Thursday, October 10, 2013

Penumbral Lunar Eclipse

A penumbral lunar eclipse will take place on night of October 18, 2013 (October 19th 2013 early morning for india), the last of three lunar eclipses in 2013.

It will be visible from the Americas (for the end), Europe, Africa, and most of Asia (the beginning of the eclipse will be visible in east and central Asia).

In India we would be seeing the eclipsed Moonset on the 19th morning and won't be able to see the whole duration of the eclipse.

Types of Lunar Eclipses
An eclipse of the moon occurs when the earth is in a direct line between the sun and the moon. The moon does not have any light of its own; instead, it reflects the sun's light. During a lunar eclipse, the moon is in the earth's shadow. It will often look dim and sometimes copper or orange in color. The lighter part of Earth's shadow is call the "penumbra" and the totally dark part is called the "umbra". If you see a chart that says the lunar eclipse is going to be penumbral, this means that the Moon will only pass through the lighter part of Earth's shadow. A partial lunar eclipse occurs when only part of the Moon passes through the umbra, or darkest part, of Earth's shadow. A penumbral lunar eclipse occurs when moon passes through penumbra, the lighter part of the shadow


Why lunar eclipses don't occur every month:
Since lunar eclipses occur always at full moon, it makes sense to ask why each full moon does not generate one. Eclipses are relatively rare because the plane in which the moon orbits around Earth is tilted 5 degrees compared to the plane of Earth's travels around the sun, a plane that astronomers call the ecliptic.
To visualize, think of two hula hoops — one big and one small — floating on the surface of a pool, and push the inner one down so that half of it is below the surface and half above. When the moon gets into the ecliptic — right at the surface of the pool — during its full phase, then a lunar eclipse occurs. (The word "ecliptic" stems from the word "eclipse.")
The geometry of any eclipse — the relative positions of the sun, Earth and moon — is eventually repeated during a set of complex cycles that each last just more than 18 years. This Saros cycle, as the whole thing is called, is behind the bunching of eclipses, too. Astronomers have figured it out and can predict eclipse timing and circumstances far into future.

Timings of the Eclipse:

Penumbral Eclipse Begins: 21:50:38 UT 18th October (03:20:38 IST 19th October)
Greatest Eclipse: 23:50:17 UT 18th October (05:20:17 IST 19th October)
Penumbral Eclipse Ends: 01:49:49 UT 18th October (07:19:49 IST 19th October)

Beginning and end of a penumbral eclipse are not visible to the eye. In fact, no shading can be detected until about 2/3 of the Moon's disk is immersed in the penumbra. This would put the period of nominal eclipse visibility from about 23:30 to 00:10 UT. Keep in mind that this is only an estimate. Atmospheric conditions and the observer's visual acuity are important factors to consider. An interesting exercise is to note when penumbral shading is first and last seen.

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