Hubble's Law
American astronomer Edwin Hubble (the space telescope was named after him) measured the speed of galaxies and their distance from Earth and obtained the following graph.
Finding out how astronomers measure the distance to a galaxy is an interesting research task (they do not use a long tape measure!) 鈥 you may even find out what a parsec means as a unit of distance.
As the graph is a straight line through the origin it represents a direct proportionality. This is knows as 'Hubble's Law' and is described in the equation:
\(v=H_{o}d\)
In the equation, \(v\) is the velocity of a receding galaxy, \(d\) is the distance to the galaxy and \(H_{o}\) is the Hubble's constant.
Hubble's constant is approximately \(2.3\times 10^{-18}s^{-1}\) if the distance is in metres and the speed in metres per second.
This relationship means that the further a galaxy is from Earth, the faster it is moving.
The real significance of Hubble's Law is that the Universe is expanding in all directions not just from Earth.
This means all matter in the Universe started at one point in space at the time of 'the Big Bang'. A small number of galaxies exhibit blueshift as they are moving towards Earth but the vast majority of galaxies are redshifted giving strong evidence for an expanding universe.
In 2012, NASA's Wilkinson Microwave Anisotropy Probe (WMAP) spacecraft estimated the age of the universe to be 13.772 卤 0.059 billion years.
The next year, the European Space Agency's Planck spacecraft comfirmed this with an age of 13.82 billion years. This was only possible using Hubble's Law and a precise knowledge of the Hubble constant.
Professor Brian Cox explains how evidence for the Big Bang can be found by analysing the colour of starlight