Moon Phases: Understanding The Waxing And Waning Cycle (2025)

The Moon is a celestial body that orbits the Earth, and its appearance changes throughout the month. These changes are known as the lunar phases, and they occur due to the Moon's position relative to the Earth and the Sun. The Moon's cycle includes eight phases, four primary and four intermediate, and it takes about 29.5 days to complete. The Moon's waxing and waning refer to the increasing and decreasing illumination of its surface, respectively. During the waxing phase, more of the Moon's surface becomes illuminated as it moves towards a full moon. Conversely, during the waning phase, the illuminated portion diminishes until it becomes a new moon. The terms waxing and waning originate from Old English, with weaxen meaning to grow or increase and wanian meaning to decrease or diminish.

Moon Characteristics as of April 23, 2025

The moon's phases in the Northern and Southern Hemispheres

The Moon's phases occur as a result of the Moon's orbit around Earth. The Moon does not produce its own light, and so the phases are caused by the position of the Moon in relation to the Sun and Earth. The Sun illuminates one half of the Moon, and the Moon's orbit around Earth means that the amount of the illuminated half that we can see from Earth changes.

The Moon has eight phases, which occur in the following order: new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, third quarter, and waning crescent. The lunar cycle takes 29.5 days to complete, and each phase lasts for about 2 to 2.5 days.

In the Northern Hemisphere, the Moon's phases can be observed as follows: during the new moon phase, the illuminated side of the Moon faces the Sun and is not visible from Earth. As the Moon moves into the waxing crescent phase, a small portion of the illuminated half becomes visible from Earth, growing larger each day. During the first quarter, half of the Moon is illuminated and visible from Earth. In the waxing gibbous phase, more than half of the Moon is illuminated, and this continues until the full moon, when the entire illuminated half is visible from Earth. Following the full moon, the Moon enters the waning gibbous phase, where less than half of the Moon is illuminated each night. During the third quarter, only half of the Moon is illuminated, and this continues to decrease during the waning crescent phase until the new moon, when the Moon is not visible from Earth.

In the Southern Hemisphere, the Moon's phases are the same, but the orientation of the Moon in the sky is reversed. For example, during the waning crescent phase, the Moon is visible in the western sky before sunrise in the Northern Hemisphere, but in the Southern Hemisphere, it would be visible in the eastern sky before sunrise. The timing of the Moon's phases is also slightly different in the Southern Hemisphere due to the tilt of the Moon's orbit and the Earth's axis. This motion is known as "libration in latitude".

How to tell if the moon is waxing or waning

The Moon's appearance changes throughout the month, and its phases can be observed from Earth. The Moon does not produce its own light, and the Sun is the solar system's only source of light. The Sun always illuminates one half of the Moon—the side facing the Sun. The Moon's phases depend on its position in orbit around the Earth.

The Moon takes about 27.3 days to orbit the Earth, but the lunar cycle takes about 29.5 days to complete. The Moon's phases are the different shapes we see at different times of the month. The eight phases are: New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Third Quarter, and Waning Crescent.

The Moon is waxing when it is increasing how much of it appears to be lit up each night. It is waning when it is decreasing in size until it disappears. If you live in the Northern Hemisphere, the Moon waxes and wanes from right to left. So, a waxing Moon is illuminated on the right side, and a waning Moon is illuminated on the left side.

In the Southern Hemisphere, the Moon waxes and wanes from left to right. Therefore, if you see the Moon lit on its left-hand side, it is waxing, and if it is lit on its right-hand side, it is waning.

Lunar eclipses and the full moon phase

The Moon's appearance changes throughout the month, and we describe these changes with the eight Moon phases. The Moon does not produce its own light, and the Sun is the only source of light in our solar system. The Sun always illuminates one half of the Moon—the side facing the Sun. The position of the Moon and the Sun during each phase results in us seeing the Moon differently from Earth.

The eight lunar phases are, in order: new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, third or last quarter, and waning crescent. The Moon goes through these eight phases in its 29.53-day lunar cycle. The four major Moon phases are Full Moon, New Moon, First Quarter, and Last Quarter. The four minor phases are Waxing Crescent, Waxing Gibbous, Waning Gibbous, and Waning Crescent.

A lunar eclipse occurs during the full moon phase, when the Moon, Earth, and Sun are in alignment, with Earth positioned precisely between the Moon and Sun. The Moon moves into the inner part of Earth's shadow, or the umbra, and Earth's shadow falls upon the Moon's surface, dimming it and sometimes turning it a reddish hue. The reddish colour is caused by sunlight interacting with Earth's atmosphere. When sunlight reaches Earth, the atmosphere scatters and filters out shorter wavelengths like blue light, while longer wavelengths like red are refracted into the umbra. Lunar eclipses are popular events for sky watchers worldwide as they can be viewed from anywhere on the night side of the Earth without any special equipment.

The lunar cycle and its duration

The Moon is a celestial body that orbits Earth and goes through various phases due to its position relative to the Sun and Earth. The Moon does not produce its own light; instead, it reflects sunlight, which creates what we call "moonlight". The Moon's appearance changes throughout the month, and these changes are known as the Moon's phases.

The Moon has eight phases, which it displays one after the other as it moves through its cycle each month. The four primary phases are new moon, first quarter, full moon, and last quarter. The four intermediate or minor phases are waxing crescent, waxing gibbous, waning gibbous, and waning crescent. The Moon's cycle repeats about once a month, every 29.5 days, although its orbital period is 27.3 days. This duration is not perfectly constant due to the eccentricity of the Moon's orbit.

The term "waxing" refers to the intermediate phase when the Moon's apparent shape is thickening, progressing from a new moon to a full moon. The amount of the Moon's illuminated surface, as seen from Earth, increases during this phase. Conversely, "waning" refers to the phase when the Moon's shape is thinning, from a full moon to a new moon. The illuminated portion of the Moon gradually decreases during this period until it returns to a new moon, where the side of the Moon facing Earth is not illuminated by the Sun.

The duration from full moon to new moon, or vice versa, varies from approximately 13 days and 22.5 hours to about 15 days. The Moon's illumination changes constantly and can vary by up to 10% each day. The Moon's position in the sky also affects how we observe its phases. The Moon appears to move jerkily, and the phases occur more slowly when it is high in the sky compared to when it is below the horizon.

The Moon's appearance changes throughout the month. This is because the Moon does not produce its own light, and our view of the Moon changes as it orbits the Earth. The Moon's phases refer to the different shapes of the Moon that we see at different times of the month.

The Moon has eight phases in a lunar month: four primary and four intermediate phases. The lunar cycle lasts about 29.5 days, just under a calendar month. The four primary phases of the moon are new moon, first quarter, full moon, and last quarter. The four primary phases occur about a week apart, with the full moon being the most dazzling stage. The first visible moon phase is the thin sliver of a waxing crescent moon. About a week later, half of the Moon's visible surface is illuminated at the first quarter. The illuminated part then 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 four intermediate phases occur between the four primary phases. The intermediate phases are the waxing crescent, waxing gibbous, waning gibbous, and waning crescent. The waxing crescent phase occurs between the new moon and the first quarter, while the waxing gibbous phase occurs between the first quarter and the full moon. The waning gibbous phase occurs after the full moon and lasts until half of the Moon's face remains lit up at the third quarter. The waning crescent phase occurs between the third quarter and the new moon, when the Moon's illumination is growing smaller each day until the new moon.

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