Planets - Calculate Rotation Period

Calculator for the duration of a rotation (sidereal day) of Sun, Moon, Earth and planets, in hours and compared to each other. This is the time, which a celestial bodies needs for a complete rotation around its own axis. The sidereal day has a different length than the solar day. Venus, Uranus and Pluto rotate clockwise, the other planets as well as Sun and Moon rotate counterclockwise. The time values are decimal, as common for astronomical values. Here they can be converted to common time formats.

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

Round to   0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15   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: Earth rotates in slightly less than one day, that is in 23 hours, 56 minutes and 4 seconds. Venus needs 243 days and Jupiter less than half a day.

The reason that for planets the sidereal day differs in length from the solar day is that a planet rotates not only on its own axis but also orbits its star. Thus, two rotational movements are superimposed. After one sidereal rotation, a point on the planet once again points in the same direction, but the star is now in a slightly different position because the planet has moved further along its orbit. In contrast, after a solar day, the Sun is back in the same relative position.
Earth's sidereal day is shorter than its solar day. This occurs when the planet's rotation and its orbital motion around the star are in the same direction. If the directions of rotation and orbit are opposite, as is the case with Venus, the sidereal day is longer.

The term sidereal is derived from the Latin sidus, which means star. It refers to the orientation relative to the background of stars, the fixed stars, which is the same after every sidereal rotation.

Planets located very close to their stars, or moons situated very close to their planets, such as our own Moon, can exhibit synchronous rotation, meaning they always present the same side to their partner. In the case of planets, this results in a sidereal day that equals a year, while the solar day is of theoretically infinite duration.

Last updated on 08/04/2026. Author: Jürgen Kummer

Calculators for Planets and Astronomy

© Jumk.de Webprojects | Online Calculators | Imprint & Privacy

German: Planeten-Rechner