BBC News - Why have the Northern Lights moved south?
5 August 2010 Last updated at 10:13 ETWhy have the Northern Lights moved south?
By Victoria Gill Science reporter, BBC NewsThe Northern lights, it seems, have moved further south and have been visible from countries including Germany and Denmark. So what exactly is causing this spectacle? And how long will it last?
A recent increase in solar activity is having an effect on Earth's magnetic field (blue) and the Northern Lights
- 1. The Northern Lights or Aurora Borealis are caused by charged particles around the Earth being excited by the interaction between the Earth's magnetic field and the solar wind, a stream of particles and magnetic field from the Sun.
- 2. The solar wind's magnetic field can "break" Earth's magnetic field lines and drag the two ends away, creating "open" field lines. When the Sun is very active, as it has been recently, more of the Earth's magnetic field lines are broken.
- 3. These lines "snap back" into a continous loop around the Earth, producing an electric current that excites gas particles in our atmosphere, making them glow. When more of Earth's magnetic field lines are broken, this reconnection - and the glow it causes - occurs further from the poles.
The Northern Lights, or Aurora Borealis, are caused by charged gas particles - that flow away from the Sun as a "solar wind" - interacting with the Earth's magnetic field.
This solar wind has its own magnetic field, which can "drag away" the Earth's magnetic field lines, disconnecting them from our planet.
Eventually though, the field lines "snap back" into the continuous loop that exits one of the Earth's magnetic poles and re-enters at the other. This snapping back or "reconnection" means that particles that were in the solar wind are pushed into the Earth's atmosphere.
The charged particles "excite" gases in our atmosphere and make make them glow - just like gas in a fluorescent tube. The colours depend on the type of gas - a red or green glow is oxygen and the blue and purple colours are produced by nitrogen.
The spectacular Aurora Borealis are usually only visible in the far north
The huge ejection of charged particles from the Sun on 3 August disconnected more of the Earth's magnetic field lines and when these snapped back to Earth the resulting auroras were visible much further south than usual.
Dr Colin Forsyth from the UCL's Mullard Space Science Laboratory explained that the boundary between "open" (or disconnected) field lines and the rest of the Earth's magnetic field is "where aurora are most likely to occur". And when more field lines are disconnected, that boundary moves south.
On Wednesday night stunning light displays were seen over parts of northern Europe, including Germany and Denmark, but so far scientists say there has not been "sufficient activity" over southern parts of the UK to produce a light show.
Professor Mike Kosch from Lancaster University said it was "possible but unlikely" that the Northern Lights would be visible from England on Thursday night.
He explained that the chances to view the results of the magnetic storms would be best in northern Scotland and northern parts of Europe. "They could be going on above our heads during the day, but we can't see them," he said.
The space storms can affect satellite communication systems, but satellite operators monitor the activity of the Sun to mitigate any potential problems.
The same phenomenon occurs around the southern magnetic pole and is known as the Aurora Australis or the southern polar lights.
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