How common are total eclipses in the universe?

[mincam]

TL;DR Summary

Approximate odds of total eclipses elsewhere

I am not sure of the definition of a total eclipse, but what I am describing as a total eclipse in my question is the kind we on Earth experience; that is to say, an eclipse where only the tiny annular ring of chromosphere is briefly visible.

I am guessing that there are many (millions?) planets with moons, and though we have not visited them, if we were able to, what are the odds that we would find that these planets, too, had total eclipses?

It seems to me that this type of eclipse must be very, very unique, because the moon's distance from its planet must be in perfect relationship with its diameter to create this phenomenon, and to me, the odds against that seem staggering.

Thus, I think that Earth's total eclipses must be extremely rare in the universe.

Am I correct, or is this a ho-hum occurrence?

So my question is: What are the approximate odds of this happening based on what we now know of the universe?

 

[russ_watters]

So my question is: What are the approximate odds of this happening based on what we now know of the universe?

Totally un-knowable, though you have also pretty strictly constrained your concept of what an eclipse should be -- and unreasonably, in my opinion. Using the normal/broader definition (any time the sun is totally obscured), it is likely that they are extremely common. I mean, they happen pretty much weekly on Jupiter.

 

[mincam]

The reason I "constrained" as I did, was because it's my understanding that our understanding of the sun was/is greatly facilitated because we have been able to extract a lot of information from our observations at "chromosphere time" that we would otherwise have found much more difficult, or impossible, to obtain.

In other words, our total eclipses provide us with unique learning experiences that other types of eclipses do not. but maybe I have it wrong. I don't really know.

So my question could be rephrased as, "What are the odds of this (supposedly) unique learning experience happening elsewhere in the universe.?"

 

[Vanadium 50]

very, very unique

Unique means "one of a kind" so you can't get any more unique than just plain unique.

This happens on the moon whenever there is a lunar eclipse, and these happen slightly more often than solar eclipses.

 

[mincam]

Well, I have to admit that I don't understand this (which is why I'm here,) but that strikes me as really, really , really amazing.

It would seem to me, perhaps wrongly, that the fact that our moon is perfectly sized and positioned to give us the "total eclipse" I describe has no influence on that type of eclipse we give to our moon.

In fact, it would seem to me that for Earth to give a chromosphere type eclipse (what I am calling a total eclipse,) to the moon, Earth would have to have a smaller diameter than the moon, for it is further from the sun than we are when we eclipse it, therefore, a diameter less than the moon's would be required. Right?

Maybe this can happen because the orbit is elliptical and not circular?

The more I think about it, the more I think that a sun and its moon cannot give each other this type of total (chromosphere) eclipse. But, as Mom always told me, “Son, your wheel's spinning, but the hamster is dead.”

I really, really, really don't understand it.

Please correct me. That is why I'm here.

 

[Janus]

The reason I "constrained" as I did, was because it's my understanding that our understanding of the sun was/is greatly facilitated because we have been able to extract a lot of information from our observations at "chromosphere time" that we would otherwise have found much more difficult, or impossible, to obtain.

In other words, our total eclipses provide us with unique learning experiences that other types of eclipses do not. but maybe I have it wrong. I don't really know.

So my question could be rephrased as, "What are the odds of this (supposedly) unique learning experience happening elsewhere in the universe.?"

One thing to consider is that The "close fit" of the Moon and Sun comes from the variance of their angular sizes overlapping to some degree. Because the Moon has an elliptical orbit around the Earth and the Earth an elliptical orbit around the Sun, The Moon's angular size varies between 29.4 and 33.5 arc minutes and the Sun's between 31.5 and 33.3 arc minutes. These overlap, so you are going to have times when they are both nearly a perfect fit.
Can this happen on another world? Probably, but for a slightly different reason. The Moon happens to be large, but is is also pretty far from the Earth (something like 60 Earth radii away). As a result, where you are on the Earth doesn't make much difference as to how large it looks compared to the Sun.
But what if you had a Moon much closer in terms of planet radii?
I'll give you an example. Europa is just a bit over 9 Jupiter radii away from Jupiter.
With Europa at the Zenith, it is about 8 arc min in size. From Jupiter's surface, the sun is about 6 arc mins in size. Europa would be 1/3 larger than the Sun.
But if you are looking at Europa while it is at near the horizon, you are 1 Jupiter radius further away, and that is enough to reduce its angular size down to 7.2 arc minutes, a fair reduction in size, making is a better fit to the Sun ( only 20% larger).
If Europa were just a bit smaller or further away, its apparent angular size when viewed from different parts of Jupiter's surface could encompass the Sun's angular size, so that if you pick the right viewing spot, you get a close fit total eclipse.
The point being is that the distance/size of the Moon doesn't have to be so perfectly tuned, and you have much more leeway in order to produce this type of eclipse at least somewhere on the surface of the planet.

