ROBERT SIEGEL, host:
Well, that letter caught our attention. So we called up Christine Pulliam, who is a colleague of Dr. Paine's at the Smithsonian Astrophysical Observatory, to find out a little more about how scientists explain what people might be seeing when they think they're seeing a UFO.
Christine Pulliam, you have seen a superior mirage phenomenon?
Ms. CHRISTINE PULLIAM (Public Affairs Specialist, Harvard-Smithsonian Center for Astrophysics): Actually, everybody has. Anyone who has seen a sunrise or a sunset. The same phenomenon occurs to the sun every day and makes it appear to be above the horizon when it's actually slightly below it.
SIEGEL: Well, the folks in Stephenville, Texas, whom Wade Goodwyn spoke with, described seeing a very large red light up in the sky 3,000 feet up, then lights like strobe lights. How would those all be created? How will that illusion be created if that's what it is?
Ms. PULLIAM: It's hard to say for sure since I haven't seen it. But there are a lot of natural phenomena that can make things look unusual in the sky. We get a lot of phone calls from people who see a bright light on the horizon that seems to be shimmering, dancing around and changing colors, and they think it might be an artificial object. But then we look it up on our planetarium software and find out that no, actually, the planet Venus was on the horizon at that time.
SIEGEL: How is it that on one night many people could see this, sort of, superior mirage but not see it on any other night? Why would it happen on one particular day as opposed to happening every week or every month? We do see the sunrise every day and every…
Ms. PULLIAM: That's right.
(Soundbite of laughter)
SIEGEL: Yes. But not this.
Ms. PULLIAM: Something like this, it would have to be unusual weather conditions, something with cooler air close to the surface and much warmer air high up.
SIEGEL: So as for the explanation that some of our listeners prefer, which is that - just a courtesy call from Venus or something like that or some distant galaxy, no point to rush to any such inference from this, you're saying.
Ms. PULLIAM: Right. I would say that extraordinary claims require extraordinary proof. And if somebody really thinks it is alien visitors or hyperdimensional travelers, they need to come up with a better explanation than eye witness reports.
SIEGEL: Well, Christine Pulliam, thank you very much for talking with us.
Ms. PULLIAM: Oh, you're welcome.
SIEGEL: That's Christine Pulliam of the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts.
MELISSA BLOCK, host:
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