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.
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.