# When Was The August 21, 2017 Eclipse First \[Accurately\] Predicted? **URL:** \ **Category:** Factual Questions\ **Created:** [August 12, 2017, 6:57pm UTC](https://boards.straightdope.com/t/when-was-the-august-21-2017-eclipse-first-accurately-predicted/793456 "2017-08-12T18:57:01Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![HeyHomie](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/heyhomie/32/207_2.png) [@HeyHomie](https://boards.straightdope.com/u/HeyHomie)\ **Post date:** [August 12, 2017, 6:57pm UTC](https://boards.straightdope.com/t/when-was-the-august-21-2017-eclipse-first-accurately-predicted/793456/1 "2017-08-12T18:57:01Z")
At what point in scientific history were mathematical models of the Solar System accurate enough that someone could reliably say “I’ll be damned, there’s going to be an eclipse across North America on August 21, 2017”? 100 years ago? 200 years ago? ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [August 12, 2017, 7:03pm UTC](https://boards.straightdope.com/t/when-was-the-august-21-2017-eclipse-first-accurately-predicted/793456/2 "2017-08-12T19:03:52Z")
Here’s an article [“Introduction to the History of Eclipses”](http://www.astronomytoday.com/eclipses/introduction.html); Astronomy Today … > [@](#): > > Early astronomers were able to predict eclipses by around 2300 BCE. Their predictions were based on empirical relationships, governing the recurrence of events by which the relative positions of the Earth, Sun and Moon reoccur the same way after 6,585 days. This doesn’t answer the question, but it does answer how long ago humans _could_ predict eclipses … when someone sat down and calculated when this particular eclipse would happen may have had to wait until the discovery of North America … ---
**Author:** ![bonzer](https://avatars.discourse-cdn.com/v4/letter/b/45deac/32.png) [@bonzer](https://boards.straightdope.com/u/bonzer)\ **Post date:** [August 12, 2017, 9:06pm UTC](https://boards.straightdope.com/t/when-was-the-august-21-2017-eclipse-first-accurately-predicted/793456/3 "2017-08-12T21:06:21Z")
That there’d be some sort of eclipse? Probably from antiquity. The Saros cycle and all that. For a detailed prediction of the path, the classic early-modern prediction is Halley’s for 1715. That’s already the very fine prediction of the path of totality. In general, I’d expect the path of totality of any later eclipses to nailed down to within a few miles or so centuries ahead of time. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [August 14, 2017, 1:06pm UTC](https://boards.straightdope.com/t/when-was-the-august-21-2017-eclipse-first-accurately-predicted/793456/4 "2017-08-14T13:06:12Z")
There’s a distinction between when somebody \*could \*predict [total eclipse on Aug 21, 2017 across North America] and when somebody _did_ predict it. Nowadays when computation is cheap bordering on free, as soon as we know how to do something we can consider it pretty well done. Back when computation was expensive the logic to do the calc may have existed for many centuries before anyone bothered to execute it by hand into their far future. This is particularly true for calcs that must be iterated rather than just jumped to. Big difference between, say, multiplying a number by 72,345 versus the need to calculate all 72,344 intermediate results to derive the 72,345th number in the series. There’s also a much different likelihood for error between those two calcs. ---
**Author:** ![Damuri\_Ajashi](https://avatars.discourse-cdn.com/v4/letter/d/898d66/32.png) [@Damuri\_Ajashi](https://boards.straightdope.com/u/Damuri_Ajashi)\ **Post date:** [August 14, 2017, 1:46pm UTC](https://boards.straightdope.com/t/when-was-the-august-21-2017-eclipse-first-accurately-predicted/793456/5 "2017-08-14T13:46:19Z")
> [@watchwolf49](#): > > Here’s an article [“Introduction to the History of Eclipses”](http://www.astronomytoday.com/eclipses/introduction.html); Astronomy Today … > > This doesn’t answer the question, but it does answer how long ago humans _could_ predict eclipses … when someone sat down and calculated when this particular eclipse would happen may have had to wait until the discovery of North America … Does this mean there is a veiwable total solar eclipse somewhere in the world every 18 years or so? If so then why is this one such a big deal? ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [August 14, 2017, 1:57pm UTC](https://boards.straightdope.com/t/when-was-the-august-21-2017-eclipse-first-accurately-predicted/793456/6 "2017-08-14T13:57:29Z")
Given that much of the world is covered by ocean, I suspect that many eclipses aren’t viewable by many people. This one is interesting to those of us in the US because the path of totality covers such a wide path through the continental US. ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [August 14, 2017, 1:58pm UTC](https://boards.straightdope.com/t/when-was-the-august-21-2017-eclipse-first-accurately-predicted/793456/7 "2017-08-14T13:58:05Z")
