The first video — posted on the European Space Agency (ESA) website — shows green curtains of auroras, sometimes called the northern and southern lights, shimmering below modules of the space station. The video was taken over the course of a space station orbit; it includes 950 images taken at an interval of half a second each.
Auroras are produced when charged particles from the sun interact with the Earth's magnetic field. These particles hit stray gas molecules high in the Earth's atmosphere and "excite" them, causing the molecules to glow. That's what produces the green lights visible in the video. [NASA's Best Earth-from-Space Photos by Astronauts in 2017 (Gallery)]
In the second video Gerst captured from space, a careful observer will see flashes of light, especially along the horizon. These are lightning bolts. Near the video's end, a green aurora erupts on the horizon, a blazing color that grows across the disk of the Earth. This video is made up of 1,675 images each taken about half a second apart.
"Lights, camera, action! The lightning captured in this time-lapse [video] taken by ESA astronaut Alexander Gerst from aboard the International Space Station is reminiscent of camera flashes in the night," ESA wrote in a statement accompanying the second video. "Alexander often sets cameras to automatically take pictures at regular intervals while he carries out scientific experiments and work on board the space station."
Gerst, however, didn't let the automatic exposures do all the work. He also posted a tweet showing lightning below, commenting, "Some of the lightning flashes we see from up here (like this thunderstorm in the southern Indian Ocean) are so incredibly bright that I can still see the flash with my eyes closed — more than 1,000 km [621 miles] away, in space."
Gerst and his Expedition 56 crewmates — NASA astronaut Serena Auñón-Chancellor and Russian cosmonaut Sergey Prokopyev — lifted off for the space station on June 6, arriving on June 8. They were welcomed on board by three other Expedition 56 astronauts, who were bedecked in Hawaiian shirts: NASA astronauts Andrew Feustel and Ricky Arnold, as well as Russian cosmonaut Oleg Artemyev.
In recent weeks, the crew performed a spacewalk to prepare the station for future commercial-crew vehicles and welcomed a SpaceX Dragon spacecraft shipment of coffee, ice cream and necessary space equipment. Crews typically perform 200 or so experiments during six-month stays in space.