Astronomy: images of the Universe: Figure 9 R-band images of the five main types of extended objects seen in optical images: (a) open cluster%%STARTOUTPUTCONTROL1:+mobile%%Clusters of up to a few thousand stars, loosely bound by gravity, that were formed from the same giant molecular cloud and so have roughly the same age. There are more than 1000 open clusters in the Milky Way, confined to the disc of the galaxy.%%ENDOUTPUTCONTROL1%%, (b) globular cluster, (c) galaxy, (d) planetary nebula and (e) diffuse nebula.

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Astronomy: images of the Universe

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Figure 9 R-band images of the five main types of extended objects seen in optical images: (a) open cluster, (b) globular cluster, (c) galaxy, (d) planetary nebula and (e) diffuse nebula.

2.3 Types of extended objects

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