Monday, August 01, 2005

Shadows

Every spherical object in the solar system wears a conical shadow pointing away from the Sun. Even the astronauts spacewalking up there with the Discovery shuttle cast shadows. If an astronaut in Earth orbit points her feet toward the Sun, she wears a wizard's cap of darkness one hundred feet long. The Moon's shadow cap, by wonderful coincidence, is almost exactly as long as the average distance of the Moon from the Earth. During a total eclipse of the Sun, the Moon's shadow brushes the Earth's surface like the tip of a feather. To see a total solar eclipse, one must be standing exactly where the shadow's tip intersects the Earth, which is why I will be on a shore of the Eastern Mediterranean next March 29.

Take a terrestrial globe such as you might have in your home, and every year or two draw a random line ten or twelve inches long across its face with a black felt-tip marker. The line can be anywhere from north pole to south pole and in any hemisphere. These marks are typical of total solar eclipse paths. It takes the Moon's shadow about 4500 years to "paint the globe black." That is, the longest you will have to wait for the Moon's shadow to brush your home is 4500 years.