[b]Aurora Alert - night of 4/5 August 2010[/b]
There's a possibility of an aurora being visible from the UK tonight - although I must stress the word *possibility* and there are no guarantees. A large outburst of charged material from the Sun is currently 'rattling' the Earth's magnetic field and this may trigger some extensive auroral displays. I've seen one lovely photograph of the aurora from last night (3rr August) taken from 56 degrees north (Denmark) already.
There are a number of factors that need to be right for the aurora to be extensive and visible and if you want to check for yourself whether there's likely to be something visible, then follow these simple steps...
1) Take a look at the POES plot which is visible here: http://www.swpc.noaa.gov/pmap/pmapN.html
This plot looks down on the North Pole and gives you an indication of where the current auroral oval is located. You can see the outline of the UK on this map and if the oval extends towards Scotland, then this is a good sign. Also, make a note of the Activity Level figure on the left of the graphic. A value of 9 or 10 is preferred.
2) Take a look at the current Kp value here: http://www.swpc.noaa.gov/rt_plots/kp_3d.html
If it's higher than 6 or preferably 7, then this is a good sign too.
3) Finally, look at the vertical component of the magnetic field associated with the particle wind. If this is north, then it's shields up time on the Earth and the chances of a good display are diminished somewhat. If it's south then this is when things get interesting! You can see the current state of the field here: http://www.swpc.noaa.gov/ace/MAG_24h.html - it's the yellow plot (second graph down) that you're interested in. If the plot is below the centre line, then that's what we want.
You can also sign up for aurora alerts and view the current activity from: http://www.digitalsky.org.uk/index.php?wrapname=linksâŠ‚=awatch
Finally, keep an eye on http://www.spaceweather.com for updates and photos of the aurora from around the world.
To see the aurora, you'll need to find a dark location and look to the northwest / north / northeast, depending on the time of night. It'll normally appear, if it's there, as a glow close to the horizon. Sometimes this glow becomes structured and shows rays and curtains. If it's an intense display, it'll show colour as well. Green is the most common colour when you're close to the aurora but if you're a long way away, the chances are that you'll only be able to see the top of the display which will be red.
The best way to check or record the sighting, is with a camera. Use as wide a lens as you have got, fully open it and set the camera on a high ISO. Take exposures of the northern horizon of varying lengths from a second to up to a minute. If there's a green glow visible, then that could be the start (or end!) of a display.
Here are a couple of auroral shots taken from my home town of Selsey, right on the south coast of the UK. The first shot was taken in October 2003 while the other was a very weak display shot in 2004...