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Open cluster with
associated nebula (This is M16---the Eagle Nebula)
Pleiades open
cluster
Open and
globular clusters in the Messier catalog
Open cluster in
the Lagoon
Nebula
Here is an image
of the open cluster M50,
which is 3000 light years from Earth and is about 20 light years across. Open
clusters such as this one have some common characteristics:
- Open clusters are preferentially found in the plane of the galaxy (thus
they are also called galactic clusters); in contrast, the globular
clusters are concentrated in the halo of the galaxy and can be very far out of
the plane.
- Open clusters tend to be more irregular in shape than the highly symmetric
globular clusters.
- Open clusters typically contain of order 100 stars, as compared with as
many as hundreds of thousands in globular clusters.
In images of open
clusters such as this one, not all stars in the field of view are members of the
cluster; some are stars between us and the cluster and some are stars beyond the
cluster. One way to distinguish members of the cluster from stars that just
happen to lie in the same direction is by measuring their proper motion on the
celestial sphere. The stars in the cluster must all have approximately the same
proper motion or the cluster would have dissipated over time, but stars not
associated with the cluster would be expected to have more random motions.
Here is a synopsis
of what the colors of stars in the cluster M50 can tell us about astrophysics.
Here is a set of links to images of open
clusters.
In the center of 30
Doradus "lies a huge cluster of the largest, hottest, most massive stars
known. R136 is composed of thousands of hot blue stars, some about 50 times more
massive than our Sun. Although the ages of stars in R136 cause it to be best
described as an open cluster, R136's density will likely make it a low mass
globular cluster in a few billion years." |