Tonight's moon phase, rendered in 3D

This is the moon as it is right now, from where you are standing. astronomy-engine works out the direction of the sun, the illuminated fraction, the phase angle and the orientation of the bright limb for your latitude, longitude and the current minute. Those numbers place a single directional light around a sphere carrying NASA Lunar Reconnaissance Orbiter maps: albedo for the colour, a normal map for the relief, roughness, and a LOLA elevation model driving the displacement.

The moon never rotates to make a phase. The sphere is set to one fixed orientation and only the light moves around it, which is how phases physically happen. It also means the terminator falls across real craters instead of across a texture that has been spun into position, and that the near side stays the near side, because the real moon is tidally locked and keeps one face to us.

Orientation is not decoration either. A waxing crescent leans one way from Melbourne and the other way from London, so the page asks for your location and reverse-geocodes it for the label. Decline and it falls back to Melbourne. Drag the time travel slider to move up to thirty days either side of now in two-hour steps, and watch the terminator sweep across the surface rather than around it.

Crafted by

Matthew Blode