Moon Rise, Set, and Zenith Times
Overview
This lecture explains how the Moon's position in its orbit impacts rise, set, and zenith times for each phase, and introduces a method to determine these times using a simple mnemonic.
Sun and Moon Visibility
- The Sun always rises at sunrise, sets at sunset, and is only out during the day.
- The Moon can be visible during both day and night, depending on its position in orbit.
- The Moon orbits Earth, causing its rise/set times to change daily.
Lunar Orbit & Calendar Connection
- The Moon completes one orbit around Earth in about 28 days, roughly four weeks.
- The word "month" originates from the word "moon," as months were once based on lunar cycles.
- The Moon rises about 50 minutes later each day due to its orbital motion.
Determining Rise, Set, and Zenith Times
- For any Moon phase (labeled A, B, C, etc.), put the phase at the top of your diagram to determine times.
- The time on the right of the diagram indicates when that Moon phase rises ("right rise").
- The time on the left represents when it sets ("left set").
- The time pointing directly up at the moon is its zenith time (when it's overhead).
Example Moon Phases and Times
- Moon A: Rises at 6:00 a.m., zenith (overhead) at noon, sets at 6:00 p.m.
- Moon C: Rises at noon, zenith at 6:00 p.m., sets at midnight.
- Moon E: Rises at 6:00 p.m., sets at 6:00 a.m. (next day).
- For phases between main points (e.g., Moon B), give a range: rises between 6:00 a.m. and noon; sets between 6:00 p.m. and midnight.
Mnemonic for Remembering Times
- Use "right rise, left set, up zenith" to easily find the rise, set, and zenith times for any lunar phase.
- Main phases (A, C, E, G) correspond to a single day and align exactly with the key times.
- Phases between main points last about six days and have range times for rise/set.
Diagram Setup Tips
- Always point "noon" toward the Sun to correctly label other times on your diagram.
Key Terms & Definitions
- Zenith — The point in the sky directly above an observer.
- Phase (of the Moon) — A specific appearance or illumination of the Moon as seen from Earth.
- Orbit — The path the Moon follows around Earth.
Action Items / Next Steps
- Practice using the "right rise, left set, up zenith" method with a Moon phase diagram.
- Ensure diagram has "noon" pointing to the Sun before labeling other times.