the bright side of the earth is is day, the dark side on the left is night and between is twilight

day is the the side of an planet or other object that is in the light of an star. For example: if earth turns the continent of Europe in the light of our sun, Europe is in day. Not on every planet is a day as long as on earth(23h 56m 4.09053083288s). On mars, one day is 24 hours, 39 minutes, and 35.244 seconds[1]. On mars a 'day' is called: a sol, and more than one sol : sols.