Today’s moon phase features a specific illumination percentage and synodic cycle position that stargazers and astronomers track continuously as the lunar disk orbits Earth.
Understanding the Synodic Lunar Cycle
During this period, the Moon transitions from dark to fully illuminated and back again. Astronomers divide this span into four primary phases—New Moon, First Quarter, Full Moon, and Last Quarter—which occur at precise moments globally, alongside four secondary phases that represent ongoing transitions.
Because the Moon follows an elliptical orbit, its distance from Earth changes continuously, dropping as close as approximately 356,500 kilometers at perigee, which alters its apparent size and angle in the night sky.
The Eight Primary and Secondary Moon Phases
The lunar cycle moves through distinct configurations that determine how much of the lunar disk is visible from Earth:
- New Moon: The Sun and Moon align on the same side of Earth, leaving the Earth-facing side in shadow.
- Waxing Crescent: A thin illuminated arc appears shortly after the New Moon, growing wider each day.
- First Quarter: Exactly half of the Moon’s visible disk is illuminated as the Moon completes one-quarter of its orbit.
- Waxing Gibbous: The illuminated portion expands past the halfway mark, moving toward full illumination.
- Full Moon: The entire Earth-facing side of the Moon receives direct sunlight.
- Waning Gibbous: Sunlight begins to recede from the disk following the Full Moon peak.
- Last Quarter: Exactly half of the visible disk is lit again, marking three-quarters of the way through the cycle.
- Waning Crescent: A shrinking crescent remains visible before the cycle resets at the next New Moon.
Frequently Asked Questions
Why does the Moon change shape every night?
The Moon does not generate its own light. As the Moon orbits Earth, our viewing angle changes, allowing us to see varying portions of that illuminated hemisphere.
What is moon age?
Do primary Moon phases happen at the same time everywhere?
Yes.
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