Open Star Clusters

Clusters in the Terragen Sphere
Image from Steve Bowers
Open clusters in the Terragen Sphere are dispersed almost at random, with some concentration in the galactic arms; they act as useful location markers in galactography

Loose structures that contain anywhere from a few dozen to a tens of thousand stars.

They are irregular in shape and there is a great range in size (1-20 pc) and in number of members; distribution is concentrated about the galactic plane. Many of the younger clusters contain gas and dust.

Most open clusters are young: generally less than a few hundred million years old. They are rich in the youngest and most heavy element-rich stars. Over millions of years, the tidal gravitational forces in the host galaxy tend to shred these clusters of thousands of stars, scattering the stars into the general population of stars wandering interstellar space.

An example of a young star cluster is the Pleiades; this cluster still retains traces of the hydrogen cloud it was formed from. A somewhat older cluster is the Hyades, which has spred out to cover a region fifty light years in diameter (and which formed the centre of the original Taurus Nexus). An older cluster which is even more dissipated is Collinder 285, familiar in the Inner Sphere as the asterism known as the Plough.

Most stars in the Terragen Sphere are thought to have formed inside open clusters, although some may have formed in globular clusters or in the galactic hub, and migrated to the galactic disk region.

Because of the large scale of the Orion Arm Civilisation, open cluster provide one of the few good landmarks for galactography. Most stars and worlds in the Terragen Sphere are within fifty light years of a cluster or of a particularly bright giant star; for this reason many volumes of space are identified by reference to such stars or clusters.

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Development Notes
Text by Chris Clowes
Initially published on 17 December 2001.

Additional Information
Data used in this map comes from several sources, including Winchell Chung's useful Galaxy Map