As this issue of Radiation Protection Today is looking at non-ionising radiation, it seemed appropriate to include something on the northern lights or“ aurora borealis”. There are also southern lights in the southern hemisphere( aurora australis).
Although normally only visible in northern parts of the British Isles, we were fortunate to see spectacular displays of the aurora borealis in the south of the UK last May and October.
So what is the aurora? Solar activity such as explosions on the surface of the sun, solar flares or coronal mass ejections produces magnetic storms of highly charged particles which are carried on the solar wind and penetrate the Earth ' s magnetosphere. As these fast-moving particles hit our upper atmosphere they interact with oxygen and nitrogen atoms producing different colours as they shed their energy. Images from space show the auroras to be in the shape of ovals around the polar ice caps, as a result of electrons travelling down the magnetic field lines at the North and South Poles. Interaction with oxygen produces green and red flares, and with nitrogen produces purple and blue. The size of the ring depends on the strength of the solar flare.
The best time to view the aurora borealis is between September and April. It can appear between 5pm and 2am, but in the UK is usually seen between 9pm and 12pm. It can last a few minutes or several hours. The aurora ' s occurrence and intensity are based on the Solar Cycle which is reaching its maximum 2024-2025, so we should see more activity over this coming year.
It is usually difficult to see the northern lights with the naked eye- they are best captured on a camera with a long exposure.
The Space Weather Prediction Centre produces regular updates on the position of the aurora oval for both poles. It uses a model, OVATION, which predicts the location and intensity of geomagnetic storms and calculates the Kp geomagnetic index( from 1-9). If Kp is in excess of 6, it is likely that the aurora will be visible in a substantial part of the UK. The Met Office also uses the OVATION model but has re-coded it to run in Python rather than the original Interactive Data Language( IDL).
Canon 700D, lens 17mm, ISO- 800, f2.8, 4.5 sec © Sheila Liddle – Levi, Finland
Useful websites are: https:// www. metoffice. gov. uk / weather / specia list-forecasts / space-weather and https:// www. swpc. noaa. gov / products / aurora- 30-minute-forecast and https:// www. visitnorway. com / things-todo / nature-attractions / northern-lights / howto-photograph /
30 Radiation Protection Today www. srp-rpt. uk