The aurora is arguably one of the most spectacular sights of the night-time sky. During intense displays, its characteristic swirls and folds of coloured light never fail to make a deep impression on the observer.
Aurorae are produced when highly energetic particles collide with and excite the atoms and molecules of the Earth’s upper-atmosphere.
These particles, protons and electrons, are of solar origin and travel via the Earth’s magnetic field to form two permanent rings of auroral light centred around the magnetic poles.
The so-called ‘auroral ovals’, during quiet solar activity, are located at arctic latitudes – too distant to be seen from the UK. However, following intense solar events and the subsequent enhancement of the solar wind, the auroral ovals, under certain conditions, expand equatorwards.
It is at such times that auroral displays are seen at temperate latitudes such as the British Isles.
Being so closely linked to solar activity, the aurora reflects the changing nature of the solar cycle. Generally, it can be said that more aurorae will be seen from UK latitudes over the few years around solar maxima.
More precisely, the aurora tends to produce two noticeable peaks. The first precedes sunspot maximum by about a year and results from solar flare activity. The second, due to solar coronal hole events, occurs over the early stages of declining solar activity, following sunspot maximum.
Strangely, at the actual time of maximum sunspot count, the aurora tends to be infrequently seen.
The visibility of the aurora also changes over a given year. Each equinox – spring and autumn – tend to be favourable observing periods.
In contrast. the solstices normally show a drop in auroral incidence. Although auroral activity follows a pattern of peaks and troughs, observers should be alert at all times – it is not unknown for good displays to be seen over England at times of solar minima!
The aurora can occur at any time during the course of a night. Periodic checks, say, every hour or so, normally suffice and can be combined with other forms of astronomical observing such as variable star or meteor work, for instance.
Displays are best seen from dark locations with good, clear northern horizons (auroral activity will always commence from the north).
Nights with bright moonlight or twilight conditions are unfavourable. Nonetheless, bright displays can, on occasion, penetrate a moonlit or twilit sky..