Huge Groups of Stars About a billion years after the Big Bang, when the Universe was still very young, stars began to group together. These groups are made of billions of stars and are called Galaxies. Galaxies travel through space together to form clusters. We don't know exactly how many galaxies there are in all, but there are probably billions and billions.

Four Main Shapes SPIRALS: turn like a pin-wheel, or like cream swirling in a cup of coffee. Our Galaxy (the Milky Way) is a spiral. Barred Spirals: look like two tadpoles joined at the head. They have a large centre with two long swirling arms. Looks a little like the letter 'S'. Elliptical: or oval-shapes galaxies look like squashed balls. It is thought that they contain much older stars. Pictured left. Irregulars: contain a lot of dust and form no definative shape.

Our Own Galaxy:

Our galaxy is the spiral-shaped type with several arms. Our Sun is about two-thirds of the way out from the centre hub and is located on the arm called Orion Spur. The Sagittarius arm is located between us and the galactic center, the Perseus Arm wraps itself behind us.

Some scientist believe there is a black hole at the centre of our Galaxy that may be slowly sucking in the surrounding light and gas. If we wanted to travel the diameter of our galaxy it would take about 100,000 years- travelling at the speed of light.

Just as the moon rotates around the Earth, and the Earth rotates around the Sun, our Sun rotates around the Galaxy's center. It takes 225 million years to rotate around the galaxy. This is called a galactic year.

Galactic Neighbours

The closest known neighbouring galaxy is the Magellanic Clouds, named after the famous explorer who first spotted them in 1521. In the 'clouds' are two irregular galaxies, one larger, containing about 10 billion stars, the other smaller and farther away.

Other galaxies that are close enough to study from the Earth are: M81 (a spiral), M51 -the Whirlpool, another spiral, about 14 million light years away, reaches out to a smaller galaxy. Then there is M77 -another spiral, M87- which sends out strong radio waves and M104-a spiral nicknamed the Sombrero because of its shape.