Jewish Calendar

bimjob has it right. A year is defined as the amount if time it takes for the earth to complete an orbit around the sun. But, the rotation of the earth (days) is not exactly synchronized to that.

So, let’s mark a spot in the orbit as the exact position of the earth at 12 midnight on jan 1 2009. When we reach that same exact spot next time around, it will not be 12 midnight jan 1 2010, it will be roughly 6am jan 1 2010, and the time after that that the earth hits that exact spot, it will not be 6am jan 1 2011, but roughly noon jan 1 2011. So every 4th year, we add an extra day to compensate for these extra 6 hour periods.

…the real story is more complicated than that, because it isn’t exactly 6 hours, and because the orbit of the earth changes over time. As a result, we also have ‘leap seconds’ from time to time, as well as very rare missing leap days.

It would be easier if we just gave up the idea of calendars altogether and just kept track of time. This is what basically happens in computer science, where (in the post 2000 bug days) time is tracked based on the number of seconds since some arbitrary known time (known as an epoch). Sadly, as a result of lack of forsight very similar to that which caused the millenium bug, we will be dealing with that type of issue again in 2038.

For those of you still around then, start investing heavily in IT stocks starting around 2030, and sell right around 2038 for a handsome profit. I accept tips for my tips, ;)

In a full year there are 365 days and 6 hours. so every 4 years those 6 hours each year add up to 24 hour which is another day hince why we have a leap year.

All calendars are mans attempt to put order on something that could not care less. The earth takes an amount of time to go around the sun, and that amount of time is not evenly divisible by 24-hour days. So the slight excess is allowed to accumulate until there is enough to make an additional day. This would be true with any calendar.

Even a ‘24-hour day’ is a bit wrong because the speed of the earth’s rotation varies with its distance from the sun (and other factors). As does the speed of earth’s revolution around the sun. (Don’t get started on leap seconds.) Aren’t you glad we don’t have to worry about anything other than remembering 1 day every 4 years? (And for you purists, I know that the year 2100 will NOT be a leap year. ;))

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