Blue Bridge,” which offered a view of the eclipse over the Grand River. With no cloud cover over the city, visitors had an unobstructed scene. The Grand Rapids Public Museum set up a series of solar telescopes.

Jill and Wes Johnson, 50 and 14, were among those awaiting max coverage. They’d considered traveling from Grand Rapids to a place with total coverage, but decided 94% coverage was worthwhile enough to stay home.

“I think people are excited to see something unique,” Jill Johnson said.

− Georgea Kovanis and Arpan Lobo, Detroit Free Press

US women's soccer team takes in eclipse ahead of title game

COLUMBUS, Ohio − The U.S. women’s national soccer team took a break from SheBelieves Cup preparation to watch the eclipse. 

Several team members, including World Cup veterans Crystal Dunn, Alyssa Naeher, Naomi Girma and Trinity Rodman, coaches and staff members donned eclipse glasses and went outside their hotel to see the rare event.

As the sky darkened and the moon moved in front of the sun, someone yelled, “Come on, keep going!” Columbus is just outside the path of totality, so all but a sliver of the sun wound up being covered. 

The USWNT is in Columbus for the final of the SheBelieves Cup on Tuesday night against Canada.

− Nancy Armour

Witnessing the first total eclipse from a cruise ship

Passengers aboard Holland America's Koningsdam cruise ship eagerly gathered on the top decks at 10 a.m. local time to watch the spectacle of a solar eclipse.

Positioned off the coast of Mazatlan, Mexico − the first city in North America to witness the total eclipse − the ship provided an ideal vantage point for viewing the celestial event. Accompanied by an astronomer, the captain meticulously adjusted the ship's position to ensure the best possible view.

Dan Fueller, an experienced eclipse observer who had previously seen similar phenomena from ships in 1991 and 1998, emphasized the advantages of viewing the eclipse from a cruise ship. He noted the flexibility of the ship's mobility allowed for optimal positioning along the eclipse's path, ensuring unobstructed views.

"You're on a cruise ship and (the best view) is a little bit farther to the west or a little bit farther to the east − along the path, there's a clear sky − the ship can move. If you're on land and there's not a road there, you better have a tank."

− Joshuan Rivera

Partial eclipse 'like a little Pac-Man taking a bite out of the sun'

In Parthenon, Arkansas, the eclipse began near the Buffalo National River. Five friends traveled from Florida to be on a rock outcropping to witness the celestial event.

“Yes! I see it!” Angie Printiss exclaimed.

“Oh ya! You can see it,” said Kate Estes. “It’s like a little Pac-Man taking a bite out of the sun.”

At 20 minutes before totality, the sky got noticeably darker. The shadow of crescent sun shapes played off the limestone rocks.

“It looks like water − like fish scales,” Estes said. “That is so weird, when the trees move you can really see it.”

− Jennifer Portman

New Englanders travel for better view of the eclipse

Crowds ballooned into the thousands midday Monday in the center of St. Johnsbury, Vermont, as the nearly cloudless sky and warm sun boosted temperatures to an unseasonably 60 degrees.

Jim and Kim Cooper drove over from New Hampton, New Hampshire, their first time doing more than just passing through the town locals call St. Jays. Their son had proposed to his girlfriend in Tennessee during the 2017 eclipse and then had an eclipse-themed wedding, but the Coopers had never seen a total eclipse for themselves, so they decided to come to the closest place where they could be assured of a good view.

Jeffrey Breau had seen that 2017 eclipse for himself and was so impressed that he convinced family members to join him this time. Breau’s girlfriend, Nell Hawley, came up with him from Cambridge, Massachusetts, while his brother Alex and his girlfriend Diana Ventura drove up from New York City. The Breau brothers' father, Walter, joined them in taking in their first eclipse.

“I would have been OK watching it in the yard,” Walter said, though he would only have seen a partial eclipse from there. “That’s what you think now,” Jeffrey said quickly. “Talk to me in two hours.”

