Whitby & District Astronomical Society

A waxing gibbous moon appears high in the east at sunset. It's nearly, but not quite, a full moon... appearing more than half lighted but less than full. This moon phase comes between one and two weeks after new moon.

The moon has moved in its orbit so that it's now relatively far from the sun in our sky. A waxing gibbous moon rises during the hours between noon and sunset. It sets in the wee hours after midnight. People sometimes 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 large fraction of the moon's day side is facing our way. Thus a waxing gibbous moon is more noticeable in the sky than a crescent moon, with only a slim fraction of the lunar day side visible. Also, a waxing gibbous moon is far from the sun on the sky's dome, so the sun's glare isn't hiding it from view.

The word "gibbous" comes from a root word that means "hump-backed." You can see the hump-backed shape of the waxing gibbous moon.