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Polaris, Rudolf’s Merry Go Round
It’s not just Saint Nick and his troop of reindeer hovering above the north pole this month. High above the northern horizon, where the stars and sky seem to pivot each evening, as well as over the course of the entire year, is the area of sky called the circumpolar region. Here is where a half dozen or so constellations reside, seemingly doing their "rally around the maypole" dance, in orbit of Polaris, the North Star. It's really just an illusion from our perspective, caused by our own world spinning about on its axis.
Should you be brave enough to venture out into the crisp December evenings, or can access a place where you can watch the sky from some relative warmth and comfort, then this month I'd like to point you toward some interesting targets along Rudolf's and Santa's flight path as they head off to work this month. They're sure to encounter some exceptional sights should they decide, like you, to gaze upward and notice the drawings that our ancestors imagined in the skies above. In this area of sky dwell the great and small bears, or as we know them, the Big and Little Dippers. They're joined by, among others, Cassiopeia, Perseus and Draco. I'd like to begin by directing your attention to the pivot point where these constellations, which never set, rotate over the course of the evening and throughout the year.
Directly above Saint Nick's head as he begins his journey south, at the north pole's zenith, Polaris glows a bright magnitude two. The 49th brightest star in the sky, contrary to some popular beliefs, it is hardly the brightest star in the sky. That title belongs to Sirius in Canis Major, the big dog running along side his master, the mighty hunter, Orion. You can see both Canis Major and Orion prominently displayed in the south, southwestern skies in the hours before sunrise. You’ll see why Sirius is, quite obviously, the brightest star in the entire sky. Point a pair of binoculars or a small telescope at it and I guarantee that you will be fascinated.
Back to Polaris. As it slowly travels closer and closer to the actual "true" north, due to what is called precession, it will finally make its closest approach to the actual celestial pole in about a hundred years from now. The reason for this is that the path of the Earth's axis projected out into space makes a fairly large loop in its precessional cycle around the actual celestial pole position, taking almost 26,000 years to return to where it will start again. In centuries past, stars other than Polaris have been closer to the actual pole. Thuban, in Draco, for instance, was much closer about 4600 years ago, during the time of Egyptian pyramid building. Prior to that, Vega, one of the three stars of the Summer Triangle, held the title some 12,000 years ago. Though it was never as close as Polaris is to the actual pole today.
Polaris is also a double star, with a faint blue companion. Since the time of Hershel it has been a test for small telescopes. See if you can split the pair. Fortunately residing a very safe 360 light years from Earth, Polaris actually shines 1600 times brighter than our own Sun. It has also been an enigma of sorts, known to ancient cultures all over the world by a variety of names. Both modern-day and ancient mariners counted on its stability to navigate the great oceans. Great structures were built by numerous ancient civilizations in honor of Polaris. Many believed it had a special place in the skies, in the realm of ancient deities. Referred to as cosmic mountains by these ancient cultures, the towering temples and obelisks they built were often used as places of worship and represented what these early peoples believed was the actual cosmic center of the universe.
To locate Polaris, use the age old method of lining up the two end stars of the Big Dipper's bucket and follow along a line drawn from the bottom star to the top star and out to Polaris, which will be the first bright star you encounter. Here, in a dark sky, you'll see Polaris as the end of the handle of the Little Dipper. All the stars of Ursae Minoris, though substantially dimmer than its larger counterpart, Ursae Major, can be seen only if the sky conditions are good. Smaller, of course, and oriented almost upside down to the Big Dipper, it has been said to look as though it is pouring its contents into its neighbor's bowl.
Lastly, while we're playing in this area of the sky, along the same line of sight, though out a few degrees to the east, with a medium to large telescope, you may encounter some interesting Messier objects, M-81 and M-82. These galaxies are spectacular in deep-sky, long-exposure photographs. What you'll see in your telescopes may differ substantially. One is an almost face-on spiral, while the other is oriented edge-on to our line of sight. Both are rather dim, but, nonetheless, will make great trophy items in your Lawnchair War Chests! Try spotting them some evening this winter when you've had your fill of sitcom reruns.
Now remember to bundle up before you go out and start to brush the snow off the old Lawnchair. If you’re taking a telescope out with you, be sure to give it time to acclimate to the outdoor temperature. Once cooled down, it should provide you with some great views of our northern neighbors. Until next year, here's wishing you and yours a great holiday season and I'll see you all in 2009!
Clear Skies!
The Lawnchair Astronomer
