The umbra is the darkest part of a shadow, where the light source is completely hidden. In a solar eclipse, only people inside the Moon's umbra see totality, and it sweeps across Earth as a spot up to a few hundred kilometres wide. In a lunar eclipse, the Moon turns red as it moves into Earth's umbra.
Understanding Umbra
Why the Moon's umbra sometimes misses Earth
How long an umbra is depends on the sizes of the two bodies and the distance between them. The Moon's averages about 374,000 km, between roughly 367,000 and 380,000 km as Earth's distance from the Sun changes through the year. The Moon's distance from Earth changes more, from about 356,500 km at perigee to 406,700 km at apogee, so the cone sometimes reaches the ground and sometimes ends in space above it. When it reaches, the eclipse is total; when it falls short, it is annular; and when it reaches only the middle of the path, where Earth's surface bulges closest to the Moon, the eclipse is a rare hybrid.
The umbra on the ground
Inside the umbra the Sun disappears for seconds to minutes, the sky falls to a deep twilight and the air can cool by several degrees. The spot races west to east at 1,700 km/h or more, and its size depends on how close the Moon is and how steeply the shadow strikes: a low Sun stretches it into a long oval. These are the total solar eclipses on Orbital Radar, each with a page that tracks the umbra live:
| Date | Where the umbra touches down | Longest totality |
|---|---|---|
| 12 August 2026 | Arctic, eastern Greenland, western Iceland, northern Spain | 2 min 18 s |
| 2 August 2027 | Southern Spain, Gibraltar, North Africa, Egypt, Arabia | 6 min 23 s |
| 22 July 2028 | Australia (Kimberley to Sydney), New Zealand's South Island | 5 min 10 s |
Earth's umbra and the red Moon
Earth's umbra stretches about 1.4 million km into space, far past the Moon's orbit, and at the Moon's distance it is about 9,200 km across. A lunar eclipse is total when the whole Moon fits inside it, and because the umbra is so much wider than the Moon, totality can last more than an hour and a half. Earth's atmosphere bends some sunlight into the umbra while scattering away most of the blue, so the eclipsed Moon glows red or copper: the blood moon. Satellites cross the same umbra on every orbit, which is why they can fade out in the middle of a pass (Earth's shadow).