- M 35 (NGC 2168) and NGC 2158
M 35 is an open cluster that lies at the left foot of Castor, one of the twins making up the constellation Gemini. It was originally discovered in 1746 by the Swiss astronomer Phillippe Loys de Cheseaux but, since his discovery was not published, an independent discovery was made by the English astronmer John Bevis. The cluster was already known to Messier when he included it in his list. M 35 lies at a distance of around 2700 LY, although some reports suggest that it might be as distant as 3600 LY. M 35 contains a mixture of stellar types, including blue-white type B giants, yellow and orange giants of types G and K, and even white dwarfs. The age of the cluster is estimated to be 100-150 MY.
Perhaps even more interesting than M 35 is the visually adjacent open cluster NGC 2158. NGC 2158 appears small compared to M 35, but this is due to its great distance— 12,000 LY, which is around two-thirds of the distance to the far edge of our galaxy. This makes NGC 2158 one of the most distant objects that we can observe in the Milky Way. This great distance is hinted by the appearance of the cluster in my image— the golden color of the cluster stars indicates that most of the blue component of their light has been attenuated by interstellar absorption and scattering along the path to us. NGC 2158 is also thought to be very old for an open cluster, with an estimated age of 2000 MY. This age also contributes to the maturity of the stars in the cluster, shifting its overall color from bluish to reddish.
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