ASTR 100 Lecture Notes - Lecture 5: Angular Diameter, Orbit
28 Jul 2017
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An object"s altitude and direction indicate its location in the night sky. Horizon: all points 90 degrees from the zenith. Meridian: arc passing through the zenith and connecting the north and south points. An object"s angular size appears smaller if it is farther away. Angular size (in radians) is physical size divided by distance. The earth rotates from west to east so the stars appear to go from east to west. We cannot see stars near the south pole. All other stars rise in the east and set in the west. Your position on earth determines which constellations stay above the horizon and visible. Earth"s position relative to the sun determine where we see the sun among the stars. The sun varies with latitude, not longitude. The sky varies as earth orbits the sun. As earth orbits the sun, the sun appears to move eastward. At midnight, the meridians are on opposite sides of the earth.
