Lunar Eclipse Color Simulator (2D)

During a total lunar eclipse the Moon does not disappear — sunlight refracted through Earth's atmosphere bathes it in a dim, reddened glow whose exact shade astronomer André-Louis Danjon catalogued in 1921 into a five-step scale from L0 (nearly invisible, ash-gray) to L4 (bright copper-orange, easily photographed). This 2D companion projects that same color science onto a flat orthographic disc instead of a lit 3D sphere: pick a Danjon level and the tint and base brightness update from the same reference table the 3D version uses, while an umbra-offset slider sweeps the light/dark boundary across the disc the way the Moon's path through Earth's umbra does. A stratospheric aerosol-optical-depth slider adds real Beer-Lambert-style attenuation — after major volcanic eruptions, stratospheric aerosols measurably darken eclipses, which is why some 20th-century eclipses were recorded as L0 while eclipses in clear years reached L3-L4. The live panel reports brightness, an eclipse magnitude estimate (via the standard m = −2.5·log₁₀(flux) relation) and an approximate colour temperature, and the crater field is an orthographically projected rotating sphere drawn with plain 2D arcs.