Lunar Phase Sequence Practice Test

Use the space-view model (not to scale). Sunlight travels from left to right. The Moon is shown at five positions around Earth in order along its orbit: 1 (left of Earth), 2 (upper-left), 3 (top), 4 (upper-right), 5 (right of Earth). The sunlit half of the Moon always faces the Sun.

If position 1 corresponds to new Moon, what phase would an observer on Earth most likely see at position 3?

(Choose the best Earth-view phase.)

A student draws this incorrect idea in words: “During the month, the Moon changes from being fully lit to not lit because the Sun lights different amounts of the Moon.”

Use the space-view model idea (not to scale): the Sun always shines from one direction, and the Moon always has one half illuminated.

Which statement must be true in a correct model of lunar phases?