100 years of modern cosmology

[Sparky]

By Glen Mackie, Lecturer in Astrophysics, Coordinator of Swinburne Astronomy Online at Swinburne University of Technology

In 1903 Lowell hired a young astronomer, Vesto Melvin Slipher. Slipher became well known by astronomers (for reasons that will become clear shortly), but he certainly wasn't a household name like Edwin Hubble, of Hubble Space Telescope fame.

In fact many astronomers would argue that Slipher helped make Hubble famous. Slipher's results transformed our understanding of our place in the universe, in the same way Copernicus, Kepler and Galileo transformed our understanding of our place in the solar system.

Slipher detected a fundamental property of space, not intuitive to us - the fact that the universe is expanding. Ultimately, Slipher's results provided an observational framework for Einstein's General Theory of Relativity and its description of our universe.

From 1906-1912, through ingenious modifications, and trial and error, Slipher improved his data collection. He found that faster (small f/ ratio) camera lenses in his spectrograph could greatly improve his ability to record useful spectra. By late 1912 he had made his spectrograph an incredible factor of 200 times more efficient.

On the night of September 17, 1912, Slipher observed the Andromeda nebula, for a total of six hours and 50 minutes. Later, he made even lengthier observations including two over consecutive nights, and one over the last three nights of 1912. It was a cosmic breakthrough.

Slipher had finally recorded useful spectra. In 1913 he announced that the Andromeda nebula was moving toward us at an astonishing rate of 300 km/s.

The few galaxies that are approaching us, such as Andromeda, are doing so because they are close and gravity wins a cosmic tug of war.

Einstein published his General Theory of Relativity in 1915, and presented it to agree with a static universe, then the preferred model.

Slipher's results made a static universe untenable. Space was not a fixed entity that galaxies were moving into. The velocities are not telling us how fast galaxies are moving away from us, but tell us how space itself is expanding.

So when you are welcoming in the New Year be sure to include a toast to one Vesto Melvin Slipher, astronomer extraordinaire, and wish modern cosmology a happy 100th anniversary.