Calendars

The exhibits I planned , related to the wide topic of 'Time', are about calendars, the way they divide the year, and the source of their months' names:





















The Jewish calendar.

A month in the Jewish calendar starts with the new moon- when the moon is not visible at all, and ends with a full moon- when its round shape is fully visible. That way the calendar is based on the moon's movement. However, this creates a problem for Jewish people because the Jewish holidays are based on agriculturist seasons, and months that are determined by the movement of the moon fall on different seasons every year.

Therefore, once every two to three years, the calendar is "fixed" according to the Earth's movement around the sun. In these years an intercalary lunar month is added in order to make the Jewish calendar catch up with the solar division of the year. That is why the Jewish calendar is considered a Lunisolar calendar- based on both the sun and the moon's movements.

The names of this calendar's months are taken from the Babylonian calendar. These names were adopted from the Babylonian religion in the time of the Jews were exiled in Babylon, for example: the month Tammuz is named after the Babylonian god of food and vegetation.

The Jewish calendar is a great example of a lunisolar calendar. By looking at it you can learn a lot about the ways people divide the year and how time can be measured considering the movement of the moon and the Earth. Additionally, you can learn about the interesting sources of the months' names.

The Georgian calendar.

The Georgian calendar is the most popular calendar in the world today. It is based on Earth movement around the sun. Therefore it is considered a solar calendar.

In this calendar there are months with 30 days, months with 31 days, and one month, February, that contains 28 days. Overall, a year in this calendar consists of 365 days and since it is based on Earth's movement around the sun every month falls exactly on the same season every year.

A full year in a solar calendar is supposed to be a complete rotation around the sun by Earth. However, the time of this rotation is a little bit more than 365 days (It's actually 365.25 days). To make the calendar more exact, every three to four years one day is added to the month February so that the year will be of 366 days.

The names of the Georgian calendar's months are taken from the Roman calendar. In this calendar, the months are named after Roman gods, names of Roman Caesars and Roman numbers. For example: the month July is named after Julius Caesar while the month November is named after the Latin word "novem" that means eleven.

This calendar is an example of a solar calendar. You can find a lot of interesting facts by comparing it to the Jewish calendar, such as the fact that both of them intercalate a year every three to four years and the fact that each one of them measures the year, and name the months in a completely different way. It's fascinating how time can be measured differently, isn't it?

sources:
material:
-Wikipedia: http://wikipedia.org/
The Georgian calendar:
http://en.wikipedia.org/wiki/Gregorian_calendar
The Jewish calendar:
http://en.wikipedia.org/wiki/Jewish_Calendar

- http://lib.cet.ac.il/Pages/item.asp?item=14464

Pictures:
- http://www2.kenyon.edu/Depts/Religion/Projects/Reln91/Gender/ROSH%20HODESH.htm

Excellent work, Amir. As always.

Daphna.