I recently finished the first book on my list for the Astronomy Reading Challenge. The History of Astronomy: A Very Short Introduction by Michael Hoskin is part of a series of “very short introductions” covering a dazzling variety of topics, published by Oxford. This very slender but dense volume covers the history of astronomy from prehistory to the mid-19th century, just before the birth of modern astrophysics. It tells the story of how humans gradually grew to understand the true nature of the solar system and started exploring the cosmos with the help of telescopes.
Astronomy began as astrology, an attempt to understand and predict events by the movement of the stars and planets. The Babylonians were particularly eager astrologers, and their meticulous records were very valuable to later researchers trying to create accurate calendars and navigational aids, and ultimately for those trying to study the physical nature of the planets and stars.
While I was reading the book I was also perusing my new Peterson Field Guide to Stars and Planets and was struck by the fact that though we know so much more about the universe than the ancients, we still talk about what we see in the sky in much the same way. Stars are still mapped on the “celestial sphere,” very much like the sphere studded with stars that early astronomers conceived, complete with north and south poles. Star charts are bisected by the “ecliptic,” the path the sun takes across the sky, even though we know it is the Earth that is moving. Astronomers talk about stars and planets rising and setting, and we still locate everything in the cosmos as we always have, relative to our position on the Earth. As much as we can turn the solar system, galaxy and universe around in our minds and view them from any angle, we only ever actually view them from the same place the ancient Greeks did, right here on our wobbly little planet, or just above it in the case of space telescopes. If a medieval astronomer used to using an astrolabe was brought here in a time machine, he would probably have a much easier time finding his way around the sky than I do, no matter how much I might know about galaxies and black holes. I actually find it quite confusing to consider the stars and planets from an Earth-centered perspective, but since I’m on Earth I had probably better get used to it!