Mercury rotates so slowly that one solar day spans 176 Earth days — two Mercurian years. Its day is 1,407.6 Earth hours, the longest day-to-year ratio in the Solar System. Temperatures swing from -180C at night to 430C at noon.
The planet orbits the Sun every 88 Earth days at speeds up to 47 km/s. Because of its slow rotation and fast orbit, the Sun would appear to rise, stop, and briefly reverse in the sky near perihelion.
Frequently Asked Questions
How long is a day on Mercury?
One solar day on Mercury lasts 176 Earth days (a sidereal day is 58.6 Earth days).
How long is a year on Mercury?
Mercury completes one orbit of the Sun every 88 Earth days.
Why is Mercury's day longer than its year?
Mercury rotates very slowly on its axis while orbiting the Sun quickly, so two full orbits happen for every one solar day.