Tonight's Sky
Sun
Sun
Moon
Moon
Mercury
Mercury
Venus
Venus
Mars
Mars
Jupiter
Jupiter
Saturn
Saturn

Tonight's Sky — Change location

OR

Searching...

Tonight's Sky — Select location

Tonight's Sky — Enter coordinates

° '
° '

Most of the photographs I see of the aurora borealis are green. Is this due to the film used?

William Taylor, Seaford, Virginia
RELATED TOPICS: AURORAE
Aurora borealis
Aurorae create many colors, but green is the most common. This mystical color arises from interactions with the atomic oxygen that’s abundant in Earth’s upper atmosphere.
Eric Betz
As the friends who joined me on the TravelQuest/Astronomy magazine Norway aurora tour in October can tell you, the northern lights are one of the few night-sky phenomena that look better in person than they do through a heavily processed image. The lights are truly green. They also can appear red, orange, yellow, magenta, and a variety of combinations. Green is the most common color.

The classic aurorae flash across the sky and move in curtains and arcs. These are called discreet aurorae, and they can be bright enough to read by. Diffuse aurorae are harder to see and typically look like fuzzy clouds, which are better detected by long camera exposures.

In either case, northern lights are just emissions of photons. The solar wind accelerates particles during their final 10,000-kilometer-plunge into the atmosphere, and then they roughly distribute perpendicularly along Earth’s magnetic field lines. That creates the arcs. Earth’s atmosphere is mostly nitrogen and oxygen. Aurorae occur when ionized nitrogen picks up an electron and smashes into oxygen and then they both return to a ground state. That is, the oxygen radiates away the energy in greenish wavelengths.

When oxygen is excited in the atmosphere, it typically happens at lower altitudes. But in intense storms, it also can happen at higher altitudes and with other gases, which creates a plethora of colors.

As you watch the northern lights dance, they also appear to have a bottom level. This is because atomic oxygen is less common below 62 miles (100 kilometers) altitude in Earth’s atmosphere.
Eric Betz
Associate Editor
0

JOIN THE DISCUSSION

Read and share your comments on this article
Comment on this article
Want to leave a comment?
Only registered members of Astronomy.com are allowed to comment on this article. Registration is FREE and only takes a couple minutes.

Login or Register now.
0 comments
ADVERTISEMENT

FREE EMAIL NEWSLETTER

Receive news, sky-event information, observing tips, and more from Astronomy's weekly email newsletter. View our Privacy Policy.

ADVERTISEMENT
ADVERTISEMENT
Apollo_RightRail

Click here to receive a FREE e-Guide exclusively from Astronomy magazine.

Find us on Facebook