Lunar eclipse

A lunar eclipse is an astronomical event which occurs when the Earth blocks out the Moon's view of the Sun. Eclipses of the moon happen once or twice a year and can only occur when the moon is at its full moon phase [1].

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Observing Lunar Eclipses

Unlike a solar eclipse, where accidental glimpses of the sun can cause damage to the eye, a lunar eclipse poses no danger to its viewers. In a lunar eclipse, the shadow of the earth slowly moves across the surface of the moon. The moon either partially passes through the shadow of the earth or moves entirely into its shadow, in which case the phenomenon is known as a total eclipse.[2] During a total eclipse, the moon is illuminated with a reddish-brown or orange light, which is caused by the sunlight being bent through the earth’s atmosphere. The red components of the light are most likely to reach the moon, giving it its distinct color [3].

The Earth casts a shadow from the sun. Since the sun is not a point of light, but a broad disk as seen from earth, part of the shadow is only a darkening because part of the sun is still visible.[4] Any shadow cast on earth has a fuzzy edge because of this effect and so the earth's shadow also has a fuzzy edge. The wide edge of the earth's shadow where the sun is only partially hidden is called the penumbra. The cone of dark shadow where the sun is completely hidden by the earth is called the Umbra. The Umbra extends approximately 860,000 miles (1,380,000 kilometers) from the earth and is large enough to completely cover the moon if it should pass near the center of the cone. A Total lunar eclipse occurs when the moon has a time in which it is completely in the umbra. A Penumbral eclipse occurs when the moon is only in the penumbra, and is darkened, but without the dark red or brown of a Total eclipse. A Partial eclipse occurs when the moon, at its greatest eclipse, is only partially covered by the umbra.

The greatest eclipse will always come when the moon is going through the middle of the deepest shadow that earth casts. This means that the greatest lunar eclipse always occurs directly overhead that part of the earth which is at local midnight. Because of time zones, an eclipse that seems, from some place on earth, to lie on the line from the Zenith (directly overhead) to the south (or north), will normally occur within a half hour of midnight in that time zone.

Lunar Eclipse Dates

NASA gives the following information about lunar eclipse dates in 2010[5].

2010 Jun 26: Partial Lunar Eclipse

2010 Dec 21: Total Lunar Eclipse

During the years 2011-2020, information from NASA[6] and other places gives the following information about Lunar eclipses. Note that the UTC time in hours (Coordinated Universal Time at the prime Meridian which passes Greenwich, England) multiplied by 15 gives the approximate degrees of longitude over which the eclipse takes place.

Since London standard time is UTC time, any eclipse with a UTC time of 18:00 to 06:00 is visible in London skies, but at 19:00 the moon would be only a little above the horizon when the eclipse occurred. Similarly, since New York is UTC - 4, an eclipse would be visible in New York from 22:00 to 10:00 UTC. From Tokyo, UTC + 9, visibility occurs between 9:00 and 21:00 UTC, and from Israel, UTC + 3, between 15:00 and 03:00, etc.