  Gaze upwards on a dark night, and you will see the 'Milky Way', a glowing ribbon made up of many individual stars. This is our first clue to the fact that that stars are not uniformly distributed throughout space, but clustered together to form galaxies.
Galaxies can vary in size between a hundred thousand and three thousand billion solar masses, and can be broadly split into different classes, depending on their shape. Our own Milky Way Galaxy contains about two hundred billion stars. It is a spiral shape, which is why, when viewed from our position about two thirds of the way along one of the arms, it appears as a band across the sky.
Gazing out into the Universe reveals thousands upon thousands of galaxies. These galaxies tend to be grouped together in clusters, and these clusters in turn are grouped into superclusters. It appears the Universe has structure on many different scales.
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Barred Spirals - Barred spiral galaxies have disctinctive 'bars' which extend between the core and the spiral arms. Many spirals show this feature to some extent, and the distinction between barred and unbarred galaxies is not always a clear one.
