The Cosmic Ballet Continues

This Monday the United States will witness the rare and majestic total solar eclipse. Not all areas will see a total eclipse, but all of North America will see at least some of the sun disappear. While not a rare event, it is unusual for a total solar eclipse to cover such a large populated area. It seems like usually they happen only over the remotest part of the Pacific Ocean or exclusively at the South Pole. This eclipse will the first total solar eclipse to hit the US since 1979. That might not be too terribly long ago, but think about this: in 1979 there were still people alive who could remember the last time the Chicago Cubs won the World Series (1908) or fought in the war against Spain in 1898.

What is a solar eclipse? When the moon passes between the sun and Earth and casts a shadow on us, that’s a solar eclipse. They can only happen during a new moon, which is when the sun’s rays hit fully on the “dark side” of the moon, so it’s the only time you’ll ever see a new moon. New moons happen every 29 days, just like a full moon, but we don’t have a solar eclipse every month because of how the sun, moon, and Earth dance with each other.

Geometry of a solar eclipse- not to scale (from Nustem)

You’ll notice the sun is a lot higher in the sky now than it was in January. Because Earth is tipped about 23̊ as were orbit the sun while spinning in our tipped circle (which also wobbles) the sun appears to ride a squashed and stretched figure 8 across the sky called the elliptical. The moon does the same, but their ellipticals don’t always match. When they do, you get an eclipse.

Distance is also important. Neither Earth’s orbit nor the moon’s is circular; both are slightly elongated (an ellipse, hence the term elliptical) so sometimes the moon close enough to block out the sun during an eclipse and sometimes it fits inside the sun like a ring. This is called an annular eclipse. Like during a total eclipse, only a narrow band will see the annular eclipse, while everyone else gets to see a partial eclipse or nothing at all.

Annular eclipse (from Universe Today)

Partial eclipse (from Huffington Post)

Always practice safe eclipse viewing! Follow these tips from NASA. Never look directly at the sun, even during an eclipse. The only exception is during totality, and that is ONLY if you have totality where you are at, and it only lasts about a minute and a half. Use eclipse glasses- if you put them on and try to see anything but the sun, you should only see blackness. Sunglasses will not do the job. Never look at the sun through binoculars or a telescope, unless you have a solar filter. If your solar filter screws on to the eyepiece, it is junk- throw it away! If you don’t have any safe viewing equipment, make a pinhole viewer by poking a hole through a piece of cardboard and let the sun shine through. During the partial phase, you will see a spot of sunlight missing a chunk in the middle of the cardboard’s shadow.

I will be in Salem, Oregon for the eclipse, immediately preceding a very special Nature Minute road trip. Sorry, no live-blogging. I can’t blog while driving, and besides, there’s no wifi in the wilderness. Check back in September or follow along on Facebook for pictures and tales from the road.

This week's credits: Nustem, Huffington Post, Universe Today, and NASA