Beyond the milky Way Galaxy:
Let us now move away from the Earth and venture into the space beyond. If we were at a point far out in space we would see scattered in space, a large number of faint, wispy tendrils of light. These are all galaxies. As we have said earlier in Sec. these galaxies are made up of billions of stars, and clouds of gas and dust. The universe is full of galaxies. Some of them are soliky wanderers. Most ofthem movein clust&s. drifting endlessly in the great cosmic dark. Shapes of galaxies The galaxies are usually found in three shapes: spiral galaxies, elliptical galaxies and irregular galaxies (see Fig. 9.9). Further refinements have been suggested in recent years, but we will not go into those details. The elliptical galaxies are so called because they have an elliptical shape on a photographic plate. Elliptical galaxies in general do not have much gas or dust from which to form new stars, and they consist of old stars. The irregular galaxies do not show any coherent structure. 'he number of elliptical and spiral galaxies is almost equal, whereas the irregular ones comprise about 10% of all salaxies.
Before going too deep into the space, let's take a closer look at, what astronomers on' Earth like to call, the Local Group of Galaxies. Its cross-section is several million light years, it is made up of around twenty galaxies. The nearest galaxies to the Milky Way Galaxy are the Large and Small Magellanic Clouds, visible in the Southern hemisphere. They are irregular in shape. The galaxy Andromeda'lies nearly two million light years away and is visible to the unaided eye. It is a spiral galaxy, three times bigger and brighter than ours. As we move further out, we find that such groupings, or clusters of galaxies, are extremely common. There are some hundreds of billions of galaxies in the universe which form clusters of all kinds. There are rich clusters containing as many as ten thousand galaxies and poor clusters having only a few galaxies. Our own galaxy is a member of a poor cluster. The nearest rich cluster, at a distance of about 70 million light years, is Virgo. It is irregular in shape and is huge, extending 7 million light years from end to end. Like galaxies, clusters are also shaped like spirals, ellipses or they may be irregular. In recent years, one more step has been added in understanding this physical structure of the universe. There is evidence to suggest that the clusters of galaxies, rich and poor, in turn form superclusters or supergalaxies (i.e. clusters of clusters) that are 200-300 million light years in diameter. They may be made up of about a 100 member clusters. The clusters, Local Group and Virgo, are members of the same supercluster. The superclusters are very much alike. They are rather evenly distributed in space. Thus, on a larger scale than this, the universe appears uniform, that is, it has the same structure and composition everywhere, it looks the same in all directions.