Lunar Eclipse Geometry: Umbra, Nodes & Eclipse Seasons (2D)

This 2D companion replaces the 3D version's single scripted eclipse pass with the actual orbital mechanics behind lunar eclipses: it builds the Moon's true umbra/penumbra shadow cone from the real radii of the Sun and Earth and the Earth–Sun distance, places the Moon on an orbit tilted by its real ~5.14° inclination, and lets you rotate the line of nodes — the key variable that decides whether a given full moon actually falls inside Earth's shadow. Drag the node-longitude slider and watch total, partial and penumbral eclipse windows open and close across the orbit, reproducing why eclipses cluster into "eclipse seasons" roughly twice a year instead of happening every full moon.