Size Does Matter - telescope designs

Big telescopes are better than small telescopes. When all other variables--such as climate, location, quality of the optics, or talent of the observer--are equal, this statement is always true. Nothing mysterious or macho here. Big telescopes collect more light than small telescopes, just as big buckets collect more rain than small buckets. When you want to see ever dimmer objects, ever bigger telescopes matter greatly.

While some controversy remains, the credit for the invention of the telescope is generally given to the Dutch spectaclemaker Hans Lippershey. In 1608 Lippershey inserted a lens at each end of a tube, enabling the viewer to see faraway things as though they were close by. What an entertaining invention it was! These simple optical devices were relatively easy to make, and everybody wanted one. I don't know much about the windows of seventeenth-century northern Europe or how wide open people kept their curtains, but the Latin name for Lippershey's device became perspicilli, commonly translated as "spyglass."

The first person to do anything meaningful with a spyglass and, in particular, to look at non-earthly heavenly bodies was the Italian mathematician, physicist, and astronomer Galileo Galilei. Beginning in 1609, Galileo built several world-class spyglasses within months of having heard about the device via the Netherlands-Italy grapevine. Of his best spyglass, Galileo wrote: "Finally, sparing no labor or expense, I progressed so far that I constructed for myself an instrument so excellent that things seen through it appear about a thousand times larger and more than thirty times closer than when observed with the natural faculty only." Galileo's best, although only a couple of inches in diameter, was powerful enough to blow open the science of astronomy and simultaneously make a mockery of church dogma, which, without regard for experiment or observation, claimed to embody divine knowledge of the ways and means of the heavens.

If you want to pretend you are Galileo for the night, just take home one of those cheap refracting telescopes you see in the display window of your local camera store. The scope will have optics superior to those of Galileo's originals, so you will be handily equipped to discover, as did Galileo, the rings of Saturn, the four brightest moons of Jupiter, the phases of Venus, and the mountains, valleys, and craters of the moon. The images produced, however, will be upside down, which is more of a problem when you're peering into someone's window than when you're looking into space.

In 1611, just two years after Galileo first looked up with his spyglass, he was invited to join the exclusive Roman Accademia del Lincei (Academy of the Lynxes). The academy was so new and exclusive that it had only five members at the time Galileo was inducted, but it would later become an influential force in promoting an empirical approach to science. During Galileo's induction banquet, his spyglass was formally named telescopium, from which we obviously derive the word "telescope."

Isaac Newton, the brilliant English physicist, was born in 1642, the year Galileo died. Newton's lens- and mirrormaking expertise, coupled with his advanced theories on the behavior of light, enabled him to build a telescope superior to all those preceding it. Using a concave mirror, which removed certain distortions of color and shape that limited the success of ordinary lenses, Newton fashioned a telescope that reflected light back toward an angled, flat mirror. This secondary mirror enabled the image to be reflected sideways and then focused through a hole in the tube, thereby elegantly solving the inherent reflector-telescope problem of the observer's head getting in the way.

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