This is a 15-year cycle. It was orginally started for the purpose of fixing the tax for a set number of years. It was originally a 5-year cycle under Diocetian and was increased to 15 years under Licinius. The indictio has no relation to astronomical phenomena. Almost any edition contains a section on tables and rules for finding the date of Easter.
Most libraries have the Book of Common Prayer.
You can also find it in the pew racks of any Episcopal Church. No English-speaking Christian should be without a copy of the Book of Common Prayer.