[♩INTRO]
It’s not often that the whole world is talking about astronomy.
A lot of the time, it’s just space nerds like us.
But a solar eclipse, especially one that travels across
the entire face of the United states, is definitely going to do it.
Just one month from now, on August 21,
the United States will experience its first total solar eclipse since 1979.
So for a lot of people, including me,
this will be your first opportunity to see one without having to leave the country.
People are calling it the Great American Eclipse,
since the path of the total solar eclipse only passes through the US,
and cuts all the way across the contiguous 48 states.
Over the last couple of centuries, solar eclipses have taught scientists a lot
about the Sun, and about the way the universe works in general.
But you don’t need to be a scientist to be captivated by watching the Sun
just suddenly go dark in the middle of the day.
If you want to experience this eclipse for yourself,
you just have to be in the right place at the right time.
A solar eclipse happens when the Moon goes between the Earth and the Sun,
casting a shadow across the Earth’s surface.
From our perspective, it looks like the Sun is being blocked out.
A total solar eclipse happens when this arrangement is perfect:
the Moon is directly between the Earth and Sun,
and it’s close enough to Earth to completely block out the Sun for a short time.
That’s exciting for anyone to watch, but for scientists, it’s also incredibly useful.
When the Moon covers the Sun, we can see the Sun’s corona
the layer of gas that surrounds the Sun.
Normally, it’s a lot harder to separate what’s happening in the corona
from what’s happening with the rest of the Sun.
Because the sun is pretty bright...
By studying the corona during eclipses, researchers have learned a ton about
what it’s made of, how it works, and even its surprisingly high temperature.
The temperature discovery happened during the 1879 eclipse,
when we found what we thought was a brand new element.
Turns out, it was just super hot gaseous iron.
For iron to be a gas, that meant the corona must have been way hotter
than the Sun’s surface — like, millions of degrees hotter.
That was totally unexpected, and almost 150 years later,
we still don’t know why the corona is so hot.
We’re launching a probe next year to help figure it out.
But probably the most important thing we ever learned from an eclipse
was in 1919, when a total solar eclipse over South America and Africa
provided the first proof of Einstein’s general theory of relativity.
One of Einstein’s greatest predictions was that gravity can bend light,
and the Sun has a strong enough gravitational pull
that it should bend the light from the stars just behind it,
shifting their position a little in the sky from our perspective here on Earth.
But normally, of course, you can’t see the stars next to the Sun in the sky,
because the sun is very bright.
So scientists couldn’t check if it was actually bending starlight until
the 1919 eclipse, while the Sun was dark enough to see the stars around it.
By measuring the positions of stars right next to the eclipse,
they found that the light from the stars was being bent by the Sun’s gravity.
Even better: the positions of the stars fit perfectly with Einstein’s equations.
And that’s how the Moon moving in front of the Sun almost a century ago
proved the theory that we still use to describe a lot of the universe.
So there are plenty of reasons for humans to be interested in eclipses
from a scientific perspective.
But also … they’re just really freakin’ cool.
If you want to see this eclipse for yourself,
you’ll first have to get to a place where it’ll be visible.
You’ll be able to see the partial eclipse
where a smaller part of the Sun is blocked, but not the whole thing
from Canada, Central America, and some parts of Western Europe.
But if you want to see the total eclipse, you’ll have to put yourself somewhere
along that slice across the US, aka the path of totality, on August 21.
The whole eclipse lasts about two and a half hours,
although totality is no more than about two and a half minutes.
It is weird that the moon and the sun are
almost exactly the same size in the sky!
Just a coincidence!
The exact timing depends where you are, because the eclipse will move
Along the path of totality as the Earth rotates and the Moon moves in its orbit.
If you’re in Oregon, the whole show will start around 9 am,
and if you’re in South Carolina, it’s more like 1pm.
There’s a link in the description where you can get
exact details for your location.
Even if you’re in the right place at the right time,
you’ll need still need to take some safety precautions to watch the eclipse.
Looking directly at the Sun, I assume we all know this,
can cause eye damage or even blindness, because your eyes
just aren’t equipped to handle that level of light intensity.
And a lot of the time the damage is painless,
and people don’t even realize it’s happening.
So the safest way to watch the eclipse is through something that
Projects the image onto something else, like a pinhole projector.
If you want to look at it directly,
there are lots of people out there selling eclipse viewing glasses,
but here’s the thing: if they have a tiny imperfection,
or aren’t made to the right standards … that could be really bad.
Because, again, you might not even realize that your eyes are being damaged.
After every solar eclipse, people end up in hospitals
because their vision starts to go weird,
even though they didn’t feel anything during the eclipse.
So, be careful.
Make sure any viewing glasses you get meet the latest standards.
A lot of them don’t.
You can watch the eclipse with the naked eye during that tiny window of totality,
if you happen to have gotten yourself to the path of totality,
but you have to make sure to have the glasses back on before totality ends.
If you miss it, the good news is that
you won’t have to wait nearly as long the next time around:
there’ll be another total solar eclipse in North America in 2024.
But if you do make it to the path of totality,
and — fingers crossed — it’s a clear day, get ready for an incredible show.
If you’re looking for a safe way to see the eclipse,
we’ve got you covered with a special SciShow pinhole projector card!
All you have to do is poke a hole in the middle,
grab a plain piece of paper to project the image onto,
and adjust the distance between the card and the paper
until you see a clear image of the eclipse.
The tiny hole acts like the lens in a camera,
focusing the light that passes through so that you can see the image
on the paper behind it.
You can get your SciShow pinhole projector at dftba.com/scishow!
[♩OUTRO]