IU Cygni is a 31-day
Cepheid with a period that varies strongly.The Maria Mitchell data for 1978-1990 are satisfied by these
elements: JD_max = 2446129.322 + 31.183 E + 0.00066E^2.This implies a period increasing at an
average rate of 0.00049+-0.00009 cycle per year.Representation by one or more abrupt changes during these
years is also possible.