0
$\begingroup$

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?

$\endgroup$
17
  • 4
    $\begingroup$ 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. $\endgroup$
    – ProfRob
    Aug 7, 2023 at 15:43
  • 1
    $\begingroup$ Why are you defining "total eclipse" as one where you can see the corona? That is not the definition. Voting to close as unclear. $\endgroup$
    – Rory Alsop
    Aug 7, 2023 at 17:32
  • 2
    $\begingroup$ @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. $\endgroup$ Aug 7, 2023 at 19:12
  • 3
    $\begingroup$ "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. $\endgroup$
    – Ruslan
    Aug 8, 2023 at 5:56
  • 1
    $\begingroup$ "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. $\endgroup$
    – Ruslan
    Aug 8, 2023 at 12:54

1 Answer 1

6
$\begingroup$

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.

$\endgroup$
15
  • $\begingroup$ 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. $\endgroup$ Aug 8, 2023 at 15:44
  • 2
    $\begingroup$ 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. $\endgroup$
    – ProfRob
    Aug 8, 2023 at 15:51
  • 1
    $\begingroup$ @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. $\endgroup$ Aug 9, 2023 at 4:12
  • 1
    $\begingroup$ 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. $\endgroup$ Aug 9, 2023 at 13:05
  • 1
    $\begingroup$ 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. $\endgroup$ Aug 10, 2023 at 12:43

Not the answer you're looking for? Browse other questions tagged .