Milky Way Globular Clusters

Introduction:

A globular cluster is a compact cluster of many thousands to millions of gravitationally bound stars that give the cluster an overall spherical appearance.

The average diameter of Milky Way globular clusters is about 70 ly (light years), with some clusters as large as two or three hundred light years.

In our galaxy, globular clusters are distributed roughly within a sphere (galactic halo) around the galactic centre and they orbit the centre in highly elliptical orbits.

The average stellar density of a globular cluster is about 1 star per cubic light year (or 1 ly between each star). This might increase to as many as 30 stars per cubic light year in the core.

Globular clusters do not display any active star formation and their component stars are mostly of similar age. They are most amongst the oldest objects in the galaxy at 10 to 12 billion years old.

The Documents:

The descriptions in the documents below are primarily about the distribution of Milky Way globular clusters, their proximity to the galactic centre, to the Sun and to each other.

As a visual observer, it is intended to add an appreciation of the globulars being observed and their spatial relationship to each other.

It is difficult to know what (if any) are the gravitational effects on motion due to clusters in relative proximity (say 2,000 ly apart).

The coordinates and distances used for these globular clusters were taken from the Catalog of Parameters for Milky Way Globular Clusters: The Database compiled by William E. Harris, McMaster University (current revision: December 2010). http://physwww.physics.mcmaster.ca/%7Eharris/mwgc.dat.

The list contains 157 known Milky Way Galaxy globular clusters.

1 ly = 1 light year, 1 kly = 1000 light years, (') = (arc minutes), RSun = distance from Sun, Rgc = distance from galactic centre, GC = Globular Cluster