Open clusters

NGC 2477

NGC 2477, a rich and very compact open cluster     [Source]

Open clusters are collections of young stars all with a similar age, typically located in the plane of a galaxy. Sometimes they can be found embedded within a nebula. Some open clusters are visible as hazy naked eye patches within the Milky Way, or in a few cases—M45 (Pleiades), for example—can be resolved into individual stars without any optical aid. They are a different kind of star cluster than a globular cluster.

Due to their young age, the majority of stars within an open cluster are still on the main sequence. Since the lifespan of a star is dependent on its mass, on a Hertzsprung-Russell (HR) diagram for any given open cluster, only the most massive stars will show a general departure from this trend (as these stars will more quickly deplete their fuel and become red giants). The juncture at which these stars begin to leave the main sequence is known as the “turn-off point”. By merely having knowledge of the average main sequence lifespan for cluster members at this point, one can effectively then estimate the age of the open cluster.

The HR diagram

The HR diagrams of open clusters M67 and NGC 188, illustrating that NGC 188 is the older cluster     [Source]


Posts on open clusters:

* Clusters with nebulosity
Extragalactic open clusters

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