Lunar eclipse

A lunar eclipse occurs when Earth passes between the Sun and Moon, causing Earth’s shadow to fall on the Moon. It can be total, partial, or penumbral.

Earth's shadow: The region behind Earth where sunlight is partly or completely blocked. Its umbra and penumbra determine which parts of the Moon darken.
Total lunar eclipse: A lunar eclipse in which the entire Moon passes through Earth’s umbra. This is the fully eclipsed form, often giving the Moon a copper-red appearance.
Aristarchus of Samos: An ancient Greek astronomer who proposed that Earth revolves around the Sun and estimated lunar and solar distances. Lunar eclipse geometry informed his estimates of the relative sizes and distances of the Sun and Moon.
Lunar eclipse prediction: The calculation of when and where lunar eclipses will occur from models of celestial motion. Predictions follow from the Moon’s orbit and the alignment needed for its passage through Earth’s shadow.
Umbra: The darkest part of a shadow, where the light source is completely obscured. A total lunar eclipse occurs when the Moon enters Earth’s umbra.
Partial lunar eclipse: A lunar eclipse in which only part of the Moon enters Earth’s umbra. The curved edge of Earth’s umbra visibly covers only a portion of the lunar disk.
Aristotle: An ancient Greek philosopher whose writings shaped natural philosophy for centuries. He cited Earth’s consistently round shadow during lunar eclipses as evidence that Earth is spherical.
Danjon scale: A five-point scale for describing the brightness and coloration of the Moon during totality. Its ratings record how clear or dusty Earth’s atmosphere appears during an eclipse.
Penumbra: The lighter outer part of a shadow, where the light source is only partly obscured. A penumbral eclipse occurs as the Moon passes through this faint region.
Penumbral lunar eclipse: A lunar eclipse in which the Moon passes through Earth’s penumbra without entering its umbra. This subtler eclipse dims the Moon without a sharply darkened section.

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