Earth and beyond

spinning and orbiting Earth

days and years

a good calendar

the best calendar so far

a simple, but bad, calendar

a good calendar

Serious thought about calendars started way back in Julius Caesar's time. Fortunately Caesar had a smart science advisor, called Sosigenes, who answered the vital question and worked out what the real length of a year was.

Sosigenes worked out that the real length of the year (the Earth's orbit around the Sun) was very close to 365.25 days. Obviously we can’t have one quarter of a day in our calendar, but what if our calendar had exactly 365 days?

after one year it would be only 1/4 of a day behind the Earth's real position in space	after two years it would be 1/2 a day behind the Earth's real position in space	after three years it would be 3/4 of a day behind the Earth's real position in space

BUT

after 4 years it would be almost exactly 1 whole day behind.

To stop it slipping any further he thought ‘why not stick an extra day into the calendar for that year?’ No reason at all, let’s do it! We now call that extra day February 29th and call the year a leap year! This was a great, and very accurate, solution. The new calendar was called the Julian calendar and it worked fine for hundreds of years.



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