Most of us don’t have a Ph.D in astrophysics, and many of us have questions about the eclipse, but like anyone with questions, well, honestly, I just feel afraid to ask some of them, worried that the answer may be obvious. Well, we’ve found some of the most popular questions that people have been afraid to ask, but still want to know the answer to. Like why doesn’t every new moon mean an eclipse, or how fast the shadow moves across the ground (hint: it varies).
The moon has to be in its “new moon” phase (no, that doesn’t mean it’s reading the Twilight books), but every new moon does not mean an eclipse. When there’s a new moon, the moon is between the earth and the sun, just like in today’s eclipse, however the moon is not on the same “plane” as the earth and sun, that’s a rare occurrence (like today).
The position of the moon in its orbit makes a difference too. The moon circles the earth on an out-of-round orbit. The moon has to be closest to the earth, plus be in new moon phase, plus be on the same plane as the earth and sun, for the eclipse to occur. That’s a lot to line up.
How fast does the shadow move across the earth? Well, that’s a tough one, it’s not a constant speed. Depending on where you are in the country it will move at a different speed. But to give you an answer, when the eclipse starts in Oregon, it’ll be moving at 2,955mph. When it crosses Kentucky, it’ll be moving at 1,462mph. When it finishes up in Charleston, SC, it’ll be moving a tiny bit faster at 1,502mph. Why the change? Shape of the earth plus its rotation, and plus its position relative to the sun, basically.
How do they predict when the next one happens? It’s a complicated equation, called the Saros Cycle. So, every 27.212 days, the moon returns to a “node.” A node is a spot where the shadow of the moon can fall onto the earth’s surface, if all the other variables are there. Every 27.554 days, the moon is at a spot where it’s closest to the earth. Every 29.530 days, the moon goes through its entire phase cycle. According to someone who already did the math, those 3 sets of numbers sync up every 18-year, 11-day, eight-hours. That doesn’t mean that’s the amount of time between eclipses though. We’ll let the pros explain that one.
Why don’t eclipses fall in the same spots? That’s because of the way the moon cycles and everything falls. There’s an extra 1/3 of a day, so the earth is an additional 8 hours rotated, which puts a different part of the globe in sunlight.
They do know when all the next eclipses will happen, and over what parts of the world, and it looks like NorCal will get a total eclipse in the year 2045. Check out the map here.
How can you see it without glasses? You can look at shadows of tree leaves on the ground, you’ll see they form a crescent shape where they fall. Also, if you hold up something with a round hole (or many, in the case of a colander), you’ll see the same thing wherever the light shines through the round holes. You can also make a box viewer with things seen here, but hurry up.
For more facts about the eclipse, with much more detail, check it out right here.