"Thirty days has September, April June and November. All the rest have 31," the famous rhyme goes.
Except February alone. Which has 28, except in leap years, such as this year, when it has 29.
And today is Feb. 29.
What's wrong with February, anyway -- messing up a perfectly good poem with its weird number of days.
The month isn't all bad. There's Valentine's Day for lovebirds. Two of our greatest presidents were born in February -- Abraham Lincoln and the father of our country, George Washington. Plus, February is Black History Month.
Still, it's a little strange, this shortest of all months trying to squeeze in one more day every four years.
What's that all about?
Leap Day is all about science. "Leap Day," explains astrophysicist Neil deGrasse Tyson, "is the result of a simple fact that the time it takes the Earth to go around the sun is not evenly divisible by what we call a day."
Tyson says that, while the calendar says it takes 365 days for the Earth to orbit the sun, in fact it takes slightly longer than that: almost 6 hours longer, or one quarter of a day.
"Now, you can't stick a quarter of a day on the calendar, that just doesn't work," Tyson adds. "So, you pocket that fraction of a day and you wait how many years? Four years, for four of these quarters to add up. You got a whole day, put it back in the calendar."
Leap Day was created by none other than Emperor Julius Caesar, who realized that the calendar was slipping. But he added too many leap days. Fifteen hundred years later, Pope Gregory XIII corrected Caesar's error, and boom, the modern Gregorian calendar was born.
"If you didn't have these leap days correcting for things," Tyson points out, "the first day of spring would start marching around the calendar and would show up in the summer, and in the winter."
With seasons aligned and the calendar correct, a new category of person was created: "leap babies."
CBS News brought together a group of leapers - all adults. But, since their birthday comes only once every four years, they say:
"I'm Arielle (Feit)and I'm 6."
"I'm Randy (Zavattieri ) and I'm 13."
"I'm Sherri (Riddle), I'm 11."
"I'm Genevieve (Primus) and I'm 12."
"I'm Brianne (Lutz) and I'm 7."
Randy says he's "13, but I'm already losing my hair."
Says Arielle, "My parents actually started a tradition ... they used to wake me up at a minute to midnights and they would say 'Happy Birthday' really quickly as it turned midnight, and give me a bite of ice cream cake, and I'd go back to sleep."
There is a real kinship among Leap babies.
"We have that special connection," says Brianne.
"We have a unique personality -- we're very energetic, very friendly, very outgoing, fun, loving, and we love to party!" Genevieve said with a laugh.
All raised their hands when asked who feels special because they were born on Leap Day. They're really proud of Leap Day and really do share a bond.
They say the toughest thing about being a Leap baby is they always have to answer the same question: When do you celebrate your birthday? Some celebrate Feb. 28 in non-leap years, and some wait until March 1.
So, Happy Birthday, leapers -- all five-million of you.
To see Seth Doane's report, click on the video in the player above.