Why the Artemis II eclipse lasted 54 minutes

During the Artemis II flyby of the Moon in April 2026, the Moon passed in front of the Sun as seen from the Orion spacecraft. For the four astronauts aboard, Reid Wiseman, Victor Glover and Christina Koch of NASA and Jeremy Hansen of the Canadian Space Agency, the Sun stayed hidden for about 54 minutes. On Earth, the longest possible total solar eclipse lasts about seven and a half minutes. The difference comes down to where you stand in the Moon’s shadow, and how fast you cross it.

The Moon’s shadow is a cone

The Sun is much larger than the Moon, so the Moon’s full shadow, the umbra, narrows with distance. Just behind the Moon it is almost as wide as the Moon itself, about 3,474 km. It tapers to a point roughly 374,000 km away on average, which is close to the distance of Earth. That coincidence is why total eclipses on Earth are brief and narrow: by the time the shadow reaches us, it is at most about 270 km wide, and some eclipses fall short of the ground altogether and are annular.

Orion was much closer to the Moon. During totality it was roughly 9,000 to 11,000 km behind the lunar surface, where the shadow is still about 3,400 km across, more than ten times wider than it ever is on Earth.

How fast you cross it

Duration is width divided by speed. On Earth the shadow sweeps across the ground at upwards of half a kilometre per second, so even the best-placed observer is inside it for a few minutes. Orion crossed the much wider shadow at about 1 km/s relative to it. Some 3,400 km at about 1 km/s gives close to an hour. Computed from Orion’s trajectory, totality ran from 00:36 to 01:30 UTC on 7 April 2026: 54 minutes, in line with NASA’s figure of nearly 54 minutes.

A Moon 32 times wider than the Sun

From Earth, the Moon and the Sun look almost exactly the same size, about half a degree, so the Moon just covers the bright disc and leaves the faint corona visible around it. From Orion, the Moon was about 17° across in mid-eclipse, 32 times the width of the Sun. It covered not only the Sun but a large area of sky around it, including the inner corona that is the highlight of an eclipse seen from Earth.

The crew’s photographs still show a glow around the dark Moon. It may be the outer corona, zodiacal light (sunlight scattered by dust in the inner Solar System), or both; that is still being studied. The night side of the Moon was not completely dark either. It was lit faintly by earthshine, sunlight reflected from Earth.

Why eclipses matter to astronomers

Eclipses are geometry made visible. The same arithmetic, sizes, distances and speeds, decides whether a planet crosses its star as seen from Earth and how long the crossing lasts. A transit is an eclipse of a star by a planet, and its depth and duration are how most planets beyond the Solar System have been found. See How the transit method finds planets.