| A | B |
|---|
| astronomy | The study of the universe, the properties of its objects, and the laws under which it operates. |
| retrograde motion | The apparent backwards motion of a planet as it crosses our sky. |
| geocentric | A model of the universe in which all objects in space are believed to revolve around the Earth in perfect circles. |
| epicycle | Ptolemy's small, circular orbit of a planet centered around its concentric orbit of the Earth. |
| deferent | Ptolemy's concentric orbit of a planet around Earth. |
| heliocentric | A model of our solar system that places the sun at the center and planets orbiting it in concentric circles. |
| Ptolemaic system | Another name for the geocentric model of the solar system |
| parallax | The most basic way of measuring the distance to an object in space by comparing its shift in apparent position over a period of time. |
| astrolabe | 2D model of the sky used to make measurements of celestial objects and their postion in the sky. |
| Keplar's Laws | Redefined the planets orbits as elliptical paths whose speed increases as the planet approaches the sun. |
| Einstein's Theory of Relativity | States that all mass distorts the "fabric" of space and time, causing light to "bend" around massive objects |
| gravitational lens | Effect of the bending of light in space to a common focal point, allowing us to see objects farther away than would be expected |
| Electromagnetic Spectrum | Classification system used for light that is based on the frequency (and energy) of the waves. |
| Dopplar Effect | The wavelength emitted by something moving away from us is shifted to a lower frequency/longer wavelength. |
| red shift | The shift toward the red end (higher wavelength) of the visible spectrum that happens over time as a star moves farther away from us. |
| cosmic microwave background radiation | Remnant heat left over from the Big Bang that creates "noise" in space. |
| Aristotle | determined the shape of Earth |
| Eratosthenes | determined the circumference of Earth |
| Galileo | first to use the telescope for astronomy |
| Copernicus | given credit for the heliocentric model |
| Brahe | created first observatory (no telescope) |
| Hipparchus | 1st star catalog |
| the Big Bang | dominant scientific theory about the origin of the universein which all matter and energy was contained in 1 infinitely dense point followed by an instantaneous filling of space |
| Radiation Era | first 500,000 years following the Big Bang in which the electromagnetic spectrum seperates out and matter begins organizing |
| Matter Era | time period greater than 500,000 years since the Big Bang where larger masses, such as stars, formed |
