TOTAL LUNAR ECLIPSE
December 10th 2011
Year 2011 end brings us another spectacle in astronomy – Total Lunar Eclipse on 10th December! The last eclipse of the year will once again be putting a show just before the year ends and next year comes with the rarest of rare astronomical events – Venus transit. It will be visible from all of Asia and Australia, seen as rising over eastern Europe, and setting over northwest North America. In the Philippines, the lunar eclipse is seen visible just after sunset.
What is an eclipse of the Moon? What causes eclipses and why? How often do eclipses happen and when is the next eclipse of the Moon?
We live in a world that seems so ordered; the Sun rises, goes across the sky and then sets. The Moon goes through its phases from new to full and back again. It all seems like clockwork, and then, something unusual happens that seems to throw the orderly timing of the cosmos into chaos. On a night when the moon rises full and beautiful, it starts to change; at first it is so subtle few notice it. But then, every so slowly, the moon begins to dim, and more alarming yet, it disappears.
One can only imagine how frightening the sight of a lunar eclipse must have been for our ancestors. Far more than us, they were in tune with the rhythms of the cosmos, the motions of the Sun, Moon and planets were the motions these people lived by. They told time by the daily passing of the Sun, or full moon to full moon gauged longer periods of time. And the very stars marked the passing of seasons. The skies were orderly and dependable, except for when an eclipse happened. During that time, chaos reigned, and our ancestors prayed and begged for the Moon to be returned to the sky.
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. In India people take bath in holy rivers to wave off the evil effect of the eclipse.
Primitive ideas about the figure of the Earth, still found in young children, hold the Earth to be flat and the heavens a physical dome spanning over it. Lunar eclipses, e.g., always have a circular edge of appox. three times the radius of the lunar disc; as these always happen when the Earth is between Sun and Moon, it suggests that the object casting the shadow is the Earth and must be spherical (and four times the size of the Moon, the lunar and solar discs being the same size).
Our ancestors saw eclipses as evil omens, often as portents of some catastrophic event or a sign from their deities. The earliest recorded eclipse was in China on October 22, 2134 BC. The two court astrologers to the Emporer lost their heads because; they had failed to predict it. The Babylonians were the first to calculate the regular intervals at which eclipses occur. Thales of Miletus predicted a solar eclipse that marked the beginning of the Greek scientific/philosophic era. Word eclipse comes from a Greek word, “ekleipsis” meaning abandonment.
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.
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.
CIRCUMSTANCES OF THE ECLIPSE
Indian Standard Time
Moon enters penumbra
Moon enters umbra
Moon enters totality
Middle of the eclipse #
Moon leaves totality
Moon leaves umbra
Moon leaves penumbra
12h 45.4 m
18h 15.4 m
Moon will rise in eclipse in delhi
Visibility of the Eclipse
Key to Eclipse Visibility Map
P1 Penumbral eclipse begins (not visible to the eye)
U1 Partial eclipse begins
U2 Total eclipse begins
U3 Total eclipse ends
U4 Partial eclipse ends
P4 Penumbral eclipse ends (not visible to the eye)
Area of visibility: The eclipse will be visible in the region covering Africa, Europe, the Middle East, Asia, Australia, North America, Greenland, and the Indian, Pacific, and Artic Ocean. The places from where the beginning of the umbral phase is visible at the time of moonset are parts of Mexico, eastern U.S.A., eastern Canada and Greeland. The places from where the ending of the umbral phase is visible at the time of moonrise are parts of Europe, Africa and some regions of Southern Ocean.