> [@Damuri\_Ajashi](#): > > Does this mean there is a veiwable total solar eclipse somewhere in the world every 18 years or so? If so then why is this one such a big deal? Actually, there’s two solar eclipses every year … however some are annual and some are seen only over the oceans … also there’s such a narrow band of totality that it’s “rare” for a total solar eclipse to occur _at one specific point_ on the Earth … This eclipse is a Big Deal™ because 36] it’s during summer; 42] it’s occurring over a rather large and populated landmass; 58] the USA hasn’t had a total eclipse for 39-1/2 years and 73] the internet says it’s a Big Deal™ … You may scoff at that point seventy-three, but remember in 1979 we were still kicking around Z-80’s and parity bits … ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [August 14, 2017, 2:36pm UTC](https://boards.straightdope.com/t/when-was-the-august-21-2017-eclipse-first-accurately-predicted/793456/8 "2017-08-14T14:36:37Z")
> [@watchwolf49](#): > > some are annual [Annular](https://en.wikipedia.org/wiki/Solar_eclipse#Terminology_for_central_eclipse), actually. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [August 14, 2017, 3:07pm UTC](https://boards.straightdope.com/t/when-was-the-august-21-2017-eclipse-first-accurately-predicted/793456/9 "2017-08-14T15:07:15Z")
> [@Dewey\_Finn](#): > > [Annular](https://en.wikipedia.org/wiki/Solar_eclipse#Terminology_for_central_eclipse), actually. Is this a correction because “annual” is ambivalent the way “biweekly” is–at least in common speech? (I’m not even sure is “biweekly” or actually has one and only one meaning…) Ie, is it a distinction unique to planetary science, or simple accurate semantics? I didn’t see what was what in the Wiki passage you cited. What I did learn, which was great, was first you get beads and then a diamond ring! \* You had me at tangential… \* ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [August 14, 2017, 3:17pm UTC](https://boards.straightdope.com/t/when-was-the-august-21-2017-eclipse-first-accurately-predicted/793456/10 "2017-08-14T15:17:36Z")
> [@Leo\_Bloom](#): > > Is this a correction because “annual” is ambivalent the way “biweekly” is–at least in common speech? (I’m not even sure is “biweekly” or actually has one and only one meaning…) Ie, is it a distinction unique to planetary science, or simple accurate semantics? > > I didn’t see what was what in the Wiki passage you cited. What I did learn, which was great, was first you get beads and then a diamond ring! \* You had me at tangential… \* Annular means that there’s not a true total eclipse. It has a ring of light around the moon and it’s not nearly as good as a total. Whether an eclipse is total or annular depends on how far away the moon is in its orbit. Its orbit is not perfectly circular, but rather elliptical, so part of the time it’s further away than other times. When it’s further away, it’s annular. There are also hybrid eclipses, where part of the eclipse is total and part is annular. ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [August 14, 2017, 3:18pm UTC](https://boards.straightdope.com/t/when-was-the-august-21-2017-eclipse-first-accurately-predicted/793456/11 "2017-08-14T15:18:33Z")
From [here](https://www.beingintheshadow.com/2013/05/07/annular-versus-total-solar-eclipse/): "I am often asked to describe the difference between a Total and an Annular Solar Eclipse. The key difference is that the Moon is further away from the Earth during an Annular as compared to a Total Eclipse. This gives the appearance of the Moon being smaller in the sky, and it no longer completely covers the Sun. Instead, a ‘ring of fire’ remains – the Sun still emits direct light. Even though the light is greatly reduced, it is still not possible to safely view with the naked eye. Filters must be used throughout. As a result, key features of the Total Solar Eclipse are missing." In short, annual and annular are completely different things. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [August 14, 2017, 3:23pm UTC](https://boards.straightdope.com/t/when-was-the-august-21-2017-eclipse-first-accurately-predicted/793456/12 "2017-08-14T15:23:57Z")
Oh, OK, and thanks. This isn’t even the type of ambiguity I thought. It’s just the same etymology, but it’s the difference between saying my anus is annular and my anus is annual. (FTR, the former.) ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [August 14, 2017, 3:28pm UTC](https://boards.straightdope.com/t/when-was-the-august-21-2017-eclipse-first-accurately-predicted/793456/13 "2017-08-14T15:28:04Z")