 

[russ_watters]

The reason I "constrained" as I did, was because it's my understanding that our understanding of the sun was/is greatly facilitated because we have been able to extract a lot of information from our observations at "chromosphere time" that we would otherwise have found much more difficult, or impossible, to obtain.

In other words, our total eclipses provide us with unique learning experiences that other types of eclipses do not. but maybe I have it wrong. I don't really know.

So my question could be rephrased as, "What are the odds of this (supposedly) unique learning experience happening elsewhere in the universe.?"

I'm not sure how unique/important it was, and that would be a matter of opinion. One could still see the chromosphere in an eclipse of a much larger shadow, just not the entire thing. And today of course we use artificial eclipses (carefully placed shadows) to view the chromosphere/corona whenever we want.

 

[mincam]

One thing to consider is that The "close fit" of the Moon and Sun comes from the variance of their angular sizes overlapping to some degree. Because the Moon has an elliptical orbit around the Earth and the Earth an elliptical orbit around the Sun, The Moon's angular size varies between 29.4 and 33.5 arc minutes and the Sun's between 31.5 and 33.3 arc minutes. These overlap, so you are going to have times when they are both nearly a perfect fit.
Can this happen on another world?

Thank you, very, very much!

Very informative and educational for me.

However, the examples you give are close but no cigar.

Would my question have been better phrased if I had said: "During a full eclipse, what are the odds of a moon's angular size being within 90 to 99.9 percent of its sun's when viewed from the moon's planet, anywhere in the known universe?"

And the answer is?

 

[hutchphd]

I have a stupid pedantic question. Are there solar "eclipses" by the moon that should actually be called "transits" ?? For instance tha annular ones? What are the defining differentiating criteria?

 

[mincam]

Or is this better? "What are the odds, anywhere in the universe, that a planet will experience an annular eclipse where the angular size of the moon is within 95 to 99 percent of the sun's?"

 

[Vanadium 50]

However, the examples you give are close but no cigar.

That's awfully demanding. You're talking to volunteers.

Would my question have been better phrased if I had said: "During a full eclipse, what are the odds of a moon's angular size being within 90 to 99.9 percent of its sun's when viewed from the moon's planet, anywhere in the known universe?"

Sure, but that's a different question than seeing the chromosphere. You can't really complain about the quality of the answers if you change the questions.

Anyway, the moon recedes from the Earth about 5/16" every orbit. In the past it covered more of the sun and in the future less. I haven't done the calculation in a while, but the kind of things we call total solar eclipses can only happen withing about a 50 million year window - about 1% of the time the Earth has been here.

One way to look at this is to think such events are rarer: it's not just the earth, but for 99% of its existence, they don't even happen on earth. The other way is that it's practically inevitable for objects that have a companion bigger than their son. The moon doesn't experience them now because the Earth is too big, but will in the future.

 

[Janus]

Thank you, very, very much!

Very informative and educational for me.

However, the examples you give are close but no cigar.

Would my question have been better phrased if I had said: "During a full eclipse, what are the odds of a moon's angular size being within 90 to 99.9 percent of its sun's when viewed from the moon's planet, anywhere in the known universe?"

And the answer is?

