Our friends at the Alexandria Zoological Park in Alexandria, Louisiana, asked, "How have advances in space technology helped us on Earth?"

We have all seen pictures of the lovely globe of Earth as seen from space. Some of the first of these pictures were taken by the astronauts of the Apollo Moon program. They described how it felt to see the entire Earth at once, our sparkling colorful planet with its delicate blanket of air and clouds, out there all alone, floating in the blackness of space. The images of Earth that have been sent back by far-away spacecraft such as Voyager and Galileo on their way to other planets in our solar system have suggested to us even more powerfully how small, fragile, and beautiful is our home. When I look at these images, I cannot help but feel proud of my world as well as grateful for it and even protective of it.

But space technology has done far more for Earth and its inhabitants than just inspire us with pretty pictures of our home. You are probably familiar with the use of satellites for transmitting TV signals and telephone calls, and for satellite navigation systems (such as those used in some cars and airplanes). You may not be as familiar with how much satellites have helped us to understand and take care of our planet. Satellites have studied oceans, the atmosphere, clouds, weather, rain forests, deserts, cities, farmlands, ice sheets, and just about everything else on—and even in—Earth.

It is very important to the future of life on our planet to understand how what we do affects the delicate balance of the environment. Using information from satellites, we are beginning to understand how pollution from our cars, factories, and even household products affects our atmosphere. For example, we know that certain kinds of air pollution destroy some of the ozone high up in the atmosphere. That ozone protects us and other living things from the Sun's harmful ultraviolet rays. Satellites have shown that the ozone is disappearing over some parts of Earth. So, we know that we must find and use chemicals that are less damaging to our atmosphere.

We use satellites to predict the weather. We may not be able to change the weather, but having an idea ahead of time what it's likely to do gives us the chance to prepare. The two GOES satellites, stationed high over the east and west coasts of the United States, let us track hurricanes and other storms as they develop. Having this view from space gives people enough warning of dangerous weather to prepare and even evacuate vulnerable areas where a hurricane might hit.

Two other satellites, TOPEX/Poseidon and Jason-1, have been studying the oceans. They have helped us to understand the complex movement of ocean water and to make long-term weather predictions. Because the oceans store a lot of heat, they have a great effect on the weather. These satellites have observed the event known as El Niño, in which unusually warm water collects in the Pacific Ocean near South America causing very heavy rain in some parts of the world and drought in others.

Some remote parts of our planet are almost impossible to keep an eye on except from space. Frequent satellite images of a rainforest can show how fast this precious habitat is shrinking. Views from space of the North and South Poles allow us to monitor the shrinking of ice sheets-important indicators of global warming and possible flooding of coastal regions.

Satellites that study Earth are not just fancy cameras in space. Many of them have special instruments that measure light that our eyes cannot see and can reveal important information such as the height of the oceans all over Earth, or the wind speed inside clouds. An instrument on a spacecraft called Earth Observing 1 is so sensitive to color that it can distinguish between different types of trees in the forest and show where trees might be diseased. Other instruments can measure the height and thickness of clouds and how much water they contain.

Space technology has helped us understand how Earth works and how we can help keep it healthy. You can see beautiful images of your world from space taken by the Landsat satellite and play the "Spuzzled" game at The Space Place. Visit spaceplace.nasa.gov and pick "Do spacey things," then click on "Solve Earth Art Spuzzles."

Thanks again for calling Dr. Marc here at The Space Place.