LINDA WERTHEIMER, HOST:
You're listening to WEEKEND EDITION from NPR News. This summer, we've been doing an occasional feature called Stargazing.
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WERTHEIMER: So we had to take note of the fact that this week, sky-watchers in the Northern Hemisphere have a special treat. Tonight, the annual meteor shower Perseid will light up the night sky with as many as 100 shooting stars an hour. And there will also be another celestial event at the same time - a supermoon. We're here with Mike Brown, professor of planetary astronomy at California Institute of Technology, to talk about the meteor shower and the supermoon. Welcome back, Mike.
MIKE BROWN: Thank you very much.
WERTHEIMER: The Perseid shower is an event many of us look forward to all year. Could you begin by explaining the phenomenon of Perseid? Why are there so many shooting stars all at one time?
BROWN: The Perseids happen every August because in August, on these dates, we're passing through the tail of a comet. It's Comet Swift-Tuttle. It takes 133 years to go around the sun. And every August, we intersect the orbit of that comet, and we get dust that came off the tail of that comet - maybe many years ago - that's entering the Earth's atmosphere.
WERTHEIMER: So if we are out in the backyard wrapped up in a sleeping bag - as I always used to be for the shower when I was a kid - when would we want to be looking up? When is the peak?
BROWN: In general, the best times to see it are on - the peak days are going to be Monday, Tuesday and Wednesday mornings. At that point in time, the Earth is traveling right into the direction of that comet tail. The problem is, at those times when we should be able to be seeing the meteor's best, the moon is going to be so bright that it's going to wash out a lot of the faint ones. So it's going to be a difficult year for the Perseids. But the bright ones will still be there.
WERTHEIMER: If you want to really see as many as you can see, you should be out -when? - like 3 o'clock in the morning, 4 o'clock - what?
BROWN: I think 4 a.m. is probably primetime. You want to be up when it's still dark but the sun is just about to start to glow on the horizon.
WERTHEIMER: Are you likely to be over-mooned at 4 a.m.?
BROWN: This year for those early morning ones, the moon is going to be very, very tough.
WERTHEIMER: Now, what I'd like to know is what is a supermoon, and what is it doing on the day of the meteor shower?
BROWN: We've had these things that people have started to describe as supermoons periodically. And what it really means is that the moon - the full moon - comes at the same time that the moon is the closest to the Earth that it gets in its orbit.
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WERTHEIMER: Mike Brown is a professor of planetary astronomy at the California Institute of Technology. Thank you very much.
BROWN: Oh, it was my pleasure.
WERTHEIMER: This is NPR News. Transcript provided by NPR, Copyright NPR.