Sun Rays
Earth
Moon
Umbra Cone
Penumbra
Sky View from Earth
Interactive 3D simulation of solar, annular, and lunar shadow alignment
An eclipse is not merely the Moon passing between the Sun and Earth; it is a strict spatial intersection of celestial shadow cones dictated by three fundamental parameters.
The Moon's orbit does not lie in Earth's orbital plane (the ecliptic). It is tilted by 5.14°. During most New and Full Moons, the Moon passes above or below the Sun-Earth axis. Eclipses can only occur when the Moon is close to one of the two intersection points called orbital nodes.
Because the Sun is an extended light source (1.39M km diameter), the Moon and Earth cast two shadow zones: the dark inner Umbra, where sunlight is completely blocked, and the outer Penumbra, where sunlight is partially blocked.
The Moon’s distance varies between perigee (~356,000 km) and apogee (~406,000 km). When near perigee, the Moon’s angular size exceeds the Sun’s, touching Earth with a total eclipse. Near apogee, the umbra cone ends before reaching Earth, creating an annular ("ring of fire") eclipse.