Mars Rotation and Orbit

We know exactly how long it takes for Mars to rotate because of "stains" that are observed on the surface - dark, well-bounded marking that make excellent reference points.

They were first observed by Huygens in 1659. He called the length of their roation a day. In 1666, Giovanni Cassini set the Martian day at 24 hours 40 min, very close to the true value.

Observations of Mars have established that the Martian day is 24 h 37 min 22.7 seconds. The Earth's rotation period is 23 hours, 56 minutes and 4.1 seconds.

The sidereal day on Mars, the amount of time it takes the planet to rotate once in relation to the stars, is 24 hour, 39 minutes and 35.3 seconds.

The solar day on Mars, the time in which it takes the Sun to return to the same meridian, is 24 hours, 41 minutes and 18.6 second.

A Mars solar day is, like a solar day on  Earth, of variable length. This is because both of these planets follow elliptical orbits around the sun and do not go smoothly around in a perfect circle. However, the variability of the length of a solar day on Mars is higher because its orbit is more eccentric.

The Martian year lasts 687 Earth days.

Because Mars revolves around the Sun at a slower speed than the Earth, when the planets pass each other, Mars appears to be moving backwards. Data on the apparent retrograde motion of Mars, which was collected by Tycho Brahe, allowed Johannes Kepler to develop his laws of planetary motion.

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