What is a galaxy?

When you look at the sky from Earth, it appears that space is made up of a mass of stars. If you were to leave the Earth and travel deep into space, you would eventually leave the stars behind. If you were to look back, you would see that the stars group together in cloud-like formations. These are called galaxies. The universe is made up of lots of galaxies. 

It has been estimated that galaxies were first formed about half a billion years after the beginning of time, also known as the 'Big Bang'. 

Galaxies are usually difficult to see with the naked eye from here on Earth. Sometimes it may be possible to see the cloudy appearance of a band belonging to our own galaxy. You are most likely to see this if you are in a very dark area away from city and suburban lights. Perhaps in remote country areas, where the skies are dark and clear, it may be possible.

It is believed that there are about 50 000 million galaxies in the universe. These galaxies are grouped together into clusters. These clusters also group together to form even bigger superclusters.

Do all galaxies look the same?

Using powerful telescopes, astronomers have discovered galaxies of many different shapes and sizes. Three different shapes of galaxies include barred spiral galaxieselliptical galaxies and irregular galaxies. Barred spiral galaxies resemble a long bar shape with curved arms at each end. Elliptical galaxies are an oval shape and irregular galaxies are often messy looking, with no particular shape.

What is the Milky Way?

Although your first thoughts may be along the lines of a chocolate treat, the Milky Way is the name of the galaxy in which our world exists. The Milky Way belongs to a cluster of galaxies called the local group. It is the second-largest galaxy in the local group. The largest galaxy in the local group is called the Andromeda Galaxy.

The Milky Way consists of roughly 200 000 million stars. All the stars that can be seen from Earth belong to our galaxy, the Milky Way. It is so enormous that a light beam would take about 100 000 years to travel from one side to the other.

The Milky Way has a dense core which is packed with stars. If you were to look at it from the side it would resemble a fried egg. It is a flat disc with a bulging core in the middle.

You may be wondering where the unusual name 'Milky Way' came from. It is the translation of the Latin words via lactea which means 'road of milk'. This image was taken from Greek legend. The legend described a trail of spilt milk belonging to baby Heracles. The band of light that we can see represents this trail of milk.

How far away are other galaxies?

Just as there are many cities that make up a country, our galaxy is only one of many galaxies that make up the universe. Galaxies are, however, a long way from each other in distance. Most galaxies lie millions of light years away. When you consider that light travels at about the speed of 299 million metres per second, this is a very long distance. As an example, the nearest galaxy to the Milky Way is so far away that light from that galaxy would take about 2.8 million light years to reach us.

With this in mind, it is difficult to believe that galaxies can sometimes be drawn together by each other's gravity. When this happens, galaxies can be pulled out of shape by the force of another or sometimes they may even collide (crash into each other).

Astronomers are able to measure distances to clusters of galaxies that are billions of light years away from us. Many of these galaxies are even bigger and brighter than the Milky Way. Some of these galaxies can be seen through telescopes. Others are so far away that astronomers are sometimes looking at clusters as they were before the sun was born. This is because the light from these galaxies takes such a long time to reach the Earth.

Astronomers have also discovered that most galaxies are actually slowly moving away from us. The galaxies themselves are not moving but the space in between galaxies is stretching as the universe continues to expand. Andromeda, our closest neighbour is one exception - it is moving towards our galaxy.

Subpages (1): Galaxies Animation