The sun undergoes an 11-year cycle of activity and as we approach a maximum, the number of storms on the solar surface which can lead to an aurora increase in both frequency and strength.
The current cycle is approaching maximum and has been much more active than recent maxima. This week has seen an unusual number of X and M class flares occur close together originating from several active regions on the sun. The charged particles which are released in one of these take several days to reach the Earth (not all come in our direction, so a solar flare does not necessarily result in an aurora).
When the charged particles react with the Earth’s magnetic field, they cause excitation of air molecules. This excitation is similar to how a neon light works. The different gases and the different levels of excitation give rise to different colours. Green is the most common colour seen, followed by red. You need a major high energy event to get other colours such as blue and purple.
Whilst aurora are commonly seen in the zones near the Earth’s magnetic poles, stronger events can be seen further away.
For the UK, northern Scotland is usually the best place to see aurora with any regularity. Stronger events will be visible further south. It is rare for an aurora to be seen over the whole of the UK.
The human eye is not sensitive to colours at low light levels. To the unaided eye an aurora often looks like a patch of mist or cloud in the sky with no obvious colour. At low light levels, we see in monochrome i.e. black and white. If the display is very intense, you may see some colour, but it’s unusual.
It’s a different story though with a camera. Most phones are capable of taking a decent image, although it will suffer from camera shake.
To take a photo with a camera, you need to have it mounted securely, e.g. on a tripod. You want a wide-angle lens, and you want it wide open. To reduce camera shake, either set the self-timer, or use a remote trigger.
Set the ISO to say 1600 and try exposures of between 1 and 5 seconds. Depending on how light polluted your skies are, you may need to play with this – increasing ISO to 3200 or reducing to 800.
Aurora are very dynamic and images a few moments apart will be different.
The display on 10/11 May 2024 is one of the best seen from the UK in the last 25 years.