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Our sun is one of a small number of stars in the 'local group', which includes Alpha Centauri, for example. Within our galaxy, especially away from the more densely packed centre, many stars are grouped into into much larger 'clusters' of two types: open and globular.

Globular Clusters

Globular clusters are a concentration of stars in a relatively small area of space. This is M13 in the constellation Hercules which contains a thousand or more stars. The huge distances create the illusion that the stars are closer than they really are, but even so, if the Sun was in such a cluster the night sky would be far fuller of bright stars.

The Hercules Cluster

The globular cluster M13

Open Clusters

By contrast, an 'open cluster' is a more widely separated collection of stars that are still held together by gravity. To be honest, it can be very hard to pinpoint such objects. A computerised 'GOTO' telescope makes it relatively easy, but the traditional (and more rewarding?) way is to 'star hop' from a known star or constellation.

The Pleiades, M45

The best known open cluster is the Pleiades or 'Seven Sisters' which is bright enough to image using a basic camera (as here). In the winter they will return together with the magnificent constellation Orion - something to look forward to getting in the scope as the autumn nights draw in.

This close up of part of the Pleiades taken with a telescope and a longer exposure reveals that it contains much nebulosity lit by the blue light of hot young stars.

The Pleiades and the Merope Nebula

The Plieades taken using a DSLR ona tracking mount and showing blue nebulosity


A rather better photograph is this one of the open cluster M103 which lies in the constellation Cassiopeia. A couple of the brighter blue stars are not in the cluster, just lined up with it. The beautiful red giant in the centre shines like a ruby among diamonds.

Open Cluster M103

M103 is a beautiful open cluster in the constellation Cassiopeia