The problem field of calendars in different cultures

Abstract

Following my presentation of the last ProMath conference I like to present this year another problem field connected with astronomy namely calendars. With a calendar we all are confronted permanent and think of our calendar as a matter of course. But in our global connected world we also hear from other calendars or rhythms, especially in the context of religion. So it is good for children at school to get to know about the background of calendars as well as to fight with problems within the field of calendars. First of all we have to collect astronomical facts and the origin of different calendars. With this we also can see how the problem of time units which are not whole numbers can be brought into special rhythms of whole numbers and how this was managed in history. Moreover we can find out that any rational number can be presented in a rhythm of whole numbers. Secondly we can compute with the Islamic calendar which is a pure moon-calendar and find out why and in which way the Islamic celebrations move in our solar calendar. Furthermore we will discuss the Christian festivities and its differences in catholic/protestant churches and the Russian-orthodox church. Especially we have to work on the problem of determining the date of Easter (the “computus ecclesius” as it was named in the middle ages). Finally we can have a look at the division of the whole world into time zones as well as different phases of the moon and the angular velocity of moon and stars in the night.