The stars and constellations, with their regular, unchanging patterns, swept across the night sky and shifted with the seasons, always returning to where they started from with regularity in a cycle, known as sidereal time.īoth the sun, the most prominent of celestial bodies, and the moon, the second-most, appear to orbit the Earth, helping give rise to the geocentric model of the universe that most people believed in until the middle of the second millennium CE, and even then for a long time after in some quarters.īut even in ancient times, there were clear indications that the Earth wasn't at the center of things.įor one, the visible planets that "wandered" across the backdrop of seemingly fixed stars or near the sun during the twilight of dawn or dusk do not obviously orbit the Earth. While this seems silly to us now, at the time, it was an easy mistake to make. Early attempts at placing ourselves in the universeĪncient astronomers used the changes in the night sky and cycle of the sun to come up with the first attempts at placing our position in the universe, and they decided that we were clearly at the center of everything. But techniques passed down through time have given us a useful set of tools that have helped us map the stars and find our place in the cosmos. Marschall of Gettysburg College in Gettysburg, Pennsylvania.Īnd given our propensity to put ourselves at the center of everything, figuring out where we really are can be more challenging still. "Finding one's location in a cloud of a hundred billion stars-when one can't travel beyond one's own planet-is like trying to map out the shape of a forest while tied to one of the trees," said Laurence A. This isn't a problem unique to astronomy, the challenge of mapping and localizing oneself in an unknown space has been a difficult challenge for explorers throughout history navigating the unknown.
![galactic disk map galactic disk map](https://www.science20.com/files/images/igps_plan.gif)
In the case of our planet and solar system, how do we know where we are in the Milky Way, the galaxy we call home?