Whats in a Date

Time is a strange thing. But has always been an essential matter for us human beings. Knowing when it is time to plant the crops is still a life or death decision for people in many parts of the world. So having a calendar of some form has been vital for eons.

Gregorian and Julian Calendars

Most of the world uses the Gregorian Calendar which is a christian calendar based on the movement of the earth around the sun and starting from the birth of Christ. However the original calculation of his date of birth was probably incorrect meaning that Christ was actually born around 3 or 4BC. A pretty neat trick if you can manage it.

However the Gregorian Calendar was not the first widely used Christian Calendar. That accolaide goes to the Julian Calendar (named after its inventor Julius Caesar, although once suspects that it was some nameless lacky that actually did the work) which stated that it took the earth 365.25 days to go around the sun. The odd quarter of a day be handled by use of a leap year every four years.

We would be using the Julian Calendar today if it weren't for one tiny snag. It actually takes the earth 365.2425 days to spin around the sun. Consequently all those Julian leap years had shifted the date by about 10 days come the 16th Century. So to rectify this Pope Gregory XIII decreed in 1582 that on the turn of the century there would only be a leap year if the year was divisable by 400. (His lackey was a physician called Aloysius Lilius).

That certainly made things a bit more accurate but we were stuck with the problem of what to do with those extra ten or so days.

The solution was simple, at first sight, we simply chopped them out so the day after September 13th was September 24th. Nice and straightforward, well it would have been but then entire world didn't do it at the same time. Most had changed by the end of the 18th century but there were still some places using the Julien Calendar right into the 20th Century.

Islamic or Hajri Calendar

Although the calendar of international use, the Greogorian is not the only calendar in use today.

Throughout parts of the Muslim world they use the Islamic or Hijri Calendar. This also has twelve months in the year but each month is denoted by the passage of the moon. As this takes roughly 29.5 days it actually means that the Hihri year is about 11 days shorter than the Gregorian one. Naturally the first year in the calendar is not related to the birth of Christ but to the date when Mohammed emigrated to Medina (AD 622). So 2005 (Gregorian) is 1426 or 1427

Jewish Calendar

There is also a Jewish calendar which is used for religious purposes and is the official calendar of Israel. This calendar is based on the movement of both the moon and the sun. Its months are based on the passage of the moon in the same way as the Hijri calendar with each month being 29 or 30 days long. But to adjust for the sun the have a Leap month every three years. There are some other wrinkles to this which is beyond the scope of this site, but there are some quite complex (and slightly bizarre) rules to actually determine the start of a year and how many days are in it.

The base date for the calendar is the begining of creation 3761 BC (we'll ignore a few billion years before that after all what does the fossel record prove!). This means that sometime during 2005 the Jewish year 5766 began.

Chinese Calendar

The chinese calendar like the Jewish one bases itself on both sun and moon and the concept of leap months. Its rules for calculating the length of a year is again subject to complex, although different rules.

The calendar is believed to have been invented by Emperor Huangdi in 2637 BC (Name of Lackey unknown). It is this year that is used as the base date, however technically the chinese calendar doesn't count years as most other calendars do. Instead it breaks time into 60 year periods, each year having two named components; the Celestial Stemm (there are 10 of these) and the Terrestrial Branch (there are 12 of these) which many people will be familiar with as they are named after animals (year of the Rat, year of the dog etc). Combining these two components gives 60 unique names. So for example the first year is Jia-zi (zi is Rat), the second is Yi-chou (chou is Ox). The eleventh year is jia-xu (xu is dog) and the thirteenth is bing-zi (Rat again).

Persian Calendar

The Persian calendar, which is used in Iran and Afganistan, is essentially the islamic calendar but solely based on the sun. Consequently each year has 365 or 366 days in it like the Gregorian calendar, although new years day is around the 18th of September. Its base date is the same as the Hajri calendar but because it is solar based like the Gregorian Calendar the date is simply the current year minus 622, hence 2005 is 1384.

Other forms

There are many other forms of calendar some still in use, some lost in the midst of time, such as the three parallel date systems of the Mayan world or the Revolutionary French calendar that attempted to decimalise the week. (There were 10 days in a week, so you had to wait nine days for a weekend, and they wondered why it was unpopular).

So you see time is different things to different people in different cultures. According to Einstein because the speed of rotation at the equator is faster than the speed at the poles, time actually runs faster there - and I thought it was just my watch!