A galaxy is a large grouping of stars, star clusters, gas and dust held together by mutual gravitation.

We are part of the Milky Way galaxy. Each of the bright, individual stars you see when you look up at the night sky is part of our Milky Way. The hazy band that is typically referred to as the Milky Way consists of billions of more distant stars intermingled with dust and gas. 

Think about standing in a forest. You can see the nearby trees clearly as individual trees but the more distant trees simply blend into “forest." So it is with the Milky Way as the nearby stars are seen individually but the more distant stars blend into, well not forest, but milky haze.

Spiral Galaxy

The Milky Way is a spiral galaxy. Spirals are flattened into disks with stars orbiting a central bulge. You might envision a spiral galaxy as a fried egg with the central bulge represented by the yolk and the egg white representing the flattened disk of spiral arms. The bulge of the Milky Way lies in the direction of Sagittarius.

As you look at Sagittarius through good binoculars the milky white haze remains, since the forest of stars is too dense to be resolved into individual stars, even in binoculars. But as you swing away from the center, through Cygnus and toward Cassiopeia, the Milky Way becomes a dazzling array of individual stars when seen in those same binoculars.

When we look beyond the local conglomeration of stars, we see many such spirals in the sky.  Some we see as “face-on” spirals (the egg seen from above) and some we see as “edge-on” spiral (the egg see from the side). Some spirals have disks consisting of well-defined arms while others do not. Some spirals have massive bulges with much less material in the arms while others are nearly all arms and no bulge. The disks of spiral galaxies have much free dust and gas and they are regions of active star formation.

Elliptical Galaxies

Some galaxies show no flattened disk. These are called ellipticals. Elliptical galaxies have very little free dust and gas, and support very little new star formation. Galaxies are of both types, along with a smattering of irregular galaxies, are found together in large clusters.   Elliptical galaxies come in two distinct size classes—giant and dwarf. It is common for the few largest galaxies in any cluster to be giant ellipticals, as they are larger than spirals. The dwarf elliptical galaxies are much smaller and fainter than spirals and can only be seen in relatively nearby clusters. Here we have images of elliptical galaxies and spiral galaxies seen in orientations ranging from nearly perfectly edge-on to nearly perfectly face-on.

Click on an image for a larger image and more details about both the the image and the galaxy.