The flickering shimmering colours of the aurora must be the most spectacular of heavenly events, especially in the darkness of midwinter. Students will explore both the science and beauty of these phenomena.
It is impossible to witness such a beautiful phenomenon without a sense of awe and yet this sentiment is not inspired by its brilliancy but rather by its delicacy in light and colour, its transparency, and above all by its tremulous evanescence of form.
- Robert Scott
Auroras, which occur in the polar regions in both hemispheres, have only been reasonably well-explained in the 20th century. They are caused by charged particles from the sun interacting with the earth's magnetic field. Some of the particles entering the upper atmosphere travel along the magnetic field lines and, as they strike atoms of the earth's thermosphere, create light which is seen from below as an aurora.
The colours in an aurora depend on the type of atom struck and the way in which its structure is altered by the collision. For example, red colours are produced by large numbers of particles of low energy unable to penetrate below about 200 km, while green light is believed to be produced by high energy particles exciting oxygen atoms in the lower parts of the thermosphere. It is not unusual for the solar wind to generate 100,000 megawatts of electricity in a three-hour auroral display. This can cause temporary interference with power lines, radio and TV broadcasts and satellite communications. By studying auroras scientists can learn more about the solar wind and how it affects the earth.
The science museum in San Francisco, The Exploratorium has beautiful aurora photos and video clips, self-guided lessons and lots of information. See also the aurora page at MichiganTech. Space Weather Today is another great site which features current views of the sun and auroras.
See an amazing image of the aurora australis taken from the Space Shuttle Discovery.
Folklore is rich with explanations for these shimmering curtains of light. Various cultures have explained them as dancing spirits or blood raining from the clouds. Among the Eskimos the descriptions are often of events that precede or follow life on earth, of the play of unborn children, or of torches held by the dead to help the living hunt in winter. Vikings thought them a reflection in the sky of Vulcan's forge. Maoris described 'the burning of the sky'. The University of Alaska's Geophysical Institute's Poker Flat Research Range site, The Aurora, includes stories and legends about the aurora from the past.
- Ask students to consider what else people might have thought the aurora could be, and to write a short description of their explanation.