− Karen Weintraub

Kids bring homemade eclipse viewers to National Mall

Lucas and Lucy Porto Banco didn’t need to buy fancy eclipse glasses – the 7- and 10-year-old siblings made their own eclipse viewers from two cardboard shoe boxes left over from a couple of their mom’s recent shoe purchases.With the help of a YouTube tutorial video, they made two holes in each box with a whittling knife and taped tin foil over. Then they used dry spaghetti to poke holes in the tin foil for the sun’s light to pass through and project onto the dark inside of the box.The kids put together the viewer in little more than five minutes, Lucy said. “Maybe 15, with covering all the gaps in the shoe box,” she said.Even with his own eclipse-viewing creation, Lucas said he may still take advantage of his eclipse glasses. “I’m going to do both,” he said.

− Cybele Mayes-Osterman

What is an 'umbra?' − and other eclipse words

Astronomers and eclipse enthusiasts used a bunch of specialized words Monday as the nation experienced its first solar eclipse since 2017 and the last one for until 2044. Here are a few of those terms and what they mean, according to the American Astronomical Society .

Baily's Beads – This refers to the beaded appearance of the moon's edge as the eclipse nears totality. Shafts of sunlight shine through deep valleys on the moon's surface, which causes the effect known to observers as Bailey's Beads.

Umbra – The darkest part of the moon’s shadow, within which the entirety of the sun's bright face is blocked. An observer standing in the umbra sees a total solar eclipse.

Penumbra: The lighter part of the moon's shadow, making up its outer portion, where light can reach.

Corona – The sun’s upper atmosphere, visible as a pearly glow around the eclipsed sun during totality.

Totality – The maximum phase of a total solar eclipse, during which the moon’s disk completely covers the sun's bright face. It can last from a fraction of a second to a maximum of 7 minutes, 31 seconds, depending on viewing location and other factors.

− Dale Denwalt, The Oklahoman

A last-minute search for glasses for 'a perfect spot'

Patsy Faoro walked toward a half dozen people gathered at the gate of Turner Farm Park in Great Falls, Virginia. The people were awaiting the opening of an eclipse viewing event complete with telescopes and educational presentations.

Faoro, who lives near the park in this upscale Northern Virginia neighborhood, just wanted glasses to safely view the eclipse.

She visited CVS, Safeway and a 7/11 convenience store, all of which had advertised the availability of glasses to view the eclipse. None of the retailers had any glasses remaining when Faoro checked this morning.

“We have this great big open space that’s a perfect spot,” said Faoro, who viewed her first eclipse in the 1970s. “We just need some glasses.”

− Ken Alltucker

Indianapolis Motor Speedway event draws tens of thousands

Tory Patrick, 41, is hoping to give her four children a once-in-a-lifetime learning opportunity. Patrick and her family traveled 160 miles to Indianapolis Motor Speedway from their home in Granger, Indiana. They were expected to have 97% totality at home, but it’s not the same as total coverage, she said.

“They will be getting the full experience that they can’t read about in textbooks,” Patrick said.

Patrick and her sister Cally Gannon, 39, from Cincinnati, met in Indianapolis to view the eclipse from the speedway. They camped outside IMS over the weekend ahead of the event and on Sunday afternoon saw a double rainbow over the speedway’s iconic pagoda. An estimated 50,000 tickets were sold for the day’s festivities, presented in partnership with NASA and Purdue University.

Elsewhere in the stands, Ryan Harper, 30, knows today is special.

“We’re right in totality,” he said. “This sometimes doesn’t happen in people’s lifetimes.

— Sarah Bowman and Jade Thomas

Family travels from Baltimore to Rochester, N.Y., to view the eclipse

When Maze Pelham of Baltimore was a fifth-grader, he watched news of the 2017 solar eclipse and vowed to witness the next notable solar eclipse. That eclipse, and that day, has come. And this is why he and his parents, Janice and Sonney Pelham, left Maryland around 1 a.m. on Monday and drove nearly seven hours to Rochester, New York.

“I said to myself I would go to the next one,” Maze Pelham said while seated with his parents on lawn chairs at downtown Rochester’s Parcel 5 park, where he and hundreds of others are awaiting a view of the full eclipse. “It’s a promise I made to myself.”

– Democrat and Chronicle, part of the USA TODAY Network

In Brooklyn: Eclipses glasses, check. Lawn chair, check.

Ralph Emerson held a pair of paper sunglasses in his hands while riding the subway to Brooklyn's sprawling Prospect Park on Monday. He exited the train with a folded lawn chair strapped across his shoulder, and said he felt energized and full of anticipation.

