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article imageToronto witnesses rare total lunar eclipse Special

By Bart B. Van Bockstaele     Dec 21, 2010 in Science
This morning, people in Toronto experienced a rare event: a total lunar eclipse on the same day as the winter solstice. Only once before has this happened in the past 2,000 years, on Dec. 21, 1638.
It was all over the media yesterday: A rare total lunar eclipse would occur during the early morning of Dec. 21, 2010. Lunar eclipses are not all that rare, and while total lunar eclipses are less common, they still happen far more often than total solar eclipses. This one, however, is rare because of a coincidence.
A solar eclipse is an event during which the moon inserts itself between the earth and the sun in such a way that it prevents direct light from the sun to touch the earth. As a result, the earth darkens and experiences a night-like event, even though it should actually be daylight.
A lunar eclipse is quite different. The moon is a dark-matter body like the earth, meaning that it does not emit visible radiation (light). When the moon is bright, it is because we see light of the sun that is being reflected by the moon, back to earth. A lunar eclipse occurs when the earth inserts itself between the sun and the moon in such a way that the moon finds itself in the shadow of the earth.
This morning, in spite of the frigid temperatures and wind chills, some people went outside around 1:30 a.m. to observe the night sky spectacle. One attractive part of a lunar eclipse is that the moon can becomes orange, brown and even blood red while it is out of reach of direct sunlight.
How is this possible, since the moon is prevented from being touched by sunlight by the earth? The earth has an atmosphere, and that atmosphere can bend light, and disperse it, allowing some of it to reach the moon. The earth's atmosphere absorbs short wavelengths, filtering out ultraviolet and blue, but red tones are let through. This gives the moon a reddish tint. At the same time, the moon is very faint because only a small fraction of the sun's light is transmitted this way.
But, if lunar eclipses are not rare, why then is this supposedly a rare event? It is rare because it occurs on the same day as the winter solstice. This is purely coincidental, but it does have the advantage that the moon is very high above the horizon. As a result, the light has to traverse less air (including pollution) and the eclipse should be easier to see.
As NASA reports, the last time the world saw a lunar eclipse coincide with the winter solstice was Dec. 21, 1638. That is 372 years ago, a mere six years after Galileo Galilei published his Dialogo sopra i due massimi sistemi del mondo (Dialogue Concerning the Two Chief World Systems) in which he compared the Copernican heliocentric theory of the solar system now accepted by science and educated humans, with the Ptolemaic geocentric model, favoured by religion.
Galileo was convicted by the Church to lifelong house arrest for his defense of the heliocentric view because it was considered heresy. He was also forced to publicly recant his views. The Church has now changed its position and accepted that while the heliocentric model is heresy, it does have the advantage of being correct and being able to predict astronomical events such as eclipses with very high accuracy.
Today, Galileo is considered by many scientists as the father of modern science and the enlightenment. This is a simplification of reality, as Galileo himself stood on the shoulders of giants, such as Polish astronomer Nicolaus Copernicus, and Johannes Kepler, author of the laws of planetary motion, who based his theories, in large part on the observations of Tycho Brahe who predicted and later observed a lunar eclipse on 8 December 1573, even though he did not use a telescope (which is now known as Brahe's eclipse).
Seeing what science has accomplished since the 1638 lunar eclipse, one can't help but wonder what science will accomplish in the next 372 years.
More about Lunar eclipse, Winter solstice, Moon, Eclipse
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