Åk 6–9

1.3 Old Measurements of Time
Man has for a long time had a need to orient himself in time.  The seasons came and when and influence life.  In Sweden, for example, there was such a large difference between the dark and the light hours of the year that people needed to accommodate their work to them.

It is not at all clear how you calculate time during a year or when a new year begins.  Around the world, different calendars have been used that have a little different ways to calculate months and year.

In the Persian calendar, the year begins at the spring equinox.

In the Muslim calendar, a month is as long as it takes for the moon to go one rotation around the Earth.  A moon rotation is a little short than 30 days and because of this Muslim year is 354.3 days.

Most countries use what we call the Gregorian calendar.  In this calendar, the year is 365 days with an additional leap day every fourth year.  It was adopted in Rome in 1582, and in Sweden it was introduced in the year 1753.

Today, the Gregorian calendar is used as well in China, but they have at the same time kept the old chinese calendar to do calculations for holidays, like for example the Chinese New Year and the time for the moon festival.  It is also used in astrology.