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ROBERT SIEGEL, host:

This week and next, we are afforded fleeting but unusually bright glimpses of the biggest man-made object in space. The International Space Station is especially visible in the evening sky, although this is decidedly appointment stargazing: The glimpses may last only a minute or perhaps a few minutes.

The Space Station circles the Earth every ninety minutes, so it's really moving up there. To explain why the Space Station is so bright just now, and how you can figure out when it's flying over your town, Kelly Beatty joins us now from Boston. He's senior contributing editor for Sky and Telescope Magazine. Thanks for joining us again.

Mr. KELLY BEATTY (Senior Contributing Editor, Sky and Telescope Magazine): My pleasure, as always, Robert.

SIEGEL: And first, when the International Space Station is unusually bright, how bright is it? What does it look like in the sky?

Mr. BEATTY: It is the brightest object in the nighttime sky except for Venus. It outshines all the stars, all the planets but Venus and actually gives Venus a run for its money.

SIEGEL: So you don't need a telescope to see it up there?

Mr. BEATTY: Absolutely not. This is eyeball astronomy at its best. Household binoculars is enough to look at the space station and detect its shape. A telescope won't do you any good because it's moving too quickly to keep track of.

That said, the motion is very stately. So you wouldn't mistake it for a meteor, because a meteor is just a momentary flash. And you won't mistake it for a jet because jets usually have blinking lights. And the Space Station is a very steady bright light that honestly will be a slam-dunk to spot no matter where you are.

SIEGEL: Why is the Space Station especially bright right now?

Mr. BEATTY: It's because the Space Station is huge. It's now reached its full size, which is about the size of a football field, including the end zones, and it's basically shiny. So it reflects sunlight from its orbit, and we see it on the ground as a shining beacon as it glides overhead in a stately fashion, even though it's moving at about five miles per second.

So we need a time of day when it's in sunlight, and we're in darkness. That happens either just after sunset or just before sunrise.

SIEGEL: And NASA actually offers lists of sighting times online, where you enter your location. I saw one other site that does it by zip code. But you can enter a town, and it'll tell you when, where in the sky and for how long you can see the space station.

Mr. BEATTY: Right. The orbit is about 225 miles up. And it's tipped with respect to our equator by 52 degrees. This puts it within view of practically every city in the world.

And that orbit is defined mathematically, and you run a few calculations - you don't have to do that, these websites do it for you - and you'll find out where and when to look in the evening sky or in the morning sky before dawn.

SIEGEL: Do you have a favorite website that can tell people when to look?

Mr. BEATTY: Well, I'd have to say that the most popular one, by far, is called Heavens-Above. That's with a hyphen, heavens-above.com. Sky and Telescope has predictions. NASA itself has predictions. There are many places you can go to get them.

SIEGEL: Now, when you say that the space station has reached its full size, it's finished. It's been a work in progress all these years, you say.

Mr. BEATTY: It has. It was first started in 1998 with the launch of a module by the Russians called Zarya, and it has grown Tinker-Toy-like over these many years, and now it's done.

SIEGEL: Now when we speak of the visibility of the International Space Station, obviously it does depend on the weather. It could be impossible to see depending on how cloudy the sky is tonight.

Mr. BEATTY: It's much easier to see when the pass is going to be nearly overhead, and that's when it'll be brightest. You can also see it when it's down lower, but it won't be as bright.

Whenever it comes overhead, I want everyone to wave because right now there are six astronauts on board. That's its permanent crew. And right now it's the 27th expedition of astronauts and cosmonauts aboard. So I'm sure they're looking forward to waving back at you, Robert.

(Soundbite of laughter)

SIEGEL: Well, Kelly, that's very thoughtful of you. Thank you very much.

Mr. BEATTY: You're very welcome, Robert.

SIEGEL: That's Kelly Beatty, senior contributing editor for Sky and Telescope Magazine.

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MICHELE NORRIS, host:

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