Thirty days has September,

April, June and November.

All the rest have 31,

Except for February alone,

To which we 28 assign

Knowledge of Leap Year comes first in early childhood, or so it was with girls of an earlier generation, who were advised: &uot;This is Leap Year.

That means you may ask your sweetheart to marry you; you may telephone a boy; you may invite one out on a date.&uot;

The reason for this short-term reversal of usual lady-like behavior was never explained, nor are statistics available on how many young women took advantage of the opportunity each Leap Year..

Those of a certain age may recall the miles that Daisy Mae chased Little Abner across cartoon strips in newspapers and comic books.

To this day, many remain convinced that her unbecoming behavior was the result of Leap Year, even in &uot;Hill Billy Land.&uot;

Actually, the reason for Leap Year is to keep the solar year in time with the sidereal day, which is another way of saying that the time it takes for the earth to rotate on its axis (a day) does not divide evenly into the time it takes for the earth to revolve around the sun (a year).

So, an extra day is required every four years to make up the difference.

The Julian calendar, instituted by Roman Emperor Julius Caesar, was simpler on first glance, with a 365-day ordinary year and a 366-day leap year every four years.

In the original Julian calendar, the months had either 30 or 31 days alternating. February had either 29 or 30 days depending on whether it was a leap year.

When Augustus became emperor after the death of his uncle Julius Caesar, he wanted a month named after himself, so he stole another day from February to give his month 31 days as his uncle had done with his own month.

Unfortunately, this gave a mean year length of 365.25days, not a very large error. But the error builds up and by the 16th century a new calendar was established in Roman Catholic countries under the authority of Pope Gregory XIII.

According to the Gregorian calendar, the civil calendar used today, years evenly divisible by 4 are leap years, with the exception of centurial years that are not evenly divisible by 400.

The years 1700, 1800, 1900 and 2100 are not leap years, but 1600, 2000 and 2400 are

In 1582 the date October 4 was followed by October 15, a correction of 10 days. When non-Catholic countries, such as Great Britain and America, adopted this Gregorian calendar in 1752, the difference had become greater than 10 days. Another change had to be made.

Incidentally, many of the calendar changeovers elicited strong emotional reactions from the populations involved. People objected to &uot;losing 10 or more days&uot; of our lives.

The present Gregorian calendar rule for leap years gives 97 leap years in 400 years.

In three thousand years the error will have built up to a full day, and another reform will be necessary.

Various schemes have been proposed, including account of the changing length of the day or the tropical year, but none has been internationally recognized.

With no obvious need to make a correction now, the solution is best left to the world’s descendants.

Information for this article came from U.S. Naval Observatory, Astronomical Applications Department, and from an article by Chris Mastrangelo, of Washington, D.C.