Earth and Space Science / Unit 9: The Solar System
9.6 Moon Phases
Notes
The Moon shines by reflected sunlight. Half is always lit; phases depend on how much of the lit half we see.
- Cycle: new, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, third quarter, waning crescent. About 29.5 days.
- At new moon the Moon is between Earth and Sun; at full moon Earth is between the Sun and Moon.
- The Moon orbits Earth in about 27.3 days and rotates once per orbit, so the same side faces Earth.
- Waxing means growing; waning means shrinking.
- Example: 7 days after a new moon is about the first quarter.
Practice
During a full moon, the Moon is:
The whole face is lit.
About how long is the cycle of Moon phases?
New moon to new moon.
Why do we always see the same side of the Moon?
Rotation period equals orbital period.
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