One man in particular is looking forward to coming home aboard Atlantis. Astronaut Dan Tani has been in orbit for four months. We're going to hear more from him in a few minutes. He's written and recorded an essay from the space station for a This I Believe segment.

But first a story about working satellites and how photographs from space are giving scientists more information about Earth. A new book, "Our Changing Planet: The View from Space," published by Cambridge University Press, uses satellite imagery to show how much our planet has changed over the past few decades and the effect humans are having on the Earth.

Earlier this week we drove out to NASA's Goddard Space Flight Center in Greenbelt, Maryland to talk to two of the scientists who edited the book.

Mr. MICHAEL KING (Senior Research Scientist, Chief Scientist, Earth Observing System, NASA Goddard Space Flight Center): Michael King. I'm a senior research scientist at NASA Goddard Space Flight Center where I've worked for about 30 years. And I'm chief scientist of the Earth Observing System, a system of 10 Earth-orbiting satellites.

Ms. CLAIRE PARKINSON (Project Scientist, Aqua Satellite, NASA Goddard Space Flight Center): Hi, I'm Claire Parkinson. I'm also at NASA Goddard Space Flight Center and I'm also project scientist for one satellite, which is the Aqua satellite that's in orbit around the Earth.

HANSEN: I know you've created a book for us to be able to see some of the images that you work with every day. Who uses this information?

Ms. PARKINSON: In this book, what we've tried to do is get scientists who are experts in their field to write just a few pages that will allow the general reader to understand what's going on. This book is written by experts so that you're getting the right information but written for the general public.

HANSEN: Michael, you're going to show us, is it a graph we're going to see? Yes. Tell us about this graph.

Mr. KING: There's an interesting story behind nitrogen dioxide, which I think people find quite interesting. Nitrogen dioxide is a gas. It is observable from satellite. It's got several - three different primary sources: automobiles, lightning and coal-fired power plants.

Because it's a short-lived gas it also shows the life cycle of man's use of transportation corridors. And so we look at the signature from this gas by day of the week and in Europe it drops on Sunday to nearly 50 percent of the value during the weekdays. This is a clear signature of the Christian holy days.

In contrast, if you look at Israel, dominant Jewish religion, it shows a low on Saturday, which is the Jewish Sabbath. And finally if you look at the Islamic cities of the Middle East where Friday is the holy day of Islam and the day of rest, it also drops noticeably to about 80 percent of what it is during the week.

You can basically see the dominant religious preferences of the world from satellite.

HANSEN: That's fascinating. Claire, let's turn to you and an image. It is labeled Destruction of the Aral Sea. What do we see here?

Ms. PARKINSON: Well, the sea, now the sea is partly Kazakhstan and partly Uzbekistan. So it was after the breakup with the Soviet Union it became split into two countries. And what we see in these two images - one is from 1964 on the left and the other is from 2006 on the right - that's the same sea and yet you look at it, it doesn't look like the same sea at all because of how much the sea has decayed.

Eighty percent of the volume of the water retreated. This is one of the greatest environmental disasters of the 20th century, and one that was definitely produced by human beings. There are two main rivers that flow into the Aral Sea and people upstream diverted the water for irrigation for cotton crops and for rice crops, meaning less water got to the Aral Sea and yet the amount of evaporation from the Aral Sea stayed the same. So you were losing water from evaporation. You were no longer getting the water added from the river inflow.

And then all that area that had been sea, that's salt, dust, sand that's being blown all over the place, it's polluting the entire region. So it's got all sorts of environmental consequences.

HANSEN: To look at those two photographs, I mean, even though one is black and white from '64 and one is color, you really can see the difference.

Ms. PARKINSON: And you can see how it has just devastatingly retreated. The sea started decaying in the 1940s and 1950s but nobody knew it except for the people living right along it and nobody was that much concerned. With satellites now anything this much of an impact, it's going to be seen from satellites and people are going to know about it and maybe can start correcting it before gets to as bad a state as what's happened with the Aral Sea.

HANSEN: Michael, you're going to show us this map, and here we are with another...

Mr. KING: So I'm going to show an image here, which is from the MODIS sensor, one of NASA's sensors on the Terra satellite. And so this is a true color image and it shows the Nile River Delta - that includes Alexandria over to the Red Sea. The vast green from the Aswan high dam through Luxor and up to Cairo and then blossoming out in the Nile River Delta. All of the agriculture and fertile land is within 20 or 30 kilometers of the Nile River. And the eastern desert, which is what's called the east side of the Nile is just sand. I've driven hours across that from snorkeling on the Red Sea and it's very desert, very desolate. So it's clearly indicating of man's activity and long use of this area for agriculture in the areas where one can support life near the water.

HANSEN: And the satellite images actually allow you to see things almost as they are happening.

Ms. PARKINSON: Two remarkable things: one, how quickly you can see it, which really is only in the past few years that that's happened. It used to take years for us to analyze data so, you know, ten years later we'd still be analyzing a bit of data and still trying to get the first research results out on it.

But the other remarkable thing about what the satellites allow is they give you the global view. So that it's no longer a case of you just have data from one little area where somebody happens to be sitting taking some measurements. You now can get the entire global view, which allows us to see so much more and understand the connection so much better than we ever could before.

HANSEN: The book is called "Our Changing Planet: The View From Space." And we've been joined at the Goddard Space Center by Michael King and Claire Parkinson, both of whom are editors of the book. Thanks for inviting us into your workspace and showing us the images.

Ms. PARKINSON: Thank you very much for coming.

Mr. KING: Thank you for having us.

(Soundbite of music)

HANSEN: You'll hear more about the effect of climate change on the Nile in the coming months when WEEKEND EDITION takes a trip to Egypt this spring with NPR's Climate Connection series. And you can see satellite pictures of the Aral Sea and learn more about its decay at our Web site,

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