<p>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.</p>
<p>I have illustrated this below graphically</p>
<p><span class="math-container">$$\\\\$$</span>
<span class="math-container">$$\\\\$$</span></p>
<p><a href="https://i.sstatic.net/traFngMy.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/traFngMy.jpg" alt="annular eclipse" /></a>
<strong>Annular eclipse (Moon (blue) smaller than Sun)</strong></p>
<p><span class="math-container">$$\\\\$$</span>
<span class="math-container">$$\\\\$$</span></p>
<p><a href="https://i.sstatic.net/yr9P5Ie0.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/yr9P5Ie0.jpg" alt="total eclipse" /></a></p>
<p><strong>Total eclipse</strong></p>
<p><span class="math-container">$$\\\\$$</span>
<span class="math-container">$$\\\\$$</span></p>
<p><a href="https://i.sstatic.net/ZL2BWAxm.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/ZL2BWAxm.jpg" alt="partial eclipse" /></a></p>
<p><strong>Partial eclipse with roughly about 99% coverage</strong></p>

CC BY-SA 4.0
2024-04-13T22:57:17.623Z
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?
Karl Knechtel
CC BY-SA 4.0
2024-04-14T17:56:58.390Z
@KarlKnechtel Please see my edit answer with graphics. This should clarify the difference between the various cases with regard to the edge effects
Thomas
CC BY-SA 4.0
2024-04-15T06:05:01.037Z
@Karl The Moon/Sun angular diameter ratio for the 2024-Apr-8 eclipse was ~1.05 https://i.sstatic.net/oThtV8YA.png lon=280.6017 E, lat=43.6667284 N, alt=126.2 m (times in UTC).
PM 2Ring
CC BY-SA 4.0
2024-04-13T14:02:10.160Z
2024-04-14T17:45:24.523Z
2024-04-14T17:45:24.523Z
Thomas
<p>It was <a href="https://astronomy.stackexchange.com/questions/57226">previously established</a> that even very &quot;deep&quot; (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.</p>
<p>However, it seems that annular eclipses <em>do</em> 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 <a href="https://en.wikipedia.org/wiki/Francis_Baily" rel="nofollow noreferrer">in which</a> Baily observed and described Baily's beads, was <a href="https://en.wikipedia.org/wiki/List_of_solar_eclipses_in_the_19th_century" rel="nofollow noreferrer">an annular eclipse with a magnitude of only .9509</a>. 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?</p>
<p>I am particularly interested in this because of the expected annular solar eclipse in July 2057, which will apparently have a comparable magnitude (<a href="https://www.timeanddate.com/eclipse/in/canada/toronto?iso=20570701" rel="nofollow noreferrer">expected to be visible in Toronto right before sunset</a>, which sounds to me like a rather dramatic show).</p>

CC BY-SA 4.0
2024-04-14T21:14:47.650Z
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.
Greg Miller
<solar-eclipse>
Eclipse phenomena in annular vs partial solar eclipses
Karl Knechtel
# Eclipse phenomena in annular vs partial solar eclipses

(Asked by: username_0 on 2024-04-13)

It was [previously established](https://astronomy.stackexchange.com/questions/57226) 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](https://en.wikipedia.org/wiki/Francis_Baily) Baily observed and described Baily's beads, was [an annular eclipse with a magnitude of only .9509](https://en.wikipedia.org/wiki/List_of_solar_eclipses_in_the_19th_century). 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](https://www.timeanddate.com/eclipse/in/canada/toronto?iso=20570701), which sounds to me like a rather dramatic show).

**Tags:** solar-eclipse

> **Comments:**
> **username_1**: 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.  

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## 1 answers

### Answer by username_2 on 2024-04-13. Score: 2 | Accepted answer

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

$$\\\\$$
$$\\\\$$

[![annular eclipse](https://i.sstatic.net/traFngMy.jpg)](https://i.sstatic.net/traFngMy.jpg)
**Annular eclipse (Moon (blue) smaller than Sun)**

$$\\\\$$
$$\\\\$$

[![total eclipse](https://i.sstatic.net/yr9P5Ie0.jpg)](https://i.sstatic.net/yr9P5Ie0.jpg)

**Total eclipse**

$$\\\\$$
$$\\\\$$

[![partial eclipse](https://i.sstatic.net/ZL2BWAxm.jpg)](https://i.sstatic.net/ZL2BWAxm.jpg)

**Partial eclipse with roughly about 99% coverage**

> **Comments:**
> **username_0**: 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?  
> **username_2**: @KarlKnechtel Please see my edit answer with graphics. This should clarify the difference between the various cases with regard to the edge effects  
> **username_3**: @Karl The Moon/Sun angular diameter ratio for the 2024-Apr-8 eclipse was ~1.05 https://i.sstatic.net/oThtV8YA.png lon=280.6017 E, lat=43.6667284 N, alt=126.2 m (times in UTC).  

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