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The Question

(Submitted February 15, 1998)

What tools did the ancient astronomer use ? Who were some ancient astronomers ? What is the History of Astronomy?

The Answer

The history of astronomy is the study of humankind's early attempts to understand the skies. All people have looked up and wondered about the Sun, Moon, planets, stars, and their complex ballet of motion. Interpretations vary widely among cultures, but often the sky is considered as the abode of gods, where humans can never touch. The consideration of stars and planets as physical objects that obey knowable laws started in the Middle East (and somewhat in China) and has spread into cultures that are the intellectual heirs of the Greeks. A fairly modern view of the heavens only started in the early 1600's when Galileo first turned the newly invented telescope to the heavens and saw worlds in their own right. With the Newtonian revolution in physics, it was realized that stars were just Suns, and all obeyed the same Laws of Physics as hold here on the Earth. In the 1900's, the detailed study of everything up in the sky has become a major pursuit which is growing exponentially. The history of astronomy looks at all these perceptions and advances.

There are many ancient astronomers from many cultures all around the world, many of whom have their name lost over the ages. For example, we do not know who or when the planets were recognized as being different from stars. In some sense, most ancient people were 'astronomers' since all lived under non-light-polluted dark skies and everyone wonders what is up there. The names of the Egyptian, Mayan, and Chaldean astronomers are all lost, even if we know of some of their results. The best known astronomers are those associated with the development of the modern scientific results. For example, Hipparchus (Greek ~3 century BC) discovered the precession of the equinoxes, Ptolemy (Greek in Alexandria ~100 AD) systematized the geocentric system of planets, Copernicus (Polish, 1500s) proposed the heliocentric system, Kepler (Czech?, ~1600) came up with detailed laws for planetary motion, Galileo (Italian early 1600s) made great discoveries with his telescope, Newton (English, late 1600s) discovered the basic laws of Physics that allow us to understand the cosmos, and Edwin Hubble (American, died ~1940) who discovered that the Universe is expanding.

The history of astronomy is a very long one and astronomy has been pursued by all cultures, so there is a very wide range of tools. Before the discovery of the telescope, the only observing devices that people could use was the human eye, perhaps aided by any of a variety of sighting devices. Thus, the Chinese used armillary spheres, Tycho Brahe (Danish late 1500's) used long sighting 'tubes', neolithic farmers made Stonehenge to point to midsummer sunrise, and Ptolemy noted planet positions with respect to stars. After the discovery of the telescope, there was a steady push to larger-and-larger telescopes. Starting around the 1800's, various instruments, like micrometers and spectrometers, were constructed to give very detailed measures of the light coming from stars. Starting around 1900, the photographic plate and then the CCD camera, have revolutionized astronomy due to their great sensitivity.

To answer your three questions in detail, it could take a year of study or more, depending on your desired depth of answer. We cannot provide you with a whole class in the history of astronomy. Fortunately, there are many resources that you can use. One of the best, is to go to your local library and check out books there. This is a time honored and effective means for learning much. On the web, here are some addresses that will allow you to branch out widely:

http://skyandtelescope.com/
http://antwrp.gsfc.nasa.gov/apod/astropix.html

Maybe the best thing for you to do, is to every night go outside and to look up. The beauty of the sky is what makes it so fascinating.

Cheers,
Brad Schaefer
Yale University

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