For First Time Since 1948, Supermoon Rises On Monday

NPR's Rachel Martin talks to astronomer Jackie Faherty about Monday's supermoon. It will be the closest the moon has been to Earth since 1948.

RACHEL MARTIN, HOST:

There's something big on the horizon - a supermoon. You might have heard of supermoons before. When the moon gets particularly close to Earth, it appears larger than usual in the night sky. And tomorrow night, the moon will be the closest it has ever been to Earth since 1948. Here to explain how it all works is Jackie Faherty. She is an astronomer at the American Museum of Natural History. Thanks so much for being with us, Jackie.

JACKIE FAHERTY: You're welcome. It's a pleasure.

MARTIN: What makes a supermoon so super?

FAHERTY: Well, anything called super must be amazing, I feel like.

MARTIN: (Laughter).

FAHERTY: But the real question is what - why is it super and what makes it super? And it's actually not a science term. It's a term that was coined by an astrologist over 30 years ago. And it didn't have much science behind it except that he coined a term for when the moon was full when it was 90 percent of its closest distance that it could be to Earth. And a couple years ago, it just caught on.

MARTIN: So just to clarify, it's not like the moon turns crazy colors or anything. It's just - it's a full moon, and it just seems bigger in the sky?

FAHERTY: Yeah. So the moon travels around the Earth every 28 days or so, and it moves in an ellipse. And that means that the distance that the moon is away from us changes. And what's happening this coming Monday is that at the same time that it's coming into its closest approach to the Earth in this orbit, it's also aligned so that you have a full moon, what we astronomers call a perigee-syzygy moon.

MARTIN: Now you're just showing off.

FAHERTY: Yeah. Well, that's also why supermoon sounds so much better.

(LAUGHTER)

MARTIN: Does it just look cool, or does it have any kind of tangible effects on the Earth?

FAHERTY: So full moon always has an effect on the Earth. We get stronger tides during that time, and that can be very, very minorly amplified when the moon is a bit closer to the Earth. If you were somebody that always went outside and looked at the moon and always saw full moons, you would notice a difference. But for the person that - like, how many times do you go outside and look at the moon? I feel like...

MARTIN: Not that often. I wish I did more in my life.

FAHERTY: So I'm hoping that this will get people to go outside and look at the moon a bit more because it is - it's fun to go out and know that as you're standing out there and looking up that it's closer to you than it's been in quite a long time.

MARTIN: What's the best way to see the supermoon?

FAHERTY: The moon is one of those great astronomical objects that even if you're in big cities you're going to be able to see it. So I like to tell people to go out and watch the moon at moonrise or moonset because there's this optical illusion which as it's rising or when it's setting, it looks really big...

MARTIN: Yeah.

FAHERTY: ...This - yeah. So that - that's not even a supermoon (laughter). That's just...

MARTIN: That's just a regular old moon.

FAHERTY: That's just a regular full moon close to the horizon, where you get this optical illusion where your brain doesn't quite know how to interpret the size of the moon with the buildings and the horizon.

MARTIN: Where are you going to be? How do you like to watch the moon? Do you have to be at work? Or are you going to be, like, in your backyard?

FAHERTY: I'm just going to be outside of my apartment in New York City, looking for the moon and knowing that it's closer to me than it's been in a long time.

MARTIN: And somehow, that makes me feel like we're all connected, if we could all just go outside and look at the moon together. Jackie Faherty from the American Museum of Natural History. She's an astronomer there. We've been talking about the supermoon. Thanks, Jackie.

FAHERTY: Thanks.

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