What Is Aurora

Although the aurora appear in the Earth's sky the forces that create it start out approximately 93 million miles away.  The sun continuously emits charged particles, protons and electrons, known as the solar wind, which travels from the sun to earth at around a million miles per hour, taking about two to three days.  The solar wind is a flow of ions continuously flowing outward from the Sun.  The Earth's magnetic field traps these particles, where they are accelerated toward Earth. Collisions between these ions and atmospheric atoms and molecules cause energy releases in the form of auroras appearing along the aurora ovals which roughly correspond with the Arctic and Antarctic circles.  The colour of the aurora depends on which atoms collide and the altitude of the collision -

Green - oxygen, up to 150 miles in altitude

Red - oxygen, above 150 miles in altitude

Blue - nitrogen, up to 60 miles in altitude

Purple/violet - nitrogen, above 60 miles in altitude

Aurora appear as a lights in the sky and can glow, not only as above, in a variety colours but also in different shapes and structures which usually change rapidly.  Activity levels increase up to midnight and the aurora begin to brighten, the height of aurora occur about midnight and the whole sky may become filled with bands and rays that move rapidly from horizon to horizon. This heightened activity can last anywhere from a few minutes to several hours before activity slows down approaching dawn. Auroras are more frequent and intense during the height of a solar cycle when Coronal mass ejections (CME) are at their peak as they increase the intensity of the solar wind.  This is why it is important to watch the sun or "space weather" to try and predict aurora activity.  According to various sources the next peak will occur in 2011 and 2012, so opportunities to see auroras outside their normal range such as the UK should be high.  Even if you miss a period of activity don't worry, It takes the sun 27 days to rotate around its axis, so 27 days after activity the region on the sun that caused the aurora will face Earth again and so should the aurora.