AST 111 Lecture Notes - Lecture 2: Lunar Eclipse, Solar Calendar, Ecliptic

• School: Tunxis Community College
• Department: Astronomy
• Course: AST 111
• Professor: Reynolds

Document Summary

Seasons occur because the tilt of earth"s axis causes sunlight to fall differently on earth at different times of year. If we did not have an axis tilt, there would be no seasons. Solstice: occurs on june 21/december 21, the longest and shortest days of the year. Equinox: occurs on march 21/september 21, when day and night are equal lengths. Modern calendars include leap years to keep the solstices and equinoxes around the same time. Precession: a gradual wobble that alters the orientation of earth"s axis in space, caused by gravity. Precession does not heavily change the amount of the axis tilt (stays close to 23. 5), so it doesn"t affect the seasons. It does, though, change the points in earth"s orbit at which the solstices and equinoxes occur, and therefore changes the constellations we see at those times. As the moon orbits earth, it returns to the same position relative to the sun in our sky every 29. 5 days.