Tuesday, 27 January 2015

The Galaxy

The Recession of Galaxies

In 1912, the American astronomer Vesto Slipher at Lowell Observatory began a study of the spectrum of the brightest galaxies. This was not an easy task for even the brightest galaxies have very low total luminosity and the fact of breaking light into its different wavelengths does not help. He thus had several nights of observation for the spectrum of a galaxy alone at the time.

In analyzing the results, Vesto Slipher noticed that the few lines present in these spectra were displaced from their theoretical position. He interpreted this as an effect of the speed of galaxies since the observed wavelength of the spectral lines of a body changes when it is moving. From the offset, Slipher could thus determine the relative speed of these galaxies compared to ours. It thus found for example that the Andromeda galaxy is approaching us at a speed of about 300 kilometers per second.

Its end result was surprising: he got eleven redshifts and four to the blue, far more galaxies away from us galaxies approaching us. If the movement of galaxies was random and without preferred direction, it should have been as many as shifts toward blue to red. Slipher's observations therefore revealed a fundamental fact about the dynamics of the Universe. Unfortunately, the discovery did not take place at this time because the sample of galaxies was not large enough to be truly meaningful.