The “Great American Eclipse” of 2017
On Monday, August 21, sky watchers across the United States are going to be treated to one of the most awesome experiences in all of nature: a total solar eclipse.
If you stay in the Clayton State area, you will only be able to experience a partial solar eclipse, which is also an awesome experience, but not quite at the same level. I have organized a bus trip to bring about 100 students, faculty, and members of the community a bit further up north—a 2-hour drive in normal conditions (but for this spectacle, the roads may be clogged with eclipse-chasers!).
There, the moon’s shadow on the Earth will completely block out the Sun (a total solar eclipse). Down in Morrow, the moon’s shadow at the maximum of the eclipse—about 2:36pm—will only cover 97 percent of the sun, known as a partial solar eclipse.
Because the eclipse happens on a Monday, many residents may be stuck at work and unable to travel to the “path of totality” where the sun will be completely blocked. Even here, if the weather is cloudy you won’t experience the eclipse except as a darkening of the sky.
If the sky is clear, here’s how to appreciate the spectacle:
First, DO NOT stare at the sun! There’s nothing especially dangerous about sunlight during an eclipse. The moon’s shadow only subtracts light and doesn’t add anything that isn’t already there. But because it’s such a spectacle, people may stare at the partial eclipse, and that can permanently damage your vision.
One option is to use safe glasses which filter out most of the light. Several glasses will be passed around campus that were donated by Clayton State alum Stephen Ramsden, founder of the Charlie Bates Solar Astronomy Project, a nonprofit organization that educates people around the world in the science of the Sun.
Another option is to use a “pinhole camera.” A piece of cardboard with a small hole (made by a pin for example) can project an image of the sun onto a screen or the ground, so you can see the dark side of the moon as it slowly moves across the sun between 1:06 p.m. and about 4 p.m.
You can get creative with pinhole cameras. Even a spaghetti-draining colander can act like a pinhole camera, with each hole causing its own image of the Sun to be safely projected onto a screen.
You might not notice it, but when sunlight passes through a tree it forms a kind of natural pinhole camera as the light streams through small gaps between the leaves. Look at the shadow of a tree during the eclipse and instead of seeing sunlight as round dots, you’ll see crescents of the partially eclipsed Sun!
Now, you may be wondering, what’s much more awesome about the total solar eclipse visible further north?
Well, for two and a half minutes, day will turn to night. The stars and planets will come out. The temperature will go down just as in night, and animals may become confused by the dramatic change in brightness in mid-afternoon.
But the most dramatic sight of all will be the sun’s corona (not REALLY named after the Mexican beer of that name—corona literally means “crown,” as the layer of hot gas surrounds the sun like a crown).
The corona is a shimmering layer of hot and thin gas that always surrounds the sun, but we never see it in normal circumstances because the lower-lying surface of the sun is too bright.
Total solar eclipses are not only an awesome spectacle for the public, but allow scientists to study this mysterious gas layer in greater detail. It’s mysterious because by a basic law of physics, heat only flows from hotter to cooler, and yet the corona is a million degrees, while the surface of the sun (which one might think is its source of heat) is only about 6000 Celsius.
Apparently, snapping magnetic fields in the turbulent outer layers somehow releases the energy to heat up the corona, but the details of how this happens are still being studied. Whatever those details are, if you are present for the total solar eclipse, the landscape around you will be lit up by an eerie light of a kind you may have never experienced before: lit by million-degree gas!
The sun will be safe to look directly at during the two minutes or so when the moon completely covers the sun’s surface leaving only the corona (if you are in the path of totality, not in Clayton County or the Atlanta area), but not before or after.
Besides helping scientists learn about the corona layer, solar eclipses also provided the first test of Albert Einstein’s General Theory of Relativity, which is still our best theory of the gravitational force. Gravity seems to pull on everything.
Does it pull on light? That might seem a puzzler, but Einstein’s theory said it did, and calculated just how much it should pull on light. How do we put Einstein’s theory to the test?
Well, the sun has more gravity than most anything nearby, which is why all the planets are in orbit around it. If a star’s light came close to the sun (gravity is always stronger and closer to the cause of the gravity), its path would be bent by the sun’s gravity.
Normally we don’t see stars in the daytime because the sun is too bright, but during an eclipse, we can. And in fact, in the year 1919, a total solar eclipse showed that when starlight passes near the Sun, it “falls” toward the sun because of gravity, and the star appears to us in a slightly different place.
Because gravity also works on light, black holes are possible, where a dead star’s gravity is so strong it can even hold in light so it doesn’t escape.
This eclipse is being called the “Great American Eclipse” because the shadow of the sun will cross the continental U.S., from Oregon to South Carolina, moving about 3 times faster than a jet airplane. The next total solar eclipse to occur in the U.S. will be in April of 2024. I haven’t seen a total solar eclipse myself, but I am hoping to see my first one with students, faculty, and friends on August 21. Some who have seen total solar eclipses say it is the most awe-inspiring sight they have ever seen!