ASTR 101 Lecture Notes - Lecture 5: Sidereal Time, Solar Time, Tropical Year
Document Summary
1 solar day = 24 solar hours. Earth revolves 360 degrees around the sun every 365. 24 solar days: called a tropical year. Meridian is a giant line that comes from north to zenith to the south. Sun won"t necessarily go through zenith, but will pass through the meridian: how we measure solar day. 1 sidereal day = 24 sidereal hours = 23 solar hours + 56 solar minutes. Earth rotates 360 degrees on its axis every sidereal day. Solar day is longer because of the earth"s orbit around the sun. Earth has to revolve a bit farther to get back on the meridian. Earth rotates 1 degree on its axis every 4 sidereal minutes. Earth revolves about 1 degree around the sun every day. After one sidereal day, earth will point at star, but may not point at sun. Stars will be rising/ setting 4 minutes earlier. 1 sidereal day + 4 minutes = 1 solar day.
