Auroras are created in the upper atmosphere when the solar wind (a stream of charged particles emitted by the Sun) interacts with the Earth’s protective magnetic field. Charged particles within the magnetosphere are accelerated down field lines toward the ionosphere, where they collide with different gases (particularly oxygen and nitrogen) and emit light as a reaction. Auroras often appear as neon green, purple, yellow, or red, depending on the gas molecules being excited. Green, for example, indicates collisions with oxygen.
Astronaut photograph ISS052-E-63378 was acquired on August 19, 2017, with a Nikon D4 digital camera using a 22 millimeter lens, by a member of the Expedition 52 crew.
Click here to see a video of the flight over the aurora.