Speaker 1: Welcome to Brainstuff from house Stuff Works dot Com, where
Speaker 1: smart happens Him Marshall Brain with today's question, why are
Speaker 1: leap years so weird? For example, how could the year
Speaker 1: two thousand be a leap year when nineteen hundred was not.
Speaker 1: We all know that February is a funny month to
Speaker 1: begin with. Every four years it has one extra day,
Speaker 1: February twenty nine instead of the normal twenty eight days.
Speaker 1: When February has twenty nine days, we call it a
Speaker 1: leap year. The year two thousand was a leap year,
Speaker 1: but nineteen hundred was not, and neither eighteen hundred nor
Speaker 1: seventeen hundred were leap years either. But seventeen hundred, eighteen hundred,
Speaker 1: nineteen hundred, and two thousand are all divisible by four,
Speaker 1: So why aren't they all leap years? And why do
Speaker 1: we have leap years in the first place. Let's start
Speaker 1: with the concept of a year. We define a year
Speaker 1: to be the amount of time it takes for the
Speaker 1: Earth to make one complete orbit around the Sun. The
Speaker 1: reason we care about our orbital position around the Sun
Speaker 1: is because of the seasons in the northern hemisphere. We
Speaker 1: expect summer weather to occur around June, July, and August,
Speaker 1: and winter weather to occur in December, January, and February.
Speaker 1: A normal calendar year is defined as three hundred sixty
Speaker 1: five days. However, if you measure the exact amount of
Speaker 1: time it takes for the Earth to orbit the Sun,
Speaker 1: the number is actually three hundred sixty five point two
Speaker 1: four to two days. By adding one extra day to
Speaker 1: every fourth year, we get an average of three hundred
Speaker 1: sixty five point to five days per year, which is
Speaker 1: pretty close to the actual number. To get even closer
Speaker 1: to the actual number, every hundred years is not a
Speaker 1: leap year, but every four hundred years is a leap year.
Speaker 1: That brings the average length of the year to three
Speaker 1: hundred six five point two four to five days, which
Speaker 1: is very close to the actual number of three sixty
Speaker 1: five point two four to two days. The remaining corrections
Speaker 1: are added with things like leap seconds. Putting all these
Speaker 1: rules together, you can see that a year is a
Speaker 1: leap year not only if it is divisible by four.
Speaker 1: It also has to be divisible by four hundred if
Speaker 1: it's a centurial year. So seventeen hundred and nineteen hundred
Speaker 1: were not leap years, but two thousand was Do you
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