Latin anulus = ring (whence the adjective anularis, anulare) annus = year ETA anulus as a diminutive of anus works as proper Classical Latin, sure 🙂 ---
**Author:** ![Duckster](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/duckster/32/1244_2.png) [@Duckster](https://boards.straightdope.com/u/Duckster)\ **Post date:** [August 14, 2017, 3:46pm UTC](https://boards.straightdope.com/t/when-was-the-august-21-2017-eclipse-first-accurately-predicted/793456/14 "2017-08-14T15:46:59Z")
The next annular eclipse across the USA will be October 20, 2023. The next total eclipse across the USA will be April 8, 2024. If you cannot wait that long, the next total eclipse will be July 2, 2019 across the southern Pacific Ocean into South America. > **[Solar and Lunar Eclipses Worldwide – Next 10 years](https://www.timeanddate.com/eclipse/list.html)** > > List of where the next solar or lunar eclipse is visible. Check if you can see it in your city. ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [August 14, 2017, 3:55pm UTC](https://boards.straightdope.com/t/when-was-the-august-21-2017-eclipse-first-accurately-predicted/793456/15 "2017-08-14T15:55:53Z")
> [@Dewey\_Finn](#): > > [snip] … In short, annual and annular are completely different things. Spelting is overratted … ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [August 14, 2017, 4:11pm UTC](https://boards.straightdope.com/t/when-was-the-august-21-2017-eclipse-first-accurately-predicted/793456/16 "2017-08-14T16:11:21Z")
Apparently so are complete sentences and periods. ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [August 14, 2017, 4:57pm UTC](https://boards.straightdope.com/t/when-was-the-august-21-2017-eclipse-first-accurately-predicted/793456/17 "2017-08-14T16:57:10Z")
What an amazing coincidence … that’s the exact same thing every one of my English teachers said to me … I guess it’s true that great minds think alike … ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [August 14, 2017, 5:11pm UTC](https://boards.straightdope.com/t/when-was-the-august-21-2017-eclipse-first-accurately-predicted/793456/18 "2017-08-14T17:11:02Z")
> [@Dewey\_Finn](#): > > Apparently so are complete sentences and periods. The funny part is that **ww49** uses too few of the former and too many of the latter. At least when compared to standard usage. Perhaps that forms a balance of sorts. An odd, off-kilter balance, but balance nonetheless. Like this: [http://thesculpturals.com/imgSC/I%20Ching-v1.jpg](http://thesculpturals.com/imgSC/I%20Ching-v1.jpg). Full of gently moving parts connected in strange ways. 🙂 ---
**Author:** ![Mahaloth](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mahaloth/32/1079_2.png) [@Mahaloth](https://boards.straightdope.com/u/Mahaloth)\ **Post date:** [August 15, 2017, 3:27am UTC](https://boards.straightdope.com/t/when-was-the-august-21-2017-eclipse-first-accurately-predicted/793456/19 "2017-08-15T03:27:15Z")
So what is the oldest reference we can find to Monday’s eclipse? ---
**Author:** ![pulykamell](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pulykamell/32/3166_2.png) [@pulykamell](https://boards.straightdope.com/u/pulykamell)\ **Post date:** [August 15, 2017, 3:44am UTC](https://boards.straightdope.com/t/when-was-the-august-21-2017-eclipse-first-accurately-predicted/793456/20 "2017-08-15T03:44:42Z")
> [@Mahaloth](#): > > So what is the oldest reference we can find to Monday’s eclipse? I’m sure there’s earlier, but let’s start with [1889](https://books.google.com/books?id=E7RAAAAAYAAJ&pg=PA92&dq=eclipse+2017&hl=en&sa=X&ved=0ahUKEwjBh_j1p9jVAhUk6IMKHXU_BkYQ6AEILjAB#v=onepage&q=eclipse%202017&f=false). There’s also [this reference from 1894](https://books.google.com/books?id=qRk4AAAAMAAJ&pg=PA241&dq=eclipse+2017&hl=en&sa=X&ved=0ahUKEwjBh_j1p9jVAhUk6IMKHXU_BkYQ6AEIKDAA#v=onepage&q=eclipse%202017&f=false). Go to page 217. > [@](#): > > But not until early in the twenty-first century will the path of any total eclipse traverse a large area of the United States: then, if the charts of OPPOLZER can be trusted, two totalities near mid-day will occur in the region of the Mississippi; the first of them, 21st August 2017, with a line from Oregon to South Carolina; and the second, 8th April 2024, with a track passing northeasterly from Austin, Texas, to the city of Washington, almost duplicating the path of the eclipse of 1900, and perhaps again exhibiting the spectacle of the corona at Boston. But present enthusiasm for these far-away darkenings of the Sun is naturally feeble. I note that the path of the second eclipse isn’t quite right. It will touch through Austin, but nowhere near DC. It continues up through Indianapolis, Buffalo, barely touches Montreal, and parts of Maine. [Next page](https://boards.straightdope.com/t/when-was-the-august-21-2017-eclipse-first-accurately-predicted/793456.md?page=2)