The clearest picture of Mercury ever taken. Because of quirks in its orbit and rotation, Mercury's days are longer than its years!

A typical day on Mercury is twice as long as its year! One orbit around the Sun, or one year, takes about 88 Earth days, while a Mercurian day is 176 Earth days. This happens for the same reason the moon always has the same side facing Earth: Spin—orbit resonance, a ratio of the number of times an object spins on its axis to times around the sun.

This results in a particularly interesting phenomenon on Mercury. If you were to stand on certain points of Mercury’s surface, you would see the sun rise about halfway, reverse direction and set before changing direction again, all within the same Mercurian day.

This long Mercurian day is referring to a “solar day” which is the time it takes the sun to get from one location in the sky to the same spot after a full rotation. This takes Mercury 176 Earth days to complete. One sidereal day, or one full spin on its axis, takes Mercury 58.7 Earth days to complete; still a pretty long time.

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