Why the Moon can blot out the Sun

A coincidence of size

The Sun is about 400 times wider than the Moon — and, right now in history, it also sits about 400 times farther away. From Earth the two discs look almost exactly the same size, so the Moon can cover the Sun’s bright face precisely. No other planet in the Solar System has a moon that does this so perfectly. It will not last forever: the Moon drifts about 3.8 cm farther away each year, and in the far future total eclipses will end.

Why not every month?

The Moon passes between Earth and Sun every month at new Moon, yet we don’t get an eclipse each time. That’s because the Moon’s orbit is tilted about 5° to Earth’s path around the Sun, so its shadow usually falls above or below us. Only when a new Moon happens near one of the two nodes — where the orbits cross — does the shadow land on Earth. That alignment recurs in eclipse “seasons,” producing a solar eclipse somewhere on Earth roughly twice a year. A total one at any given place, though, is rare: on average a spot on Earth waits about 375 years between totalities.

The Saros cycle

Eclipses repeat. After 18 years, 11 days and 8 hours — one Saros — the Sun, Moon and nodes return to nearly the same geometry and a very similar eclipse occurs, shifted about 120° west in longitude. The August 12, 2026 eclipse belongs to Saros series 126. Tracking these cycles is how astronomers map eclipses centuries ahead.

Why this one is total — and brief

The Moon’s orbit is elliptical, so its apparent size changes. When it is near perigee (its closest point) it looks slightly larger than the Sun and can cover it completely — a total eclipse. Nearapogee it looks smaller and leaves a bright ring: an annular eclipse. In 2026 the Moon is close enough for totality, but only just entering that range, so the maximum totality is a relatively short 2 minutes 18 seconds.

The first in a generation for Europe

Mainland Europe last saw totality on August 11, 1999. Spain’s previous total eclipse was in1905; Iceland’s was in 1954. For most people watching in 2026, this is a once-in-a-lifetime event on home soil.

What comes next

• August 2, 2027 — remarkably, less than a year later, another total eclipse crosses southern Spain, North Africa and the Middle East, with over 6 minutes of totality near Luxor, Egypt: one of the longest of the century.
• August 12, 2026 → 2027 back-to-back August eclipses make Spain the best-placed country in the world for totality two years running.

Eclipses as science

Totality is one of the few chances to study the Sun’s faint corona from the ground, and the abrupt change in sunlight lets researchers probe the upper atmosphere and even animal behavior. TheUnistellar Network, in partnership with the SETI Institute, turns a community of citizen astronomers into a distributed observatory — the same network logged more than 15,000 scientific observations in 2025.Explore citizen astronomy.