Watching the Skies for Deep Impact NASA's Deep Impact projectile run into Comet Tempel 1 at 23,000 mph. The collision should be visible in the United States, west of the Mississippi River, Sunday night; the aftermath should be visible July 4. Robert Siegel talks with Kelly Beatty of Night Sky and Sky and Telescope magazines.

Watching the Skies for Deep Impact

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ROBERT SIEGEL, host:

And what about those of us who don't want to wait for the pictures? What about the view from down here on Earth? Well, joining us from Boston is Kelly Beatty who is the editor of Night Sky magazine and executive editor of Sky & Telescope magazine.

Welcome back, Kelly.

Mr. KELLY BEATTY (Night Sky Magazine; Sky & Telescope Magazine): My pleasure, Robert.

SIEGEL: I want you to tell us when and where the amateur stargazer might catch a glimpse of this collision.

Mr. BEATTY: If you happen to be living anywhere west of the Mississippi River, you have a chance to see this impact as it's occurring. Anyone east of there, like those of us on the East Coast, unfortunately the comet will have already set below the horizon. But for those in the West, the comet will be above the horizon in darkness and you have a shot at it. It's a question of knowing where to look in the sky, and that's where our maps come in handy.

SIEGEL: Well, roughly where does one look in the sky from west of the Mississippi?

Mr. BEATTY: Ah, yes. Well, if you look to the west after the sun goes down and it gets dark--and these days it doesn't really get dark until 9:30 or so--you'll see a very bright star high in the Southwest. That's actually the planet Jupiter. To Jupiter's left, about the width of your hand at arm's length, is the bright star Spica. If you take two fingers and extend them at arm's length and put them right above Spica, that's a very good indication of where the comet is in the sky.

SIEGEL: Now that's OK if you're west of the Mississippi. What about us Easterners? Do we ever get a glimpse of this thing?

Mr. BEATTY: Those directions apply for everybody in the Northern Hemisphere. It's just that for those of us in the East we're going to have to wait until the night of July Fourth--about, you know, 24 hours after the impact happens--to see the comet above the horizon and in darkness. Now we don't know how long the comet will stay bright. What's going to happen is a big splash of debris will be thrown out into space. That debris is rock and ice and dust. It catches sunlight and reflects it, making the comet a lot brighter than it otherwise might be. So if that splash of debris stays bright for, say, 24 hours then on the night of July 4th you can go out and see that comet no matter where you're living. It won't look like a giant burst of light in the sky. It will look a little more like a fuzzy star. You'll probably need a pair of binoculars or a small telescope.

SIEGEL: Have we actually seen anything in the sky like the impact that's going to occur to give us an idea of what it will look like? Or is a 300-pound copper slug riding into the gut of a comet an unprecedented astronomic event?

Mr. BEATTY: Well, for most of us looking on through telescopes, it will be like a light switch. The comet won't be there and then suddenly it will be there. It's not going to be a profound event, a big glowing object or a glowing ball, but you will know that this is happening at a distance of 83 million miles. You know, the comet is not that large. It's about half the size of Manhattan. So to be able to see it at all will be something of an accomplishment.

SIEGEL: Again, I don't want to be too Eastern-centric here, but for those east of the Mississippi, 10 PM on the Fourth could be a conflict among bright things happening in the sky at that time. Fireworks.

Mr. BEATTY: Well, that's right. And, in fact, the good thing is that the fireworks tend to be very early in the evening because kids want to get to bed and such. The comet will be best visible once it gets really, truly dark, which is not until 10:30 or 11:00. And if you've still got fireworks going on at that time, boy, you've got one good fireworks budget.

SIEGEL: Thank you, Kelly.

That's Kelly Beatty, who is the editor of Night Sky magazine, talking with us about Deep Impact and what might be seen in the sky very late at night on July 3rd or later on on July Fourth. And there are tips, by the way, for comet watchers hoping to catch a glimpse of Tempel 1 after it collides with NASA's spacecraft at our Web site, npr.org.

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