Total solar eclipse on August 21

Dr. William Warren
Flint River Astronomy Club

As you may already know, there’s going to be a total solar eclipse this month. It’s likely to be the biggest event in astronomy this year. Here, in Q&A form, are some things you need to know about eclipses, and the August 21st total eclipse of the Sun in particular:

What is a solar eclipse?
It’s when, during some New Moon phases, the Moon’s orbital path takes it directly between Earth and the Sun, blocking all or part of the Sun’s light from our view for a brief period. That happens between 2-5 times every year, but we seldom get to see them.

Why not? Why isn’t there an eclipse every month?
The Moon orbits the Earth, and Earth orbits the Sun. But the Moon’s orbital path is not in the same plane as Earth’s orbital path, so most of the time they are not properly aligned with the Sun to produce an eclipse. It’s a big sky out there; there’s plenty of room for the Earth and Moon to pass each other without producing an eclipse.

Even when they are aligned properly, though, we don’t see most of them.

Again, why not?
The Earth is six times larger than the Moon, so when the Earth’s orbital path takes it between the Moon and the Sun in a lunar eclipse, Earth’s dark shadow (called the umbra) is large enough to cover the entire lunar surface.

In a solar eclipse, however, the shadow cast by the Moon onto Earth is much smaller. Unless you’re inside that lunar umbral shadow – which in the case of the August eclipse is about 67 miles in diameter – you won’t see a total eclipse. (The umbra’s path across the U. S. is called the area of totality.)

Griffin, Fayetteville, McDonough, and Barnesville are not in the area of totality.

So if I stay home on August 21st, will I miss the eclipse?
No, you’ll still see it – but as a partial eclipse. Less than 10% of the Sun’s light will remain visible throughout the eclipse – but that’s enough to be harmful to your eyes if you aren’t careful.

Elsewhere in the U. S., how much of the Sun remains visible during the eclipse will depend on how close you are to the area of totality. Most of the U. S. will see up to 90% of the Sun covered by the Moon.

Where will the path of totality be?
The Moon is a sphere, so the umbral shadow it casts on Earth is small and round. As the Moon travels across the sky on August 21st, the umbra will enter the U. S. in Oregon and forge a path through twelve states before heading out to sea near Charleston, S. C. (Those states are: Oregon, Idaho, Wyoming, Nebraska, Kansas, southern Illinois, Missouri, western Kentucky, Tennessee, western North Carolina, northeast Georgia and South Carolina.)

That’s right. If you get a Georgia map and draw a line from Cleveland, Ga. to Cornelia and extend it to the northwest and southeast, everywhere north of that line in Georgia lies in the area of totality. That area includes four state parks (Vogel, Unicoi, Moccasin Creek and Black Rock Mountain); Brasstown Bald (at 4,784 ft. in elevation, it’s Ga.’s highest mountain); and towns such as Blue Ridge, Blairsville, Helen, Hiawassee, Clarkesville, Toccoa and Clayton.

Of those towns, Clayton will have the longest period of totality – 2m 34s. At the other extreme, Cleveland and Cornelia will have about 1m 30s of totality. The greatest period of totality anywhere along the umbral path will be 2m 40s near Hopkinsville, Ky.

Why are so many people planning to drive to the area of totality just for a minute or two of eclipse? What’s the big deal?
First, the eclipse doesn’t begin or end with totality; there’s also the periods of partial eclipse on either side of it. For example, in Atlanta (which isn’t in the path of totality) the partial eclipse will begin at 1:05 p.m.; maximum darkness will be at 2:36 p.m.; and the eclipse will end at 4:01 p.m. (Those times also apply to our area.)

More importantly, total eclipses are rare: the chances of Griffin (or any other specific location in the U. S.) lying in the path of totality are once in every 330 years – and this isn’t one of those years. The state of Delaware hasn’t experienced a total solar eclipse in 539 years.

Beyond that, this will be the first total solar eclipse to be visible as a partial eclipse in all 48 states (excluding Hawaii and Alaska) since 1979. And the last time one was visible from coast to coast was in 1918. So from a historical perspective, this one really is a big deal.

