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🌑 Eclipse Shadow-Cone Lab

A 3D Sun-Earth-Moon model that builds the Moon's real umbra and penumbra shadow cones from their actual radii and distances, so you can see exactly why the same alignment gives a total eclipse near perigee and an annular eclipse near apogee.

Physics & Mechanics3DAdvanced60 FPS

A 3D Sun-Earth-Moon model that builds the Moon's real umbra and penumbra shadow cones from actual radii and distances, so you can see exactly why the same Sun-Moon-Earth alignment gives a total eclipse near perigee and an annular "ring of fire" eclipse near apogee.

🔬 What It Demonstrates

The umbra's cone length is fixed by similar triangles from the Sun's and Moon's radii. Whether the Moon's distance is shorter or longer than that length decides total vs. annular; the Moon's tilt off the ecliptic decides whether any eclipse happens at all.

🎮 How to Use

Drag the Moon distance slider across the umbra's ~374,300 km length to flip between total and annular. Increase the ecliptic latitude slider to watch the shadow miss Earth entirely, just like most new moons.

💡 Did You Know?

The Moon's umbra length and its average orbital distance are within a few percent of each other — a geometric coincidence that will end in roughly 600 million years as the Moon slowly drifts farther from Earth.

⚙ Under the hood

eclipseshadowssunearthmoongeometry3d-modelThree.js

3D · Three.js / WebGL renderer · 60 FPS target · runs fully client-side, no install