It was previously established that even very "deep" (magnitude close to 1) partial solar eclipses - for example, such as viewed from Toronto a few days ago - don't exhibit most of the interesting phenomena associated with totality.

However, it seems that annular eclipses do show some of these phenomena - in particular, Baily's beads - even though far more of the Sun's light shows through. For example, the May 1836 eclipse in which Baily observed and described Baily's beads, was an annular eclipse with a magnitude of only .9509. With only about 90% obscuration, why would phenomena such as this occur, that are not seen with a partial (non-central) eclipse that blocks the Sun more effectively?

I am particularly interested in this because of the expected annular solar eclipse in July 2057, which will apparently have a comparable magnitude (expected to be visible in Toronto right before sunset, which sounds to me like a rather dramatic show).

  • $\begingroup$ Baily's beads are the actual surface of the Sun, so they appear just as bright as the parts of the Sun visible around. Unlike the corona, which is much dimmer than the Sun's surface, so very little of the Sun's surface can drown out its visibility. $\endgroup$ Commented Apr 14 at 21:14

1 Answer 1


At a so-called annular eclipse the Moon still moves sufficiently central across the Sun so that the whole disk of the Moon is contained within the solar disk at some point. So when coming in and going out, the trailing/leading edge of the moon still coincides with the edge of the Sun over a certain range (despite their slightly different radii of curvature). Because of this, edge effects similar to a total eclipse may occur. The difference is obviously that for the annular eclipse there is still a large amount of sunlight interfering, so the effects may be difficult to see. For a partial eclipse on the other hand the edges of the Moon and the Sun don't match up at all but cut each other at some angle.

I have illustrated this below graphically

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annular eclipse Annular eclipse (Moon (blue) smaller than Sun)

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total eclipse

Total eclipse

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partial eclipse

Partial eclipse with roughly about 99% coverage

  • $\begingroup$ I'm talking about partial eclipses of magnitude, say, >0.99. Why wouldn't the edges line up about as well in this case? For that matter, how is the edge lining up in a total eclipse where the Moon's apparent radius is significantly larger than the Sun's? $\endgroup$ Commented Apr 13 at 22:57
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    $\begingroup$ @KarlKnechtel Please see my edit answer with graphics. This should clarify the difference between the various cases with regard to the edge effects $\endgroup$
    – Thomas
    Commented Apr 14 at 17:56
  • $\begingroup$ @Karl The Moon/Sun angular diameter ratio for the 2024-Apr-8 eclipse was ~1.05 i.sstatic.net/oThtV8YA.png lon=280.6017 E, lat=43.6667284 N, alt=126.2 m (times in UTC). $\endgroup$
    – PM 2Ring
    Commented Apr 15 at 6:05

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