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Galaxies & Clusters of Galaxies
Part 1: Galaxies (M31) Part 2: Clusters of Galaxies (Coma)

Education Activities To Accompany Chandra Data Analysis Software
M31 & Coma

Big, Bigger, Biggest

For I dipped into the Future
Far as the human eye could see;
Saw the vision of the world
And all the wonder that
would be.

- Alfred, Lord Tennyson, 1842

Part I: Galaxies

When Edwin Hubble uncovered the key to the sizes of galaxies in the 1920's, we were awestruck by the sheer enormity of these "island universes". It is hard to fathom an object that is so large that light, which is capable of traveling over 7 times around the world in one second, takes over 100,000 years to get from one end of a typical spiral galaxy to the other. Could there possibly be anything larger than this in the universe?

The answer was not long in coming; within 10 years of Hubble's epochal discovery, it was clear that galaxies were not distributed randomly about the sky. Instead, many vast clusters of galaxies exist, sometimes containing thousands of individual galaxies, each of which, in turn, contain up to 100 billion stars similar to our own Sun. (Interestingly, Sir William Herschel recognized the existence of the Virgo cluster, but at that time in the 18th century, it was not known whether or not these objects were part of our own galaxy, the Milky Way. Incidentally, many of the larger clusters are named after the constellation in which they are located.)

To get some idea of these enormous structures, let us look at our own neighborhood. The Milky Way is in a small group, with the only other large galaxy being M31 (the Andromeda spiral). However, if we were located in the center of the Coma cluster, we would see 100 large galaxies in the same volume of space contained in a cubical box enclosing us and M31. The sky would be littered with fuzzy patches of light every 20 degrees, which corresponds approximately to the distance between the top and bottom of the constellation of Orion.


Last updated: 07/11/11


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