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CNN Live Saturday

Interview With Astronomer Geoff Chester

Aired April 20, 2002 - 18:24   ET

THIS IS A RUSH TRANSCRIPT. THIS COPY MAY NOT BE IN ITS FINAL FORM AND MAY BE UPDATED.

THIS IS A RUSH TRANSCRIPT. THIS COPY MAY NOT BE IN ITS FINAL FORM AND MAY BE UPDATED.
CATHERINE CALLAWAY, CNN ANCHOR: In the skies overhead, a celestial light show's forming during the next few weeks. Five planets will soon group together over the Western sky, a sight that hasn't been seen since 1940, and an event that will not come to pass again for another 40 years.

Our next guest is Geoff Chester. He's an astronomer from the U.S. Naval Observatory. Thank you for being with us, Jeff. I want to start off by saying we've got some breaking news, as you just heard, coming out of Nablus, and so we're going to have to rush through this quickly, but I wanted to make sure we got you in because what you have to say is quite interesting, on what we can actually see out there now.

We've got five planets -- what they're saying -- I guess they call them the naked planets because you can see them with the naked eye. Tell us what makes this so unusual.

GEOFF CHESTER, ASTRONOMER, U.S. NAVAL OBSERVATORY: Well, what makes this so unusual is the fact that we have all five of the planets that were known to the ancients; the classical planets that have been visible with the naked eye for thousands of years. They are all grouped together in a relatively small part of the sky at the same time for the next couple of weeks.

Now, groupings such as this do not occur very often. Typically, they occur at intervals of about every 20 years or so because that's when we get Jupiter and Saturn together. But we also have to thrown Mercury, Venus and Mars into the mix, and because of the fact that Mercury and Venus are only visible in evening twilight or morning twilight, to have them all compressed in that particular part of the sky is a comparatively rare event.

CALLAWAY: OK, we're watching this now -- this animation -- I don't know if you have a -- where you can see it, where it actually goes to -- I guess, what, 35 degrees from something like 50 degrees to 35, you're obviously better at explaining this, but...

CHESTER: Yeah, they initially span an area of the sky that's about 35 degrees across -- or 50 degrees across, I'm sorry. If you hold your fist at arm's length, that spans about 10 degrees of the sky. So, it initially starts off at about five widths of your fist. By the time the planets are closest together, during the first week of May, they will span about 35 degrees. That's a comparatively small span of sky to deal with...

CALLAWAY: Now, isn't there something about -- I'm going to interrupt you, because I want to ask you about Mercury...isn't that normally Mercury below the horizon? Isn't it unusual that -- it's going to be visible so high up?

CHESTER: Well, Mercury is typically visible from any given location, once or twice a year in the evening sky, and once or twice a year in the morning sky. The most favorable times for us to see it in the temperate climates in the United States are typically in the spring or in the dead of winter. So, this happens to coincide with one of the times when Mercury is at its best possible viewing circumstances for this particular year. We also have these other planets thrown in as well.

So it's really an opportunity to go out and just sort of get a perspective of where we are in this whole thing, I mean, your previous guest talked about the earth as a planet. Here is a chance for us to see our planet in the context of all the others in the solar system.

CALLAWAY: Jeff, just yes or no. Is evening -- twilight hours -- the best time to see this?

CHESTER: Yes, evening twilight, about a half hour after sunset is the best time to go.

CALLAWAY: All right. Good couple of weeks ahead for us, then. Geoff Chester, thank you very much for joining us. I'm sorry we had to rush through that. We'll be watching the sky, so we'll be watching the skies for you. Thanks, Geoff.

CHESTER: All right.

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