ME 2334 Chapter : SI Session Pg. 1
Document Summary
Astronomical unit (au) average distance between sun and earth. Light year (ly) distance light travels in one year. = 0. 307 parsecs (pc) km is appropriate for distances on or near earth. The sun to neptune is 30 au or 0. 00047 ly. Carina nebula = gas cloud that makes stars (3. 1 ly) Milky way to andromeda galaxy (m31) = 2. 5 x 106 ly. Distances between galaxy groups are best measured in millions of ly (mly). Hubble deep field cross star artifact of telescope-- Distances across the universe are best measured in billions of ly (bly). Philosophical ideas of the ancient greeks: heavens = perfection, immutable (unchanging) circle = perfect shape. The almagest, written by ptolemy, is the only surviving ancient comprehensive book on astronomy. 2nd century ad ptolemy built comprehensive model of the solar system based on. Earth = center, did not move everything in the sky goes around earth stars fixed to celestial sphere, which is farthest from the earth.
