open cluster

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open cluster:

see star clusterstar cluster,
a group of stars near each other in space and resembling each other in certain characteristics that suggest a common origin for the group. Stars in the same cluster move at the same rate and in the same direction.
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open cluster

(galactic cluster) A loose cluster of stars that contains at most a few thousand stars and sometimes fewer than twenty. Examples visible to the naked eye are the Hyades and the Pleiades. About 1200 open clusters are known. They are population I systems and occur in or close to the plane of the Galaxy. The brightest stars in an open cluster can be either red or blue giants, depending upon its age. Stars in the older clusters, such as M67 in Cancer, are similar in appearance to those in globular clusters, although with some subtle differences due to the higher metal content of the material from which they were formed. Open clusters are more loosely bound systems than globular clusters and they tend to be gradually dispersed by the combined effects of the differential rotation of the Galaxy and perturbations due to close encounters with interstellar clouds. Calculations suggest that many will not survive more than one or two circuits of the Galaxy. Hence most open clusters are comparatively young systems. Some, such as NGC 2264, are less than 10 million years old and in these clusters star-formation is probably still taking place (see OB cluster). See also Hertzsprung–Russell diagram; moving cluster; turnoff point.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006

open cluster

[′ō·pən ′kləs·tər]
(astronomy)
One of the groupings of stars that are concentrated along the central plane of the Milky Way; most have an asymmetrical appearance and are loosely assembled, and the stars are concentrated in their central region; they may contain from a dozen to many hundreds of stars. Also known as galactic cluster.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Unlike their globular cousins, open star clusters usually have fewer and younger stars.
It is one of the most spectacular open star clusters in the whole sky.
The Pleiades are an open star cluster in the constellation of Taurus and the most obvious to the naked eye in the night sky.
And it's also about the same gain I experienced when viewing the open star cluster M67 in Cancer with and without the monocular a few minutes later using the Sky-Watcher 18-inch Stargate Dobsonian reviewed in the April issue, page 58.
The open star cluster NGC 3231 is located in the far north of the constellation.
K2-25b is within the Hyades Cluster, the closest open star cluster to Earth about (http://earthsky.org/favorite-star-patterns/v-shaped-hyades-star-cluster-easy-to-find) 150 light-years  away.
Alicante 1, a small open star cluster located around 13,000 light-years away from the Earth, nestled the star system.
Caption: William Herschel discovered the open star cluster NGC 2194 in 1784; but Skiff J0614+12.9 is a much more recent discovery.
Sweeping a bit farther north takes us to the open star cluster NGC 1981.
By the morning of August 25th, Venus has crossed into Cancer, where the planet ends the month as it began: on the verge of passing a big open star cluster, in this case M44, the Beehive.