Clusters Near and Far - Messier 35 and NGC 2158
The contrasting open star clusters Messier 35 and NGC 2158 are located in the constellation Gemini. First discovered by the astronomer Philippe Loys de Chéseaux in 1745, it was later included by Charles Messier in his "Catalogue des Nébuleuses et des Amas d'Étoiles" ("Catalogue of Nebulae and Star Clusters"); the famous list of Messier objects.
Messier 35 in the upper left of the image is a nearby young star cluster, some 2800 light years distant and about 150 million years old. It covers an area of sky similar to that of the full Moon and contains approximately 2500 stars. Most are bright and blue, having not yet burned out their supply of Hydrogen.
Southwest of Messier 35, in the bottom right, lies NGC 2158 which is nearly four times more distant and contains many more stars. It is also much older, estimated to be some 2 billion years old. All its blue giant stars have burned out long ago and only the orange glow of its older stars remain. NGC 2158 was once though to be a globular cluster due to its compact nature.
Open star clusters are groups of stars that have formed from a single cloud of gas and dust at roughly the same time. Their individual stars are more or less bound to each other by gravity but may become dispersed over time as the cluster orbits through the plane of the Milky Way and interact with other clusters and clouds.
Date: 19th February 2017
Exposure: LRGB: 75:25:25:25 mins, total 2 hours 30 mins @ -25C
Telescope: Homebuilt 12.5" f/4 Serrurier Truss Newtonian
Camera: QSI 683wsg with Lodestar guider
Filters: Astrodon LRGB E-Series Gen 2
Taken from my observatory in Auckland, New Zealand