"Thirty days hath September,
April, June, and November;
All the rest have thirty-one
Excepting February alone
Which has twenty-eight days, clear,
And twenty-nine in each leap year."

February 29 is a bissextile - the day added to the Gregorian calendar to account for the difference between a solar year, and the typical 365 day calendar year. Over your lifetime, you will see this leap day occur approximately once every 1461 days (once every 4 years). However, over the course of history, Feb 29 actually occurs less frequently - about once every 1506 days. This is because a year is only a leap year if it is:

• divisible by 4 and not divisible by 100
or
• it is divisible by 400

For this reason 1900 was not a leap year, but 2000 was. Over the course of 400 years, this means that there are 97 instead of 100 occurrences of February 29. For information on how all of this started, check out Gregorian Calendar.

### February 29 Birthdays

You may wonder when leap day babies celebrate their birthday. Some celebrate it on February 28, and some celebrate it on March 1. If it is not a leap year, for all legal purposes, it should be celebrated on March 1. Why? Try to get your drivers license when you are 15 going on 16, or try going out for a drink when you are 20 going on 21 when it is February 28 - they will tell you to come back tomorrow. However, it's actually much more tricky than this. While everyone is having pity on these people with leap year births, no one thinks that they too have the same problem.

We all celebrate our birthdays incorrectly

What most people actually celebrate is their birth date. If you consider your birthday to be the day you turn another year older, then on average, you actually celebrate your birthday incorrectly 1/4 to 3/4 of the time (the longer you live, the closer it gets to 3/4). Since a year is 365.2425 days (or as we typically estimate it to 365.25), your birthday actually fluctuates in both date and time.

As an example, look at the first four years of the life of a baby born at noon on January 1, 2000 (a leap year).

```       Assuming                (Incorrectly) Assuming
Age    365.2425 days/year      365.2500 days/year
---------------------------------------------------
00     2000-01-01 12:00:00     2000-01-01 12:00:00
01     2000-12-31 17:49:12     2000-12-31 18:00:00
02     2001-12-31 23:38:24     2002-01-01 00:00:00
03     2003-01-01 05:27:36     2003-01-01 06:00:00
04     2004-01-01 11:16:48     2004-01-01 12:00:00
```

You will notice in column 1, that not only does the date and time fluctuate, but the baby would celebrate two birthdays in one calendar year in 2000, and not have a birthday at all in 2002! A similar occurrence is seen in column 2. It is for this reason that we celebrate birth dates instead of birthdays. However, I digress: using the same logic as above, here is how someone born at noon on February 29, 2000 should celebrate their first 25 birthdays:

```       Assuming                (Incorrectly) Assuming
Age    365.2425 days/year      365.2500 days/year
---------------------------------------------------
00     2000-02-29 12:00:00     2000-02-29 12:00:00
01     2001-02-28 17:49:12     2001-02-28 18:00:00
02     2002-02-28 23:38:24     2002-03-01 00:00:00
03     2003-03-01 05:27:36     2003-03-01 06:00:00
04     2004-02-29 11:16:48     2004-02-29 12:00:00
05     2005-02-28 17:06:00     2005-02-28 18:00:00
06     2006-02-28 22:55:12     2006-03-01 00:00:00
07     2007-03-01 04:44:24     2007-03-01 06:00:00
08     2008-02-29 10:33:36     2008-02-29 12:00:00
09     2009-02-28 16:22:48     2009-02-28 18:00:00
10     2010-02-28 22:12:00     2010-03-01 00:00:00
11     2011-03-01 04:01:12     2011-03-01 06:00:00
12     2012-02-29 09:50:24     2012-02-29 12:00:00
13     2013-02-28 15:39:36     2013-02-28 18:00:00
14     2014-02-28 21:28:48     2014-03-01 00:00:00
15     2015-03-01 03:18:00     2015-03-01 06:00:00
16     2016-02-29 09:07:12     2016-02-29 12:00:00
17     2017-02-28 14:56:24     2017-02-28 18:00:00
18     2018-02-28 20:45:36     2018-03-01 00:00:00
19     2019-03-01 02:34:48     2019-03-01 06:00:00
20     2020-02-29 08:24:00     2020-02-29 12:00:00
21     2021-02-28 14:13:12     2021-02-28 18:00:00
22     2022-02-28 20:02:24     2022-03-01 00:00:00
23     2023-03-01 01:51:36     2023-03-01 06:00:00
24     2024-02-29 07:40:48     2024-02-29 12:00:00
25     2025-02-28 13:30:00     2025-02-28 18:00:00
```

If you couldn't tell, the date format above is YYYY-MM-DD hh:mm:ss (using 24 hour time)

Famous Births