On Monday, the moon will completely eclipse the sun, and people all over the U.S. will watch.
For those who have been boning up on eclipse trivia for weeks, congratulations. For everyone else, here are the things you need to know about the phenomenon.
Where can I see the eclipse?
A partial solar eclipse will be visible everywhere in the contiguous United States, but to see the total solar eclipse, you'll need to be in a sash of land that cuts from Oregon to South Carolina.
A lot of people are extremely excited, and are traveling enormous distances (and paying lots of money) to get to the the so-called path of totality. This is the first coast-to-coast solar eclipse in 99 years. People in parts of the contiguous U.S. last saw a total solar eclipse in 1979.
NASA is also live-streaming the eclipse for four and a half hours, beginning at 11:45 a.m. ET.
Can the eclipse hurt my eyes?
Yes. Never look directly at the sun during the eclipse without appropriate eye protection. And no, sunglasses don't count. Real solar viewers are thousands of times darker than regular sunglasses.
"The only time it will be safe to look with the naked eye is during the brief window of so-called totality, when the sun is completely blocked by the moon. ... When any part of the sun is uncovered and the eclipse is only partial, viewers need eye protection — even if there's just a tiny crescent of sun left in the sky, [says Ralph] Chou, [a professor emeritus of optometry and vision science at the University of Waterloo].
" 'That crescent of sun is glowing every bit as brightly as it would on a day when there isn't a solar eclipse,' he says. 'The difference is that instead of leaving a round burn on the back of the eye, it will leave a crescent-shaped burn at the back of the eye.'
"Don't think it's safe to take quick, surreptitious glances, he warns.
" 'Actually, those quick little glances do add up,' says Chou, 'and they can, in fact, accumulate to the point where you do get damage at the back of the eye.' "
If you're buying eclipse glasses, beware of scammers selling fraudulent products. The American Astronomical Society has a list of legitimate brands.
Wait, what is a total solar eclipse again?
A total solar eclipse is when the moon, the sun and the Earth all line up such that the moon completely blocks out the sun to viewers on part of Earth's surface.
It's easier to imagine with a diagram.
We residents of Earth are pretty lucky to see total solar eclipses. A lot of factors all need to align (so to speak). The moon needs to be just the right size and distance from Earth, and that's before you even consider the cosmic fluke that is humans with eyes living on solid ground and able to turn our faces to the heavens.
And in about 600 million years, earthlings won't see total solar eclipses anymore, because the moon is still moving away from Earth.
Are scientists really still interested in eclipses?
Total solar eclipses have been happening for as long as humans have been around, but there's still a lot to learn.
For one thing, it's a very useful moment for people who study the flaming corona of the sun that's left exposed during the eclipse. The corona is the outer atmosphere of the sun, and during a total eclipse, the moon exposes part of the corona that is particularly interesting to researchers because it's involved in space weather.
But the moon moves quickly, giving scientists in any one location just a couple minutes to study the corona. To buy more time, volunteer citizen-scientists will take photos at 68 sites across the U.S. as part of Citizen CATE: the Continental-America Telescopic Eclipse experiment.
"With that many telescopes, you can get continuous coverage of the eclipse from coast-to-coast during totality," Bob Baer of Southern Illinois University told NPR's Nell Greenfieldboyce. If everything goes as planned, the CATE team will end up with 93 minutes of continuous total eclipse.
What if I miss the eclipse?
Despair not. There will be solar eclipses visible from parts of the contiguous U.S. on Oct. 14, 2023, and April 8, 2024. The one in 2024 will be a total solar eclipse visible from Texas to Maine.