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I've seen it referenced often that "total solar eclipses" (of the kind we see today where the corona of the Sun is visible as opposed to all of it being blocked) have become possible only recently (in geological time) since the moon has been receding from us. But no where have I seen an estimate of how ancient we think these kinds of eclipses are. I have read that the oldest recorded one might be about 5000 years old. But not how old they might be in absolute terms. Did the dinosaurs see the famous ring we see today or did they simply see total darkness for a few minutes?

Note: for the terminology on "total" vs other kinds of solar eclipses, I'm going by what this website uses: https://www.timeanddate.com/eclipse/list.html. When they say "total solar eclipse", they mean the ones where a very thin ring of light is visible.

The following image has been taken from the NASA website (note you can see a ring in both kinds): https://solarsystem.nasa.gov/eclipses/future-eclipses/

enter image description here

EDIT: Here, by total solar eclipse, I mean the kinds we currently see on Earth where a ring of light (from the Sun) is visible and it isn't simply occluded completely. This requires precise conditions where the Moon should be at the right distance and the right size in relation to the Sun. Quoting from another answer:

Quoting from this answer: https://astronomy.stackexchange.com/a/10219/9312

"The criterion for an exoplanet to have solar eclipses like the spectacular ones we have here on Earth is a moon that happens to have an angular size large enough to cover the photosphere, but not so large that it also hides the corona."

This article answers the related question on when the last such eclipse will be (in 650 million years): https://www.forbes.com/sites/startswithabang/2017/08/18/earths-final-total-solar-eclipse-will-happen-in-less-than-a-billion-years/?sh=3c7b038a635a

Here is a highly related question (pointed out by someone later in the comments that are now moved): When did the first annular eclipse happen? and also this one: How rare are earth-like solar eclipses?

Rohit Pandey
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  • Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on [meta], or in [chat]. Comments continuing discussion may be removed. – Connor Garcia Aug 07 '23 at 03:18
  • You mean "annular eclipse" not a total eclipse? – ProfRob Aug 07 '23 at 09:32
  • @ProfRob - No, I mean total eclipses. Right now, it is impossible for the moon to completely block the Sun. The most it does is block the photosphere but still renders the corona visible. Those eclipses are called "total solar eclipses". In the Annular ones, it doesn't even block the photosphere completely and those feel simply like cloudy days (unless you look directly at the Sun). See here: https://www.timeanddate.com/eclipse/list.html – Rohit Pandey Aug 07 '23 at 15:23
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    So what you mean is how long ago were there no annular eclipses? Since all eclipses would have been "total" in the distant past by your definition - the corona has no well-defined extent. When the Moon was closer it would have easily blocked the photosphere leaving the corona visible. I feel you need to completely clarify your question and eclipse definitions. – ProfRob Aug 07 '23 at 15:43
  • Yeah, I agree those definitions are murky. Hence, I'm going by the terminology in the link I included above. I can add that to the question. – Rohit Pandey Aug 07 '23 at 16:03
  • For a total eclipse the moon does block the sun completely by all practical means - unless you come up with a definition of what you call the sun / the outer boundary of its corona. Your understanding of the extent of the sun seems to deviate there a lot from established terminology which uses the photosphere or chromosphere for definition of extent. Your question didn't get cleared in the last 30 hours despite the edits – planetmaker Aug 07 '23 at 17:04
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    Why are you defining "total eclipse" as one where you can see the corona? That is not the definition. Voting to close as unclear. – Rory Alsop Aug 07 '23 at 17:32
  • I don't think I said Corona. I said a small ring of light is visible. As mentioned in the question, I took the definition from websites like this: https://www.timeanddate.com/eclipse/list.html and also the NASA website. – Rohit Pandey Aug 07 '23 at 18:46
  • I'm asking about the kind of eclipse that is going to happen in Apr 2024. The website above calls it a total solar eclipse and it won't be completely covering the Sun. Let me know what I can change in the question to align with that. – Rohit Pandey Aug 07 '23 at 18:50
  • @planetmaker - one of the practical means is to just look at it with your naked eye. And you can still see it. So no, it is not blocked by all practical means. – Rohit Pandey Aug 07 '23 at 18:53
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    @RohitPandey that "small ring of light" is the (inner) corona. And it's dramatically less bright than photosphere or chromosphere - and only visible against the night sky with decreasing outward area brightness - visible from Earth only during exactly that: a total eclipse where the complete sun is hidden by the moon (as opposed to a partial or annular eclispe). If you take photos without adjusting exposure settings, the images will then be dark. The human eye with its logarithmic sensitivity is quick enough to adjust. – planetmaker Aug 07 '23 at 19:12
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    "I've seen it referenced often that solar eclipses have become possible only recently [...] since the moon has been receding from us" — this doesn't make sense: if the Moon has always been receding, its angular size has always been decreasing, so if it can cover the 0.5°-diameter solar disk now, it could cover it all the time it existed. – Ruslan Aug 08 '23 at 05:56
  • The solar eclipses as they're defined today don't cover the whole Sun. They leave a small ring of light. See the first link in my question. That's how it makes sense. – Rohit Pandey Aug 08 '23 at 07:01
  • Your link to timeanddate does not define it the way you argue here – planetmaker Aug 08 '23 at 08:42
  • I actually went and saw the one in Salem, OR in 2017 with my own eyes. They called that a total solar eclipse and I could see the ring. There is no total eclipse on current Earth where you can't see a ring. I'm going to stop responding on comments now, – Rohit Pandey Aug 08 '23 at 09:23
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    "That's how it makes sense" — well, it still doesn't: your title asks "How old are total solar eclipses?", which implies that they do exist now and didn't exist at some point in the past, while in the comments you say that today's eclipses are not really eclipses. Your question is really quite unclear, it would be better if you rephrased it so that it was more apparent what you're asking. – Ruslan Aug 08 '23 at 12:54
  • Yeah, today's eclipses aren't really "total", but they're still called "total". Not by me, but the wider community of people who are interested in them, just search for "solar eclipse schedule" or look at my links. I did make some edits to clarify this. – Rohit Pandey Aug 08 '23 at 15:17

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Possibly as old as the moon itself - it may be that the moon has never fully occluded the corona.