"This is special," Emerson, 61, said. "I haven't woken up with this much excitement since the Super Bowl."

Walking to the park's botanic garden, Emerson said appreciating natural phenomena makes it easier to manage the stresses that come with living in a big city. Also like a big sports game, the eclipse will draw lots of people together to experience something much larger than themselves, in community, he said.

"A lot of times it's tragedies that bring us together, but sometimes things like this do," he said.

− Claire Thornton

Texas Eclipse Festival cut short by weather

The Texas Eclipse Festival was canceled Monday in Burnet County, 50 miles northwest of Austin, because of weather concerns. The festival, which included bands and other events, began Sunday and was supposed to wrap up Tuesday.

"We regret to inform you of the severe weather forecast, including risks of high winds, tornadic activity, large hail, and thunderstorms for later today, including during the eclipse, Tuesday, and Wednesday," festival organizers said on their website. "Your safety is our top priority."

Festivalgoers were urged to leave early for safety and to beat traffic. Guests, however, were allowed to stay "provided they pack and are prepared to depart after totality."

Traffic jams, collisions mar eclipse watchers' travel

Traffic crashes and road delays were reported across the nation as Americans flocked to prime locations to gaze up at the rare solar eclipse . Local roads and highways in states including Texas, Ohio, Illinois, Indiana, Vermont and New Hampshire were overwhelmed with eclipse chasers, many of whom were from out of state. The most intense bottlenecks appeared to be in the path of totality , where spectators will be able to view the full eclipse.

In Oklahoma, a crash around 7:30 a.m. local time narrowed eastbound lanes on I-40, a major transcontinental highway that runs from California to North Carolina. The crash occurred not far from several state parks that were hosting eclipse events, and it's also within driving distance of the full eclipse path, which includes parts of southeastern Oklahoma and Arkansas.

Multiple crashes were reported on an interstate in Waco, Texas, a city in the path of totality, where several festivities and eclipse viewing events were scheduled. The crashes all occurred on I-35, which runs from southern Texas to Minnesota.

"Expect major traffic delays in this area," the Texas Department of Transportation said in a statement .

− Christopher Cann

Airport draws a crowd of jets for eclipse

EAGLE PASS, Texas − Maverick County International Airport in Eagle Pass, Texas, usually sees maybe three private planes a day. By 10 a.m. CT on Monday, more than 10 planes crowded the tarmac, including Cessnas, Pipers and at least one corporate jet − all there to catch an early glimpse of the total solar eclipse. Eagle Pass will be one of the first American cities to witness the phenomenon. Some watchers, like Brandon Beck, 43, flew in Sunday night from San Diego and spent the night in a sleeping bag on the tarmac next to his friend’s Mooney single-prop piston four-seater.“We’re so lucky to be on a planet where the sun is the perfect size and perfect distance to create that effect,” he said. “It’s obligatory. We have to see it.”

First the Cherry Blossoms, then the eclipse

WASHINGTON − The Cherry Blossoms brought Ali and Aurore Youssouf to the city all the way from Paris, but the pair were delighted to learn that their trip would overlap with the eclipse. The day is extra special for Aurore Youssouf, 43, who has never seen an eclipse before. On Monday morning, the couple arrived by chance at the National Mall early enough to snag a few pairs of free eclipse glasses distributed by the Smithsonian National Air and Space Museum for the occasion.“We didn’t even know. We just ended up here and found out that they were giving away some glasses,” said Ali Youssouf, 46.

Awaiting eclipse − and hail − in Texas

KERRVILLE, Texas − Forecasts called for considerable cloudiness, rain and possible hail, but retired NASA engineer Jeff Stone stayed positive as he and his wife prepared to host more than a dozen people for a watch party at their hilltop home in Texas Hill Country. Stone, an eclipse enthusiast who had met family in Missouri to watch the solar eclipse of 2017, said he recently reviewed video footage of that event and said current conditions weren’t that much different than they were back then.

“I’m outside and seeing patches of blue among scattered clouds, so we’re remaining hopeful,” he said.

About 150 miles to the northeast in Gatesville, lead pastor Eric Moffett of Coryell Community Church said a similar forecast did little to deter an expected gathering of about 800 visitors for the church’s family-oriented “Eclipse at the Crosses” event. Many, if not most, were from out of town or even out of country − Canada, Wales, France, Italy. Many locals were staying home to avoid the crowd, he said.

