On Sunday evening, the northern lights, or aurora borealis, were seen further south than usual, with glimpses even possible in Cornwall, in south-west England. These displays of green 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 this week – particularly on Monday.
What are the northern lights?
They 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 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 aurorae.
The type of excited molecule, along with the altitude of the collisions, determine the colour of the aurorae. The most common are pale yellow and green from oxygen molecules around 120 to 180 kilometres up. Less frequent are red aurorae, generated from oxygen around 200 km above the ground, while red-purple aurorae come from nitrogen below 100 km.
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.
Where will the northern lights be visible tonight?
The stronger the solar flare, the further south they 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. The UK’s Met Office says the lights are likely to be visible there again on Monday night, perhaps even in central or southern England. For the rest of the week, keep an eye on forecasts like the Met Office and other aurora prediction apps.
When should you look for the lights?
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, 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 in it 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. 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 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. If you have a digital camera and a tripod, try a long exposure with the shutter speed set to a few seconds.