Earth’s shadow

Earth’s shadow is the region of space where Earth blocks some or all direct sunlight. It has a dark central umbra and a lighter surrounding penumbra.

Umbra: The darkest part of a shadow, where the light source is completely blocked. Earth’s umbra is the central region in which the Sun is completely hidden.
Aristotle: An ancient Greek philosopher whose works covered natural philosophy, ethics, politics, and logic. Aristotle cited Earth’s consistently curved shadow on the Moon as evidence that Earth is spherical.
Solar eclipse: An eclipse in which the Moon passes between Earth and the Sun, obscuring the Sun from some locations. A solar eclipse is caused by the Moon’s shadow falling on Earth, the reverse projection.
Total lunar eclipse: A lunar eclipse in which the Moon passes entirely into Earth’s umbra. The Moon’s passage through the full umbra makes the shadow’s curved boundary especially clear.
Penumbra: The partly shaded region where an object blocks only part of an extended light source. Earth’s penumbra surrounds its umbra, where sunlight is only partly blocked.
Eratosthenes: An ancient Greek scholar who estimated Earth’s circumference using measurements of sunlight and distance. His shadow-based geometry shows how sunlight can reveal Earth’s size without observing its outline from space.
Moon’s shadow: The region of space where the Moon blocks some or all direct sunlight. Its much smaller shadow falls on Earth during a solar eclipse, unlike Earth’s shadow on the Moon.
Partial lunar eclipse: A lunar eclipse in which only part of the Moon enters Earth’s umbra. The boundary between the umbra and the illuminated Moon is directly visible.
Antumbra: The region beyond an umbra where an occluding object appears smaller than the light source. Beyond Earth’s umbra, its shadow geometry can produce an antumbra during an annular eclipse.
Lunar eclipse: An eclipse in which the Moon passes into Earth’s shadow. Observers can use the Moon crossing the shadow to study its shape and structure.

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Belt of VenusRelated: The band appears directly above this shadow as twilight advances.