With the passing of time, Man has been able to look increasingly further into the depths of space. Each step has produced new in¬sight into the nature of the Universe and our position within it. To the Greeks and Romans, the Earth was the centre of all things. The furthest they could see was the Milky Way, although its true nature was not realized until well over a thousand years later when Galileo resolved it into stars with the first telescopes. At the beginning of the nineteenth century, William Herschel studied the Milky Way in greater detail and estimated distances to the stars. At that time, it was not realized that the so-called ‘nebulae’, the cloud-like objects catalogued by Messier and the Herschels, were in fact other galaxies so distant that their individual stars could not be resolved. Using his giant 72-inch reflecting telescope, Lord Rosse later dis¬covered that some of these objects possessed spiral structure. But it was the advent of astronomical photography during the last years of that century that heralded the birth of extragalactic astronomy. The first photographs of ‘nebulae’ revealed complex and beautiful structures that Lord Rosse’s telescope could only hint at. Until that time, little was known about the relationship between these systems and the Milky Way, but the new photo¬graphs inspired a number of eminent scientists to speculate about the nature of the nebulae.

The major point of contention during the early part of this century was: how far away are the nebulae ? At that time, Harlow Shapley was able to map out the scale of the Milky Way by using Bailey’s discovery of RR Lyrae stars in globular clusters and Leavitt’s discovery of Cepheid variables in the Magellanic clouds. He put the Sun at some 10kpc from the galactic centre, that is, about two-thirds the way to the edge of the Galaxy. The distances to the nebulae, however, did not come for another decade. After much heated debate, Edwin Hubble presented convincing evidence that the three nebulae M31, M33 and NGC6822 were systems considerably more distant than the most remote parts of our Milky Way. Notwithstanding a few inconsistencies between various distance estimates, there was no longer any doubt that these were indeed ‘island universes’ not unlike the Milky Way.

Hubble then turned his attention to the systematic study of these extragalactic systems and OBSERVATIONAL COSMOLOGY was born No longer was cosmology the domain only of the philosopher and theologian, it had entered the arena of the scientist.

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