The Moon’s Phases

Written by: Sitara Nair

The Moon takes about 29.5 days to orbit Earth, and that near-month span is where the word month originally came from. During the journey we always see the same lunar face, yet its appearance changes because different portions of that face catch sunlight at different angles! These changing views are called the eight phases.

The Eight Phases in Order

New Moon The Moon sits between Earth and the Sun, so its sunlit half faces away from us and the sky looks empty.

Waxing Crescent A thin right-hand “banana” of light grows each night. Waxing means the lit part is increasing.

First Quarter The right half is bright, the left half dark; the Moon has completed one-quarter of its trip around Earth.

Waxing Gibbous More than half is lit but it isn’t yet a full circle.

Full Moon Earth is between the Sun and Moon, letting us see the entire sunlit side as a bright white disc.

Waning Gibbous The lit area now shrinks. Waning means the bright part is getting smaller.

Third (Last) Quarter The left half is illuminated, the right half dark, showing the Moon is three-quarters through its orbit.

Waning Crescent Only a slim left-hand crescent remains, usually visible just before sunrise, before the cycle restarts.

Why the Phases Look the Way They Do

Same face, different lighting: The Moon turns once on its axis in the same time it orbits Earth, so we always see one side. As it moves, sunlight strikes that side from new directions, creating each phase.

Day-or-night visibility: Whether you spot the Moon in daylight or at night depends on which half is lit. For example, a Full Moon rises at sunset and sets at dawn, while a First Quarter Moon is visible in the afternoon and early evening.

A simple memory trick to remember what’s happening is that waxing means the light increases on the right for those in the Northern Hemisphere, while waning indicates that light diminishes on the left; this is reversed in the Southern Hemisphere

Phases and Ocean Tides

The Moon’s pull on Earth’s oceans changes with its phases. During New Moon and Full Moon the Sun, Earth, and Moon lie roughly in a line, so their gravities combine to create spring tides; the highest highs and lowest lows of the month. Around First and Third Quarter the Sun’s tug partly cancels the Moon’s, producing gentler neap tides. Watching the tide chart is another way to track where the Moon is in its 29½-day cycle. Read our article about Solar Eclipses to learn more!

Eclipses and Calendars

When the Sun, Earth, and Moon line up perfectly at New Moon, the Moon can hide the Sun in a solar eclipse; when they align at Full Moon, Earth’s shadow can turn the Moon copper-red in a lunar eclipse. Many cultures still have celebrations: such as Ramadan, Lunar New Year, and Easter, to acknowledge these monthly phases.