You Know About This Summer's Spectacular Solar Eclipse, Right?

7 min
Total solar eclipse over Queensland, Australia. A tiny portion of the Sun's disk peeks behind the moon, which is surrounded by the halo of a the solar corona. (Phil Hart)

Save the date: August 21st. On that Monday, across the United States, millions of people will be granted a rare chance to see a total solar eclipse. The last time a total solar eclipse crossed the contiguous U.S., Jimmy Carter was president (1979). It has been nearly a century since an eclipse swept the country from coast to coast (1918).

"It's not often that celestial events favor our own country in such a way," says Seth Shostak, senior astronomer at the SETI Institute. "And this gives the opportunity to a lot of people to see something that really shouldn't be missed."

The eclipse will first be visible by land at Lincoln Beach, Oregon. At 8:04 a.m. the moon will begin to edge in on the sun, taking a tiny chip out of it.

Eclipses are possible thanks to a happy coincidence: The Sun is 400 times the diameter of the moon, while also being 400 times farther away from Earth. To us, both the moon and the Sun appear to be the same size allowing the moon to block light from the sun during solar eclipses.

As the 70 million million million metric tons of rock that we know as our moon slide across the solar disc, darkness will descend, sweeping in from the west. The temperature will drop. Birds may cease singing, squirrels may give up their foraging. The stars will come out.

Observers of past eclipses say life seems suspended in animation, as the shadow of the moon sweeps over them. Looking up they see a "hole in the sky" surrounded by flowing flames. Or, "a black sunflower with the most delicate of silver petals," as Frank Close writes in Eclipse: Journeys to the Dark Side of the Moon.

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These 'petals' are the sun's corona. Curiously, this outer atmosphere of the sun is far, far hotter (up to 450 times hotter) than the surface of the sun. But why this is so is still a mystery.

The stage where the corona is visible to the naked eye is the moment of total eclipse, called "totality." You will see the total eclipse only if you are inside the 50-mile wide band marked out on the map below, a path that will sweep across the country stretching from just west of Salem, Oregon to Charleston, South Carolina. (Check out the Eclipse Megamovie Project, a joint project of Google and UC Berkeley. Type a  location into their simulator to see what the eclipse will look like from there.)

A word on safety: Don't look directly at the sun. Ever.

For the first hour of the eclipse, the moon with be sliding over the disc of the sun taking, as Shostak says, "bigger and bigger cookie bites."

Even if it is partially blocked, if you look into the sun it may be the last thing you'll ever see. You can, however, watch with eclipse glasses, which are equipped with protective film. Or, cut a hole in a piece of paper or cardboard and project the eclipse onto a surface, such as the ground or a wall. Once the moon has completely blocked out the sun (during totality) it is okay to look up. In fact, don't miss looking up! You can even take a peek through your binoculars or telescope.

https://dts.podtrac.com/redirect.mp3/www.kqed.org/.stream/mp3splice/radio/science/2017/06/Eclipse_170619.mp3

Shostak recommends Oregon as the most practical locale for Californians to view the eclipse, if they're willing to travel. "You might think 'Gosh! That's a long trip for two minutes of celestial fireworks,'" says Shostak. "But I can assure you, seeing the moon get in front of the sun is something you will always remember."

Read more KQED eclipse coverage:

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Americans Prepare for First Coast-to-Coast Total Solar Eclipse in Century (KQED Forum)
Don’t Be in the Dark: Answers To Your Burning Questions About the August Eclipse
Help Make History: Eclipse Projects for Citizen Scientists

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