1. http://www.schoolsobservatory.org.uk/astro/cosmo s/redshift

2. The Big Bang theory states that about 13.7 billion years ago all the matter in the Universe was concentrated into a single incredibly tiny point. This began to enlarge rapidly, and it is still expanding today.

3. Light takes a long time to travel across the Universe, so when we look at very distant galaxies, we are also looking back in time. We can see that galaxies a long time ago were quite different from those today, showing that the Universe has changed.

4. Evidence for an expanding universe: 1.Redshift of Galaxies-shows galaxies are moving away Every distant galaxy, in every direction, shows a red-shift in its radiation. Hubble Law states galaxies appear to be moving away from us at speeds proportional to their distance. (1889-1953) who discovered this phenomenon in 1929. The further away they are, the faster these galaxies are travelling

6. Redshift of distant galaxies: light is "stretched" slightly and appears a bit redder (lower frequency) as it is moving away. This is similar to Doppler effect. When a sound is moving towards you, the siren it quite high pitched. When it is moving away from you, the pitch drops and it sounds lower. With light, "lower" means more red and "higher" means more blue.  http://www.youtube.com/watch?v=h4OnBYr http://www.youtube.com/watch?v=h4OnBYr  bCjY bCjY

7. Hubble’s observations showed that the light from distant galaxies was ‘red-shifted’. This was due to the ‘Doppler Effect’. By Golly, just look at that! The dark lines in the spectrum on the right hand side are ‘red shifted’. Light from the Sun Light from distant galaxies

8. Explaining Doppler Shift

9. 2: Cosmic Microwave Background Very early in its history, the whole Universe was very hot. As it expanded, this heat left behind a "glow" that fills the entire Universe. The Big Bang theory not only predicts that this glow should exist, but that it should be visible as microwaves - part of the Electromagnetic Spectrum.

10. 3. Mixture of Elements As the Universe expanded and cooled down, some of the elements that we see today were created. The Big Bang theory predicts how much of each element should have been made in the early universe, and what we see in very distant galaxies and old stars is just right. However, new stars, like the Sun, will be very different from the composition of stars that existed 7 billion years ago, shortly after the Big Bang, as they are made from recycled stars.

12. Galaxy Redshift Most galaxies appear to be moving away from us. This means that the light from them is "stretched" slightlygalaxies and appears a bit redder that it would otherwise do. This is similar to what happens to sound. Imagine that a fire engine is driving past you with its siren on. When it is moving towards you, the siren it quite high pitched. When it is moving away from you, the pitch drops and it sounds lower. With light, "lower" means more red and "higher" means more blue. You can see what this looks like in the diagram below, where two galaxy spectra are compared.spectra Example of how absorption/emission lines in a spectrum can be redshifted. In fact, the further away a galaxy is, the faster it appears to be moving, and hence the more the spectrum is redshifted. Astronomers can, therefore, measure the distance to a galaxy by taking a spectrum and seeing how much the lines that you would expect to see have been shifted.