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.
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-backed 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).
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.
Best time to see a waning gibbous moon
You’ll find a waning gibbous moon high in the pre-dawn sky around two to three days after a full moon.
A waning gibbous moon is easily visible in the morning, as the sunlight reflected from it is bright enough to be seen against the daytime blue sky.
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 = 7.38 days.
Orientation of a waning gibbous moon
A waning gibbous moon appears more than half-illuminated but less than full 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, the illuminated part appears on the left side, and in the Southern Hemisphere, it appears on the right side.
The phases of the moon
The moon goes through phases as it orbits Earth. Follow the links below to understand the phases of the moon.
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