Sun-Earth-Moon Patterns

The Sun, Earth, and Moon move together in patterns we can observe and predict. Earth spins like a top while orbiting the Sun, and the Moon orbits Earth. These motions cause day and night, and the changing shapes of the Moon across the month.

Day and Night — Earth's Rotation

• Earth rotates (spins) on its axis once every 24 hours.
• The side facing the Sun has daytime; the opposite side has nighttime.
• The Sun only seems to move across the sky — really, Earth is turning.
• Sunrise and sunset are caused by Earth's rotation, not the Sun moving.

The Moon Orbits Earth

The Moon takes about 29.5 days to orbit Earth. We always see the same side of the Moon because it rotates at the same rate it revolves. The shape we see (the phase) depends on how much of the lit side is facing Earth.

The 8 Moon Phases (in order)

1. New Moon — Moon is between Sun and Earth; the lit side faces away, so we see no Moon.
2. Waxing Crescent — a thin sliver of light grows on the right side.
3. First Quarter — the right half is lit (looks like a half-circle).
4. Waxing Gibbous — more than half lit, growing toward full.
5. Full Moon — Earth is between Sun and Moon; the whole face is lit.
6. Waning Gibbous — more than half lit, but shrinking now.
7. Last Quarter — the left half is lit (the other half-circle).
8. Waning Crescent — a thin sliver of light on the left, getting dimmer.

Waxing vs Waning

• Waxing = getting brighter (lit side grows from new to full).
• Waning = getting dimmer (lit side shrinks from full back to new).
• Crescent = less than half lit; Gibbous = more than half lit.
• Quarter = exactly half lit (it is one quarter of the whole cycle).