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North American Skywatchers Prepare For Transit Of Mercury

NOEL KING, HOST:

OK. You have absolutely heard this before, but it's worth repeating. You should never, ever look directly into the sun.

STEVE INSKEEP, HOST:

Not even for a moment.

KING: Protect your eyes. But there is something amazing happening this morning that might make you want to peek. It's a rare astronomical event called the Mercury transit.

ALEX YOUNG: The planet Mercury is going to move across the disk of the sun.

INSKEEP: That does sound cool. Alex Young is an astrophysicist at NASA's Goddard Space Flight Center, where he studies the sun. Via Skype, he explained that depending on where you are and, of course, the weather, you have a chance to see at least part of the transit this morning - a small, black dot sailing across the sun for almost five and a half hours.

KING: Scientists get amped about this because they use these transits to fine tune their space telescopes. And NASA and other research outfits use the transit method to find distant planets.

YOUNG: We see a slight dip in the light coming from another star and we know that, depending on how big that dip is, that tells us something about the location and the size of that extrasolar planet.

INSKEEP: A very slight dip. When a planet glides over a distant star, the light dims by about - just to be precise - 84 parts per million.

KING: So if you want to watch the transit today, the glasses you used for the eclipse back in 2017, they are not enough. Mercury is so small that you need some kind of magnifying device with a sun filter. Alex Young is all ready.

YOUNG: I have my solar binoculars, and I'm going to go outside, and I'm going to take a look with my own eyes.

INSKEEP: If you're not properly prepared, you can watch it online. And it is good to have a look. But another reminder - don't stare directly at the sun. The next Mercury transit that will be visible from the United States comes, by the way, in 30 years.

(SOUNDBITE OF SONG, "MERCURY BLUES")

STEVE MILLER BAND: (Singing) I'm going to buy me a Mercury. Transcript provided by NPR, Copyright NPR.