On the evening of 25 September in the northern hemisphere, the northern lights, or aurora borealis, were seen creating bright displays further south than usual. These expanses of green, purple and red flickering glows in the night sky, created by particles from the sun, are a wonder to behold. But if you missed them on Sunday, don’t worry, there is still a chance to see them.
The northern lights tend to be brighter when the sun has been more active. Recent observations of sunspots, a measure of how active the sun is, show a dramatic increase from this time last year, and we are approaching the expected peak of the 11-year solar cycle in 2024 or 2025. This means that over the next few months in the northern hemisphere, the northern lights will probably be stronger than they have been for at least a decade.
What are the northern lights?
The northern lights are generated by the solar wind – a stream of charged particles travelling from the outer layer of the sun, or corona. Bursts of solar wind, called solar flares, slam into Earth’s magnetic field, which acts like a shield around the planet that deflects most of the particles. But at its weakest points around the poles, some particles penetrate into the upper atmosphere, where they collide with and excite, or energise, gas molecules. As these molecules lose energy again, they release photons of light that make the auroras.
The type of excited molecule, along with the altitude of the collisions, determines the colour of each aurora. The most common are pale yellow and green from oxygen molecules around 120 to 180 kilometres up. Less frequent are red auroras, generated from oxygen around 200 km above the ground, while red-purple auroras come from nitrogen below 100 km.
Where will the northern lights be visible?
The stronger the solar flare, the further south the northern lights will be visible. The particles take around a day to travel to Earth, so we can predict up to a day in advance how strong the aurora is likely to be. Keep an eye on forecasts and aurora prediction apps.
When is the best time to see the northern lights?
If the solar wind is active, the aurora can be seen as soon as it is dark. But the level of activity can change quickly, so the best bet is to keep an eye on live reports of solar activity.
There are websites and organisations monitoring the sun that can give a forecast for the coming day or even week. The US National Oceanic and Atmospheric Administration site, for example, provides observations for the past three days along with 30-minute predictions of solar activity. This is measured using the planetary K-index, or Kp, on a scale from 0 to 9. The greater the value, the higher the activity.
To see the lights with the naked eye in central England, for example, a Kp value of 8 is usually necessary. The free app AuroraWatch UK also has half-hourly aurora forecasts and you can set up an email alert to make sure you are ready for any celestial light shows.
How can you see the northern lights?
Get to a dark spot as far from any light pollution as possible. It is more likely you will see them from rural areas than urban ones, but if it’s bright enough you can see them even in a city.
If you are unsure where to go, find somewhere dark and look towards the northern horizon. Then you need to wait and let your eyes adjust. But don’t expect to see aurorae in the stunning, bright colours shown in photos. When you view them with the naked eye, the aurorae are much subtler and can be tricky to spot the first time you try.
If you have a camera with a digital display, looking through the display can help confirm that you are looking at aurorae, as sometimes they can appear greenish-white to the eye, but very green in the camera. Keep an eye on the weather forecast, too, as you won’t see any northern lights if you have a cloudy sky.
How to take photographs of the display
Most smartphone cameras will be able to pick up the green hues of the northern lights, and the red and purple if it is there. If you have a digital camera and a tripod, try a long exposure with the shutter speed set to a few seconds.