The geometry: a Moon that is too far away
The Moon’s orbit around Earth is an ellipse. At its closest, called perigee, the Moon is about 363,000 kilometers away; at its farthest, apogee, about 405,000 kilometers. That difference changes how large the Moon looks in our sky by more than 10 percent.
The Sun’s apparent size changes slightly too, because Earth’s own orbit is an ellipse. When a new Moon lines up exactly with the Sun while the Moon is far from Earth, its apparent disk is smaller than the Sun’s. The tip of the Moon’s dark shadow cone, the umbra, ends before it reaches Earth. Beyond that tip lies a region called the antumbra, and anyone standing in it sees the Sun as a ring around the Moon.
If the Moon is close enough to look larger than the Sun, the same alignment gives a total solar eclipse instead. For how far away the Moon is and why it varies, see how far is the moon.
The path of annularity
As Earth turns, the antumbra traces a narrow track across the surface, called the path of annularity. Outside it, a much wider area sees a partial solar eclipse. Near the edges of the path, the ring looks lopsided, thin on one side and broken into Baily’s beads. Near the center line, the ring is even all the way around.
Because the Moon is farther away during an annular eclipse, its shadow is spread over a wider region and the path of annularity is often wider than a typical path of totality.
What you see
The stages mirror those of a total eclipse:
| Stage | What happens |
|---|---|
| First contact | The Moon starts to cover the Sun’s edge |
| Partial phase | The visible Sun becomes a crescent |
| Second contact | The ring forms as the Moon moves fully inside the Sun’s disk |
| Annularity | The ring of fire, centered or off-center |
| Third contact | The ring breaks |
| Partial phase | The crescent grows again |
| Fourth contact | The eclipse ends |
During annularity, daylight dims noticeably but does not turn to night. The light takes on an odd, flat quality, and the temperature may drop a little. Gaps between tree leaves project hundreds of tiny rings onto the ground, one of the most memorable sights of an annular eclipse.
How long annularity lasts
Because the Moon’s disk is smaller than the Sun’s, it takes longer to cross the center of the Sun than during a total eclipse. Annularity can last more than 12 minutes in extreme cases, much longer than the longest totality. Many annular eclipses, however, have annularity lasting only a few minutes, and when the Moon is only just too small, the ring may last mere seconds and be very thin.
How often it happens
Annular eclipses are slightly more common than total ones, making up roughly a third of all solar eclipses. Several can occur within a few years, but as with totality, any single location sees one only rarely. Check the eclipse calendar for upcoming paths.
Safety: the ring is never safe to look at
This is the most important difference from a total eclipse. There is no stage of an annular eclipse when it is safe to look at the Sun without protection. Even at the peak, the ring of exposed Sun is extremely bright, and looking at it directly can damage your eyes.
- Use certified solar eclipse glasses or a solar viewer from start to finish.
- Fit telescopes, binoculars and camera lenses with a proper solar filter on the front.
- Use projection, such as a pinhole projector, as a safe indirect alternative.
Full guidance is in solar eclipse eye safety.