Visualization of the relative sunlight time over Mercury's surface. Cold colors represent the spots that received sunlight for a shorter time, warm colors for a longer time. Mercury has a 3:2 spin-orbit resonance. In consequence, the surface is evenly lit periodically, except for a band of surface which receives less light because of the surface roughness (simulated here with a twilight). The orbit is computed using Kepler's law. A multiplicative inverse function was used to simulate twilight.