Albert Einstein once made a statment which said, "The most incomprehensible thing about the universe is that it is comprehensible." I wonder if he was referring to the fact that a total eclipse is actually seen by such a few people on Earth, mainly because the shadow of the eclipse covers such a tiny bit of our planet-a fact very people realize as they are all too busy searching for one. The word penumbra refers to a partial shadow (such as in an eclipse) that is located between an area of complete shadow and one of complete illumination. In Astronomy, the penumbra of an eclipse refers to an area of partial eclipse from behind the moon which allows us to see some part of the sun. Yet it must occur from where the dark umbra touches our planet, and only then will we be able to see the sun completely covered enough to witness a total eclipse.
Penumbral eclipses are only one of the three eclipse types-total and partial the remaining two. The total lunar eclipse is referred to as the best one to view which involves the Earth passing directly in front of a full moon-casting its gentle shadow on the Moon's surface. As the moon is always orbiting our planet, and the earth is always orbiting the sun while rotating on its axis-the umbra location is always moving while tracing out a path to follow. Yet when a penumbral eclipse is occuring, the Moon's area does not enter Earth's dark umbral shadow. This is the reason no distinct outline of Earth's shadow is shown by the Moon, yet will pass through the outer part of the shadow of our planet, dimming the Moon ever-so-much. A darkening can occur when the edge of the Moon passes nearest to the umbra, but approximatley 70% of the disk of the Moon needs to be inside the penumbra before it can be seen by the naked eye.
The next penumbral eclipses will occur next year in 2009.
* February 9, 2009: Easterm Europe, Asia, Australia, Pacific, Western North America
* July 7, 2009: Australia, Pacific, and Americas
* August 6, 2008: Americas, Europe, Africa, and Western Asia
* November 28, 2012: Europe, Eastern Africa, Asia, Australia, Pacific, North America
In March 14th of 2006, the penumbral eclipse was an extreme rarity as compared to most of them. The Moon had arrived two days earlier on the 12th at its furthest distance from the Earth-252,446 miles which allowed the moon to appear about 7% smaller than normal. This resulted in the Moon interacting with the shadow of the Earth, immersing in its small size within the penumbra-yet large enough to touch the umbra-for one hour. This is a rare occurence called the total penumbral eclipse, one of five cases occuring in the entire 21st century, with the next one occurring until August 29, 2053. When they do occur, the area of the Moon which is closest to the umbra will appear darker than the rest of the Moon-as the Moon is lying "exclusively" inside the Earth's penumbra.
The penumbral and full eclipse were found to be connected to Stonehenge by Sharon Challener, professor of physics and astronomy at Clarion University in Pennsylvania. She had inherited her father's fascination with the ancient sites, both spending years attempting to figure it out. Quite by accident she discovered tables of 47 lunar months in southern England, when she began associating the ruins with the moon and its eclipses. What she found out was that within each 47-month cycle, a family was developed through their eclipse separation time of 47 months-forming a special group of their own.
What she found was fascinating was every group-or family-would begin as either a parial eclipse or a penumbral eclipse every 47 months. And every time it would occur, it would happen closer and closer to a total eclipse. In each family a dozen or so total eclipses would occur before they would grow as more partial eclipses until the eclipse would eventually disappear. Once the family, or group, was finished it would be marked and retired. Unfortunately, she has found there never was any support in archaelogical artifacts to prove this other than her own life's work.