“It’s partly cloudy, but the sun is shining on me right now,” he said. “We are praying that it stays that way.”

− Marc Ramirez

What is the difference between a solar eclipse and a lunar eclipse?

A  total solar eclipse  occurs when the moon comes in between the Earth and the sun, blocking its light from reaching our planet, leading to a period of darkness lasting several minutes. A total lunar eclipse occurs when the moon and the sun are on exact opposite sides of Earth. The Earth blocks the sunlight that normally reaches the moon. Instead of that sunlight hitting the moon’s surface, Earth's shadow falls on it.

A lunar eclipse can last for a few hours, while a solar eclipse lasts only a few minutes. Solar eclipses also rarely occur, while lunar eclipses are comparatively more frequent. While at least two partial lunar eclipses happen every year, total lunar eclipses are still rare, NASA says. Another major difference: No special glasses or gizmos are needed to view the a lunar eclipse, and people can directly stare at the moon.

− Saman Shafiq

Solar eclipse, lunar eclipse: What is the difference?

Can you drive during the solar eclipse?

The  2024 solar eclipse  will shroud much of the United States in darkness on Monday, leaving many people to wonder: Is it safe to drive during the solar eclipse?

It is safe to drive during an eclipse as long as you don't look up at the sky. AAA is telling drivers to be focused on the road if they are operating a car during the total solar eclipse. But the automobile insurance company is advising Americans who want to safely view the total eclipse to "find a safe place to park (not on the side of a road or highway) away from other traffic and then wear your eclipse glasses," said Aixa Diaz, a spokeswoman from AAA.

"Pack your patience, whether traveling a great distance or locally," Diaz said. "People will be out and about to catch a glimpse of the eclipse."

A similar scenario  played out in 2017 during the nation's last total solar eclipse : Congestion in some areas lasted for up to 13 hours after totality,  according to Transportation Research News , a National Research Council publication. An analysis of traffic patterns from that year suggests the worst of the traffic – on interstates and rural back roads alike – will kick off after the eclipse ends and everyone tries to leave all at once.

− Kayla Jimenez

When will the next solar eclipse happen?

It will be 20 years before there's a chance to  witness a total solar eclipse  in the United States again. According to NASA, after Monday's total solar  eclipse , the next one viewable from the contiguous U.S. will be on Aug. 23, 2044.

Unfortunately, the 2044 total  solar eclipse  won't have the broad reach across the U.S. as the 2024 eclipse. The path of totality during the 2044 eclipse will only touch three states, according to the Planetary Society, a nonprofit involved in research, public outreach and political space advocacy. The eclipse will begin in Greenland, sweep through Canada and end around sunset in Montana, North Dakota and South Dakota.

But another eclipse scheduledfor Saturday, Aug. 12, 2045, will trace a path of totality over California, Nevada, Utah, Colorado, New Mexico, Oklahoma, Kansas, Texas, Arkansas, Missouri, Mississippi, Louisiana, Alabama, Florida and Georgia.

− Mary Walrath-Holdridge, Gabe Hauari and Eric Lagatta

Eclipse and pets: It's not the sky that's the problem

An  eclipse  itself isn't dangerous for domestic animals such as dogs and cats, but experts say it's probably best to not bring pets to  experience the April 2024 total solar eclipse . Experts' biggest concern is not what’s happening in the sky but on the ground as crowds of excited and  eager people gather , said Dr. Rena Carlson, president of the American Veterinary Medical Association. Dogs especially will take their cues from their owners rather than  the celestial event.

“Rather than the effects of the eclipse, I would be more worried about the excitement and all of the people,” Carlson said.

− Elizabeth Weise

A guide to the solar eclipse for kids

Here's an easy-to read, illustrated guide to help kids understand what the  April 8 total solar eclipse  means, where it will be visible and how you can watch it safely. It also shows them how an ordinary kitchen colander can easily be used to view a solar eclipse − the colander's holes can project crescent images of the sun onto the ground. There are even pages that can be downloaded and colored.

