Aurora borealis - "Northern Lights"

Solar activity, which has caused spectacular light shows in the night sky over the past week is set to continue this week.

The aurora borealis, or “Northern lights” is caused when energetic electrons collide with the gases of the upper atmosphere at height of 100 km and higher. The characteristic red and green colours are produced when oxygen atoms, excited by the electrons, lose their extra energy by emitting light. Under normal circumstances auroral activity is confined to bands known as the “auroral zones” which encircle the northern and southern magnetic poles at high latitudes.

The progress of the storm can be monitored by devices known as “magnetometers”, sensitive instruments for measuring the Earth's magnetic field. Lancaster University's Department of Communication Systems operates the UK Sub-Auroral Magnetometer Network (SAMNET) an array of magnetometers across the UK and northern Europe funded Particle Physics and Astronomy Research Council (PPARC)..

The data from the magnetometer is processed as it is recorded and used to show the current activity level on a web page. (http://www.dcs.lancs.ac.uk/iono/aurorawatch) Interested individuals can sign up to an e-mail mailing list to receive alerts when the activity is high when there is a chance that aurora may be seen. This system, known as “AuroraWatch” was taken over by Lancaster University this year.

Professor Honary from Lancaster University’s department of Communications Systems explained “At 11:00 on 28th October 2003, an event known as a “solar flare” occurred on the Sun. This is an explosive release of energy tied up in the Sun's complicated magnetic field. The flare produced a very strong X-ray emission. This was an exceptional event of a magnitude which occurs very rarely.

“In Lancaster the aurora could be seen from around 20:00 as a green glow to the north through broken cloud. Patient observing paid off though as the cloud cover varied during the evening but broke sufficiently to the north around midnight to reveal a band of green rays which slowly moved about with occasional sudden bursts of brightening which seemed to flicker up the rays.”