This flat equirectangular map fixes longitude to the horizontal axis and latitude to the vertical one, so — unlike the 3D globe's real lighting — the day/night shading here is computed directly per pixel from the solar zenith-angle formula: cos(Z) = sin(φ)·sin(δ) + cos(φ)·cos(δ)·cos(H), where φ is latitude, δ is the sun's declination (set by the day-of-year slider) and H is the local hour angle (15°·(local solar time − 12)). A point is in daylight whenever cos(Z) > 0.
The map is redrawn every frame from that formula, so the whole terminator band sweeps sideways as the simulated UTC clock advances — the flat-map equivalent of the globe's rotation, but modelled independently rather than reprojected from the 3D scene.
- Time speed — simulated hours per real second.
- Day of year — sets solar declination δ, tilting the terminator's curve toward whichever hemisphere is in summer.
- Reference timezone — a UTC offset to compare against.
- Click the map — reads longitude/latitude under the cursor and its idealized 15°-band local time.