Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Aurora borealis
Name: Amanda Smith, Jeff, Burce S MacCallum, and Jan S Belzer
Status: Other
Age: N/A
Location: N/A
Country: N/A
Date: N/A 

What is an aurora borealis made of and why does it only appear sometimes? Why do aurorae appear near the magnetic poles? What is the ionosphere?

Aurora Borealis is made of charged particles moving in Earth's magnetic field. These particles emit light as they interact with the ionosphere. These particles are emitted by Sun in small quantities (as compared to Sun's mass) and whenever these cross Earth, we see the display. Solar activity has an 11 year period so the Auroral activity also varies over this period.

The ionosphere is the uppermost layer of atmosphere. It is completely ionized (hence the name ionosphere) by the radiation from the Sun and cosmic rays. Near magnetic poles, the lines of magnetic field (of Earth) enter the atmosphere. Charged particles emitted by the Sun move along the lines of magnetic field. Therefore they enter the atmosphere where the lines enter the atmosphere -- at the magnetic poles. Here they interact with a atmo- sphere and produce Aurora.

Jasjeet S Bagla

The Sun is continually sending out particles (mostly protons and electrons) into space; some are blasted out by solar flares and sunspots, others "boil" off from the very hot corona (the Sun's upper atmosphere) into the solar system. This is called the solar wind. The Earth's magnetic field shields the Earth from most of these particles; some get trapped in doughnut-shaped regions surrounding the Earth called the Van Allen belts. Particles continually "leak" from these regions, traveling down along the Earth's magnetic field lines (that is the reason they are usually seen only near the north and south poles), until they crash into the Earth's upper atmosphere. The collisions transfer energy to atoms of gas, which then give off light, just like a neon sign. Pictures from space show that there is a permanent "ring" of auroral activity around the poles; but during times when the Sun is very active, northern auroras may be seen as far south as Mexico.

RC Winther

Click here to return to the Astronomy Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory