Enjoy a rare solar phenomenon, but protect your eyes
In the classic story, “Nightfall,” author Isaac Asimov describes a far-distant world whose inhabitants, because their planet has seven suns, have never seen the stars. But when an eclipse occurs that plunges their world into darkness, billions of points of light suddenly appear -- and drive them all mad.
We Earthlings have no need to worry about such a drastic occurrence when an eclipse of the sun takes place Aug. 21, but we do need to take precautions.
“You don’t want to look at the sun directly with your unprotected eyes,” noted Matt Bobrowsky, an astronomy professor at Delaware State University.
When most people think of an eclipse, they expect to see the sun completely covered and the world around them go dark. In some instances, as on Asimov’s fictional planet, stars even appear in the middle of the day.
“A solar eclipse occurs when the moon comes between the Earth and the sun and the moon’s shadow hits the Earth,” he said. “There’s a central, dark part of the shadow, called the umbra, and if you’re standing in the umbra you’ll see the sun completely blocked out.”
The August eclipse won’t be quite that dramatic for folks on Delmarva: at best Bobrowsky said only about 78 percent of the sun will be covered.
“What most of the country will observe, including in Delaware, is a partial eclipse because we’ll be in the penumbra,” he said.
The penumbra is the area to either side of the roughly 70-mile-wide umbra.
“It’s where we see only part of the sun blocked out by the moon,” Bobrowsky said.
A cosmic dance
A maximum of five solar eclipses can take place every year, but they’re rarely seen because many occur over the 75 percent of the planet that’s covered by water. Astronomers have been known to fly to far distance parts of the world to study eclipses; NASA even operated a heavily modified C-141 aircraft to observe the phenomenon while in flight.
It takes a unique set of circumstances for a solar eclipse to take place: as it orbits the Earth, the moon regularly moves overhead, but a solar eclipse only takes place when its orbit passes the same spot in the sky occupied by the sun.
As the eclipse takes place, the moon’s shadow passes across the surface of the Earth, always in a west-to-east direction.
“A partial eclipse is visible over a very large area,” Bobrowsky said. “Total eclipses are much rarer, and from any one location on the average, you’ll see one only once every 300 years.”
In fact, it’s been calculated that the last time a total solar eclipse crossed Delaware was long before Europeans set foot in what became the First State: it was at 6:32 a.m. Monday, July 29, 1478.
None of us will be around to see it happens again, Bobrowsky said: Delaware’s next total solar eclipse won’t take place for more than 425 years.
“However, if you’re able to travel, there will be many opportunities in the coming years when you can go to locations where a total eclipse will be visible,” Bobrowsky said.
But even though Doverites won’t see a total eclipse, they still can enjoy the partial one. However, it’s important to be properly prepared, as it’s just as dangerous to look at the sun during a partial eclipse as when it’s fully visible: the result can be irreparable damage to the eye.
Despite these warnings, some people still may try to look directly at the eclipse.
The best protection is using special filters that protect the eyes while looking up, Bobrowsky said.
DSU schedules monthly public presentations on astronomy at its observatory and Bobrowsky will use the next two occasions, on July 1 and Aug. 5, to hand out filtered glasses for those wanting to watch the eclipse. The glasses also may be used to observe the sun during the rest of the year.
Another way to safely see the eclipse is to make a pinhole camera.
This is an ancient technique where a tiny hole is punched into a piece of paper. The light from the sun shines through the hole and creates an inverted image of the eclipse. There are no lenses involved. This effect, once called a camera obscura, was known to the Greeks as long as 2,300 years ago.
And there’s even a natural version of the pinhole camera: looking at the ground beneath a tree. The sunlight filters through the leaves, creating images of the sun.
On Aug. 21, between 2:30 and 3 p.m., each of those images will show a crescent sun, Bobrowsky said.
“You can do this with anything with holes in it,” he said. “If you hold a colander out and look at the sunlight passing through the holes and landing on white paper, it will show little crescent suns.”
Also, unlike during a total eclipse, it won’t get totally dark, although some effect, such as a slight change in colors may be seen.
Bobrowsky expects a lot of people will be looking up -- with proper eye protection -- on Aug. 21.
“Any time you have a natural phenomenon that’s rare, it tends to be more interesting,” he said. “A sunrise over the ocean is spectacular, but if it happens every day people don’t think of it as very special.
“But if something happens only every few years, people will turn out in throngs to see it. An eclipse gives us the chance to see something we don’t normally see.
“We’re very lucky to be living in a time when we can see this extraordinary event.”