Castor and Pollux in Gemini

December 09, 2016

Castor_and_Pollux_small (2)

Photographer: Greg Parker
Summary Authors: Greg Parker; Jim Foster

Shown above are Castor (top) and Pollux (bottom), the two brightest stars in the constellation of Gemini the Twins. Gemini, a zodiac constellation, can be seen in the eastern sky not long after nightfall. Not only are Castor and Pollux close in brightness (at 1.93 magnitude and 1.14 magnitude, respectively), but the line of stars trailing them have similar brightnesses as well and are also similarly positioned. So, it's pretty easy to understand how this constellation was named the Twins. Castor, a conspicuous white star, is actually part of a multiple star system, some 52 light years away. Pollux, an orange giant, is slightly brighter than Castor and about 34 light years away. Though they appear near each other in the sky and are nearly equally bright, they have no gravitational attraction to each other.

The annual Geminid meteor shower (December 10-13) emanates from the Twins. Unfortunately, this year's peak, on the night of the 13th/14th, will be spoiled by the full Cold Moon. Nonetheless, take a look toward the Twins the next few nights, you might be pleasantly surprised.

Photo Details: Taken with the Canon 200mm lenses and M26C OSC CCDs. This is a 2-frame image; the Castor frame composed of 20 x 10 minute subs and the Pollux frame composed of 18 x 10 minute subs. Artificial star spikes using Noel Carboni's Star Spikes Pro4 software.