The First Quarter Moon / Half Moon

The First Quarter Moon is a primary Moon phase when we can see exactly half of the Moon's surface illuminated. If it is the left or right half, depends on where you are on Earth.

When is it Half Moon?

50% Illuminated

The First Quarter Moon is often called a Half Moon because we can see exactly 50% of the Moon's surface illuminated.

Sun Lights Up the Moon

The Moon does not radiate its own light, but the Moon's surface reflects the Sun’s rays.

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 refer to this as a Moon phase.

Second Primary Moon Phase

In Western Culture, we divide the lunar month into four primary and four intermediate Moon phases.

First Quarter Moon is the second primary Moon phase when the Moon has reached the first quarter of its orbit around Earth, hence the name.

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

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

Same Phase Looks Different

Moon phases are the same all over the world. The same percentage and area of the Moon are illuminated no matter where on Earth you are. However, 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.

At First Quarter in the northern regions of the world, the right half of the Moon is lit up, while the left half is illuminated in the southern regions. Near the equator, the upper part is bright after moonrise, and the lower part is bright before moonset.

Visible in the Evenings

The First Quarter Moon rises near the middle of the day and sets around the middle of the night in most areas. In general, people see the First Quarter Moon more frequently than the Third Quarter Moon, which is primarily in the sky after midnight.

Affects the Tides

The ocean tides on Earth are mostly generated by the Moon’s gravitational pull. At 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 during around Full Moon and New Moon. During these Moon phases, the gravitational forces of the Moon and the Sun combine to pull the ocean’s water in the same direction. These tides are known as spring tides or king tides.

First Quarter Moon in Calendars

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

The other primary Moon phase symbols in calendars are:
= New Moon, = Full Moon, = Third Quarter

Calendar with Moon phases

The Moon phase calendar symbols reflect the Moon's appearance in the Northern Hemisphere, which can be confusing for people in the Southern Hemisphere, where the opposite side is illuminated at the First and Third Quarter.

The Moon illustration on our Moon phase pages indicates more precisely, although not perfectly, which part of the Moon is lit up in more than 5000 locations worldwide.

Topics: Moon, Astronomy, Calendar