A waning gibbous moon is an intermediate phase of the lunar cycle that starts right after the full moon and lasts until it becomes a third quarter moon (half-moon).
Sixth phase of the lunar cycle
A waning gibbous moon is the sixth phase of the lunar cycle, as it comes after a new moon, a waxing crescent moon, a first quarter moon, a waxing gibbous moon and a full moon.
The meaning of a waning gibbous moon
A waning gibbous moon consists of two terms: waning and gibbous.
“Waning” means decreasing or shrinking. After a full moon, the illuminated area of the moon decreases day by day. That’s why it’s called a waning moon.
The illuminated area of a waning gibbous moon decreases from 100% to 50%.
“Gibbous” comes from a Latin word “gibbosus” that means “hump-backed”. The moon looks like a hump-back or convex shape between a full moon and a third quarter moon. That’s why it’s called a gibbous moon.
So a waning gibbous moon indicates the shape of the moon.
Age of a waning gibbous moon
A full moon occurs about two weeks after a new moon and a third quarter moon occurs about three weeks after a new moon.
So the age of a waning gibbous moon is greater than two weeks but less than three weeks.
Rise and set time of a waning gibbous moon
A waning gibbous moon rises in the evening (between sunset and midnight), reaches its highest point in the sky (overhead point) after midnight, and sets in the morning (between sunrise and noon).
A waning gibbous moon is best visible around two to three days after the full moon from the late evening through the early morning.
Please remember, a waning gibbous moon does not rise and set at the same time every day. On consecutive days, a waning gibbous moon rises and sets about 50 minutes later.
A waning gibbous moon is visible in the daytime
A waning gibbous moon is visible in the morning because the sunlight reflected from a waning gibbous moon is bright enough to be seen against the daytime blue sky.
The duration of a waning gibbous moon
The moon takes about 29.5 days to complete a lunar cycle.
Now, a lunar cycle has eight phases in total. These are the new moon, waxing crescent moon, first quarter moon, waxing gibbous moon, full moon, waning gibbous moon, third quarter moon, and waning crescent moon.
Four primary phases (new moon, first quarter, full moon, and third quarter) have no duration as they occur at a specific moment in time.
So the duration of four intermediate phases (waxing crescent, waxing gibbous, waning gibbous, and waning crescent) is 29.5 days in total.
So the duration of a waning gibbous moon is about 29.5/4 = 7.3 days.
Looks opposite in opposite hemispheres
A waning gibbous moon appears as a hump-back or convex shape in the sky from anywhere in the world. Its percentage of illumination is also the same. However, it looks opposite in opposite hemispheres.
In the northern hemisphere, more than the left half of the moon is visible, and in the southern hemisphere, more than the right half of the moon is visible.
People living in the southern hemisphere (south of the equator) observe the same waning gibbous moon from opposite angles than the people living in the northern hemisphere (north of the equator). As a result, a waning gibbous moon looks upside down.
Read about all eight phases of the moon:
New moon
Waxing crescent moon
First quarter moon
Waxing gibbous moon
Full moon
Waning gibbous moon
Third quarter moon
Waning crescent moon
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