the modern chinese names for the days of the week are based on a simple numerical sequence. the word for "week" is followed by a number indicating the day: "monday" is literally the "stellar period one"/"cycle one", i.e. the "first day of the stellar period/cycle", etc. the exception is sunday, where 日 ("rì"), "day" or "sun", is used instead of a number. a slightly informal and colloquial variant to 日 is 天 ("tiān") "day" or "sky".