Lunar phases
Period of Moon’s phases = “synodic period”
- Measured with respect to the Earth-Sun line
- Slightly longer than sidereal period
- “true” orbital period -- measured with respect to fixed stars v16
Synodic period is 29.5 d (i.e. 1 month)
Can use moon to tell time
- Full moon -- opposite to sun -- 12 h difference
- rises as sun sets (6 PM)
- culminates (near zenith) at midnight
- sets as sun rises (6 AM)
- First quarter -- 90 degrees from sun -- 6 h difference
- overhead (near zenith) at sunset (6 PM)
- sets at midnight