PHYSICS 20A Lecture Notes - Lecture 3: Midnight Sun, Celestial Equator, Right Ascension
Document Summary
Right ascension (ra, ) like longitude for the celestial sphere. Declination (dec, ) like latitude for the celestial sphere: ncp is at = +90 , scp is at = -90 , celestial equator is at = 0 . For some reason, ra is usually measured in units of time (hrs, min, sec). From irvine, polaris is at roughly 33 declination. Earth orbits the sun in a plane called the ecliptic: it takes 24 hrs for the earth to rotate on its axis, it takes 365. 25 days (8,766 hrs) for the earth to orbit the sun. Earth"s axis of rotation is tilted relative to the ecliptic: tilted at around 23. 5 . Summer in irvine: the sun is north of the celestial equator: it spends more than 12 hours above the horizon, the sun is higher in the sky we get more concentrated rays of light.
