On Mercury One Day Lasts Two Years

Mercury has the most noncircular or eccentric orbit of any nondwarf planet in the solar system. This eccentricity has trapped Mercury in a 3:2 spin-orbit resonance, where it rotates three times for every two revolutions. When nearest Sun at perihelion, Sun’s tidal forces are greatest, Mercury’s spin and orbit (or rotation and revolution) nearly match, and Sun momentarily reverses in Mercury’s sky.

For long times, Mercury’s orbit precesses due to the gravity of Jupiter, the oblateness of Sun, and spacetime curvature, first described by Albert Einstein’s theory of General Relativity. For short times, as the animation shows, one solar day lasts two years!

Mercury spins 3 times for every 2 orbits, and 1 day lasts 2 years

Mercury spins 3 times for every 2 orbits, and 1 day lasts 2 years

About John F. Lindner

John F. Lindner was born in Sleepy Hollow, New York, and educated at the University of Vermont and Caltech. He is an emeritus professor of physics and astronomy at The College of Wooster and a visiting professor at North Carolina State University. He has enjoyed multiple yearlong sabbaticals at Georgia Tech, University of Portland, University of Hawai'i, and NCSU. His research interests include nonlinear dynamics, celestial mechanics, and neural networks.
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2 Responses to On Mercury One Day Lasts Two Years

  1. Lina Hadid says:

    Is it possible to download the GIF ?


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