Why does the phase disc render with vertical stripes of code instead of a texture?

The lit region isn't drawn from an image — it's computed per column from the same sphere-illumination formula astronomers use: a surface point is lit when the Sun direction and the surface normal point the same way. That is exactly the geometry the 3D original evaluates per-pixel on the GPU; this page evaluates it on the CPU, column by column.

Does the orbital tilt slider change the Moon's phase?

No — tilt only changes how far the Moon's orbit appears to swing above or below the Sun-Earth line in the top-down view, which is what makes eclipses rare even though the Moon lines up with the Sun every cycle. The phase itself depends only on the Moon's position along its orbit.

Home▸Space & Astronomy▸Moon Phases: Illumination & Orbit Geometry (2D)

Moon Phases: Illumination & Orbit Geometry (2D)

2D moon-phase diagram: a Sun-Earth-Moon orbit view paired with a physically rendered phase disc computed from the same sphere-illumination geometry as the 3D original — scrub the cycle, tilt the orbit, and adjust earthshine.

Space & Astronomy2DEasy60 FPS📱 Mobile-adapted⇄ 3D version

This 2D companion drives the same sphere-illumination geometry as the 3D original through a plain canvas view: a top-down Sun-Earth-Moon orbit diagram sits next to a phase disc whose lit region is computed column by column from the angle between Moon, Earth and Sun — not painted from a texture — so scrubbing the day-of-cycle slider reproduces the real new/crescent/quarter/gibbous/full sequence, the tilt slider shows why the Moon usually clears the Sun's glare instead of eclipsing it every month, and the earthshine slider reveals the faint glow on the dark limb that sunlight reflected off Earth actually produces.

⚙ Under the hood

2D Sun-Earth-Moon orbit view paired with a phase disc computed per-column from sphere-illumination geometry, with day-of-cycle, orbital-tilt and earthshine controls.

moon phasescelestial mechanicsorbital geometryilluminationsynodic monthastronomy

2D · HTML5 Canvas 2D · 60 FPS target · runs fully client-side, no install