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Star Gazing: The little known facts surrounding leap years

Snow blinding micro-Moon will be in the sky this month, and why we could be without a leap year at the end of the century
The Great Orbax.

Each month, GuelphToday will share a Star Gazing Guide presented and organized by The Great Orbax, a science communicator from the University of Guelph's Department of Physics and local science education advocate.

Greetings Star Gazers!

Orbax here.

I’m a Science Communicator from the Department of Physics at the University of Guelph and I’m here to fill you in on what our February night skies hold for the Astro-curious out there, young and old.

In this month’s video we chat about some lesser-known constellations, discuss the snow blinding micro-Moon and even spot four of the visible planets hanging out alongside our Moon. 

There’s something else though about February that has always had me a little confused, and that’s leap years.

Now don’t get me wrong, I understood the basic concept of leap years and leap days but I didn’t really ‘get’ how important it was to toss that 29th day onto February until I learned some more about it.

To start with, we define a day as the time it takes for the Earth to complete one full rotation on its axis, and we define a year as the time it takes for the Earth to complete one full orbit around the sun. We say that this takes 365 days, but it actually takes 365 days and six hours to get all the way back to where we started in our orbit. 

This means that instead of celebrating New Year’s at midnight on the 31st, it should actually be at 6 a.m.! Now that doesn’t really make much sense so after four years we’ve saved up enough time to add an extra day, which we pop on to the end of February and call it a leap year.

But wait, it’s not quite that simple. When I said it took 365 days and six hours to complete our circumnavigation around the Sun, I was rounding off to make things easy. It actually takes 365 days, five hours, 48 minutes and 46 seconds. That means that every four years, we’re 45 minutes short of that extra day we added, and over the course of 100 years we end up a whole day shorter! We manage to fix this shortcoming by cancelling our leap year every 100 years.

But hey, why stop there?

It turns out that rounding off hurts us again and overcorrects the situation, and so every 400 years, we need to add that leap day back in and have a leap year again. This means that in the year 2000, we had a leap year and we thought that was just normal. Another four years had passed. But it was truly rare since we did not have a leap year in the year 1900, or 1800, or 1700…or going the other way we won’t have one in 2100, 2200, or 2300…not until 2400!

Seems confusing right? So why do we even bother? Well, if we didn’t bother with this small – and pedantic – correction, then the seasons would shift throughout the calendar year. As a matter of fact, in just the span of 700 years, the summer that we currently experience in June would shift to December!

I hope you enjoy this month’s Star Gazing Guide. If you want to learn more, check out the February Star Gazing Guide video on the Guelph Physics YouTube channel. Not only is Star Gazing a great way to learn about space, planets and the stars, but it’s also a great way to spend time with other curious minds.

And hey if you’re interested in Star Gazing, you should join us in our inflatable planetarium on February 17th and 18th on campus at the University of Guelph for some FREE planetarium shows as part of the Curiosity Carnival. You’ll need to sign up in advance though so go here for more information.

Until next month I wish you clear skies and I hope you take some time… to look up.


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