for National Geographic News
On Saturday night the full moon will slip into Earth's shadow and darken to an orange-reddish glow, giving sky-watchers their second chance this year to catch an astronomer's delight: a total lunar eclipse.
The celestial show will be visible throughout most of the Americas, Europe, Africa, and western and southern Asia, giving up to three billion peopleweather permittinga rewarding view of the cosmic display.
"It should be quite colorful, whitish on one pole to more copper-red on the other," said Michael Reynolds, an author and eclipse coordinator for the Association of Lunar and Planetary Observers in Jacksonville, Florida.
The spectacle officially begins at 5:15 p.m. ET on Saturday when the full moon makes contact with the outer portion of Earth's shadow, called the penumbra. Most observers will not notice any changes until 6:32 p.m. when the moon makes contact with Earth's dark inner shadow, known as the umbra.
Totality, the phase when the Earth's shadow completely immerses the moon, begins at 8:08 p.m. and lasts for 25 minutes, making it a relatively short total lunar eclipse. The moon exits the umbra at 10:04 p.m. and the whole event comes to an end at 11:22 p.m.
While viewers in the eastern United States, Europe, and Africa can watch the whole show, viewers along the west coast of North America will witness the moon rise partially eclipsed. Viewers in western Asia, meanwhile, will watch the partially-eclipsed moon set.
Short and Bright
Total lunar eclipses occur when the moon passes through the Earth's shadow. Because the projection of the Earth's shadow reaching the moon is much larger than the diameter of the moon itself, the moon does not have to move through the center of the shadow to be totally eclipsed.
For this particular eclipse, the moon will pass through the southern edge of Earth's umbral shadow.
Unlike a center-shadow lunar eclipse, Saturday's event will be shorter, brighter and/or more colorful, Reynolds said. "Since this is just barely total, both should apply for this eclipse."
During total lunar eclipses, the moon does not go completely dark. While the Earth stands between the Sun and moon during totality, a certain amount of light is bent, or refracted, by Earth's atmosphere and illuminates the moon.
Fred Espenak, an eclipse expert at NASA's Goddard Space Flight Center in Greenbelt, Maryland, likens the effect to sitting at the edge of a pool or lake and putting a stick in the water.
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