Solar eclipses
Drag the Moon over the Sun, find out why it fits so exactly, and follow the shadow of 2 August 2027 across Spain and Egypt.
Cover the Sun
Slide the Moon across the Sun. Watch the daylight as you go.
Totality. The sky goes dark and the corona appears: the Sun’s outer atmosphere, over a million degrees, normally drowned out by the glare.
With 90% of the Sun covered, there’s still about a tenth of the daylight left, and your eyes adapt to it. Most people barely notice. The real drop comes in the last minute, then the last few seconds.
The corona is hotter than the Sun’s surface: over a million degrees, against about 5,500 °C below. Why is still an open question, called the coronal heating problem. NASA’s Parker Solar Probe was sent to fly through it.
The corona’s streamers here are illustrative: the real shape changes with the Sun’s 11-year cycle.
A perfect fit
The Moon’s distance changes over each month. Push it farther away.
Past about 380,000 km, the Moon looks smaller than the Sun and can’t cover it: an annular eclipse, a ring of fire. Up close, it covers it with room to spare.
The Sun is about 400 times wider than the Moon (1,391,000 km against 3,476 km), and about 390 times farther away. So the two look almost the same size, about half a degree.
The Moon’s distance swings between about 363,000 km and 405,500 km on average, so sometimes it wins and sometimes the Sun does.
It won’t last. Laser beams bounced off mirrors left by Apollo astronauts show the Moon moving away by 3.8 cm a year. In roughly 600 million years, total eclipses start to become rare, and the very last may be about 1.2 billion years from now.
Why not every month?
Every month, the new moon passes between Earth and the Sun. Step through the months and watch where its shadow goes.
The Moon’s orbit is tilted by about 5°. Most months the shadow passes above or below Earth. It only lands when a new moon falls near a node, where the two orbits cross. That happens about every six months.
At new moon, the Moon sits about 5.1° × sin F above or below the Sun–Earth line, where F is how far the Sun is from a node. At F = 90° that’s about 34,500 km, more than five Earth radii, so the shadow misses completely. The shadow needs F within about 16° to touch Earth at all, and about 11° for a total or annular eclipse.
Each new moon moves F on by about 30.7°, so a “window” comes round roughly every 173 days. That’s why there are at least two solar eclipses a year (somewhere on Earth), and never more than five.
The diagram squashes distances so it fits. The heights are true to Earth’s size.
Chase the shadow
On 2 August 2027, the Moon’s shadow crosses Spain, North Africa and Arabia. Drag the time.
Over Luxor at about 1:05 pm local time, the Sun nearly overhead. Totality there lasts about 6 minutes 20 seconds, and 6 minutes 23 seconds at its longest, just to the northwest.
Eclipse maps are computed from Besselian elements: NASA’s description of the Moon’s shadow, hour by hour, on a plane through Earth’s centre. This page runs NASA’s elements for this eclipse live. It reproduces NASA’s published figures: 6 min 23 s at the point of greatest duration, and a path about 258 km wide.
The shadow crosses the ground at about 4,800 km/h over the Strait of Gibraltar, where the Sun is low and it lands at a slant, and slows to about 2,400 km/h over Egypt.
Only one total eclipse this century lasts longer: 22 July 2009, at 6 min 39 s, at its longest over the Pacific.
The diamond ring
A close-up of the Sun’s edge in the final seconds. Slide towards zero.
The Moon’s valleys let sunlight through as Baily’s beads. The last one blazes as the diamond ring, then goes out. Only now is it safe to look without eclipse glasses.
Francis Baily described the beads after the annular eclipse of 15 May 1836. Edmond Halley had seen them in 1715. Real lunar mountains change the Moon’s edge by only a couple of arcseconds. They’re drawn deeper here so they show on a phone.
Safety. NASA’s advice: look without protection only when the Moon completely covers the Sun’s bright face. Before and after totality, including the diamond ring, use eclipse glasses that meet the ISO 12312-2 standard.
Where will you stand?
Pick a place on the path and drag the time. Totality is shortest near the edges and the ends of the path, and longest in the middle.
Durations come from NASA’s elements at sea level and ignore the Moon’s mountains, so treat them as good to a few seconds. Local times use summer time where it applies in August 2027. On average, any one spot on Earth sees a total eclipse only once every 375 years or so.
When's yours?
Use your location, or tap anywhere on the globe. Drag to spin it.
Most places wait a long time for totality. The paths list shows the total eclipses passing near you in the coming decades, worth a trip.
The eclipses are computed in your browser with astronomy-engine, an open-source astronomy library, from the positions of the Sun and Moon. For 2027 it agrees with NASA’s predictions to within a couple of kilometres on the path and about five seconds on durations.
Your location never leaves your device: nothing is sent anywhere.
Far-future dates are less exact. Eclipse paths depend on exactly how fast Earth spins, which varies slightly and unpredictably, so predictions a century or more ahead can shift. If you’re right at the edge of a path, treat it as a maybe.