According to this source, shortly after the moon's formation, it would have been close enough to appear 15 times larger that it does currently. According to this source, the solar corona extends out to 10-20 solar radii, meaning it has 10-20 times the angular size of the sun itself. If we use the upper limit of the size of the corona, the moon was never close enough to fully block it. At the lower end, a freshly formed moon might have been able to block the entire corona for a time, but would have receded enough to make it impossible within hundreds of millions of years. The entire corona hasn't been occluded by the moon for at least 4 billion years, if it ever was.

This answer assumes that the size of the sun and corona haven't changed meaningfully since the moon's formation, and also that the very edges of the corona would be visible during the eclipse. The moon's angular size has generally been smaller than the corona's angular size, but whether the corona is actually visible I expect will depend on lots of specifics related to the observer.

Nuclear Hoagie
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  • A very interesting point. I'd be very interested in whether the corona back then would have been visible with a human naked eye. In the eclipses of today, its already quite faint. – Rohit Pandey Aug 08 '23 at 15:44
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    Actually, the visible corona would have been brighter and probably more extended in the past because of a much denser corona and more powerful magnetic heating. It is the coronal density that matters, since the white light corona is simply photospheric light scattered from free electrons. – ProfRob Aug 08 '23 at 15:51
  • Isn't it also true that the Sun was smaller in the past? – Rohit Pandey Aug 08 '23 at 16:18
  • @NuclearHoagie - doesn't your answer fly directly in the face of the "cosmic coincidence" referenced here: https://solarsystem.nasa.gov/eclipses/science/geometry/#:~:text=A%20total%20solar%20eclipse%20happens,same%20size%20in%20our%20sky. – Rohit Pandey Aug 08 '23 at 23:07
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    @RohitPandey In what way does this answer violate cosmic coincidence? It is indeed a coincidence that we are alive at a time when the moon and the sun are the same angular size - I specifically mention a time when that was not the case, shortly after the moon was formed. It's a coincidence both that it's even possible to have the moon appear the same angular size as the sun, and that it's happening during a time when anyone can appreciate it. – Nuclear Hoagie Aug 09 '23 at 04:12
  • But the NASA link says that cosmic coincidence is required for the kinds of solar eclipses we're seeing today. Your answer states that this exact size match isn't required to see those same kinds of solar eclipses and that we would see them even when the moon was 15 times larger. – Rohit Pandey Aug 09 '23 at 05:45
  • Quoting from the article: "A total solar eclipse happens when the Moon completely blocks the face of the Sun.

    It is the result of a cosmic coincidence... "

     – Rohit Pandey Aug 09 '23 at 05:47
  • @RohitPandey It wouldn't really be a coincidence if the moon were not the same size as the sun, as it was when the moon was formed. The coincidence isn't that we can still see the corona, as you can still see it with a much larger moon without precisely matching the sun and moon size. The coincidence is that the sun and moon are almost identical angular sizes. There is no coincidence regarding the size of the moon and the size of the corona. I'm not sure why you'd call an eclipse where you can barely see the corona as "the same" as one where the disk is barely covered... – Nuclear Hoagie Aug 09 '23 at 13:01
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    They're both total eclipses in that the sun is entirely occluded, but when the moon is much larger than the sun, it may be better called an occultation than an eclipse. – Nuclear Hoagie Aug 09 '23 at 13:05
  • The nasa article I linked above says that the total solar eclipses are the result of a cosmic coincidence. What do they mean by that? – Rohit Pandey Aug 10 '23 at 00:08
  • @RohitPandey It's a coincidence that the moon just barely covers the disk of the sun. For most planet-moon pairs, it's never even possible for that to happen since the moon is too small or too far to completely cover the sun. Not only is it a remarkable configuration in space, but also in time - billions of years ago the moon appeared much larger than the sun, and billions of years from now it will appear smaller. There is no particular reason why the one planet with life should have this highly unusual configuration at this point in time, it's remarkable we can observe it. – Nuclear Hoagie Aug 10 '23 at 12:41
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    On most other planets, you either will never have a total solar eclipse as the moon doesn't cover the sun (moon too small), or you'll have an occultation, where the moon completely blocks the sun for a longer period of time (moon too large). The types of total solar eclipses we see here, where the moon barely but fully covers the sun for a short duration are quite rare. – Nuclear Hoagie Aug 10 '23 at 12:43
  • Right. And if the Corona would be visible even if the moon was much larger, then how would our current eclipses change? Your answer says the Corona would still be visible. Is it just that the Corona would be much less bright? Perhaps not bright enough to see with the naked eye (like we can for the current ones)? – Rohit Pandey Aug 11 '23 at 07:45
  • @RohitPandey This my last comment on the matter - the coincidence is that the moon is the same size as the sun. It's not a coincidence when the moon is 15x the size of the sun, whether you can see the corona or not. – Nuclear Hoagie Aug 11 '23 at 11:34
  • Sure, sounds good. My point is that the NASA article isn't simply saying that it's a coincidence that the moon is the same angular size as the Sun. They're saying the eclipses we have now are a result of that coincidence. The article is about Solar eclipses, not about the sizes of the moon and sun. – Rohit Pandey Aug 11 '23 at 16:02