What's so special about a total eclipse of the Sun?

If you've ever seen a solar eclipse on television or seen pictures in a book, dismiss those images. They don't begin to tell the story. If that's all there were to the event, there wouldn't be tens of thousands of people traveling across countries and continents to get to the eclipse. Everyone would watch it on the evening news.

Here's a brief overview of what the TV images cannot show you. The partial eclipse begins about an hour before the total eclipse. During that period, the silhouette of the Moon starts to pass in front of the disc of the Sun. If you look toward the bright Sun through a protective filter, you can see by eye that the black outline of the Moon's disc is creeping across the Sun's disc very gradually. All around you, the air takes on a strange hue and an eeriness that is not seen under any other conditions. As the eclipse advances, all of nature senses the change. Birds come to roost, cocks will crow, and all manner of animals and plants revert to their nighttime posture even in the middle of the day. So you can already see that the phenomenon is considerably more influential to nature than, say, the Sun going behind a cloud. Clouds block the light of the Sun, but eclipses block all wavelengths of solar radiation.

The landscape gets progressively darker, and temperatures start to drop. Only those standing under the approaching shadow sense these effects. If one looks at the ground under a tree with leaves, or anywhere light from the Sun passes through small spaces, each such hole will project an image of the crescent Sun blocked by the advancing Moon on the ground. Hundreds of crescent images may be visible all over the ground.

If one has a view toward the west, the advancing shadow of the total eclipse may be visible even before it arrives. It is especially noticeable if a cloud bank or bright landscape is in the direction where the blackness will cover it before it reaches your own position. The shadow advances at an average rate of 50 km (30 miles) per minute.

In the final minutes before the eclipse becomes total, many more things happen. Shadow bands may suddenly appear and shimmer over all ground objects. The Sun's atmosphere, called its corona, starts to become visible as a bright ring around the black lunar disk. The disappearing crescent shrinks to a brilliant gem on the edge of the brightening corona. This effect is called the "diamond ring". Mountains along the lunar limb break up the last of the crescent into "Baily's beads". The inner solar atmosphere, called the chromosphere, makes its reddish presence known -- called the "flash spectrum". Brighter stars and planets appear. Solar prominences, gigantic explosions along the Sun's limb, may be seen with the aid of binoculars. A total solar eclipse is a multifaceted experience, and the impression it leaves on the viewer is one of awe.