night, evening

夜 depicts a man stretching his body, the moon is on the right while a line pointing at his armpits is on the left. 夜 can be seen as the compound of 亦(the picture of a man showing his armpits) and 月(the moon), the original meaning of 亦 is armpit, armpits are alway covered, which has the meaning of darkness. night is dark but has the moon hanging in the sky.