Why Is a Day Longer Than a Year On the Planet Mercury and How Long Is a Day On Mercury?

A Mercurial year, or the time it takes for Mercury to revolve around the Sun once, is the equivalent of about 88 Earth days (2,112 hours).

A Mercurial solar day, the time it takes for the Sun to go from high noon to high noon as seen from Mercury’s surface, takes 176 Earth days (4,224 hours), twice as long as a Mercurial year.

After one orbit, Mercury has rotated 1.5 times around its axis.

As a result, a Mercury year is about 0.5 Mercury days long, and one Mercury day lasts approximately two Mercury years.