AST101H1 Chapter : good notes

• School: UTSG
• Department: Astronomy & Astrophysics
• Course: AST101H1
• Professor: Michael Reid

Document Summary

Supplementary chapter 1 celestial timekeeping and navigation. How do we define the day, month, year, and planetary periods? y. The length of the month y our month comes from the moons 29. 5 day cycle of phases. Like the sidereal day, the sidereal month gets its name because it describes how long it takes the moon to complete an orbit relative to the positions of distant stars. This time periods, called a tropical year, is about 20 minutes shorter than the sidereal year. y the difference between the sidereal year and the tropical year arises from. Earth s 26,000 year cycle of axis precession. y precession not only changes the orientation of the axis in space but also changes the locations in earth s orbit at which the seasons occur. When it does happen, it s because their orbital planes are slightly tilted compared to.