A day on Mercury, defined as one full solar day (sunrise to sunrise), lasts about 176 Earth days. This is because Mercury rotates very slowly on its axis, taking approximately 59 Earth days to complete one full rotation, but due to its orbital motion around the Sun (which takes about 88 Earth days), the solar day ends up being roughly twice as long as its year

. To clarify:

• Mercury's sidereal day (rotation period relative to distant stars) is about 59 Earth days.
• Mercury's orbital period (year) is about 88 Earth days.
• The solar day (sunrise to sunrise) on Mercury is about 176 Earth days, meaning the Sun takes that long to return to the same position in the sky as seen from Mercury's surface

This unique situation means that a single day on Mercury is longer than its year, so if you were standing on Mercury, you would experience one full day- night cycle over nearly two Earth years