ASTRO-110 Lecture Notes - Lecture 29: Celestial Equator, Cosmic Calendar, Constellation
22 Sep 2020
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Document Summary
Each month represents a little more than 1 billion years. Early september: our solar system and planet formed. Dec 26th: early dinosaurs appeared and instantly disappeared. Dec 31st: humans began to walk upright. Most basic motions of earth are rotation and orbit. Earth rotates once each day around its axis from west to east (counter clockwise) Sun rises in the east and sets in the west. Earth orbits the sun completing one orbit a year (also counter clockwise) Earths axis is tilted by 23 degrees from a line perpendicular to the ecliptic plane. Axis tilt is pointed almost directly to polaris our north star. (1) our solar system moves relative to nearby stars in our local solar neighbourhood the region of our sun and nearby stars. (2) rotation of the milky way galaxy: completes one orbit in about 230 million years @ 800 000km/h stars at different distances from the galactic center orbit at different speeds.
