Vicky Rauch enlightened me a little today. In reality, the length of the year is closer to 365.2421897 days, and that's if you are measuring the mean distance between equinoxes, which is probably a good idea so that seasons stay intact. With this figure in mind, it has been calculated that we only need to have 97 leap years every 400 years! So, that's what we do. We, in fact, skip the leap year at the turn of the century 3 out of every 4 times. So, 2000 WAS a leap year, but 2100, 2200, and 2300 will not be. Cool.

But, here's a question, because surely even this system will not be entirely accurate:

**How long will it take before the calendar will be off by a full day, despite our leap year alterations?**And for all you scientists out there, the tropical year (measurement based upon equinoxes) varies slightly from the sidereal year (measurement based upon earth's orbit in relation to fixed stars).**How would the calendar change if it was based on the sidereal year (****365.256363004 days)****?**And dare I even mention that the tropical year varies slowly as the years progress? The calendar is such an easy thing to take for granted!

Some fascinating classroom discussion and fabulous mathematics work might just ensue on Wednesday. Happy Leap Day!

Emily, I'm glad that we mathematicians can learn from each other. I have had more blog views on this posting than on any other. You are not alone in thinking that leap year occurred every four years. Together, maybe we have enlightened the world!

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