Hubble's Law

American astronomer Edwin Hubble was the first person to discover that the Universe was expanding but in addition to this, he found that the Universe obeys the same rules as the balloon we just saw. The further away a galaxy is, the faster it is receding from us. This is known as Hubbble's Law .

Hubble plotted a graph of the relationship between distance and speed of certain galaxies. The following diagram shows the result.

Unfortunately, to plot the graph, we need to know the distances of the galaxies we are looking at. These must be found by other not always accurate methods and we are not entirely sure exactly how steep the line on the graph should be.

* Click here for an example of this method

* Click here to find out how astronomers work out how fast a galaxy is going away from us