All About the Summer Solstice Summer solstice, the longest day of the year, is here again. Astrophysicist Charles Liu of New York's Hayden Planetarium makes good use of the extra time.
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All About the Summer Solstice

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All About the Summer Solstice

All About the Summer Solstice

All About the Summer Solstice

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  • <iframe src="" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
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Summer solstice, the longest day of the year, is here again. Astrophysicist Charles Liu of New York's Hayden Planetarium makes good use of the extra time.

A file photo of the stone circle of Stonehenge at sunrise during the Summer Solstice. Carl De Souza hide caption

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Carl De Souza


The crowd is assembling at Stonehenge. In Fairbanks, Alaska, the minor-league team, the Goldpanners, will play an all-night game of baseball under the midnight sun, and I, right now, in this very radio studio, am trying to balance an egg on its end. No, I am not. In fact, that may be a myth. But here it is again, the summer solstice, the longest day of the year.

Charles Liu is a professor of astrophysics and an associate at the America Museum of Natural History's Hayden Planetarium. Lots of fieldtrips there when I was a kid. He studies quasars, colliding galaxies and star formations, history of the universe, and he's here to answer a few questions far below his pay grade about the Summer Solstice. Hello, Professor Liu.

Dr. CHARLES LIU (Astrophysics, City University of New York, Hayden Planetarium): Not at all. It's great to be here. Thanks for having me.

PESCA: Are you a solstice enthusiast?

Dr. LIU: Well, we are having a wine-and-cheese party today after work. But then again, we do that pretty much every Friday during the summer, so...

PESCA: Yeah, that's how the astrophysicists roll.

Dr. LIU: Hah, pretty much.

PESCA: So tell us about, you know, the solstice has the longest day of the year. What happens on the solstice?

Dr. LIU: OK, well, you know, if you spin a quarter on a desk, just before it falls flat onto the desktop it kind of wobbles as it spins. Well, Earth does that, too. As it spins, it also wobbles, but one wobble takes 26,000 years or so. So the North Pole and the South Pole are kind of pointed diagonally with its respect to the path around the Sun. And today, the North Pole just happens to be pointed more toward the Sun than on any other day this year, so that's why it's the solstice.

PESCA: And in fact, the seasons - nothing to do with closeness or farness - what would be the word "farness," anyway? How close...

Dr. LIU: Farness, is that a word?

PESCA: Yeah, yeah. How close and far you are from the Sun? It's all tilt, right?

Dr. LIU: That's right. Here on Earth, the tilt is pretty much it. And it's pretty much on other planets, too. But Mars - for example, Mars' solstice is actually happening in a few days as well, by coincidence, this year. And it actually does have a more elliptical orbit. So for Mars, seasons are affected a little bit more by distance, but here on Earth - no. In fact, we're actually closer to the Sun in January than we are in June.

PESCA: Isn't a day on Venus longer than a year? Like a lot longer?

Dr. LIU: Yeah. Venus - every planet is cool. Actually, they all have...

PESCA: Yeah, they're all cool.

Dr. LIU: Venus kind of, yes, takes much longer - a few days longer to go round once on its axis than it does to go around the Sun. So it has some very strange sunrise/sunset things.

PESCA: All right, that was a digression. Back to the solstice.

(Soundbite of laughter)

Dr. LIU: OK.

PESCA: You're an astronomer. What about astrology? Do you think it's all junk science or - I mean, it's all based on planetary positions and stuff. What do you think about it?

Dr. LIU: Well, you know, that's interesting. You mentioned that I'm a professor, I teach at the College of Staten Island, here in New York. And well, I often get that very same question, you know, do you believe in astrology, does is make sense? The bottom line is astrology was invented thousands of years ago, before science was invented.

People mapped the sky, tried to understand the stars, didn't have the tools, really, that we do today to understand them. But they made educated guesses. So that's really where astrology came from. And today we have better than educated guesses, and so we have the science of astronomy. People still like to look at the stars, though. And like a lot of things in the world, we believe things that aren't necessarily scientific. We just need to know the difference between what is and what isn't science.

PESCA: People used astrology to try to explain human behavior. Astronomy, is there any way to - does it have an effect on human behavior as opposed to, you know, other than the fact that it's hot in the summer?

Dr. LIU: Right, good question. And the answer's completely no. Scientifically speaking, we know for sure that the positions of the stars and the planets and so forth, there is absolutely no effect, even the moon, physically speaking, on human behavior. But you know, we humans, we allow lots of different things to affect our behavior, whether they're scientific or not, so it's a matter of what you want to think about, how you want to run your world, how you want to run your life.

Bottom line is, believe what you will, scientifically, astrology is completely nonscientific. That's what it is. But you know, if you want to look at the horoscope and find out that, hey, you know, today you'll come into money, and you find a quarter on the street, you know, what the heck, right?

PESCA: Yeah, see how long the quarter will spin. Yeah.

Dr. LIU: Exactly.

PESCA: Do you, you know, Stonehenge out there, obviously it has some relation to the solstice on the solstice day.

Dr. LIU: Definitely.

PESCA: It's shedding light right directly above it. What - do you have any other - do you follow Stonehenge? Because every so often, a new discovery is made about Stonehenge

PESCA: So do you have any theories about Stonehenge?

Dr. LIU: I personally don't. Here's the deal with Stonehenge in my opinion, and also lots of these other places. The pyramids in Egypt or Machu Picchu, you know, the Inca Empires, Mesa Verde in Colorado. We're learning more and more about our ancestors every day, as we do our archeological studies all around the world.

And what we're learning is that our ancient ancestors, even the prehistoric ones, really knew a lot about the motions of the sun, the moon, the stars, and the planets. So I'm not surprised at all that the ancient Celtic Druids also understood that there would be one day every year when there would be more sunlight than any other day or one day of the year where there'd be not as much as any other day, that would be sort of in midwinter, right?

So I think that as we learn more about any of these places, we learn more about how creative and how clever our ancestors were. We think that right now, if you look carefully at the overall layout of Stonehenge, not just the few rocks in the center but all the different pieces of it all around, that it may have been used to predict solar and lunar eclipses. So that's pretty sophisticated math. And these guys really knew what they were doing.

PESCA: Cool. Charlie Liu, he teaches astrophysics at CUNY College of Staten Island. His forthcoming book is called "The Handy Astronomy Answer Book." Thank you, Charles.

Dr. LIU: Thank you very much, Mike.

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