The point I was making is that in a situation where the orbital distance to planetary radius ratio is relatively low, you have much more leeway with the orbital distance/moon size configuration and still see a total eclipse from somewhere on the planet. So with a moon at Europa orbital distance and Jupiter-sized planet, you have about 10% of "wiggle room" for the Moon's size, and still allow for a total eclipse to be viewed from some point of the planet. At Io's orbital distance, this increase to 20% of wiggle room. Given that the first 8 moons out from Jupiter range from 20 to 2403 km in radius, there seems to be a large range of possible moon radii. Combine this with the fact that large Jupiter-sized planets tend to collect a good number of moons, which increases the odds of having one that falls in the right radius to distance range, And I think the odds are pretty good of it happening somewhere.
Also, you need to consider that moons tend to migrate. Our own Moon is drifting slowly away. In the past it was significantly larger than the Sun, and sometime in the future, it will be significantly smaller.
So let's take a moon like Io which is presently a bit further from Jupiter than the Moon is from the Earth, and has a slightly larger radius. If you put Jupiter at Earth orbit distance from the Sun( such "Hot Jupiters" are not particularly rare), IO would be just a tad larger than the Sun as viewed from any part of Jupiter's surface. But as it drifts away due to tidal interaction, it would eventually get to a distance where it would fit exactly over the Sun as viewed while near the horizon and then, over time, this perfect viewing would drift to be while it is at the zenith.
In this case, our IO sized moon will produce a near-fit total eclipse somewhere on the planet over a much longer time span than over which such an eclipse is visible from Earth.

Then there is the aforementioned eccentricities of the orbits involved. While Earth varies its orbital distance by about 4%, Mars varies its by nearly 20%. This produces a comparable variation in visible Sun size as viewed from the planet. This in turn allows for a larger range for the Moon radius/distance combination that can produce a near-fit total eclipse.

The factors involved are just too varied to give any kind of accurate guess as to how common such events are.

 

[mincam]

Or is this better? "What are the odds, anywhere in the universe, that a planet will experience an annular eclipse where the angular size of the moon is within 95 to 99 percent of the sun's?"

 

[mincam]

I'm in way over my head.

But what I am understanding is that the larger you make the radius of the planet, the better your odds are.

Why? I'm not sure but I think it's because by moving around on the planet you can change the moon's annular size faster than the sun's. But I still think the 95 to 99% ratio must be maintained for the eclipse I am looking for.

I am know even less of statistics than I do of stars, but it seems to me that it is an exceedingly rare event. Even exceedingly, exceedingly. If you can assure me that it even happens elsewhere within our solar system, I will eat those words with a thankful smile.

 

[PeroK]

I am know even less of statistics than I do of stars, but it seems to me that it is an exceedingly rare event.

The question is really how many planets have something rare about them? If it's not the solar eclipse it might be something else. If you stack up enough characteristics of anything you get something highly improbable.

For example, there might be a planet whose year is (almost) exactly a whole number of days. Or, it might have a more useful number of days than 365. Like 200 or 400.

There's likely to be something on most planets that you could look at and say: that's an interesting coincidence.

 

[Ibix]

I think you are misunderstanding the arguments here.

Almost any size object can blot out the Sun exactly if it happens to be at the right distance. DO NOT TRY THIS, but a finger tip at a full arm's length would do it (try it with the Moon - the same apparent size and you won't go blind). Something the size of the Moon will blot out the Sun if it's about 40,000km away. A dark object the same size as the Sun would blot it out if it were 93 million miles away (i.e., just this side of the Sun itself).

And orbital distances are not stable long term. So it's quite likely that at some point in history any reasonably large moon could perfectly blot out the Sun from the surface of the moon's planet. That we happen to be in a position to see it might be considered fortunate, but I don't think it's a "never to be seen again anywhere in the galaxy" thing.

 

[Vanadium 50]

but it seems to me

Is not a good explanation in science.

If you can assure me that it even happens elsewhere within our solar system

Have you done the math? Remember, most moons are too large, not too small. That's because they are far from the sun. So you have hundreds to check.

 

[hmmm27]

Hmm... would gravitational lensing by the Moon be useful in any respect ? increase the resolution of the Sun's chromosphere by a bit.

 

[Ibix]

Hmm... would gravitational lensing by the Moon be useful in any respect ? increase the resolution of the Sun's chromosphere by a bit.

Gravitational lenses are worse than the bottom of a beer bottle, from an optical engineering perspective. And it's a wholly negligible effect from the moon anyway.

 

[Janus]

Gravitational lenses are worse than the bottom of a beer bottle, from an optical engineering perspective. And it's a wholly negligible effect from the moon anyway.

Besides, to use the Moon's gravitational lensing as a telescope, you would need to be at the focal distance from the Moon, which is at some 5300 AU

 

[Motore]

Here are the Sun/moon ratios for the planets in our solar system (for which we have the data):
https://www.eclipse-chasers.com/php/SolarSystemEclipses.php?D=1

 

[Vanadium 50]

And from that table there are two Saturnian moons, Pandora and Epimetheus, that eclipse the sun.