LIGHT AND SHADOW · ECLIPSES
How eclipse shadows are represented
See how aligned moons create soft, efficient eclipse shadows on Earth, Jupiter, and Neptune.
Alignment decides whether a shadow exists
A normal date does not guarantee a visible eclipse. The moon must pass close to the Sun–planet line and its shadow must intersect the visible hemisphere. The Moon's orbit is tilted relative to Earth's orbital plane, so most new moons pass above or below the Sun. Europa crosses Jupiter more often, but visibility still depends on time and camera side.
The event controls move the simulation to a prepared alignment. They are exploration aids, not professional contact-time predictions.
The dark centre and soft edge have different roles
The umbra is where the light source is fully blocked. The penumbra is a transition where only part is blocked. A hard black disc looks pasted onto a texture, while an excessively broad blur becomes invisible. Solar Time combines a dark centre with a graded edge so illumination appears to fall across a curved surface.
Earth adds oceans, clouds, atmosphere, night lights, and specular reflection. Jupiter has bright, comparatively uniform cloud bands. The same nominal opacity can therefore appear weaker on Earth. The shadow needs to be evaluated with the parent material rather than matched by one alpha value alone.
Displayed moon size and physical scale differ
In normal view, the Moon and Europa can be enlarged for inspection. Solar Time links the educational shadow footprint to the displayed moon size, then reduces it so it does not become an implausibly huge disc. Compressed orbit spacing can also strengthen the visual demonstration.
Actual-size mode keeps the footprint tied to the physical-style ratio regardless of the moon size slider. A presentation control should not redefine a true-scale comparison.
Only the relevant parent receives the shadow
The Moon shadow affects Earth and Europa's shadow affects Jupiter. Testing every moon against every planet would add work without educational value and could create false intersections in an adjusted layout. The parent restriction is both faster and clearer.
Try it in Solar Time
- Open the Moon card and choose an eclipse. Pause and move around Earth to find the receiving hemisphere.
- Change the Moon's display size in normal view, then repeat in actual-size mode.
- Return to real time. If the bodies are not aligned, no shadow is expected.
- Repeat with Europa and compare contrast against Jupiter's cloud texture.
Sources and further reading
- NASA Science — Eclipse Geometry
- NASA Science — Europa
- Solar Time — Readable scale and actual-size mode