un eclipsing

Science Dictionary
eclipse   (ĭ-klĭps')  Pronunciation Key 

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The partial or total blocking of light of one celestial object by another. An eclipse of the Sun or Moon occurs when the Earth, Moon, and Sun are aligned. ◇ In a solar eclipse the Moon comes between the Sun and Earth. During a total solar eclipse the disk of the Moon fully covers that of the Sun, and only the Sun's corona is visible. ◇ An annular eclipse occurs when the Moon is farthest in its orbit from the Earth so that its disk does not fully cover that of the Sun, and part of the Sun's photosphere is visible as a ring around the Moon. ◇ In a lunar eclipse all or a part of the Moon's disk enters the umbra of the Earth's shadow and is no longer illuminated by the Sun. Lunar eclipses occur only during a full moon, when the Moon is directly opposite the Sun.

Our Living Language  : The Sun is about 400 times wider than the Moon and 400 times farther from Earth, causing the two to appear to be almost exactly the same size in our sky. This relationship is also responsible for the phenomenon of the total solar eclipse, an eclipse of the Sun in which the disk of the Moon fully covers that of the Sun, blocking the Sun's light and causing the Moon's shadow to fall across the Earth. A total solar eclipse can be viewed only from a very narrow area on Earth, or zone of totality, where the dark central shadow of the Moon, or umbra, falls. From this perspective one can view the Sun's delicate corona—tendrils of charged gases that surround the Sun but are invisible to the unaided eye in normal daylight. This is also the only time when stars are visible in the day sky. Those viewing the eclipse from where the edges of the Moon's shadow, or penumbra, fall to Earth will see only a partial solar eclipse. The orbits of the Earth around the Sun and of the Moon around the Earth are not perfect circles, causing slight variations in how large the Sun and Moon appear to us and in the length of solar eclipses. The maximum duration of a total solar eclipse when the Earth is farthest from the Sun and the Moon is closest to the Earth is seven and a half minutes.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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