Today is a leap day, so here are things you may or may not know about leap years:

1. Every fourth year is a leap year, as a rule of thumb. But that’s not the end of the story. A year that is divisible by 100, but not by 400, is not. So 2000 was a leap year, as was 1600. But 1700, 1800 and 1900 are not leap years. “It seems a bit arbitrary,” says Ian Stewart, emeritus professor of mathematics at Warwick University. But there’s a good reason behind it.

The year is 365 days and a quarter long – but not exactly. If it was exactly, then you could say it was every four years. But it is very slightly less. The answer arrived at by Pope Gregory XIII and his astronomers when they introduced the Gregorian calendar in 1582, was to lose three leap days every 400 years. The maths has hung together ever since. It will need to be rethought in about 10,000 years’ time, Stewart warns. But by then mankind might have come up with a new system.

2. Why is February 29, not February 31, a leap year day? All the other months have 30 or 31 days, but February suffered from the ego of Roman Emperor Caesar Augustus, says Stewart. Under Julius Caesar, February had 30 days, but when Caesar Augustus was emperor he was peeved that his month – August – had only 29 days, whereas the month named after his predecessor Julius – July – had 31. “He pinched a couple of days for August to make it the same as July. And it was poor old February that lost out,” says Prof Stewart.

3. The tradition of a woman proposing on a leap year has been attributed to various historical figures. One, although much disputed, was St Bridget in the 5th Century. She is said to have complained to St Patrick that women had to wait too long for their suitors to propose. St Patrick then supposedly gave women a single day in a leap year to pop the question – the last day of the shortest month. Another popular story is that Queen Margaret of Scotland brought in a law setting fines for men who turned down marriage proposals put by women on a leap year. Sceptics have pointed out that Margaret was five years old at the time and living far away in Norway. The tradition is not thought to have become commonplace until the 19th Century.

It is believed that the right of every woman to propose on this day goes back to the times when the leap year day was not recognised by English law. It was believed that if the day had no legal status, it was acceptable to break with tradition.

4. A prayer has been written by a female cleric for people planning a leap year day marriage proposal. The prayer, for 29 February, asks for blessings on the engaged couple. It reminds them that wedding plans should not overtake preparations for a lifetime together. The prayer has been taken from Pocket Prayers of Blessing by the Venerable Jan McFarlane, Archdeacon of Norwich:

“God of love, please bless N and N as they prepare for the commitment of marriage. May the plans for the wedding not overtake the more important preparation for their lifetime together. Please bless their family and friends as they prepare for this special day and may your blessing be upon them now and always. Amen.”

5. The practice of women proposing in a leap year is different around the world. In Denmark, it is not supposed to be 29 but 24 February, which hails back to the time of Julius Caesar. A refusal to marry by Danish men means they must give the woman 12 pairs of gloves. In Finland, it is not gloves but fabric for a skirt and in Greece, marriage in a leap year is considered unlucky, leading many couples to avoid it…

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(via BBC)