Mercury performs two rotations around the Sun in the same period of time it takes to rotate three times around its axis. Therefore, one solar day on Mercury lasts for 176 Earth days, i.e., exactly for 2 mercurial years. Mercury lazily turns around its axis in comparison with its rapid movement along its orbit. This relationship between the rotation periods is known as gravity resonance, and it occurs because of the planet's proximity to Sun.
The Sun is displayed in the center of this model. Mercury rotates around it. A line that is perpendicular to Mercury's rotation axis is shown to make the planetary rotation more visible.
Press "Run" button to initiate the model. Special box counts Earth years and months. "Stop" and "Reset" suspend the animation, and return it to its initial state, respectively.