A solar year is the time it takes the earth to go around the sun…but a calendar year has not always been equal to this time. In 4236 BC Egyptian astronomy was so accurate that the time the Earth takes to go round the sun (a year) was determined as exactly 365 1/4 days. The Romans were not so sure. They thought a year lasted 304 days, but changed their minds in 700 BC and decided a year lasted 355 days. Finally, on the 1st January 45BC they used the Julian Calendar (named after Julius Caesar) using a year of 365 1/4 days. This system included the idea of leap years. Unfortunately because they had been using a different calendar the months and the seasons no longer matched up, so, for that year alone, they added another 80 days! Are you confused? They certainly were, and 45BC was known as the "Year of Confusion"! Unfortunately the Julian Calendar was not completely accurate. It was 11 minutes and 14 seconds too long! Which was unnoticeable at first, but over the years caused quite a problem. So in 1582, Pope Gregory deleted the dates 5-14 October to bring the year back on track. He then introduced a sophisticated compensating scheme, involving leap centuries. (Yes we did say ‘leap centuries’. Unless the century is divisible by 400 it's NOT a leap year, even if it's divisible by 4. So there’s no extra day… Are you keeping up?!) We didn’t use this Gregorian Calendar in Britain until 1752, by which time we were 11 days short and had to skip the dates 3-13 September. It wasn’t until 1st October 1949 when Mao Zedong agreed that China would follow the Gregorian Calendar that the whole world worked on the same calendar. And you thought that time differences were complicated! Actually the Gregorian Calendar is off from the true solar year by almost 26 seconds per year. We’ve all heard of leap years, but did you know leap seconds exist too? Nowadays the calendar is controlled by inserting and subtracting leap seconds where necessary. How’s this done? The scientific community decides every six months if we need another second, and the ‘extra’ seconds occur at midnight GMT on 30th June or midnight on 31st Jan. But there won't be one this year - the last was Dec 31st 1998. There are 61 seconds in a minute carrying a positive leap second. This occurs at the same instant throughout the world, as the six pips on the radio time signal turns to seven.

	Why not make your own Science Calendar.
	Search the internet for science pictures, or you could take your own photographs of science objects or some home experiments. Print out 12 one for each month and make your own custom Calendar.