PHYS 1600 Lecture Notes - Lecture 2: Equinox, Celestial Equator, Solar Time
Document Summary
Rotation is a planets movement around an axis: the counter clockwise direction of earth"s rotation is called prograde. Motion and is the dominant motion in the solar system: when something rotates or revolves in the opposite direction it is called retrograde motion. Revolution is a planets movement around another astronomical object(orbit: earth takes approximately 365 days to complete one full revolution around the sun. Diurnal motion is a planet/object"s daily motion. Sidereal period is the length of any cycle of motion that is measured with respect to stars (ex. earths orbit around the sun) Zenith is the point directly overhead anywhere on earth; this is where no stars rise or set. Stars and constellations that never go below the horizon are circumpolar. At the equator, all stars seem to rise straight up, and set straight down. None of the stars seen from the equator are circumpolar. This is because earth"s orbit around the sun is not perfectly circular.