Galaxies - Frequently asked questions

What is a galaxy ?

A spiral galaxy Stars are not spread out randomly across the universe. They tend to gather together in large groups held together by gravitational attraction. These large groups are galaxies. Every star that is visible when you look up at the night sky is part of our own galaxy.
Galaxies themselves also tend to hang around in groups. Our own galaxy is part of a local group that consists of a few large systems and more than twenty smaller ones. Well beyond our local group astronomers know of galaxies that are 13,000 million light years away.

How many stars are there in a galaxy ?

Estimates for our own galaxy put the number of stars at about 100,000 million stars. However our own galaxy is one of the larger systems and most galaxies contain a lot less.

What is the milky way ?

This is the name given to the misty band of stars that can be seen on a good clear night. This misty band is caused by the shape of our galaxy. When we look at the milky way we are looking along the crowded plane of our galaxy. Although we can't make out individually the billions of stars we are looking at, their combined light makes a pearly glow across the night sky.
Just to make matters a little bit confusing, the Milky Way is also the name we give to our own galaxy.

Is our sun near the centre of our galaxy ?

Our place in the galactic suburbia Galaxies are sometimes referred to as great cities of stars. Well if this is the case, our sun (and the earth) is in the leafy suburbs, about 25,000 light years from the bustling galactic centre. That's 25,000 x 9.46 million million km, in cosmic terms a short train ride away.

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