The aurora in this photo has two colors of light, green and purple. Oxygen atoms give off the green light. The purple light comes from nitrogen molecules.
Click on image for full size
Image courtesy of Jan Curtis.

Colors of the Aurora

The aurora (Northern Lights and Southern Lights) are caused by collisions between energetic particles in Earth's magnetosphere and atoms or molecules in the upper atmosphere. Particles, mostly electrons and protons, are accelerated to high speeds and energies as they spiral along Earth's magnetic field lines. The particles bounce back and forth between Earth's magnetic poles, where magnetic field lines dip into the planet's upper atmosphere. Some of the energetic particles collide with atoms and molecules of oxygen and nitrogen in the upper atmosphere near the poles.

These collisions add energy to the atoms, which in turn shed the excess energy by emitting light. The brilliant displays of auroral lights have characteristic colors which depend on the type of atoms or molecules which are giving off the light. Oxygen atoms emit green light that is seen in many auroral displays. Oxygen atoms above 150 km (93 miles) in altitude can also give off red light. Energized nitrogen molecules emit red, blue, and violet light.

Last modified March 29, 2010 by Randy Russell.

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

Particle Radiation

Text for this level has not been written yet. Please see the "Intermediate" text for this page if you want to learn about this topic. To get to the "Intermediate" text, click on the blue "Intermediate"...more

The Earth as a Magnet

The Earth has a magnetic field with north and south poles. The magnetic field of the Earth is surrounded by the magnetosphere. The magnetosphere keeps most of the particles from the sun, carried in solar...more

The Thermosphere

The thermosphere is the fourth layer of the Earth's atmosphere. It is found above the mesosphere. The air is really thin that high up. The temperature changes with the solar activity. If the sun is active,...more

Basic Facts About Spiral Motion

Sometimes protons and electrons are forced to spiral around magnetic field lines. Electrons cirle the field line in one direction, protons in the opposite direction....more

Basic Facts About Bounce Motion

Some particles do move along the field lines of the Earth. They bounce back and forth from one pole of the Earth to the other....more

Earth's Magnetic Poles

Earth has a magnetic field. If you imagine a gigantic bar magnet inside of Earth, you'll have a pretty good idea what Earth's magnetic field is shaped like. Of course, Earth DOESN'T have a giant bar magnet...more


Oxygen (O2) is a kind of gas. A lot of the air you breathe is oxygen. That's a good thing, since we need oxygen to stay alive! About 4/5ths of the air in Earth's atmosphere is nitrogen (N2). Almost all...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA