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What is a waxing gibbous moon?

We’ve now passed first quarter moon, and the moon is waxing toward full. Full moon will come on September 24-25, 2018.

A waxing gibbous moon from Odilon Simões Corrêa in Brazil.

The moon is said to be in a waxing gibbous phase when it appears more than half-lighted but less that full – when it rises between noon and sunset – and when it sets in the wee hours after midnight. You’ll always see a waxing gibbous moon between a first quarter moon and full moon.

Any moon that appears more than half lighted but less than full – whether waxing or waning – is said to be a gibbous moon. The word gibbous comes from a root word that means hump-backed.

People often see a waxing gibbous moon in the afternoon, shortly after moonrise, while it’s ascending in the east as the sun is descending in the west. It’s easy to see a waxing gibbous moon in the daytime because, at this phase of the moon, a respectably large fraction of the moon’s dayside faces our way.

Read more: Harvest Moon 2018 coming up September 24-25

Point of interest on a waxing gibbous moon: Sinus Iridum (Bay of Rainbows) surrounded by the Jura Mountains. Photo via Lunar 101-Moon Book in Toronto, Canada.

As the moon orbits Earth, it changes phase in an orderly way. Follow these links to understand the various phases of the moon.

New moon
Waxing crescent moon
First quarter moon
Waxing gibbous moon
Full moon
Waning gibbous moon
Last quarter moon
Waning crescent moon

Read more: 4 keys to understanding moon phases

Bottom line: A waxing gibbous moon comes between first quarter moon and full moon. It appears more than half illuminated, but less than full. The next full moon – Harvest Moon for the northern hemisphere – will be September 24-25, 2018.

Check out EarthSky’s guide to the bright planets.

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Deborah Byrd

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