Today we have the possibility of viewing the solar system as a whole. In 1990 Voyager 2, after a 13 year journey, passed the furthest flung planets confirmed the Copernican/Galileo/ Kepler view, and showing the earth as a tiny blue dot, delicate and vulnerable in the abyss of space. Only a thin veneer of atmosphere protects it from the countless cosmic assaults, which only occasionally get through to devastate huge areas of the earth. (As recently as 1908 in Siberia parts of a comet got through most of the atmosphere and caused major impact damage.)

The modern view of the universe took shape after a landmark observation by American astronomer Edwin Hubble in 1929. The standard cosmological model of science these days, the best "how" theory of the origin of the universe, is called the "big bang" theory. The term "Big Bang" is used to describe the theory in which the entire physical universe - all matter, energy, even space and time burst forth from a volume smaller that a pin head in a state of near infinite density. The first measurements that pushed people to think in this way were done by Hubble, after whom the telescope was named.

Hubble discovered his law by noticing that light from distant galaxies was shifted toward the red end of the spectrum, clear evidence of the galaxies moving away from us. This spectrum shift is called the red shift. The characteristic "spectral lines" associated with several elements (like hydrogen,and helium) were clearly identifiable, but had moved from their normal position toward the red end of the violet-indigo-blue-green-yellow orange-red spectrum. The colour emitted by a violet colour on earth might appear as indigo when emitted in a distant galaxy and then seen from earth. This is something we expect if stars are moving relative to us.

This effect is similar to what is called the "Doppler effect" in sound. You might have observed it in the changing pitch of a horn on a moving car, or a whistle on a train. The car horn rises in pitch as it approaches, and falls again as it travels away form you. Just as a drop in pitch indicates a receding sound source, so a red shift indicates a receding light source. Thus Hubble concluded that all galaxies seemed to be moving away from earth and hence that the universe is expanding. Until this discovery it was the thought the universe was static and eternal, and that any movement of stars was part of the indiscriminate movement of the entire universe. (This description of a universe simultaneously expanding and slowing down, is precisely what Einstein had predicted.)

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