Moon Phases & Eclipses
The Moon’s appearance changes night by night because we see different portions of its sunlit half as it orbits Earth. The classic eight phases—from new to full and back—repeat on average every ~29.5 days (the synodic month). This cycle underlies many timing techniques in astrology and is a cornerstone for planning observations.
The eight phases (quick guide)
- New Moon → Waxing Crescent → First Quarter → Waxing Gibbous
- Full Moon → Waning Gibbous → Third Quarter → Waning Crescent
For a clear, concise primer and visuals, see NASA’s Moon Phases pages and Space Place explainers.
Why eclipses happen (and why not every month)
Eclipses require near-perfect alignment of Sun–Earth–Moon and happen only when the Moon is near a node (where its orbit crosses the ecliptic). Because the Moon’s orbital plane is tilted by about 5°, most new and full Moons miss exact alignment—so eclipses cluster in two “seasons” each year.
- Lunar eclipse (at Full Moon): Earth’s shadow falls on the Moon; scattered red/orange light can tint it (“blood moon”).
- Solar eclipse (at New Moon): the Moon briefly blocks the Sun for observers along the shadow path on Earth.