Tuesday, December 14, 2010

The Winter Hexagon and a Lunar Eclipse

This image is edited from a Stellarium screenshot.  Stellarium is an excellent, free, planetarium program.  Click for a larger view.
"Orion's Belt", part of the constellation Orion, is a well known and easily recognized asterism in the northern hemisphere's winter sky (between Betelgeuse and Rigel on the image above).  Six bright stars surround Orion's belt forming the Winter Hexagon, outlined in the image above.  Those stars are easy to find on a dark, clear night - follow the line formed by Orion's Belt to the left to locate the bright and twinkling star Sirius, drop down perpendicular to the Belt to find blue-white Rigel, follow the belt to the left to spot Aldebaran (the orange "eye of the bull" in the constellation Taurus).  Look up from Aldebaran to find Capella (in the constellation Auriga), to the left of Capella find Pollux (the brighter of the twins of Gemini), and the sixth star of the hexagon is Procyon, below Pollux on the way back to Sirius.
The Moon passes through the Winter Hexagon each month in its orbit around the Earth, and this month it will be December's Full Moon passing through on the night of 12/20 - 21/2010.  Go out and take a look on Monday, 12/20 - the brightest stars you'll see around the Moon are the stars of the Winter Hexagon. And on this particular night, the position of the Moon marks an important position in the sky...the exact spot the Sun will be on June 21, six months from now - a place in the sky called the "summer solstice".  Tonight's Full Moon will trace the same path across the sky that the summer sun will follow in June!  On this night, too, the Sun is directly opposite the Moon on the other side of the Earth:
 This image is a composite of Google Earth images cobbled together to show the relative locations of the Moon, Earth and Sun during the upcoming eclipse. Click for a larger view

At around 1:30 AM (EST) the Moon will enter the darkest part of the Earth's shadow (called the umbra).  For the next 3 1/2 hours, the Moon will move from right to left through the Earth's shadow, darkened to an orangey-red in the dim light of the Earth's shadow.
If you're willing to stay up, or wake up around 2 AM (EST) on the morning of Tuesdsay 12/21, you can view the last lunar eclipse of 2010.  Worth it, I say!
Here are some photos I took during the lunar eclipse of February, 2008.  That eclipse happened in the constellation of Leo and some of my photos included images of the bright star Regulus (Leo's "heart") and the planet Saturn with its rings tipped toward us.

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