Sky-Watchers Await Total Lunar Eclipse on Thursday

John Roach
for National Geographic News
May 12, 2003

On the night of May 15 the full moon will slip into Earth's shadow and darken to an orange-reddish glow during the first of four total lunar eclipses to occur over the course of the next 17 months.

The celestial show promises to capture the attention of both amateur and professional astronomers and remind them of Earth's place within the cosmos.

"The lunar eclipse can be appreciated and celebrated as an event which vividly illustrates our connection and place among the planets in the solar system," said Fred Espenak, NASA's eclipse expert at the Goddard Space Flight Center in Greenbelt, Maryland.

The eclipse will be visible to sky-watchers throughout the Americas, Europe, and Africa. It officially begins Thursday night at 9:05 p.m. ET when the moon enters the outer portion of the Earth's shadow, known as the penumbra.

Casual observers will notice a marked change about an hour later at 10:03 p.m. when the eastern edge of the moon enters the inner, darker part of Earth's shadow, called the umbra.

Totality, as the phase when the entire moon is inside the umbra is known, begins at 11:14 p.m. ET and will last for 53 minutes, until 12:07 a.m. ET. The moon will fully exit the Earth's umbra at 1:17 a.m. and make last contact with the penumbra at 2:15 a.m.

The most recent total lunar eclipse occurred on January 9, 2001. The next chance to catch a total lunar eclipse will be November 9, followed by total lunar eclipses on May 4 and October 28 in 2004. After this run, the moon will not completely slip into Earth's umbra until March 3, 2007.

Moon Color

During a total solar eclipse, the new moon passes in front of the sun and momentarily casts day into the darkness of night. But during a total lunar eclipse, the moon remains at least partially lit during the event.

Even though Earth blocks the moon from direct sunlight during an eclipse, some sunlight is refracted, or bent, by the Earth's atmosphere and illuminates the moon. The atmosphere scatters most of short wavelengths of light—blue, green, and yellow—out of the refracted light so that primarily the orange and red rays reach the moon, said Espenak.

"The more dust the atmosphere has, the more scattering takes place and the redder, and darker, the moon appears," he said.

Since there have not been any major volcanic eruptions or extensive forest fires recently, astronomers believe the atmosphere is relatively clear of the type of particles that could cause a deep-red eclipse.

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