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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.

First Quarter Moon in spring (Northern Hemisphere)

A First Quarter Moon.

This First Quarter Moon is in the Northern Hemisphere and mirrors approximately the calendar symbol.

©iStockphoto.com/Piergiov

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 4 primary and 4 intermediate Moon phases.

Illustration of the Moon's position in space in relation to Earth and the Sun at First Quarter Moon
The Moon's position at First Quarter Moon.
The Moon has reached the 1st quarter of its orbit around Earth.
@timeanddate.com

First Quarter Moon is the 2nd primary Moon phase when the Moon has reached the 1st quarter of its orbit around Earth, hence the name.

The 1st primary Moon phase is New Moon, while the 3rd 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 lower tides.

First Quarter Moon in Calendars

symbol of a First Quarter Moon

The symbol for First 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 are:
New Moon = New Moon, full = Full Moon, 3rd quarter = Third Quarter

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

Next First Quarter

Apr 3, 2017 at 2:39 pm

Previous First Quarter

Mar 5, 2017 at 6:32 am

Times for First Quarter can vary by time zone. Dates are based on the local time in Washington DC. Change location

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The Moon Phases

  1. The Lunar Month
  2. New Moon
  3. Waxing Crescent Moon
  4. First Quarter Moon
  5. Waxing Gibbous Moon
  6. Full Moon
  7. Waning Gibbous Moon
  8. Third Quarter Moon
  9. Waning Crescent Moon

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  1. What Is a Supermoon?
  2. The Moon Phases
  3. What Is a Micro Moon?
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  5. The Moon's Orbit
  6. What Is a Black Moon?
  7. What Are Moonbows?
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