THE FENLAND SKY AT NIGHT -- The Aurora Borealis

The aurora borealis, or the northern lights, is at its simplest a bright glow in the night sky. As the picture above, taken from an aircraft above Northern Finland in December 2006, shows this is a weak description! The lights at the bottom of the image are the lights of the town of Kuusamo, near to the Russian border, and they're slightly blurred because of the length of exposure necessary to get the aurora to register properly.

The aurora -- named after the either the Roman goddess of the dawn or the Greek god of the North wind -- is an electro-magnetic phenomenon. Charged particles that originated in sunspot explosions stream towards the earth's upper atmosphere, where they collide with atoms of the gases that make up the atmosphere and fluoresce in exactly the same way as a 'neon' light. The predominant colour is green, which results from oxygen collisions, by far the most frequent. But other colours are seen, notably blue and purple from two forms of nitrogen.

The auroras -- as well as the aurora borealis in the northern hemisphere, there's a parallel aurora australis in the south -- are basically polar phenomena, which is why we tend to associate them with northern latitudes such as Finland. In which case, the photograph below should surprise you:

This photograph was taken (in October 2003) from Selsey on the south coast of Britain. In this image, you can see another characteristic of the aurora -- the curtain like striations in the display, something caused by the fact that the excited gas particles tend to line up with the earth's magnetic field in a way reminiscent of those school-day experiments with magnets and iron filings.

Our information is that you could expect to see around eight displays each year on the south coast, but as many as a couple of dozen in Lincolnshire. So Nordelph, with relatively minor light pollution, could be an excellent place for some stunning displays. The problem is knowing when to look out for them -- a clear night may be worth a glance, but if you want to maximise your chances you need to know when to look. Generally in the northern hemisphere, displays occur in September and October and in March and April -- so sorry for raising your hopes as we post this in December!

More seriously, you can employ the resources of the Internet. Sunspot activity is just a weather phenomenon and the website www.spaceweather.com is devoted to that type of weather. The home page is headed with a constantly-updated 'weather forecast' for the sun, signalling when you can expect to see significant auroral displays.

We would be proud if any of these images -- the one above is the same 2003 display from Selsey -- were ones that we had taken. However, they're used (by permission) from the collection posted on the web by Pete Lawrence at www.digitalsky.org.uk. Pete is an astronomer who regularly conducts expeditions to see the aurora (and eclipses), either to northern latitudes where sightings are more reliable, or in the 'Northern Lights Flights' you have possibly seen advertised (departures from Norwich are included in the programme). These give you a presentation on what to expect, and then take off for a three-hour flight north. On sighting the aurora, cabin and navigation lights are turned out -- even the 'no smoking' signs are taped over -- and the plane circles so that everyone gets a view.

You might deduce that we've been on one of these flights -- actually, not so! We took one of the land-based expeditions (to Finland) and it rained all weekend. The image above is the aurora we saw, but only on the return flight. Instead, we spent a day in an unseasonably warm Finnish winter, enjoying a sledging trip with huskies and trying to look as if we weren't part of the group that had come to visit Father Christmas!

We strongly recommend Pete's website (above). As well as many many stunning images, there's a wealth of astronomical information, and links to many useful websites -- including the one that you can access to watch the satellite weather photographs that you see so often on television, animating across your computer screen.