Moonrise Moment

Eclipses glossary

What is penumbra?

Penumbra is the lighter outer part of a shadow where the light source is only partially blocked.

Five stages of a lunar eclipse culminating in a copper-red Moon.
A visual guide to penumbra. Original Moonrise Moment illustration.

What it means

Penumbra is part of eclipse geometry and timing. Eclipses require the Sun, Earth, and Moon to align near the points where the Moon's tilted orbit crosses the ecliptic. That tilt is why an eclipse does not occur at every new or full Moon.

Keep exploring

Eclipses Blood Moon

A popular name for the reddish Moon seen during a total lunar eclipse, when sunlight filtered through Earth's atmosphere reaches the lunar surface.

 Eclipses Eclipse

An event in which one celestial body moves into another body's shadow or blocks the observer's view of another body.

 Eclipses Eclipse Magnitude

A measure of how much of an eclipsed body's diameter is covered by a shadow at a specified time, commonly at greatest eclipse.

 Eclipses Eclipse Season

A period of several weeks when the Sun is close enough to a lunar node for solar or lunar eclipses to occur.

Sources and further reading

This definition was written in plain language and checked against these science references.

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