What is a “Waxing” Moon?

19 June 2014       

The Short Answer (TSA)

“Waxing” means to get bigger.  So, when the Moon is said to be “waxing,” it means that the sunlit part of the Moon is getting bigger.  The Moon goes through a complete cycle of “phases” every 29.6 days.

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 will reappear 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.  From the time of the New Moon phase to the Full Moon phase, the Moon is said to be waxing.

In terms of phases, the Moon disappears at the New Moon.  Then, the Moon, first, reappears in the night sky as a “crescent,” a small sliver of light on the right side of the face of the Moon.  Next, at the “1st Quarter” phase, the right half of the Moon is sunlit and the left half is dark. The Moon continues to grow until the whole face of the Moon is sunlit – the Full Moon phase.

After the Full Moon, the sunlit part of the Moon begins to get smaller and smaller.  When the sunlit part of the Moon keeps getting smaller, the Moon is said to “waning” instead of “waxing.”

The light of the waxing Moon first appears on the right outer edge of the Moon
and moves to the left

Even if you don’t know or remember when the Moon was New or Full, there is a way to tell whether or not the Moon is “waxing” or “waning.”  If the Moon is sunlit from the right side, it is waxing.  If the moon is sunlit from the left side, it is waning.  In other words, if the right outer edge of the moon is sunlit, it’s waxing.  If the left outer edge of the Moon is sunlit, it’s waning.

M Grossmann of Hazelwood, Missouri
(& Belleville, Illinois)
About the Author
Thursday 19 June 2014              

*Note: The Moon actually takes 27.32 days to complete a single orbit — travel once completely around the Earth.  But the Earth is “gaining” on the Moon a little bit every day.  So, from the viewpoint of an observer on Earth, it takes about 29.53 days for the Moon to complete a full cycle of phases — for example, new moon to new moon.

Think of it this way. Suppose you are a runner. You can run a mile in 10 minutes. You find a mile long circular track and start running from the starting line. But, while you’re running, someone moves the finish line one tenth of mile farther down the track. Instead of 10 minutes, it will take you 11 minutes to reach the “new” finish line. You come back the next day and start running from the new start/finish line. But, while you are running, someone moves the finish line one tenth of a mile farther down the track – again. It will take you 11 minutes to reach the “new” finish line.

So, even though you run a mile in 10 minutes and the track is only a mile long, it will always take you 11 minutes to finish. This is because, as you are running, the finish line keeps moving farther ahead!

That’s what’s happening to the Moon