Trump's eclipse experience lit up internet in 2017

Seven years ago, when the last  total solar eclipse  crossed over North America, a photo of then-President Donald Trump  seemingly gazing at the sun with his naked eyes set the internet ablaze . During the afternoon of Aug. 21, 2017, Trump, who was president at the time, was joined by then first lady Melania Trump and their son Barron  to watch the rare phenomenon from the Truman Balcony  at the White House. Photos taken by members of the media captured all three donning eclipse glasses while looking at the eclipse.

But at one point during the viewing, the former president was captured in photos and videos without proper eye protection, seemingly gazing directly at the sun. Looking at an eclipse before or after the brief phase of totality without proper eyewear  can lead to eye damage .

− Natalie Neysa Alund

When is the next total solar eclipse? What to know about the next eclipse's path, timing

How to make a solar eclipse viewer

People who didn't manage to get their  hands on glasses  are not completely down and out. There are other safe ways to view the eclipse , say experts, and a lot of them only require a little bit of craftiness and items you can find lying around the house.

Steps to make the cereal box eclipse viewer (And here is a video aid) :

• Get an empty, clean cereal box.
• Cut a white piece of cardboard that will fit snuggly in the bottom of the box, or secure it permanently by gluing it in place.
• Cut the top of the cereal box, removing both ends and leaving the center intact.
• Put a piece of tape across the center of the top to securely hold it closed.
• Tape a piece of heavy-duty foil or double a single layer for additional strength, covering one of the openings at the top of the cereal box. The other opening will remain open for viewing.
• Using a small nail (approximately 3mm in diameter) push a hole in the foil.
• Cover the entire box with construction paper, leaving the single-viewing opening and the foil uncovered.

The finished box should be held with the pin-hole side facing the sun. It may take a little practice pointing the box. With your back facing the sun, look through the viewing opening. A small image of the sun, about ½ cm in diameter, can be seen projected on the white paper inside the box.

− Mary Walrath-Holdrid

What is the path of the solar eclipse called?

Those in the direct line of the eclipse will be treated to an incredible sight as the moon completely blots out the sun's disk, ushering in uncharacteristic darkness and revealing the sun's elusive outermost layer called the corona. That moment is called "totality" and this year the path of totality crosses through 13 U.S. states.

The last total solar eclipse to cut through North America was in August 2017.

How to look at eclipse without glasses

A total solar eclipse offers skygazers the rare opportunity to witness the eclipse with the naked eye. However,  solar eclipse glasses  are still needed until totality is reached. 

Certified solar eclipse  glasses are crucial for spectators to avoid the sun's retina-damaging rays. But when the moon moves completely in front of the sun and blocks its light, you'll know it's  safe to remove the glasses  for a short period of time.

How fast does an eclipse shadow travel?

According to a post from the  National Weather Service  in Indianapolis on X, an eclipse shadow travels at speeds from 1,100 to 5,000 mph. Near the equator, it travels at around 1,100 mph and increases in speed as it approaches the poles.

The eclipse party is over? Time to recycle those glasses!

Astronomers Without Borders , or AWB, a non-profit organization running its second nationwide  eclipse glasses recycling drive . Her business will join over 300 schools, museums, city governments, commercial businesses, community organizations and local libraries that will collect and ship an estimated  millions of glasses  to be repurposed for use by underserved communities around the world in  future solar eclipses .

AWB launched its first run of the program after the last solar eclipse in 2017 when volunteer centers across the country collected millions of the glass. After vetting them for reuse, more than  half a million glasses were distributed to Africa, Asia and South America.

People can visit  AWB's website  to find their nearest participating collection center and learn more about recycling the glasses, said Andrew Fazekas, the organization's communication manager.  

"We figure there's probably going to be tens of millions of glasses out there at the very least," he said. "And most of them are probably very gently used."

Watch CBS News

Why is looking at a solar eclipse dangerous without special glasses? Eye doctors explain.

By Sara Moniuszko

Edited By Allison Elyse Gualtieri

Updated on: April 8, 2024 / 8:54 AM EDT / CBS News

The solar eclipse will be visible for millions of Americans on April 8, 2024, making many excited to see it — but how you watch it matters, since it can be dangerous for your eyes. 

A  solar eclipse occurs when the moon passes between the sun and Earth, blocking the sun's light . When the moon blocks some of the sun, it's a partial solar eclipse, but when moon lines up with the sun, blocking all of its light, a total solar eclipse occurs,  NASA explains . Either way, you need eye protection when viewing.