What should I do if I want to experience totality?
There are numerous eclipse route maps on the web; Google one.

Since travel to and from anywhere along that path will involve several hours of driving each way, you might want to stay somewhere overnight.

Forget the state parks and small towns in northeast Georgia (and probably everywhere else along the path). There will be hundreds of thousands (or possibly even millions) of eclipse enthusiasts from all over the U. S. and abroad coming to see it. They won’t all be coming to Georgia, of course, but camping sites at the state parks assuredly have already filled their reservation quotas, and the small towns don’t have much in the way of motel accommodations. They may also be filled up on eclipse day, too.

Your best bet might be to select a city such as Knoxville or Chattanooga (which lie slightly outside the area of totality), and drive less than 40 mi. from there to see it.

Another suggestion might be to try to find a motel vacancy in Nashville, TN, or in Greenville, Spartanburg, Columbia or Charleston, S. C. – all of which are within the area of totality. (On the other hand, those cities are the closest ones to millions of Americans living along the East Coast, so they may fill up too, motel-wise.)

I understand that the Sun won’t be visible during totality, and that it’s important to wear solar sunglasses or use a solar filter on my telescope to protect my eyes while any part of the Sun is still visible. But what about ordinary sunglasses? Will they protect my eyes?

Only if you stack thirteen pairs on top of each other. (But then you won’t see anything.) Otherwise, your retinas are in for a big – and very dangerous – shock if you look at the Sun through regular sunglasses.

Specially made solar sunglasses are completely safe. Unlike ordinary sunglasses, they block out all of the Sun’s harmful rays. You can buy them on the web by Googling “solar sunglasses.” They cost about $2.50 a pair. Do not look at the exposed sun for prolonged periods unless you are wearing solar sunglasses!

Are there any other safe ways to view the eclipse?

You can buy a pane of #14 welder’s glass for about $25; it’s what welders use to protect their eyes from the intense glare of an acetylene torch, and it’s perfectly safe. (Be sure it’s #14; others aren’t safe for an eclipse.)

The simplest, cheapest and safest way of all, however, is pinhole projection.

Lay an index card on the ground, then use a pencil point to punch a hole in a second index card. Hold the second card about 3-4 ft. above the one on the ground and align it with the Sun. (Don’t look at the Sun while you are doing that.) The eclipsed Sun will project through the hole onto the card on the ground. The larger you make the hole, the larger the Sun will appear.

What will I see during the eclipse?
If you stay home, you’ll see the Moon slowly eat a very large chunk out of the Sun, and the sky will darken considerably. You’ll see the same thing during the partial eclipse if you travel to the area of totality, but during totality the sky will be as dark as midnight. The Sun won’t be visible at all, so you won’t need your solar sunglasses until it reappears a minute or so later. During that time, you’ll see stars that you can’t normally see during the daytime.

Even if the sky is completely overcast, you’ll know when the eclipse is occurring: you’ll see sunset, the darkness of night and sunrise compressed into three hours between 1-4 p.m. Birds and farm animals will bed down for the night, and roosters will crow during the false dawn.

If you watch the eclipse through a telescope with a solar filter attached to the tube, you’ll see the Sun’s outermost layer of gases (called the corona). Just before and after totality, you’ll see tiny beads of sunlight called Baily’s beads in gaps in the lunar surface along the Moon’s leading or trailing edge. When just one bead is left, you’ll see it as a “diamond ring.” (You won’t see them without a telescope; they’re too small for that.) Those effects last just a few seconds, but they’re lovely. Most telescopic observers regard seeing Baily’s beads and the diamond ring as one of the highlights (pun intended) of their total solar eclipse experience.

Finally, it bears repeating: looking directly at the Sun without adequate protection for your eyes is extremely dangerous. The total solar eclipse of August 21st will be a once-in-a-lifetime event, but you do NOT want to risk losing your eyesight permanently by staring at the Sun unless you are wearing solar sunglasses or watching the eclipse through a pane of #14 welder’s glass.