Planets - Calculate Day Length

Calculator for the length of a day on the Moon, on Earth and on the other planets, in hours and compared to each other. The solar day length is the duration between two noons on any place of a planet or moon. It is not identical with the rotation period, because the planets orbit the Sun and the Moon also orbits Earth. The time values are decimal, as common for astronomical values. Here they can be converted to common time formats.

Round to decimal places.

Please enter one value, the other values will be calculated. Days (d) refers to the 24 hours of a day on Earth.

Example: one hundred days on Earth are like 97 days on Mars, or a bit more than half a day on Mercury. Mercury has the longest day in the solar system, while Jupiter has the shortest, even though it is the largest planet in our system.

Planets that are close to their star, like Mercury, often have a slow rotation and therefore a long day. This is caused by the star's strong gravitational pull counteracting the rotation, thus slowing it down. In extreme cases, the rotation is synchronized with the orbit. This means that the planet rotates at the same speed as it orbits its star. So it always presents the same side to the star. The side of a synchronized planet facing away from the star is very cold, as is the case with Mercury, which has a day length of 176 Earth days.
The sun is a yellow star. Most stars in the known universe are red dwarfs, which are dimmer. For a planet around such a star to have temperatures suitable for life, it must be closer to its star. If the star's mass is less than about half the mass of the sun, then such a planet is likely to have a synchronized orbit, also called locked rotation. So the living conditions there are very different from those here.

Hours (h):
Days (d):
Length
Moon:
Mercury:
Venus:
Earth:
Mars:
Jupiter:
Saturn:
Uranus:
Neptune:
Pluto: