Phases of the Moon: Practice Problem Solutions

1. Half of the Moon is always lit by the Sun. As the Moon orbits Earth, we see more or less of that lit half.

2. About 29.5 days.

3. Waxing: the lit part is growing. Waning: the lit part is shrinking.

4. About sunset.

5. First quarter. Afterward it waxes (grows) toward full.

6. Earth's shadow falls on the Moon only during a lunar eclipse, which is rare. Phases happen every month and appear even when the Moon is nowhere near Earth's shadow.

7. During the 27.3 days, Earth also moves along its orbit around the Sun, so the Moon must travel a bit farther (about 2 more days) to be in the same position relative to the Sun and Earth.