They range from dramatic shots of the eruption of Mount Etna in Italy and the collapse of the Kolka Glacier in Russia to unique images of San Francisco Bay and the Great Pyramids of Egypt.

The crews that have lived and worked on board the International Space Station have taken more than 100,000 photographs of the Earth. Earth observation with handheld cameras began on board the ISS in November 2000. The photographs record observable Earth surface changes over time, as well as more fleeting events such as storms, floods, fires and volcanic eruptions. Together they provide researchers on Earth with vital, continuous images needed to better understand the planet.

"NASA’s ‘Earth smart’ astronauts on board the International Space Station have achieved an important milestone," said Kamlesh Lulla, NASA chief scientist for Earth and Imaging Sciences at Johnson Space Center. "They have significantly added to our astronaut Earth photography database of more than 500,000 images. This database is a national treasure used daily by thousands of researchers, educators and the public.

"I want to congratulate the entire ISS team on this accomplishment. These images will allow scientists across the globe to develop a better understanding of our planetary processes. This ISS activity is an integral part of NASA’s mission to ‘understand and protect Planet Earth.’"

The Space Station offers an ideal vantage point for crewmembers to photograph the Earth. Its average altitude is about 240 miles (384 km) above the Earth, and its orbital inclination includes most of the coastlines and heavily populated areas of the world. Station crews can observe 75 percent of the Earth’s land area and about 95 percent of the Earth’s population.

"A continuous presence in space allows much more extensive observations of the Earth including seeing major dynamic events such as volcanic eruptions, hurricanes and winter storms," said Julie Robinson, Lockheed Martin senior scientist and Earth science applications lead at JSC. "The total number of astronaut photographs from Gemini to now is 544,003, meaning that one-fifth of the photographs taken of the Earth from human spaceflight missions are from Station. Because photography of Earth began with the first human space missions more than 40 years ago, this represents the longest continuous record of the state of the planet as observed from orbit."

Station crewmembers are trained in scientific observation of geological, oceanographic, environmental and meteorological phenomena and in the use of photographic equipment and techniques. Messages are routinely sent to Station crewmembers listing the best opportunities to be photographed based on input from scientists on the ground.

Photographic techniques have advanced over the past three years. "Recent advances from the Space Station include the crewmembers learning to compensate for motion as they take photographs with high-magnification lenses," said Robinson. "This allows each pixel in a select new set of digital photographs to represent areas on the ground that are smaller than 6 meters. It takes time adapting to the floating environment on the Space Station before astronauts learn to track the motion and take these kinds of pictures."

NASA makes digital versions of astronaut photographs available to the public for free download on the "Gateway to Astronaut Photography of Earth" Web site:

More than 500,000 photographs are downloaded from this Web site each month, and the site receives 12 to 15 million "hits" each month. The project is maintained by a team of interdisciplinary scientists who train astronauts in the Earth sciences, provide a daily message to crews in orbit, assemble metadata and distribute the images on the Web, and work with scientists and educators to use the photographs in research and teaching applications.

"We continue to receive much positive feedback from people around the country who download the free images from our site and use them to supplement their science teaching, add to their research data or simply view their hometowns," said Greg Byrne, assistant manager of the JSC Office for Human Exploration Science, which includes the Earth observation project.