Eclipse Geometry: Shadows in Space
Drag the Moon or the teal nodes to explore eclipse geometry.
Phase
$\Delta$
deg
$\beta$
deg
Solar
Lunar
Node
deg
- Observable: eclipses only happen when the Moon is near a node — where its tilted orbit crosses the Sun–Earth plane — and at New or Full phase.
- Model: the Moon’s orbit is tilted ~5° from the ecliptic, so it usually passes above or below the Sun/Earth’s shadow.
- Inference: eclipses are rare because two conditions must align — most New/Full Moons miss. Try setting tilt to 0° to see what would happen without tilt.
- We model eclipse geometry using similar triangles for the umbra/penumbra and compute physically motivated thresholds (in degrees) for eclipse visibility.
- $\beta$ is the Moon's ecliptic latitude; when $|\beta|$ is small, the Moon is close to a node and an eclipse is possible at New/Full.
- Earth–Moon distance affects shadow size: at perigee a central solar eclipse can be total; at apogee it can be annular.