The International Space Station (ISS) is constantly in motion. The football pitch-sized object rotates as it cruises at about 29,000 kilometers (18,000 miles) per hour—so fast that it orbits Earth every 90 minutes.
For astronaut photographers on board, that motion has consequences. For one, it makes it challenging to take photos. Even with digital cameras that take pictures within 1/1000th of a second, the Space Station moves so quickly that images can easily lose focus or become distorted.
However, the same motion makes it possible to shoot spectacular photos like the one above. The image is compiled from a series of photographs taken by NASA astronaut Don Pettit while he was onboard the ISS in April 2012. This composite was made from more than 72 individual long-exposure photographs taken over several minutes as the ISS traveled over the Caribbean Sea, across South America, and over the South Atlantic Ocean.
As Pettit explained in a blog post, long-exposure pictures from the Station show star trails as circular arcs, with the center of rotation being the poles of the station. Stars close to the center of rotation make the tight circles near the middle of the image, while stars farther from it make the larger arcs visible along the edges.
“My star trail images are made by taking a time exposure of about 10 to 15 minutes,” Pettit wrote. “However, with modern digital cameras, 30 seconds is about the longest exposure possible, due to electronic detector noise effectively snowing out the image. To achieve the longer exposures, I do what many amateur astronomers do. I take multiple 30-second exposures, then stack them using imaging software, thus producing the longer exposure.”
The image includes many natural and artificial lights that astronauts see while passing over the night side of Earth. On the ground, stationary features like cities appear as pale yellow-white streaks. The thinner, dotted lines with orange hues are likely caused by small fires burning in South America.
Looking toward the horizon, thunderstorms dot the landscape. Many of the compiled frames captured bright white lightning flashes. Above the horizon, a faint green-yellow phenomenon called airglow hugs the upper atmosphere. Look carefully at the large version of this image for at least one streak of light that is not aligned with all the others. That is a satellite.
Learn more about astronaut photography in the Picturing Earth video series: part 1 Astronaut Photography in Focus; part 2 Window on the World; and part 3 Behind the Scenes.
Astronaut photographs ISS030-E-271644 – ISS030-E-271714 were acquired on April 23, 2012, and is provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit, Johnson Space Center. The image was taken by a member of the Expedition 30 crew. The image has been cropped and enhanced to improve contrast, and lens artifacts have been removed. The International Space Station Program supports the laboratory as part of the ISS National Lab to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth. Caption by Adam Voiland.