I am a novelist working on a new book, titled Werewolves In The Christmas City, which happens to be Bethlehem, Pa. In 2010 when I was working on a book titled The Christmas City Vampire, a lunar eclipse on the Winter Solstice occurred. As you know it was the first one since 1638. On the 2010 occurrence, I added the resurrection of two werewolves-twins-turned during that eclipse of 1638. My question is: How would my professor character figure out that the event will occur in 2010. The time frame I am in right now is 1947. I would appreciate any help you can give me. Math is certainly not one of my strong suites.

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    $\begingroup$ Possible duplicate of What is the formula to predict lunar and solar eclipses accurately? $\endgroup$
    – James K
    Sep 22, 2016 at 19:31
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    $\begingroup$ @JamesK This may be a different question. Larry is specifically asking how his character who lives in 1947 might perform these calculations. They obviously can't just call up NASA. I think the crux of this question is not so much how to do the physical calculations, but rather how someone from the 1940's might go about learning/finding the information to even do the calculations. Correct me if I'm interpreting your question incorrectly Larry. $\endgroup$
    – zephyr
    Sep 22, 2016 at 20:06
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    $\begingroup$ @zephyr This question and the question I linked ask how eclipses are predicted. The answers given describe the process. The second answer, for example describes using Bessellian elements. How would the Prof predict a 2010 eclipse? He would use the methods described in the linked page, hence a duplicate. The linked page doesn't suggest calling up nasa. It uses Nasa a convenient reference. The prof would know this method because he is a professor. The calculations don't require electronic computation. $\endgroup$
    – James K
    Sep 22, 2016 at 20:19
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    $\begingroup$ I assume you're aware of the ephemerides published prior to 1947, and none of them have what you want? If not, search books.google.com for "ephemeris eclipses" (no quotes), books in the 20th century ordered by date and jump to page 5 or 6. The journal "Popular Astronomy" and the "The American Ephemeris and Nautical Almanac" may have this information even as early as 1947. USNO has been publishing yearly ephemerides since the 19th century. $\endgroup$
    – user21
    Sep 23, 2016 at 21:52
  • $\begingroup$ I do not know anything about this subject. What I would like is if one of you could pretend you are my learned professor in 1947 and explain to me how you determined that the lunar eclipse of 12/21'2010 would occur on the Winter's Solstice. $\endgroup$ Sep 24, 2016 at 21:45

1 Answer 1


A university library in 1947 might have a copy of T. von Oppolzer, Canon der Finsternisse (1887), which lists those lunar eclipses on pages 368 and 374. A reader with a working knowledge of astronomy could make sense of the tables even if not proficient in mathematics or German.

If that reference were not available, a text such as R. Buchanan, The Mathematical Theory of Eclipses (1904), would equip the professor to work it out from scratch. As lunar eclipses are visible from the entire night hemisphere, they are simpler to compute than solar eclipses, which are total only along a narrow path.

Eclipses recur in saros cycles of 18 years and 11.3 days. Given dates of some contemporary eclipses, one could trace saros 119 back: 1945-06-25, 1927-06-15, ..., 1638-12-21; or trace saros 125 forward: 1938-11-07, 1956-11-18, ..., 2010-12-21. The saros numbers were not assigned until 1955, but the cycles were known to ancient astronomers.

  • $\begingroup$ It might be more fun if the protagonist was able to sneak into Bletchley and run his calculations. $\endgroup$ Sep 23, 2016 at 14:29
  • $\begingroup$ My book takes place mainly in Bethlehem, Pa from 1638 to 2015. I would like my professor character to tell another professor how he went about finding that the eclipse would be on 12/21/10 in laymen's terms. ie: What I did was to use this formula, whatever that formula is, to determine the exact date. Could one of you please explain it to me in this manner. Thanks. $\endgroup$ Sep 23, 2016 at 21:37
  • $\begingroup$ Thank you all. I like Mike's answer, however the setting is 1947 not 1955. Saros 119 does not show the 2010 eclipse. What I would really like is for the professor to tell my professor how he came about with 12/21/10. If one of you could explain this in laymen's terms, I would be grateful. Thanks. $\endgroup$ Sep 23, 2016 at 21:45
  • $\begingroup$ Updated, hopefully clarified. $\endgroup$
    – Mike G
    Sep 23, 2016 at 23:18

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