The character 月 (yuè): moon

A pale twilight sky, powder blue at the top, turning mauve then cream towards the horizon, with a scatter of small stars, and at the upper left a large cream yellow crescent moon. Along the bottom, a line of bluish hills above pale still water. In the middle of the sky, the character 月 in very dark brown: a left stroke that curves outwards as it falls, a right side ending in a hook, and two bars inside.

Pronunciation: yuè
Strokes: 4
Level: HSK 1
Radical: 月

What it means

moon; month; monthly; CL:個|个[ge4],輪|轮[lun2]

Where its shape comes from

A crescent, and the choice was not an idle one: the sun is drawn full, the moon is drawn notched, because that is how it is seen most of the time. Xu Shen glosses it accordingly as "what is lacking". A pictogram.

Source: Xu Shen, Shuowen Jiezi (121 CE); the Chinese University of Hong Kong character database.

A way to remember it

The stroke on the left curves outwards as it comes down: that is the back of the crescent, and it is what keeps 月 from reading as a plain straight frame. Two bars inside, not one and not three.

This is a memory aid, not the origin of the character.

Words it appears in

月亮 yuè liang · HSK 3 the moon
岁月 suì yuè · HSK 6 years; time
正月 zhēng yuè · HSK 6 first month of the lunar year
本月 běn yuè this month; the current month
每月 měi yuè each month
月光 yuè guāng moonlight

Writing it

See the stroke order of 月, animated stroke by stroke.