Twenty years ago this month, astronauts on the space shuttle Discovery used the spacecraft's robotic arm to launch the Upper Atmosphere Research Satellite into orbit around the Earth.
From a vantage point about 360 km (225 miles) over the Earth, Space Station crewmembers photographed the crescent moon through the upper layers of Earth’s atmosphere. At the bottom of the image, a closed deck of clouds is probably at about 6 km (3 miles). The shades of blue grading to black are caused by the scatter of light as it strikes gas molecules of the very low density upper atmosphere.
Atmospheric gases scatter blue wavelengths of visible light more than other wavelengths, giving the Earth’s visible edge a blue halo. At higher and higher altitudes, the atmosphere becomes so thin that it essentially ceases to exist. Gradually, the atmospheric halo fades into the blackness of space. This astronaut photograph captured on July 20, 2006, shows a nearly translucent moon emerging from behind the halo.
Orbiting the Earth at nearly 17,000 miles per hour, NASA's Ice, Cloud and land Elevation Satellite (ICESat) is collecting spectacular new three-dimensional measurements of the Earth's surface and atmosphere.
Long before man journeyed to the moon and looked back at the tiny, fragile planet that houses humanity, lunar orbiters were sending back pictures of home.