FLORENCE-On Monday, August 21st, there will be a total eclipse of the Sun that will be visible along a path that runs from the northeastern United States to the southeast. Most of the rest of the country will see a partial solar eclipse of varying amounts depending how far from the total eclipse path that you happen to be located. Florence Alabama will experience 96% of the Sun being blocked by the Sun at maximum. For our area the eclipse will start just before noon and reach maximum eclipse at about 1:26pm and end about 2:55 p.m.
Solar eclipses occur because of the interesting coincidence that the moon on the sky is about one half degree on the sky, and the disk of the Sun is also about one half degree on the sky. The sun is much bigger than the Moon, but also much farther away. To get an idea of how big a half degree is, hold your hand out with your thumb up, and your thumb will make just over a half-degree. Because they are both on average the same size, the Moon in its orbit around the earth can block out the light of the Sun, causing an eclipse. This happens at new moon, when the Sun and Moon are both in the same direction in the sky. The Moon’s orbit around the earth is tilted about 5 degrees to the orbit of the earth around the Sun, so most of the time the moon’s shadow misses the earth. When the geometry is just right we see a total eclipse. Total eclipses are rare from any one location, with sometimes 300 or more years between eclipses. Since they were so rare and dramatic, they were often seen as signs of doom. The Sun suddenly going dark could not be a good thing!
During a total eclipse the bright yellow disk of the Sun is entirely blocked. We then see the corona of the Sun, the faint but hot outer atmosphere of the Sun. The gas in the corona is over a million degrees, but is also very low density, and so is not bright. The light from the visible part of the Sun overwhelms it and we normally do not see it – expect for during a total eclipse.
On August 21st, Florence will see the first part of the eclipse as a tiny nibble, kind of like a cookie bite taken out of the Sun. The nibble will get bigger and bigger until we see just a tiny arc of the Sun remaining, at about 1:26 p.m. The Sun will then slowly emerge and by 2:55 p.m. the eclipse will be over.
The easiest way to view the eclipse is to take piece of cardboard and cut a hole in it, and then tape a piece of aluminum foil over it. Then take a needle and put a little hole in it. The pin-hole will show the shape of the eclipse on the ground or a piece of paper. You can also us eclipse glasses which are designed or viewing eh Sun. UNA planetarium will be holding programs about the eclipse at 7 p.m. Monday to Friday, at August 14 – 18th to inform the public about the eclipse and to give eclipse glasses to attendees.
Dept. Physics and earth Science University of North Alabama/Mel Blake
