Moon Phases Overview
Overview
This lecture explains the appearance, naming, and phases of the Moon as seen from Earth, focusing on the first quarter, waxing gibbous, and full moon phases.
First Quarter Moon (Moon C)
- Draw a straight line down the middle of the moon to show half is lit.
- Only the right half is visible and lit from Earth during this phase.
- Commonly called a "Halfmoon," but astronomers call it "First Quarter Moon."
- The name "First Quarter" refers to the moon's position: one-fourth of its orbit completed.
- Avoid common drawing mistakes, like triangle or "Pac-Man" shaped moons.
Timing of the First Quarter Moon
- The first quarter moon rises at noon, is overhead at 6:00 p.m., and sets at midnight.
Waxing Gibbous Moon (Mundi)
- More than half of the moon's face is lit, with a sliver of darkness on the left.
- The lit portion is not crescent-shaped, so it's not a crescent moon.
- Called "Waxing Gibbous" because the lit part grows and is more than half ("gibbous" means swollen).
- The darkness on the left side indicates it's waxing, not waning.
Full Moon (Moon II)
- Entire face of the moon is lit and visible from Earth.
- The full moon phase lasts only one day—must be 100% lit to be considered "full."
- In media, the full moon often appears longer, but astronomically it's a single day.
- The day before full moon may look full but is still considered waxing gibbous.
Key Terms & Definitions
- First Quarter Moon — Phase when half the moon's face is lit (right side) and one-fourth of its orbit is completed.
- Waxing — The moon's lit portion is increasing.
- Gibbous — More than half but not fully lit; "swollen" appearance.
- Full Moon — Moon phase when the entire visible face is lit.
- Crescent — Less than half of the moon's face is lit, shaped like a croissant.
Action Items / Next Steps
- Practice drawing each moon phase accurately.
- Remember the timing and appearance associated with each phase.
- Review definitions to avoid common misunderstandings.