Not All Seasons Are Created Equal : Krulwich Wonders... Seasonal equinoxes and solstices seem to divide the year into four equal parts, but if you live in the Northern Hemisphere, summer is five days longer than winter. A quick trip around the sun explains why.

Not All Seasons Are Created Equal

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From NPR News, it's DAY TO DAY.

Well, you've waited and you've waited, and now, at last, the crocuses are croaking, the frogs are croaking, the daffodils, the grass peeping through. Finally, it's spring. It feels like it was a long time coming. But not so, says NPR's Robert Krulwich.

(Soundbite of song, "Going to the Chapel")

Unidentified Man: (Singing) Spring is here. The sky is blue. Birds all sing as if they knew.


Yes, finally, finally, the long winter is over. It is April at last, and here is the surprise. It turns out, that where we live in the Northern Hemisphere, winter is the shortest season of the year. That's what I was told by an expert.

DR. BING QUOCK (Acting Chairman, Morrison Planetarium, California Academy of Sciences): Okay. My name, Bing Quock, I'm the acting chairman of the Morrison Planetarium at the California Academy of Sciences in San Francisco.

KRULWICH: And according to Dr. Quock, if you start on the shortest day of the year, the Winter Solstice, and go on to count all the days that we officially call winter...

Dr. QUOCK: Winter is about 89 days long.

KRULWICH: And autumn?

Dr. QUOCK: Autumn is the next longest. That's about 90 days long.

KRULWICH: And then longer still?

Dr. QUOCK: That is the spring, and that's 93 days long.

KRULWICH: And the longest season of all?

Dr. QUOCK: The longest season is summer, which is 94 days long.

KRULWICH: So, if you think then of the spring and the summer as getting warmer seasons, and fall and winter as getting colder seasons--not that every spring day is going to be warm, or every winter day is going to be cold, but still, thinking seasonally, how many bonus or extra getting warmer days do we get?

Dr. QUOCK: The difference can be as much as about seven days.

KRULWICH: Seven days.

Dr. QUOCK: So, the getting warmer period can be seven days longer than the getting colder period.

KRULWICH: Which is kind of surprising, says Dr. Quock, because most people think that the four seasons should be about equal. But they're not.

Dr. QUOCK: Because of the way the earth orbits the sun. If the earth's orbit were a perfect circle with the sun dead center, then all the seasons would be exactly the same length of time. But because it's not, the earth's orbit is actually an ellipse or sort of an oval with the sun just a it off center, that means that the earth doesn't orbit our sun at a consistent or uniform rate. When it's a little bit closer, it actually moves a little faster.

(Soundbite of Theremin humming)

KRULWICH: So, as the earth gets closer and closer to the sun, it speeds up, whips around, is flung out, and slows down. Then, it comes back, speeds up again. And this happens year after year.

Dr. QUOCK: When we're closer to the sun, which is actually during--around January, which is the winter for the Northern Hemisphere, that's when we're moving faster, and so we zip through that season, leaving a little bit less time.

KRULWICH: And then, when the earth starts to move away from the sun and starts to slow down, that's the time of year we in the north call spring and then summer.

Dr. QUOCK: So, we're moving a little slower. It takes a little longer to pass through the summer period.

KRULWICH: So, therefore, if like me, you happen to like getting warmer more than getting colder, it's a good thing to live in the Northern Hemisphere, because above the equator, if you spend say...

(Soundbite of song, "April in Paris")

Unidentified Man: (Singing) Springtime in Paris.

KRULWICH: Or in New York, Detroit, Rome.

(Soundbite of song, "April in Paris")

Unidentified Man: (Singing) Springtime in Paris.

KRULWICH: Yeah, Paris. Also, Minsk. Delhi.

(Soundbite of song "April in Paris")

Unidentified Man: (Singing) Springtime in Paris.

KRULWICH: In any of those northern places, springtime lasts just a little longer. It's the opposite, however, if you go below the equator. So, if you go to Australia and you spend say...

(Soundbite of song "April in Sydney," played at a fast speed)

Unidentified Man: (Singing) Springtime in Sydney. Springtime in Sydney.

KRULWICH: Springtime goes a little faster down there.

Dr. QUOCK: Sure, yeah.

KRULWICH: Robert Krulwich, NPR News.

(Soundbite of song "April in Sydney," played at a fast speed)

CHIPMUNK (singing): Springtime in Sydney with you.

CHADWICK: Our apologies to Yip Harberg and Vernon Duke for slightly rewriting their song, April in Paris. And for vocals, special thanks to Stephan Marolochakis(ph) of Brooklyn, New York.

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