Phases

Definition

Phases are the different appearances of the Moon as seen from Earth, which change in a predictable cycle. These phases result from the relative positions of the Earth, Moon, and Sun.

5 Must Know Facts For Your Next Test

1. The lunar cycle, or synodic month, is approximately 29.5 days long.
2. The primary phases include New Moon, First Quarter, Full Moon, and Third Quarter.
3. Waxing phases occur after a New Moon and before a Full Moon; waning phases occur after a Full Moon and before a New Moon.
4. A solar eclipse can only happen during a New Moon phase, while a lunar eclipse can only happen during a Full Moon phase.
5. The same side of the Moon always faces Earth due to synchronous rotation.

Review Questions

• What causes the different phases of the Moon?
• How long does it take for the Moon to complete one full cycle of phases?
• Which phase occurs when the entire face of the Moon is illuminated?

Related terms

NewMoon: The phase when the moon is positioned between Earth and Sun and its illuminated side is facing away from Earth.

FullMoon: The phase when Earth is between the Sun and the moon and its fully illuminated side faces Earth.

SynchronousRotation: The phenomenon where an astronomical body rotates at the same rate that it orbits another body, resulting in the same face always pointing towards that body.