Apollo astronauts this week on planetary radio.

Hi everyone and welcome to Public Radio's travel show that takes you to the

stars. I'm Mad Kaplan. Happy Apollo 11 35th anniversary.

Yes, it's been three and a half decades

since the eagle landed in the Sea of Tranquility.

We'll talk with two of the astronauts who got us there.

Bruce Betts drops by with his What's Up

review of the Sky and our latest space trivia contest. Let's get started with

Emily. She has the tale of three planets, one that was too hot, one that was too cold, and one that was just

right.

And she knows one reason why.

I'll be right back. Hi, I'm Emily Loch Duwala with questions and answers. A listener asked, if a planet's greenhouse gases won't let

its radiated heat escape into space, how does the sun's heat get past them in the first place?

If the Earth simply reflected the sun's light, there would be no greenhouse effect.

But that's not what actually happens.

The Sun's radiation is concentrated at visible and near infrared wavelengths of light,

but the materials on the surface of the Earth

absorb this radiation and then re-radiate it at much longer wavelengths of light called

thermal infrared or heat. There is nearly no overlap between the wavelength of the incoming sunlight

and the wavelength of the heat radiated back by the earth. Greenhouse gases like water vapor

and carbon dioxide act like windows to sunlight but walls to

thermal infrared light. This so-called greenhouse effect can be both a blessing and

...