Aurora in the Red

Photograph courtesy NASA

Many auroras appear green, but sometimes other colors such as red show up—as in this picture taken from the International Space Station on September 26.

An aurora's colors depend on which types of atoms cause the splash of light. In most cases, auroral lights appear when charged particles from the solar wind collide with oxygen atoms in Earth's atmosphere, according to a NASA statement.

"This produces a green photon, so most auroras appear green. However, lower-energy oxygen collisions—as well as collisions with nitrogen atoms—can produce red photons, so sometimes auroras also show a red band, as seen here."