A map of the Universe The Universe consists of everything that we know to exist: stars, planets, rocks, people, and so on. It even includes empty space. Nearly all the visible matter in the Universe is contained in galaxies. About 100 billion galaxies are grouped into giant clouds, called superclusters, spread out like a net. The “holes” between them are vast empty spaces, known as voids. The Universe probably began life in a hot, dense explosion called the Big Bang, which took place about 13.7 billion years ago.
The Universe is unimaginably vast: billions upon billions of kilometres wide. Distances in it are so great that a special measure is needed to record them. This is a light year, or the distance that light, which moves at a speed of 299,792,458 metres per second (186,282 mph), travels in one year: about 9,460,528,405,000 kilometres or about 6 trillion miles (6 followed by 12 noughts). The nearest star to Earth after the Sun, Proxima Centauri, is 4.2 light years away. The most distant objects we know in the Universe are more than 13 billion light years away.
The pattern of superclusters in the Universe Nearly all the matter in the Universe is contained in galaxies, enormous masses of stars, gas and dust. There may be about about 100 billion galaxies, each containing hundreds of billions of stars. Galaxies are grouped into giant “clouds” of galaxies, called superclusters. These are spread round the Universe like a net, made up of strings and knots. In between there are gigantic empty spaces, known as voids.
Clusters of galaxies
The superclusters are, themselves, made up of smaller clusters of galaxies. One of these, a cluster of 30 galaxies or so, is called the Local Group. It contains the Milky Way Galaxy, the vast spiral of stars to which our own local star, the Sun, belongs. Astronomers have discovered that all the galaxies in the Universe are rushing away from one another. This means that, a long time ago, they were once all close together. So the Universe had a definite beginning—and may have an end.
Consultant: Dave Hawksett