Earth's shadow

Earth's shadow (or Earth shadow) is the shadow that Earth itself casts through its atmosphere and into outer space, toward the antisolar point. During the twilight period (both early dusk and late dawn), the shadow's visible fringe – sometimes called the dark segment or twilight wedge^[1] – appears as a dark and diffuse band just above the horizon, most distinct when the sky is clear.

Since the angular diameters of the Sun and the Moon as viewed from Earth's surface are almost the same, the ratio of the length of Earth's shadow to the distance between Earth and the Moon will be almost equal to the ratio of the diameters of Earth and the Moon.

Since Earth's diameter is 3.7 times the Moon's, the length of the planet's umbra is correspondingly 3.7 times the average distance from the Moon to Earth: about 1.4 million km (870,000 mi). The diameter of Earth's shadow at lunar distance is about 9,000 km (5,600 mi), or 2.6 lunar diameters, which allows observation of total lunar eclipses from Earth.^[2]