A phased view of Mercury, showing both day and night.
Image: NASA / Johns Hopkins University Applied Physics Laboratory / Carnegie Institution of Washington.

A day on Mercury is complicated. One full rotation of Mercury on its axis takes 58.6 Earth days. This is a sidereal day, or one rotation with respect to the stars. To go from one sunrise to the next takes 176 Earth days; officially, a day on Mercury is twice as long as its year.