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.
The first lunar eclipse of 2009 is one of four such events during the year. The first three eclipses are penumbral while the last (on Dec. 31) is partial. The Feb 09 event is the deepest penumbral eclipse of the year with a penumbral magnitude of 0.899. It will be easily visible to the naked eye as dusky shading in the northern half of the Moon. The times of the major phases on earth are listed below.
Penumbral Eclipse Begins: 12:38:46 UT (18:08:46 IST)
Greatest Eclipse: 14:38:15 UT (20:08:15 IST)
Eclipse Ends: 16:37:40 UT (22:07:40 IST)
The 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 eclipse visibility from approximately 14:00 to 15:20 UT (19:30 IST to 20:50 IST). 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.
Visibility of the eclipse:
Parts of Western and southern India will witness the moon rising in eclipse whereas rest of the country will see the total duration of the eclipse. Eastern Canada and the USA will miss the eclipse entirely since the eclipse begins after moonset. Observers in western Canada and the USA will have the best views with moonset occurring sometime after mid-eclipse. To catch the entire event, one must be in Alaska, Hawaii, Australia, or East Asia.
Eclipse Myths:
Myths die hard. In Japan, some people still cover wells to avoid being poisoned by the disease of the moon during an eclipse. Native residents of Arctic regions are known to turn over their utensils to avoid contamination. In other cultures, people yell at the moon during an eclipse, or they bang pots or even shoot into the air.
When the moon disappeared in 413 B.C., Athenians saw it as a bad omen and delayed their planned retreat from the Sicilian city of Syracuse, where they had fought for two years in the Peloponnesian War. The Syracusans used the delay as an opportunity to break the siege, contributing — some believe — to the fall of Greek civilization.
Christopher Columbus actually used an eclipse knowingly to perhaps alter history. Stranded in Jamaica in 1504, on his fourth voyage, Columbus and his crew were wearing out their welcome with the natives, who were feeding them. Columbus knew a lunar eclipse was coming, so he "predicted" the moon’s disappearance. The natives begged him to bring it back and, of course, he did, in due time.
C B Devgun
President, SPACE