"The solar eclipse will be beautiful, so I hope that everyone experiences it — but they need to experience it in the right way," said Dr. Jason P. Brinton, an ophthalmologist and medical director at Brinton Vision in St. Louis.

Here's what to know to stay safe.

Why is looking at a solar eclipse dangerous?

Looking at the sun — even when it's partially covered like during an eclipse — can cause eye damage.

There is no safe dose of solar ultraviolet rays or infrared radiation, said  Dr. Yehia Hashad , an ophthalmologist, retinal specialist and the chief medical officer at eye health company Bausch + Lomb.

"A very small dose could cause harm to some people," he said. "That's why we say the partial eclipse could also be damaging. And that's why we protect our eyes with the partial as well as with the full sun."

Some say that during a total eclipse, it's safe to view the brief period time when the moon completely blocks the sun without eye protection. But experts warn against it. 

"Totality of the eclipse lasts only about 1 to 3 minutes based on geographic location, and bright sunlight suddenly can appear as the moon continues to move," notes an eclipse viewing guide published in JAMA , adding, "even a few seconds of viewing the sun during an eclipse" can temporarily or permanently damage your vision. 

Do I need special glasses for eclipse viewing?

Yes.  Eclipse glasses are needed to protect your eyes if you want to look at the eclipse.

Regular sunglasses aren't protective enough for eclipse viewing — even if you stack more than one. 

"There's no amount of sunglasses that people can put on that will make up for the filtering that the ISO standard filters and the eclipse glasses provide," Brinton said.

You also shouldn't look at the eclipse through a camera lens, phone, binoculars or telescope, according to NASA, even while wearing eclipse glasses. The solar rays can burn through the lens and cause serious eye injury.

Eclipse glasses must comply with the  ISO 12312-2 international safety standard , according to NASA, and should have an "ISO" label printed on them to show they comply. The American Astronomical Society  has a list  of approved solar viewers.

Can't find these, or they're sold out near you? You can also  make homemade viewers ,   which allow you to observe the eclipse indirectly — just don't accidentally look at the sun while using one.

How to keep kids safe during the solar eclipse

Since this eclipse is expected to occur around the time of dismissal for many schools across the country, it may be tempting for students to view it without the proper safety precautions while getting to and from their buses. That's why some school districts are  canceling classes early so kids can enjoy the event safely with their families.

Dr. Avnish Deobhakta, vitreoretinal surgeon at New York Eye and Ear Infirmary at Mount Sinai, said parents should also be careful because it can be difficult for children to listen or keep solar eclipse glasses on. 

"You want to actually, in my opinion, kind of avoid them even looking at the eclipse, if possible," he said. "Never look directly at the sun, always wear the right eclipse sunglasses if you are going to look at the sun and make sure that those are coming from a reliable source."

Brinton recommends everyone starts their eclipse "viewing" early, by looking at professional photos and videos of an eclipse online or visiting a local planetarium. 

That way, you "have an idea of what to expect," he said. 

He also recommends the foundation  Prevent Blindness , which has resources for families about eclipse safety.

What happens if you look at a solar eclipse without eclipse glasses?

While your eyes likely won't hurt in the moment if you look at the eclipse without protection, due to lowered brightness and where damage occurs in the eye, beware: The rays can still cause damage .

The harm may not be apparent immediately. Sometimes trouble starts to appear one to a few days following the event. It could affect just one or both eyes.

And while some will regain normal visual function, sometimes the damage is permanent. 

"Often there will be some recovery of the vision in the first few months after it, but sometimes there is no recovery and sometimes there's a degree to which it is permanent," Brinton said. 

How long do you have to look at the eclipse to damage your eyes?

Any amount of time looking at the eclipse without protection is too long, experts say. 

"If someone briefly looks at the eclipse, if it's extremely brief, in some cases there won't be damage. But damage can happen even within a fraction of a second in some cases," Brinton said. He said he's had patients who have suffered from solar retinopathy, the official name for the condition.

Deobhakta treated a patient who watched the 2017 solar eclipse for 20 seconds without proper eye protection. She now has permanent damage in the shape of a crescent that interferes with her vision. 

"The crescent that is burned into the retina, the patient sees as black in her visual field," he said. "The visual deficit that she has will never go away."

