My chosen astronomer is Edwin Hubble and his evidence of an expanding universe.
Edwin Hubble was born in Missouri in 1889. His parents moved to Chicago in 1898 where at high school he became a promising pupil. He had remarkable athletic skills, especially the high jump. He broke the Illinois high jump record.
In the 1920s Hubble played a key roll in establishing just what galaxies are. In 1924 he measured the distance to the Andromeda nebula and confirmed that it was a galaxy.
Hubble made his great discoveries with the best telescope in the world at that time..the 100 inch telescope on Mount Wilson in California. Today his name is carried by the best telescope we have, not on Earth, but a satellite observatory orbiting our planet. The Hubble Space Telescope is continuing the work he begun to map our Universe.
It was during the 1920s that Edwin Hubble provided the first evidence that we live in an expanding Universe. Hubble discovered that there is a simple relationship between the distance to a remote galaxy and the redshift in the spectral lines from that galaxy.This redshift is known as the cosmological redshift. Hubble`s observations showed that the greater the distance to a galaxy, the greater the redshift in its spectral lines. These measurements strongly indicated that galaxies appear to be moving away from us with speeds proportional to their distance. This observation is made in whatever direction you may look in the sky, giving the false impression that our Solar System is at the centre of the Universe. The net effect of this motion is that as time goes on the galaxies are getting further and further apart. Astronomers describe this as an expanding Universe.
A simple analogy can be used with the aid of a ballon. Reference points are marked on a baloon. The baloon is illustrative of the universe and the reference points galaxies. As the baloon is inflated each reference point moves further away from the other, so from any reference point within the baloon every other reference point appears to be moving away from the observer. The observer does not have to be at the centre of the ballon to make the observation This analogy breaks down only because on the skin of the baloon the reference points will expand, as well as the distance between them. In the Universe the expansion takes place in the space between the galaxies. The galaxies themselves do not expand. A very important consequence for observations which lead us to infer an expanding Universe is that at some point in the past the matter which is becoming increasingly distant must have been concentrated all in one place. Astronomers believe that at this point in time, the biginning of the Universe and the biginning of time, all the matter of the Universe was concentrated in an infinitely small volume and was in a state of infinite density. The huge explosion which led to the expansion of the Universe is the event known as the Big Bang.