On Saturday (September 17) the moon will enter the stage of its phase called the last quarter – also called the third quarter – during which time it will be half illuminated as seen from Earth.
Both last quarter and third quarter may be confusing names for this stage initially, as the moon is half-illuminated, but they actually refer to the moon having completed 3/4 of its orbit around of the Earth at this point.
The half-illuminated moon will be visible in New York around 11:00 PM EDT (03:00 GMT September 18) and will disappear from view at dawn on Sunday (September 18) around 6: 7 a.m. EDT. (1019 GMT). At this time, the last quarter moon will reach an altitude of about 74 degrees above the horizon in the southeast (about seven fist-widths at arm’s length).
Related: Night sky, September 2022: What you can see tonight [maps]
During the lunar cycle, which takes about 29.5 days to complete, the moon is seen in different stages of illumination and at different times of the day.
In the last quarter, the moon rises around midnight and is at its highest height above the horizon around dawn. It sets around noon.
During the stage of the lunar cycle that includes the last quarter, the moon’s illumination recedes as its phase changes from full moon to new moon.
Related: What’s the Moon Phase Today? Moon phases 2022
The moon is said to be waning at this time, as it passes from the full moon, its most illuminated state, to its least illuminated phase, called the new moon. The illuminated side of the moon is shrinking because its orbit is taking it out of view from our perspective here on Earth.
The next stage of the moon’s cycle after the last quarter is the waning crescent. At this point, the moon will look like little more than an arc of silvery light, as it is almost back to the point in its orbit where it faces the sun directly.
After that is the new moon, when the illuminated side of the moon is fully facing the sun which appears almost invisible from here on Earth. At this point, the moon rises and sets with the sun, meaning it is out for the day. After this, the illuminated side of the moon grows and the moon begins to rise later each day, during which it is described as waxing, continuing until it is fully illuminated again during the next full moon.
The split between the light side and the dark side of the moon is called the “lunar terminator” and during the last quarter, it marks sunset on the moon. On the other hand, during the first quarter, the lunar terminator shows the sunrise on the moon.
During the first and last quarter from the moon’s axis, the lunar terminator aligns with the Earth’s termination line that divides night and day on our planet.
The next lunar cycle begins with the new moon on September 25th, with the next full moon on October 9th and then the next last quarter moon rising on October 17th.
Be sure to check out our guides to the best binoculars and best telescopes for spotting the last quarter moon. To capture the best images of the moon you can, check out our guide to photographing the moon, along with our recommendations for the best astrophotography cameras and the best astrophotography lenses.
Editor’s note: If you take a photo of the last quarter moon and want to share it with Space.com readers, send your photos, comments, and your name and location to spacephotos@space.com.
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