The geometry: a borderline alignment
Whether a central solar eclipse is total or annular depends on whether the tip of the Moon’s dark shadow cone, the umbra, reaches Earth’s surface:
- If it does, observers in the shadow see a total solar eclipse.
- If it falls short, observers beyond the tip see an annular solar eclipse, with a ring of sunlight around the Moon.
A hybrid eclipse happens when the tip of the umbra is right on the edge, ending very close to Earth’s surface. In that case, the outcome changes along the path.
Why Earth’s curvature matters
Earth is a sphere, about 12,700 kilometers across. As the Moon’s shadow sweeps across it, the part of the surface beneath the middle of the path, where the Sun is high in the sky, bulges toward the Moon. Places there are closer to the Moon by up to roughly one Earth radius, about 6,400 kilometers, than places near the ends of the path, where the eclipse happens at sunrise or sunset.
That difference is enough to tip the balance:
- At the start and end of the path, near sunrise and sunset, the observer is farther from the Moon. The umbra does not quite reach, so the eclipse is annular.
- In the middle of the path, the observer is closer. The umbra reaches the ground, so the eclipse is total.
When the alignment is slightly different, the switch happens only once, giving a hybrid that changes from annular to total or the other way around.
What you see depends on where you stand
From a single location, you see either a total or an annular eclipse, not both. Near the transition points, the Moon and Sun look almost exactly the same size, so the result is extreme:
- In the total part, totality is often very brief. The Moon’s rugged edge lets sunlight through its valleys, so Baily’s beads may flicker almost the whole time.
- In the annular part, the ring may be extremely thin and broken into beads.
- Close to the transition, observers can see an eclipse made almost entirely of beads, with the corona and prominences glimpsed between them.
Outside the central path, the much wider surrounding region sees an ordinary partial solar eclipse.
How rare are hybrid eclipses?
Hybrids are the rarest type of solar eclipse, making up only around 5 percent of all solar eclipses. Several decades can pass between them. A recent example was the hybrid eclipse of 20 April 2023, whose short total phase was seen from parts of Western Australia, Timor-Leste and Indonesia, while the beginning and end of its track were annular over the ocean.
For dates of future hybrid and other eclipses, see the eclipse calendar, and for how they compare to the other kinds, see types of eclipses.
Safety during a hybrid eclipse
The safety rules depend on what you see at your location:
- If you are in the annular part of the path, or anywhere in the partial zone, there is no safe moment to look without a proper solar filter.
- If you are in the total part, you may look without protection only during totality, once the Sun’s surface is completely hidden. Because hybrid totality is so short and beaded, it can be hard to judge, so many observers keep filters close at hand and put them back on at the first sign of a bright bead.
Use certified eclipse glasses, filtered optics, or indirect projection. The complete guidance is in solar eclipse eye safety.