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Wow, that’s slick. It was taken on May 29th by an Expedition 23 astronaut aboard the International Space Station (it’s unknown which one; NASA and the astronauts decided to give the expedition the credit, not an individual crew member). At that moment, the ISS was 350 km (190 miles) above the Indian ocean, and the astronaut was looking south. You can see the limb of the Earth and some stars in the background as well.
This aurora was probably caused by subatomic particles from an explosive event called a coronal mass ejection from the Sun five days earlier. The particles interact with our magnetic field, which channels them to the north and south poles. They slam into the air, ripping electrons off the atoms and molecules. When the atoms recombine, they give off light. The green glow seen here is characteristic of oxygen.
The aurorae are usually between 80 – 160 km (50 – 100 miles) above the Earth’s surface, so the ISS was actually higher up. However, the station was a couple of thousand kilometers away from the lights when this shot was taken.
I’ve only seen the northern lights (technically, the aurora borealis) once, when I lived in Maryland years ago… and it was just a faint red smear to the north. Someday I hope to see it in its full glory. But even then, it must pale — literally — to seeing such a thing from space.
