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	SEEING IS BELIEVING - cont.


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	The picture of the Sun lying at the center of the universe held sway until early this century, though by then astronomers were beginning to realize that the universe was bigger than they had presumed. Back in the 18th century, they started to suspect that the Sun was part of a large system of stars, called a galaxy, but the general consensus was that the Sun lay at the center. Then, in the 1910s, the American astronomer Harlow Shapley showed that we actually reside in the galaxy’s backwaters, some 30,000 light-years from the center of a system that itself measures about 100,000 light-years across. The heliocentric view was dead, replaced by the new “galactocentric” idea.

Spiral Galaxy


	Our view of the universe was just beginning to grow larger. One big question remained: What was the nature of the fuzzy patches of light known as nebulae? The 18th-century French comet hunter Charles Messier had catalogued more than 100 such objects, some of which appeared to have a spiral shape. By the 1920s, literally thousands of these objects were known. Although the 18th-century philosopher Immanuel Kant had speculated that they were large star systems like our own, it fell to Edwin Hubble to prove it. Using the 100-inch telescope at Mt. Wilson in California in the 1920s, Hubble observed individual stars in some of these fuzzy patches and, based on their apparent brightness, calculated them to be far outside our own galaxy. The universe suddenly became filled with thousands, if not millions, of galaxies.


	It was only a matter of time, and just a few short years at that, before the galaxies themselves were found to be moving. Hubble proved that the universe is expanding, with every galaxy flying away from every other galaxy in response to a prodigious “Big Bang” that occurred some 10 to 15 billion years ago. We’ve come a long way in the last few millennia, from a small, quiet universe existing above a flat Earth to a vast, dynamic one with Earth out in the boondocks. Despite our sophisticated theories and in-depth knowledge, we still have a way to go before we know everything about our universe. As Newton once said: “To explain all nature is too difficult a task for any one man or even for any one age. ’Tis much better to do a little with certainty, and leave the rest for others that come after you, than to explain all things.”


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