Groundbreaking Scientific Experiments, Inventions, and Discoveries of the 17th Century

Nebula (1609–1656): Even with the unaided eye the night sky appears to be full of objects. A casual examination reveals not only an abundance of stars and the predictable motions of the moon and planets, but also the possibility of an occasional appearance by a meteorite or comet. However, with a more detailed look one can detect smudges in the night sky, areas where the stars appear to be blurred. These areas are called nebulae after the Latin word for cloud or mist. The early Greek astronomers provide some of the first written descriptions of nebulae in their early preparation of sky charts. The Greek astronomer Hipparchus produced some of the most detailed and significant records of astronomical observations during ancient times. Hipparchus made many contributions to astronomy including assigning brightness, or magnitude, to stars, identifying new stars or novas, and refining calculations on lunar motion and equinoxes. This database, which formed the basis of subsequent efforts in Greek astronomy, mentions the positions of two nebulae. Two centuries later, Ptolemy’s Almagest, a compilation of Greek astronomical and mathematical accomplishments, contains two volumes dedicated to star maps (see STAR ATLASES). In this work Ptolemy lists information on over 1,000 stars, including three additional nebula-like objects. However, further investigation into the nature of these objects would have to wait until centuries later.

The invention of the telescope revolutionized observational astronomy. With the aid of the telescope the vast, complex nature of the heavens was revealed. To the unaided eye, nebulae all appear to be faint glowing clouds or smudges of light. However, with the increased magnification available using the telescope, many nebulae were ob-

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