Observers on the eastern seaboard will be able to see just the beginning of the eclipse at dawn. Before entering the main umbra, or cone of shadow, the Moon must pass through the penumbra, or zone of partial shadow, which exists because the sun is a disk and not a point source of light. Even during a total lunar eclipse, when the Moon passes entirely through the umbral shadow, the Moon is not completely dark. That's because sunlight is refracted as it passes through Earth's atmosphere and bent toward the lunar surface. The depth of shadow and the orange hue of the lunar surface during an eclipse are influenced by the amount of dust or ash in the earth's upper atmosphere.
Eclipses following volcanic eruptions on Earth can appear especially dark and coppery-colored.
A lunar eclipse is always a beautiful sight, but the fate of Lunar Prospector may add some drama to the event for sky watchers viewing the orange-colored, shadowy Moon next Wednesday morning. For more information about the lunar eclipse, and eclipses in general, see Fred Espanek's Eclipse Home Page at the Goddard Space Flight Center. Astronomers prepare to observe the crash of Lunar Prospector on July 31, 1999.