The Waxing Gibbous Moon

This intermediate Moon phase starts after the First Quarter Moon and lasts until the Full Moon.

50.1% to 99.9% Illuminated

Just after the First Quarter Moon, when we can see exactly half of the face of the Moon illuminated, the intermediate phase called Waxing Gibbous Moon starts.

Waxing means that it is getting bigger. Gibbous refers to the shape, which is less than the full circle of a Full Moon, but larger than the semicircle shape of the Moon at Third Quarter.

With some exceptions, the Waxing Gibbous Moon rises during the day, after noon. It is usually visible in the evening and sets after midnight.

During this period, the lit up portion of the Moon increases from 50.1% to 99.9%.

Technically, this phase lasts until the moment of Full Moon. However, it can be difficult to differentiate the last stage of a Waxing Gibbous Moon from a Full Moon when as much as 98% to 99% of the Moon's surface is 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.

Primary and Intermediate Moon Phases

In Western culture, we divide the lunar month into 4 primary and 4 intermediate Moon phases.

The Moon phases start with the invisible New Moon. The first visible Moon phase is the thin sliver of a Waxing Crescent Moon. Around a week later, half of the Moon’s surface is illuminated at First Quarter Moon.

The illuminated part continues to grow into a Waxing Gibbous Moon, until 14 to 15 days into the cycle, we see the entire face of the Moon lit up at Full Moon.

The illuminated part then gradually shrinks into a Waning Gibbous Moon, and when it reaches Third Quarter, the opposite half from the First Quarter is illuminated. From there, it fades into a Waning Crescent Moon. Finally, the Moon disappears completely from view into another New Moon phase, only to reemerge and repeat this cycle over and over.

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 of a Waxing Gibbous Moon can appear on the left, the right, the top, or the bottom.

The line–or curve–dividing the illuminated and dark parts of the Moon is called the terminator. The terminator of a Waxing Gibbous Moon can be on the right side, the left, the top, or the bottom.

No Gibbous Moon in Calendars

There is no symbol for the Waxing Gibbous Moon in calendars as it is an intermediate Moon phase. Only the 4 primary phases are shown in calendars with the following symbols:
= New Moon = First Quarter = Full Moon = Third Quarter

These symbols reflect the Moon's appearance in the Northern Hemisphere, which can be confusing for people in the Southern Hemisphere, where the opposite side may be illuminated.

The Moon illustration on our Moon phase pages changes as time passes, and indicates more accurately, although not perfectly, which part of the Moon is illuminated in more than 5000 locations worldwide.

Topics: Moon, Astronomy