The American folk singer Lee Hays used to say that in the farm country where he grew up, a family might have only two books in the house: The Bible, to prepare them for the next world, and an almanac, to help them through this one. Even today, almanacs — though less authoritative than they once were — retain a place in American life, especially rural life. Published annually, they typically offer a wide array of information about the coming year: timetables for the rising and setting of the sun and moon, for the tides and the constellations, and for eclipses and meteor showers, along with dates of moveable holidays and feast days. But an almanac is more than a calendar. It’s a book for predicting the future — certain aspects of it, anyway.