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Wednesday, Aug. 24, 2016

Fun with asterisms

Thursday, January 3, 2013

I trust you all had the merriest of Christmases and the safest and sanest of New Years. Now, on to business.

There are 88 officially recognized constellations in the northern and southern skies.

There are also many unofficial asterisms, or star patterns, that while not ordained by the International Astronomical Union, they are recognized by astronomers and star gazers around the world.

Two of the most famous are the Big and Little Dippers. In and of themselves, they are not constellations but are star patterns that are well known to anyone who looks up at the northern sky.

We have discussed here before the Summer Triangle; Vega in Lyra, the Harp, Altair, in Aquila, the Eagle, and Deneb, in Cygnus, the Swan. It also is not a recognized constellation, but is an easily recognized asterism.

The asterism I want to examine today has two names, the Winter Circle or the Winter Hexagon. It just depends if you like straight lines or not.

We don't even need a particularly dark sky as the seven stars in this asterism are among the 23 brightest stars in the sky.

To find them let's start at our old friend Orion, the Hunter.

Go outside any evening this week at about 8:30 p.m. local time and look to the southeast. There you will find the hourglass shape of Orion. Two bright stars marking his shoulders; the three stars of his belt, and the two stars of his knees.

Start at Orion's belt and draw a line from the top to the bottom, extend that line down toward the horizon until you find the brightest star in the sky, Sirius, the Dog Star.

Sirius is the closest of the circle's stars at almost nine light years. A light year is about six trillion miles, so you do the math.

Travel up and slightly right to Orion's left knee (remember, his left, not ours) for Rigel. Rigel is the farthest of the circle's stars at almost 800 light years.

Next go almost straight up to find orange-colored Aldebaran, the brightest star in Taurus, the Bull. Look for the "V" shape of the horns of the bull. Above Aldebaran these winter evenings is our old friend, the planet Jupiter.

The next star is Capella in the constellation Auriga, the Charioteer. Capella is up and left of Aldebaran and is almost overhead.

Left and slightly down are the twin stars, Castor and Pollux, in Gemini, then straight down to Procyon, in Canis Minor.

To finish the circle, or hexagon, return to Sirius.

There is another asterism in this area of the sky, the Winter Triangle. Use two of the stars we have already found, Procyon and Sirius, and find bright, reddish, Betelgeuse, the right shoulder star of Orion. If you have trouble finding it draw a line from Rigel, through the center star of the belt and extend it up and left.

The fun thing about asterisms is you can make up your own. Just go outside and look up; then as we imagine the clouds in different shapes, make up your own star patterns and share them with your friends. Who knows, one day the one you imagine might be recognized around the world.

SKY WATCH: Yesterday, Earth was at its closest point in its orbit to the sun. Third quarter moon, Friday, Jan. 4. Moon and Saturn in conjunction in the east early Sunday morning about an hour before local sunrise.

NEXT WEEK: More astronomical blathering.

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Vernon Whetstone
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