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The Third Quarter Moon is a Half Moon

The Third Quarter Moon is when the opposite half of the Moon is illuminated compared to the First Quarter. Which half you see lit up depends on where you are on Earth.

A Last Quarter Moon, also called Half Moon, where the left half of the Moon is lit up.

The Third Quarter Moon is the last of the four primary Moon phases.

©iStockphoto.com/Lio22

Next Third Quarter Moon

Jul 1, 2021 at 5:10 pm

Previous Third Quarter Moon

Jun 2, 2021 at 3:24 am

Times for the Third Quarter Moon vary by time zone. Times and dates are based on the local time in Washington DC. Change location

Half the Moon Is Lit Up

The Third or Last Quarter Moon is also called a Half Moon because the Sun's rays illuminate exactly 50% of the Moon's surface.

Half of the Moon’s surface is always illuminated by direct sunlight, except during lunar eclipses when Earth casts its shadow on the Moon. Just how much of that light we can see from Earth varies every day, and we call this a Moon phase.

Half Moon Visible During the Day

The Moon is the only astronomical object you can easily see in the day blue sky apart from the Sun. The Third Quarter Moon rises in the middle of the night and sets in the middle of the day. This is the opposite of a First Quarter Moon, which rises around midday and sets around midnight.

Last Primary Moon Phase

In western culture, we divide the lunar month into four primary and four intermediate Moon phases.

Illustration of the Moon's position in space in relation to Earth and the Sun at Third Quarter Moon.
Illustration of the Moon's position in space in relation to Earth and the Sun at Third Quarter Moon.

The Moon's position at Third Quarter Moon.

©timeanddate.com

Third Quarter Moon is the last primary phase when the Moon has reached the third, or last, quarter of its orbit around Earth, hence the name.

A Primary Phase Is an Exact Time

The first primary Moon phase is New Moon, while the second is First Quarter Moon, and the third is called Full Moon.

The primary Moon phases occur at a specific moment in time, and the intermediate Moon phases are the time between the primary phases. These are the Waxing Crescent Moon, the Waxing Gibbous Moon, the Waning Gibbous Moon, and the Waning Crescent Moon.

Looks Different Around the Globe

Even though the Moon phases are the same all over the world, the Moon can look different in the sky. The same percentage and area of the Moon are lit up, but the Moon is rotated in different ways depending on the time, the date, your location, and the Moon's position in the sky. Therefore, the illuminated part can appear on the left, the right, the top, or the bottom.

Illustration of the eight phases of the Moon with an arrow showing the order they appear in, seen from Earth.
Illustration of the eight phases of the Moon with an arrow showing the order they appear in, seen from Earth.

It takes around 29.5 days to move through the eight Moon phases.

©timeanddate.com

Opposite Sides in Opposite Hemispheres

At the Third Quarter in the Northern Hemisphere, the left half of the Moon is lit up, while the right half is illuminated in the Southern Hemisphere. Near the Equator, the lower part is bright after moonrise, and the upper part is bright before moonset.

Third Quarter Moon in Calendars

symbol of a third Quarter Moon

The symbol for Third Quarter Moon in modern calendars is a circle split down the middle with the left side white and the right side black.

The other primary Moon phase symbols in calendars:
symbol of a New Moon = New Moon symbol of a First Quarter = First Quarter symbol of a Full Moon = Full Moon

The Moon illustration on our Moon phase pages indicates more accurately, although not perfectly, which part of the Moon is lit up.

Affects the Tides

The ocean tides on Earth are mostly generated by the Moon’s gravitational pull. At the First and Third Quarter, the Moon and Sun pull in different directions, producing the smallest difference between high and low tide, known as neaps or neap tide.

The largest tidal range is around Full Moon and New Moon. During these Moon phases, the Moon and the Sun's gravitational forces combine to pull the ocean’s water in the same direction. These tides are known as spring tides or king tides.

Topics: Moon, Astronomy, Calendar