How fast does the eclipse shadow travel? About 4,500 km/h over the Strait and 2,400 in Egypt

It depends on the stretch. Over the Strait of Gibraltar, between Tarifa, at the southern tip of Spain, and Tangier in Morocco, the Moon’s shadow will travel at about 4,400-4,600 km/h, more than a kilometre per second. Near the point of greatest eclipse, in Egypt, it slows to about 2,400 km/h, and at either end, where it meets the Earth with the Sun very low, it goes faster than 18,000 km/h. In all it covers about 13,900 km of central line in 3 h 22 min, from 08:26 to 11:48 UTC: an average of about 4,100 km/h. Its centre crosses the Spanish part of the path in under five minutes.

Stretch by stretch

NASA publishes the eclipse’s central line point by point, every two minutes. Measuring the distance from one point to the next gives the speed of the shadow over the ground:

08:46 UTC is 10:46 in mainland Spain (CEST, UTC+2). In those minutes the shadow passes from the Atlantic to the Alboran Sea over the Strait, and in two minutes it moves about 150 km.

Why its speed changes

There are two reasons. The first is the angle. At the start and end of its route the shadow arrives side-on, with the Sun 8° or 12° above the horizon, and stretches out over the ground: a small shift in space becomes a huge jump on the surface. NASA explained it this way for the 2017 eclipse: because of the Earth’s shape, the shadow meets the surface at a slant at the start and end of its track, and that is where it moves fastest. Michael Zeiler, an eclipse cartographer quoted by Space.com, puts it another way: the oblique angle of the shadow on a curved Earth gives it more speed over the ground.

The second is the Earth’s rotation. The Earth turns from west to east, the same direction the shadow travels, so the ground “chases” the shadow and takes some of its speed away.

As a result, the shadow moves most slowly where the Sun is highest, near the point of greatest eclipse. In our data, the slowest stretch, at 2,401 km/h, runs from 10:04 to 10:06 UTC, with the Sun at 82°, next to the maximum at 10:06:37 UT. The same happened in the 2024 eclipse: according to the calculation quoted by Space.com, the shadow was slowest near Nazas (Mexico), at about 2,519 km/h.

Slower means more seconds

The more slowly the shadow passes, the longer it takes to cross a given point. Over the Strait, at about 4,500 km/h, totality on the central line lasts between 4 min 48 s and 4 min 54 s; in Egypt, at 2,400 km/h, 6 min 23 s. Speed isn’t the only factor. According to NASA’s table, the path widens from 213 km where it meets the Earth to 258 km at the maximum, and the Moon looks slightly larger relative to the Sun: the ratio of their diameters goes from 1.063 to 1.079. That’s why Luxor will see one of the longest totalities of the century, as we explain in why is it called the eclipse of the century.

Across Spain in under five minutes

Totality begins in Barbate at 10:45:03 and ends in Melilla at 10:52:48, by our times (those of the IGN, Spain’s National Geographic Institute, come about ten seconds earlier). In between, the centre of the shadow brings maximum eclipse to one town after another, from west to east:

From maximum in Rota to maximum in Roquetas de Mar takes four and a half minutes. The whole route, with each country’s clock, is in the shadow’s journey, the path on the ground in the map, and the countries it crosses in the countries in the path of totality.

Sources: Path of the Total Solar Eclipse of 2027 Aug 02 — NASA (central line every two minutes, duration, path width, diameter ratio and the Sun’s altitude); So Many Ways to View an Eclipse — NASA Earth Observatory (why the shadow moves faster at the start and end of its route); How fast will April’s total solar eclipse travel? — Space.com (the oblique angle on a curved Earth, the Earth’s rotation and the minimum speed in 2024); eclipseando data (speeds calculated between NASA’s points; times in Spain from the skyfield + DE440s engine).