Why Eclipses Are Rare
A companion to Moon phases. New moon and full moon happen every month, but eclipses do not, because the Moon's orbit is tilted. Eclipses only happen when the Moon is both in the right phase and near a node where its tilted path crosses the Sun-Earth plane. Canvas 2D · astronomy.
1 · If the orbit were flat, eclipses would be monthly
With zero tilt, every new moon lines up with the Sun and Earth. That would make solar eclipses ordinary.
2 · The Moon usually misses
The real lunar orbit is tilted about five degrees. From above it still looks aligned, but from the side the Moon often passes above or below the shadow.
3 · Nodes are the crossing points
The tilted orbit crosses Earth's orbital plane at two nodes. Only near those crossings can the Sun, Earth, and Moon share one line.
4 · Eclipse season
When new moon happens near a node, the Moon's shadow can touch Earth: solar eclipse season.
5 · The full-moon version
Half an orbit later, Earth can cast its shadow onto the full Moon. Same node condition, opposite phase.
6 · Your turn
Drag around the orbit and move the node slider. The label flips from miss to eclipse only when phase and node line up together.