What is a “Waning Moon”?

9 July 2014

The Short Answer (TSA)

“Waning” means to get smaller.  So, when the Moon is said to be “waning,” it means that the sunlit part of the Moon's face is getting smaller.  The changes in the size of the sunlit area of the face of the Moon are called “phases.”  The Moon goes through a complete cycle of “phases” every 29.6 days.

Moon's Phases (Northern Hemisphere)

The cycle of phases begins with the New Moon, a time when the Moon cannot be seen in the night sky at all.  After the Moon disappears, it reappears as a crescent – a small sliver of light on the right outer edge of the face of the Moon.  With each night, the sunlit part of Moon will increase in size until the face of the Moon is completely sunlit – the “Full Moon” phase.

During the time from the New to the Full Moon, the Moon is said to “waxing.”  Waxing means to get bigger.   But, right after the Full Moon, the sunlit part of the Moon’s face begins to “wane” getting smaller and smaller.

Waning Moon

Even if you don’t know or remember when the Moon was “New” or “Full,” you can still tell whether or not the Moon is “waxing” or “waning.”  If the right outer edge of the Moon is sunlit, it is waxing.  If the left outer edge of the Moon is sunlit, it is waning.

Waxing (with right outer edge sunlit) to Full, then, Waning (with left outer edge sunlit)

But there’s a catch.  If you live in the Southern Hemisphere, Australia, Chile, Brazil, Argentina, or South Africa, the right-left rule is reversed.  So, in the Southern Hemisphere, if the left outer edge of the Moon is sunlit, it is waxing.  If the right outer edge of the Moon is sunlit, it is waning.

M Grossmann of Hazelwood, Missouri
(& Belleville, Illinois)
About the Author

Thursday 9 July 2014