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How long is a day on Mercury in Earth days?
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Mercury
Mercury as seen by the Messenger probe, January 14, 2008. This image shows half of the hemisphere missed by Mariner 10 in 1974–75 and was snapped by Messenger's Wide Angle Camera when it was about 27,000 km (17,000 miles) from the planet.
The length of a day on Mercury depends on how it is measured:
- Sidereal day: The time it takes for Mercury to complete one rotation with respect to the stars is approximately 58.6 Earth days.12
- Solar day: The time it takes for the Sun to return to the same position in the sky (a full circuit from sunrise to sunrise) is 176 Earth days.12
Because Mercury’s rotation and revolution periods are linked, the planet rotates three times for every two times it orbits the Sun, resulting in these distinct measurements for its day.1