View source for Lesson:What Is a Leap Year?/ExerciseL1

==Listening Exercise==

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{Watch the video and complete the text according to what you can understand.
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You probably { know _4 } that this year 2012 is a leap year. And that means that this year we get an { extra _5 } day on February, 29th. So instead of having 365 days this year, there will be 366. Great! An extra day, who really cares? Well people born on February, 29th on some { previous _8 } leap year, also known as leaplings, they care, because they { finally _7 } get to celebrate their real birthday. But, for the rest of us it's just a day like any other day. Whoopdy doo. So, why do we go to all the { trouble _7 } to have a leap year? Well, I'll { explain _7 }, now we all understand that day. One full day is { actually _8 } how long it takes for the Earth to spin around exactly once. And a year is how long it takes for the Earth to orbit the Sun exactly once. So while the Earth orbits around the Sun in a full year, it spins around three { hundred _7 } and sixty five point two five times. In other words, one full year { equals _6 } 365.25 days. This is called the { astronomical _12 } year. But here is the problem, our calendar year is only 365 days and that's because there's { really _6 } no way to have a .25 day. And so those extra .25 days they just keep { accumulating _12 } and what they do is make it so that the stars { slowly _6 } drift out of sync with our calendar. So this is where leap year comes in to save the day. Every year we set aside those .25 days until the { fourth _6 } year when they equal one full day. And then on the fourth year we put that extra day on February 29th , then we call it leap day. Bamm, we're back in sync. That's why February, 29th exists. Cool! But the real { interesting _11 } thing, is how we humans figured this all out. It really was the { Egyptians _9 }, who first figured out leap year.<br>

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They noticed by { watching _8 } the stars, specifically the Sirius star. That the astronomical year was actually 365.25 days and they { noticed _7 } this by seeing the Sirius star slowly drifting out of sync. But the western world wasn't so fast to figure this all out. It wasn't until many centuries later when Julio Cesar with the help of an astronomer, discovered just like the Egyptians first did that a year is really 365.25 days and they { created _7 } the Julian calendar with the leap year that we know and love to fix that problem. Well done Julius! Well, not so fast. You see, if you want to get really exact about it, the astronomical year is actually 365.2422 days which is 11min. 14 sec. { shorter _7 } than the Julian calendar. And that means in a hundred and twenty eight years from now, if we use the Julian calendar, we'll be { off _3 } again by one full day. So today, we use a { revised _7 } version of the Julian calendar.<br>
It's called the Gregorian calendar because pope Gregory { initiated _9 } it. The Gregorian calendar is just like the Julian calendar, but it has got a few more rules, so while every fourth year is a leap year. Every year that's { divisible _9 } by 100 are now no longer leap years. That means that years 1700, 1800, 1900 those were not leap years even knowing they { normally _8 } would be. And here is another rule, if the year is also divisible by 400, then it is still a leap year. Which means that the year 2000 that was a leap year. And without those complicated { rules _5 }, our calendars can stay in sync with the star for millennia to come. But, one more thing. Did you know that the Earth's { rotation _8 } is slowing at a way of .005 seconds per year? And that means in about two { billion _7 } years we're gonna have to add one more leap year to { keep us _7 } in sync. But don't worry we've got { plenty _6 } of time to revise the calendar and fix that.
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