Transit of Mercury Will Be Last for 10 Years Gazing at the galaxy is usually a nighttime activity. But Wednesday, one planet will quite literally have its moment in the sun. The planet Mercury will slowly slide across the face of the sun Wednesday in a rare transit that won't happen again until 2016.

Transit of Mercury Will Be Last for 10 Years

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MICHELE NORRIS, host:

Gazing at the galaxy is usually a nighttime activity. But tomorrow, one of the planets will, quite literally, have its moment in the sun. The planet Mercury will slowly slide across the face of the sun for about five hours on Wednesday. The so-called transit is a relatively rare occurrence. It won't happen again until 2016. And so for a period of time, if you're well prepared, you'll be able to glimpse Mercury in broad daylight, appearing like a tiny spot moving across the sun.

One person who's sure to be gazing skyward is Kelly Beatty. He's the editor for Night Sky Magazine and the executive editor of Sky and Telescope magazine. Mr. Beatty, thanks for being with us.

Mr. KELLY BEATTY (Night Sky Magazine): My pleasure, Michele.

NORRIS: So when does the fun begin tomorrow?

Mr. BEATTY: Well, if you're on the East Coast, it's at 2:12 p.m. Take your time zone correction, that would be 1:12 Central, 12:12 Mountain and 11:12 Pacific, and as you mentioned, it lasts about five hours. It's a real slow motion event.

NORRIS: So what do you actually begin to see as Mercury starts to edge toward the face of the sun?

Mr. BEATTY: When you look at the sun, you'll see Mercury as a little dot, a little BB-hole in the sun, if you will. So it will start to slide across the sun, taking a couple of minutes to enter, and then it's going to be just this slow dance. It will look like a black spot, blacker than any of the sun-spots in its vicinity, and five hours later it exits stage right.

NORRIS: Now you say when we look at the sun - we should say that you don't look directly at the sun.

Mr. BEATTY: Oh, be sun safe, folks. I mean, you don't ever want to look at the sun with your naked eye, and especially with a telescope or binoculars, because that just serves to concentrate the sun's light.

There are a couple of ways that I can recommend. One is to use a telescope that has a safe solar filter, a filter designed to go over the front of your telescope, and that will rule out and block 99.99 percent of the sun's light.

Another way, if you don't have that, is not to look through the telescope directly, but to let the eyepiece project the sun onto a white card, or even a wall, that's held a couple of feet away.

NORRIS: And we should note that NASA also has an excellent Web site with details on the best time for viewing in spots all over the world. You can find information about that at our Web site, NPR.org.

Because of the timing on this, some locations won't be able to actually see the transit. Who's left out?

Mr. BEATTY: I'm afraid I'm left out. Those of us on the East Coast will be able to see a couple of hours of the transit before the sun sets. The farther west in the country you are, the more of it you'll get to see. By the time you're, oh, from the Rocky Mountains westward to the West Coast, you'll be able to see the whole thing before sunset.

NORRIS: Now this last happened in May 2003, won't happen again for a decade. What are the circumstances that lead to these kinds of events?

Mr. BEATTY: You know, if Mercury had an orbit that was in the same plane as Earth's orbit, we'd see a transit every time Mercury came between us and the sun. But it's orbit is tipped a little bit. And so consequently, there are only two times a year, in May and November, when that virtual line of Mercury's orbit crosses the sun. If Mercury happens to be there during those little windows, then we'll see a transit.

NORRIS: Now you're a man of science, so perhaps it's not fair for me to ask you this question, but are there certain kinds of phenomena or events or myth that go along with this kind of transit?

Mr. BEATTY: There's certainly a lot of history. Transits of Mercury cannot be seen except with a telescope, and so the first one wasn't seen until 1631. But in very short order, astronomers realized that these transits of Mercury and Venus held the key to determining the distance from the Earth to the sun, something that wasn't known up until that point. It was the kind of thing that would send astronomers on ships for years to view this event from some far-flung land that was positioned to see it at the time.

NORRIS: Kelly Beatty is the editor for Night Sky Magazine and the executive editor of Sky and Telescope magazine, and Kelly, before we let you go, where are you going to watch the transit?

Mr. BEATTY: Well, it's supposed to be cloudy here. If the clouds break, we have a nice hill right next to our office. We're all going to sort of shut down for the day and clamber up to the top of that hill and set up our telescopes and take a peek.

NORRIS: Late lunch.

Mr. BEATTY: Late lunch indeed.

NORRIS: That's Kelly Beatty, editor of Night Sky Magazine.

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