Skywise Unlimited

 
ASTRO 101

Analemma
Asteroids
Aurora
Big Bang
Black Holes
Bode Titius
Brightest Stars
Comets
Constellations
Coordinates
Cosmology
Cruithne
Dark Matter
Eclipses
Galaxies
Historical
HR Diagram
Hubble's Law
Intelligent Life
Kepler's Laws
Leap Year
Light Waves
Lunar Libration
Messier Objects
Meteors
Milky Way
Moon
Moon Phases
Planets
Precession
Rainbows
Redshift
Seasons
Stellar Evolution
Stardust
Sun & Fusion
Telescopes
Tides
Time of Day
Twilight
Zodiac
 
Aurora
"Peacock Aurora" © 2007 photo by RL.Dietz

Auroral activity strongly correlates with solar activity. Peak activity repeats on an 11-year cycle. The story begins with the solar surface which continuously emits charged particles such as protons and electrons. These particles are collectively known as the Solar Wind. The particles stream through the solar system at 400 km/s (about a million miles per hour). They collide with the Earth's magnetic field and are directed along those lines of force towards the Earth's magnetic poles. The particles then energize the atoms of rarified gases in the upper atmosphere causing them to "fluoresce" with colors.

Aurora Borealis (northern lights) and Aurora Australis (southern lights) are usually found to occur at heights of 100 to 120 km, but a few are higher than 500 km. They are most intense in an area known as the "aurora ovals" which range roughly from 12 to 23 degrees from the magnetic polar regions of Earth. The oval is largest on the night side of Earth and smallest on the dayside, hence the oval shape.

The colorful lights in the sky appear in a variety of shapes that can change quickly. There are several terms astronomers use to describe the different forms of Aurora. For instance...

  • Arc: a simple slightly curving arc of light.
  • Band: an irregular shape with kinks or folds.
  • Patch: region resembling a cloud.
  • Veil: a very large area of uniform light.
  • Ray: straight vertical shafts aligned with the Earth's magnetic field lines.
  • Picket Fence: a row of several rays.
  • Curtain: resembling folds of drapery.

click to enlarge
"Aurora at the South Pole" © 2007 photo by Katherine Rawlins
Auroral Events are also classified according to their behavior.

  • Quiet: a uniform intensity over a longer period of time (minutes).
  • Pulsating: brightness changing in a periodic manner.
  • Flickering: brightness changing about 5-10 times per second.
  • Flaming: bursts of light appearing at the base then rapidly moving up and disappearing at the top.
  • Break Out: sudden growth of activity across a large area of the sky.


click to enlarge
"Aurora from Space" STS-39 Crew, NASA
Auroral brightness is rated on a scale of 0 to 4, 0 being a barely visible Aurora, and 4 being a very bright Aurora. Auroral colors can cover the entire light spectrum. On rare occasions sounds such as hissing, swishing, rustling or crackling were reported, to accompany an Aurora.

The name "Aurora" was given to the events by Galileo. It refers to a character from Greek mythology, the herald of the dawn.

American Indian legends of the aurora.
NOTICE: All of the images provided here are intended for private use only. Reselling, adding to a collection or any other use not specifically granted, is prohibited. All images are copyrighted © by the respective artists. Downloading any image from this site indicates acceptance of the terms and conditions as stated here. Please contact the individual artists regarding other permissions or for additional information.