A (long) Day on Mercury

astronomy simulation

Instructions: Press the play button to start the animation. Use the slider to manually control the orbit of Mercury.
Explanation: Mercury is tidally locked to the sun which leads to a special relation between its own rotation and its orbit around the sun. During two orbits, Mercury will rotate around its own axis three times. This has the effect of creating very long periods of brightness and darkness for an observer on the surface of Mercury. Another interesting moment occurs when the sun appears to stop and then move backwards during its diurnal motion. (see if you can find this point!)

Link to stand-alone sim: Here is a link to view the sim on its own, with no distractions.

View this sim →


mercury orbit
a day on mercury
orbital simulation

Embed code: Use this sim on a webpage. Copy the code block below, and include it anywhere on a webpage to show the sim.


  1. Kepler's equation solver (http://www.jgiesen.de/kepler/kepler.html)
  2. Mercury Orbital Parameters (https://nssdc.gsfc.nasa.gov/planetary/factsheet/mercuryfact.html)
  3. Inspired by http://www.messenger-education.org/Interactives/ANIMATIONS/Day_On_Mercury/day_on_mercury_full.htm