Trying to make up a calendar for a home-brew setting, and in looking at other fantasy calendars this thought occurred to me. Starday is found in several fantasy calendars, but none describe exactly why or how it came to be called that.
If you're going to have (and most fantasy calendars I've seen do) a "Sun-day" and a "Moon-day", the next thing that would come to most minds would be: Sun, Moon...Stars!