leap years

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elderford E
elderford Mar 25, 2006 17:31:02
Replying to tuesday

Leap years are to do with keeping the "proper names and dates" of each month in the right place.

Every four years each day would slip back one day.

So in eight years you'd be two days out and so on.

So every 100 years (bear with me, I'm doing this in my head) the calendar will slip 25 days or so (call it a month, so every month would be a month out of wack (?)

So, in 600 years Christmas would be in Summer (?)

THAT SAID
If prehistoric people essentially want to know when to plant and harvest crops, the actual day is unimportant. March 3rd could infact now be December the 5. The date given to the day is not important. Its position in relation to a lunar and solar cycle is much more relevant.

Much of our calendar is to do with the working out where Easter falls as it is a moveable feast unlike say Christmas Day. although that also is based on lunar events and counting days (not including Sundays I believe), to correctly celebrate Lent, Good Friday, Palm Sunday, etc.

F FourWinds
FourWinds Mar 25, 2006 18:02:21
Replying to elderford

"Much of our calendar is to do with the working out where Easter falls as it is a moveable feast unlike say Christmas Day. although that also is based on lunar events and counting days (not including Sundays I believe), to correctly celebrate Lent, Good Friday, Palm Sunday, etc."

Yep. Much of calculus was driven by this need, yet I could never see entirely why. The date for Easter could easily be worked out using a stone row aligned east-west. Easter Sunday is always the first Sunday after the first full moon after the Vernal Equinox. So, once you know when the Equinox is (with the help of your stone row) you can work out when Easter is.

I would imagine that the original pre-Ctristian feast was on the day of the full-moon or the day after.

C Cursuswalker
Cursuswalker Mar 26, 2006 15:32:51
Replying to elderford

To summarise:

Every 4 years we add a day to the year, making it a leap year.

Without this the seasons would slip by one day through the calendar every four years.

Every century we miss out a leap year, in order to correct the smaller error in the other direction created by leap years.

Every 4 centuries we still have the leap year at the turn of the century, in order to correct the even smaller error back in the original direction created by missing out a leap year every century. We call this a leap century.

There was one in 1600 (Or should have been). there was also one in 2000.

I have no doubt a further correction will be needed eventually, possibly by missing out a leap century in the year 12000, assuming that the corrections have to alternate by a factor of 4 then 25.

But then again, by then we may be able to steer the Earth and will have gone over to a decimal calendar :-)

S Steve Gray
Steve Gray Mar 28, 2006 15:21:26
Replying to elderford

Maybe they didn't try to divide the year up into fixed pieces like we do. Maybe they related everything to the solstices and equinoxes and then to the lunar cycles and then to days. In other words you might plant a particular crop on the third day after the second full moon following the spring equinox. So variations in the length of the year would be essentially irrelevant.

The relationship of the lunar cycles to the equinoxes, however, might seem quite mysterious and perhaps that was what gave rise to the need for religious interpretation and the construction of stone circles.

I like J R R Tolkien's Hobbit calendar. Every year has 13 months of 28 days, so days of the month always fall on the same day of the week. That accounts for 364 days. New Year's Day is a special day that's independent of the weekdays and every fourth year there's an extra "leap day" that follows after New Year's Day.