How to know if you've damaged your eyes from looking at the eclipse

Signs and symptoms of eye damage following an eclipse viewing include headaches, blurred vision, dark spots, changes to how you see color, lines and shapes. 

Unfortunately, there isn't a treatment for solar retinopathy.

"Seeing an eye care professional to solidify the diagnosis and for education I think is reasonable," Brinton said, but added, "right now there is nothing that we do for this. Just wait and give it time and the body does tend to heal up a measure of it."

Sara Moniuszko is a health and lifestyle reporter at CBSNews.com. Previously, she wrote for USA Today, where she was selected to help launch the newspaper's wellness vertical. She now covers breaking and trending news for CBS News' HealthWatch.

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This diagram shows what happens during a total solar eclipse

• A total solar eclipse will be visible from Texas to Maine on Monday.
• This cosmic event occurs when the Earth, sun, and moon align perfectly.
• One diagram shows how a total solar eclipse works, and why it darkens the sky in the middle of the day.

A total solar eclipse will turn afternoon skies dark from Texas to Maine on Monday.

During the eclipse, the moon will cross between the Earth and the sun, completely blocking out the sun's light. If you're in the moon's shadow, the sky will go dark for about three to four minutes, depending on your location.

It's the climax of a cosmic dance between our planet , the moon, and the sun.

What causes a total solar eclipse

During a total solar eclipse, three key conditions happen at the same time: The moon is in the "new moon" phase; the moon crosses the plane of the Earth's orbit ; and the moon is at its closest point to Earth in its orbit.

When those conditions are just right, the Earth, sun, and moon line up. This diagram shows how that looks:

Then, if you're in the path of totality — which is basically the center of the moon's shadow, called the umbra — the moon appears to obscure the sun.

If you're in the penumbra — the outer region of the moon's shadow — you'll see a partial solar eclipse , where the moon appears to partially overlap the sun.

A total solar eclipse happens somewhere on Earth about every 18 months on average. It's rare for one to occur in any single place, though, because of the complex movements of the Earth and moon.

The moon orbits Earth every 29.5 days, while Earth has its own orbit around the sun. The moon's orbit is tilted about five degrees, which is large enough to keep its shadow off the Earth and the Earth's shadow off the moon most of the time.

There are two points — called nodes — where the moon's orbit crosses the Earth's plane. In the diagram above, the moon is lined up on a node.

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The moon aligns with the nodes and the sun about twice per year, which is how we get eclipses. A solar eclipse happens when the moon is between the Earth and sun. A lunar eclipse happens when the moon is on the other side of the Earth, farthest from the sun.

What the total solar eclipse will look like

In the path of totality on Monday, where the moon's umbra falls over Earth, the total solar eclipse will have 10 distinct phases , each with different amounts of the sun visible from the ground.

The phenomenon kicks off with what's called first contact, when the moon starts to pass across the sun. After about an hour, the moon will almost completely mask the sun, and you'll start to see a bright light radiate out of the sliver of remaining sun, known as the "diamond ring."

Then the moon will fully eclipse the sun, turning the sky dark in the middle of the day.

During totality only the sun's outermost atmosphere, called the corona, will be visible glowing around the dark disc of the moon.

After that, the moon will continue to travel across the sky to form another crescent. The eclipse ends when the moon ceases to cover the sun.

Types of solar eclipses

There are three types of solar eclipses .

Total solar eclipses, like this one, occur when the moon appears to completely cover the sun. If the moon only somewhat covers the sun, that's a partial eclipse . Many people who are near the path of totality, but not in it, on Monday will see a partial eclipse.

The third type, an annular eclipse , occurs when the moon is too far from Earth to fully block out the sun from our perspective. The outer edge of the sun remains visible as a bright ring around the moon.

A total solar eclipse is considered the most spectacular. Globally, only about a third of all solar eclipses are total.

The next total solar eclipse in the contiguous US will be in 2044.

How to watch the eclipse

If you plan to watch the eclipse, make sure you are wearing ISO-certified eclipse glasses . These are 1,000 times darker than regular sunglasses. Without them, staring at the sun could damage your eyes.

The only safe time to look at the eclipse without glasses is during totality.

Leanna Garfield and Anaele Pelisson contributed to an earlier version of this post .

Watch: Why the sun has two giant holes, and what that means for Earth

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