December 26, 2010

What's Up in January
Year begins with good views of giant stars and planets


The full beauty of the brilliant stars in the winter hexagon become evident in January, as the entire group is well above the southeastern horizon and perfectly placed for viewing by 8 p.m. Although they may look somewhat alike at first glance, the eight stars tell unique and astounding stories.

click image to enlarge

This chart represents the sky as it appears over Maine in January. The stars are shown as they appear at 9:30 p.m. early in the month, at 8:30 p.m. at midmonth and at 7:30 p.m. at monthâ s end. Jupiter is shown in its midmonth position. To use the map, hold it vertically and turn it so the direction you are facing is at the bottom.

Sky chart prepared by George Ayers

Beginning at the top of this hexagon, you will see Capella in Auriga. Proceed clockwise to Aldebaran in Taurus, an orange giant star 65 light years away whose name in Arabic means "the follower," since it appears to follow the Pleiades through the sky.

Continue on to Rigel, marking the left knee of Orion the Hunter. This is a blue super giant star 800 light years away that is 17 times the mass of our sun and 85,000 times as luminous. Then you will see the lowest star in this group and also the brightest in the whole sky, Sirius in Canis Major. It is one of the closest stars to earth at only 8 light years away. Then proceed up the left side to Procyon in Canis Minor and finish the circle with Castor and Pollux in Gemini. Both Castor and Pollux, the mortal and immortal twins in Greek mythology, are actually multiple star systems.

Near the middle of this hexagon, sometimes also called the Winter Circle or Heavenly G, is the red supergiant star named Betelgeuse. This one is by far the most amazing and exciting star in the whole group.

It varies a full magnitude in brightness and it is the first star other than our sun on which we have seen an extended disk and sunspots, even though it is located about 700 light years away. That is because this star is so huge, fully 1,000 times the radius of our sun.

To appreciate this size, make the earth a tiny pearl one millimeter across and our sun the size of a mango, 100 times larger than Earth. Then Sirius would be a soccer ball and Betelgeuse would be the size of the entire football stadium, making it one of the largest stars in our whole Milky Way galaxy of over 200 billion stars.

Even though Betelgeuse is young, only about 10 million years old, this voracious star has already burned through almost all of its fuel. It exhausted its hydrogen long ago and is now fusing helium into carbon and oxygen. It will soon be fusing heavier elements, including neon, magnesium, sodium and silicon, all the way up to iron, after which it will collapse and explode as a type II supernova.

Betelgeuse could be one of only a handful of stars that may have already exploded, or it may take another few thousand years. The reason these huge stars have to burn through their prodigious amounts of fuel so quickly is to maintain their perfect gravitational balance of the weight of all the gas pressing inward with the fusion forces pushing outward as they consume and transform all this gas.

Once it explodes as a cataclysmic supernova, all of these newly forged elements get released back into our galaxy as the ultimate recycling process. These elements get swept up by massive density waves continually pulsing through our galaxy, turning all this material back into new stars and planets, and in at least one case and probably many more, into plants and animals and humans. We are more powerfully linked to the stars than we can imagine.


The other highlights for this first month of the year include another meteor shower, Jupiter still gracing our evening sky, and Saturn and Venus adorning our morning sky.

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