Displayed time: 1969-07-21 02:56 UTC (Apollo 11 EVA)
Beta: this is a public beta. The terrain is measured data of the Apollo 11 landing site (Tranquility Base) — a ~2 km square centred on the lunar module, cut from the 2 m/px LROC NAC DTM — loaded first at low resolution, then swapped to full resolution. Observation artefacts (interpolation steps) are suppressed by curvature-selective smoothing that preserves crater shapes. Only if the data cannot be fetched does the page fall back to synthetic terrain (and says so here).
Current terrain: synthetic terrain (the measured data could not be fetched)
The motion, though, is measured. Gravity is 1.62 m/s²; walking and jumping use the two sets of values the toggle above switches between. With no atmosphere, a thrown object traces an exact parabola, the sky stays black, and shadow edges stay hard. There is no physics engine — for walking on a heightfield, an analytically correct integrator is both lighter and a more honest claim.
The FPS readout, upper right, is a one-second rolling average. Measuring that number on real devices is the entire point of this prototype. The default instant is pinned to the Apollo 11 EVA (1969-07-21 02:56 UTC) — switch the toggle above to "Now" for real-time lighting, including lunar night.
Sources for the constants: NASA NSSDC / JPL Horizons (gravity) · NASA TN D-3363 (one-sixth-g walking trials) · PLOS ONE "The Apollo Number" (walk-to-run transition) · video analysis of Apollo 16 (jump height, secondary source). Terrain and imagery: NASA/GSFC/Arizona State University (LROC NAC DTM, public domain).
The Moon has essentially no atmosphere — surface pressure is less than a trillionth of Earth's. A blue daytime sky comes from air molecules scattering sunlight (Rayleigh scattering); with nothing to scatter it, light only reaches your eye from the direction it is actually travelling, and the space around the Sun stays black even at local noon. That is why Apollo astronauts, walking in full daylight, had a jet-black sky overhead.
NASA NSSDC: Moon Fact Sheet
With no scattered skylight to fill them in, shadows on the Moon have knife-hard edges. The one source of ambient light is earthshine — sunlight reflected off Earth, landing on the lunar surface — and it is 20 to 30 times brighter than full moonlight seen from Earth. The ambient light in this prototype comes from earthshine alone, and nothing else.
arXiv:1904.00236
Lunar gravity is one-sixth of Earth's (1.62 m/s²), so the same leg power that launches you on Earth should in theory carry you 2.71 m into the air here. But video analysis of Apollo 16's John Young shows he only cleared about 0.42 m (1.45 s of hang time). The gap is not gravity — it is the EMU spacesuit restricting his range of motion, plus the real risk of not being able to get back up after a fall.
Apollo 16 video analysis (Rhett Allain); NASA TN D-3363
Throw something on Earth and air resistance bends its path; on the Moon there is no air at all, so gravity (1.62 m/s²) is the only force acting on a thrown object. With initial speed v₀, velocity falls off exactly as v = v₀ − gt — a textbook parabola with no drag correction needed. That is precisely why this prototype draws its throws with hand-written kinematics instead of a physics engine: the exact solution is both simpler and more honest.
NASA NSSDC / JPL Horizons (lunar gravity)
With no wind, water or atmosphere, lunar footprints do not weather away or wash out the way they would on Earth. The only eraser is "gardening" — the slow churn of the regolith by a constant rain of micrometeorites — and it works on a very long timescale. The footprints left at the Apollo 11 site are estimated to persist on the order of 10 million years.
NASA: Apollo lunar site preservation (micrometeorite gardening rate)