Looking Up: Seeing double
There are a lot of pairs in the night sky. We have the double star Mizar-Alcor in the Big Dipper handle; the two moons of Mars; the beautiful Double Cluster of Perseus and the Twin Stars, Castor and Pollux.
Like many twins, we need to get used to which one is which. The stars are actually quite different, and they aren't even associated with each other. They just happen to be two bright stars a few degrees apart, and they mark the "heads"of the constellation Gemini the Twins.
Castor and Pollux are among numerous bright stars populating the winter evening sky. No where else in the heavens as seen from Earth (an important point, since the starry arrangement is totally different wherever you go in the Milky Way) are there so many brilliant stars- magnitude +1 and brighter- so near each other.
It is hard to take your eyes from majestic Orion with its fiery red Betelgeuse, gleaming Rigel and the three stars of the Belt. Then there is bright red-orange Aldebaran with gloriously bright planet Jupiter nearby this year. Nearly overhead is bright yellow Capella. Down to the left of Orion is bright Procyon and brilliant blue-white Sirius. Castor and Pollux are farthest to the east, which is left as seen from the Northern Hemisphere (or to the right if you stand on your head).
Seen rising in the east early on a mid-winter evening, Pollux is the one at bottom and is pale orange or yellow in hue. Castor is just above it, nice and white.
Although the moon is full on Jan. 26 and situated not far below Castor and Pollux in the east, the bright winter stars will still punctuate the glow of moonlight. Wait a few nights and look before the moon rises, to see the dazzle of the constellations where these bright stars reside. A winter star chart found in many astronomy field guides likely available at the library, or online, will help you trace the star patterns.
Castor is 52 light years away and is actually a sextuple system. That means there are six stars orbiting one another. Pollux is a bit brighter than Castor, and is 34 lights years distant.
On a reasonably dark night, scan the stars of Gemini; while in the east, The "head" stars described above are on the left. The "bodies" of the "Twins" stretch to the right, and end before you get to Orion. The "feet" stars of the "Twins" are on the right end. With binoculars, examine these stars for a marvelous hazy patch of light, which you may be able to discern as a tight cluster of dim stars. This is M35, an open star cluster which is a fine sight in a small telescope. You should be able to see it with unaided eyes on a moonless night, away from town and city lights- once you let your eyes adapt to the darkness.
M35 is one of thousands of star clusters you can find in a backyard telescope.
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Keep looking up!