This diagram explains the geometry of the lunar eclipse.
When the moon is entirely in the Earth's umbra (known as a total lunar eclipse or umbral eclipse), all sunlight reaching the lunar surface has been refracted or scattered through Earth's atmosphere. When the moon is in the Earth's penumbra (known as a penumbral eclipse), illumination comes from both direct sunlight and sunlight refracted and scattered through the planet's atmosphere. This is similar to an exoplanet transit observation.
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Last Update: 1 September 2020