Posted by: bkivey | 29 February 2012

Leap Day

Today is Leap Day, the quadrennial adjustment made to keep the calendar synchronized with the seasons. Without this modification, the equinoxes and solstices would slowly drift from their appointed places, although at a difference of eight days every thousand years, it would take a while to notice.

Besides those who only get to celebrate their ‘real’ birthday every four years, I considered what regular events might occur on Leap Day, and how rare they might be. Let’s look to the sky for a little fun and education.

My first curiosity was how often a ‘blue moon’, the second full moon in a month, might occur on February 29th. The answer is: never! Because the time required for the moon to cycle through it’s phases is 29.5 days as seen from Earth (synodic period), even if the first full moon of February occurred at midnight on 1 February, the next full moon would take place at noon on 1 March. If you were to observe the moon from outside the Earth-Moon system, you’d notice that the time between full moons was 27.2 days (sidereal period), so it would be possible to observe two full moons in any given month, whether or not it was a leap year.

OK, we’re never going to see a blue moon in February, what about a lunar eclipse on 29 February? Things are a little more promising here. Lunar eclipses are fairly common, with between 4 and 7 visible from Earth in any given year. There will be four visible from North America between 2014 and 2015 alone. As for lunar eclipses on Leap Day, things aren’t so great. This handy list  gives all of the lunar eclipses from 0 – 3000, although there wasn’t any Year 0.  There are 3 lunar eclipses on the day in the 3000 year period, two of which are total. There haven’t been any Leap Day total lunar eclipses since Year 1, and the only two on 29 February will occur in 2268 and 2640.

Lunar eclipses are fun to watch, but what about solar eclipses? The next one visible from the US will occur on 21 August 2017. The bad news is that in a 3000 year period there are no total solar eclipses on 29 February. If you’re willing to settle for an annular eclipse, where the Moon obscures the sun but is too far away to occlude it, then you could have seen ones in 648 and 1188 on the 29th. The next Leap Day annular solar eclipse will occur in 2044.

Today in History!

1504Columbus uses a lunar eclipse to frighten hostile Jamaican Indians

1908 – Dutch scientists produce solid helium

1940 – “Gone with the Wind,” wins 8 Oscars

1940 – Hattie McDaniel becomes 1st black woman to win an Oscar

1960 – 1st Playboy Club, featuring bunnies, opens in Chicago

1964 – NC high school basketball teams play to 56-54 score in 13 overtime

1968 – 1st pulsar announced (CP 1919 by Jocelyn Burnell at Cambridge)

1968 – Beatles’ “Sgt Pepper’s Lonely Hearts Club Band” wins Grammy






  1. Now how many of those leap day lunar eclipses were/ will be during a full moon?

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