Last night, Oxford was treated to another spectacular display of the Northern Lights. For many students, this marked the second time this year they felt robbed, missing out on this natural wonder due to an untimely “early night”. The good news is that we’re still in a period of heightened solar activity, and you might have a third shot at getting your once-in-a-lifetime night in Oxford this year.
I’ve been privileged to see and photograph the Northern Lights both times they toured our city of dreaming spires, having also chased them in Alaska and Norway. Through this process, I like to think – or, at least my parents do – that I’ve become a (very) amateur heliophysicist. Here’s my crash course on why the Lights are showing up so frequently this year, and my tips for making sure you don’t miss their next visit.
The aurora borealis (the Northern Lights, cf. the aurora australis or Southern Lights) are a visual phenomenon that occur as a result of charged particles from the sun interacting with gases in our atmosphere. The amount and frequency of these solar particles reaching Earth fluctuates over time, in accordance with a roughly 11-year solar cycle. We’ve seen an increased number of strong auroral events this year because we’re nearing the peak (or “solar maximum”) of our current solar cycle. While it isn’t possible to know when exactly the solar maximum is until afterward, the National Oceanic and Atmospheric Administration (NOAA) predicts that the current solar maximum will be between late 2024 and early 2026.
As we enter this peak period, the sun emits an increased number of coronal mass ejections (CMEs), big masses of magnetised plasma that contain the charged particles we need to see auroras from here on Earth. Being aware of when these CMEs (and solar flares, a similar solar event) are identified is the first step to being ready for an auroral event in Oxford. Solar energy takes time to travel the 150 million kilometres between the sun and the Earth, so we typically have a (roughly) two-day heads up when one might be coming our way. A number of sites (e.g., SpaceWeatherLive.com) allow you to subscribe to news updates on this front for free, so you can have plenty of warning before considering a late night.
Note however that it takes a relatively strong CME or flare for the aurora to be visible as far south as Oxford. Sitting at a latitude of 52 degrees north, it takes a substantially greater amount of solar activity to be in the so-called ‘auroral oval’ (the belt-like region in which aurora may be visible) compared to somewhere like Fairbanks, Alaska (at 65 degrees) or Tromsø, Norway (70 degrees). Predicting the extent of solar activity is very difficult until just before impact, but various online models do provide approximated forecasts that can help you make a decision about how high to keep your hopes. The value to pay attention to here is the planetary K index, or Kp, a number which ranges from 0 to 9 – with 9 being highest, and what we observed in May – which represents the real-time strength of geomagnetic activity worldwide. At higher latitudes, the aurora can be seen with a very low Kp value. In Oxford, I’ve only been able to see the Lights with my eyes when the value reaches 8 (as it did last night). If you see a strong CME or flare event, keep an eye on the Kp forecasts; I’d only consider going out if the Kp forecast shows at least 7.
Lastly, solar activity on its own unfortunately isn’t enough; the north-south direction (represented as Bz on space weather sites) of the interplanetary magnetic field (IMF; this is the part where my parents think I’m Einstein) is also critical. Aurorae are only visible when the Bz value is in the negative, meaning the magnetic field has flipped south. So, if you’re tracking the numbers online and see that the Kp is above 8, watch the IMF and head outside only once you see that the Bz has turned negative. The only consideration at this point is the weather. Given the aurora dance at an altitude of 120–400 kilometres, anything between us and them can obstruct our show. In cities, this means light pollution. Anywhere, this means fog and clouds. On a strong night (Kp ≥ 8), I’ve seen the aurora from the city centre, but if you want to try your luck when the Kp is hovering on the border, you might see a glow from somewhere like Port Meadow.
Once you’re out there chasing, start by scanning the northern horizon with your smartphone camera in night vision mode (or a comparable low-light setting, available on most post-2016 models). Camera lenses are more sensitive to light than our eyes, so your phone will spot the aurora before you do. If you see something decidedly green, purple, pink, or red (the colour depends on what gases the solar particles are interacting with), let your eyes adjust to the dark, which can take up to 30 minutes. It’s also helpful to manage your expectations – unless there’s a particularly strong geomagnetic event, it’s possible that you might only see a faint glow in the sky, akin to a coloured cloud. Or, you won’t even see the show, but your smartphone camera does. These little disappointments hurt, but keeping your hopes relatively calm will help you appreciate any future event significantly more. Finally, do keep warm in the process, and happy chasing!
In terms of prime spots for taking photos in Oxford, look to be on the southern side of iconic landmarks such that you can have the Lights above them in the north-facing sky. The church side of the Radcliffe Camera and the Broad Street side of the Sheldonian Theatre are both great candidates for this kind of set-up, as is any high-up vantage point in a central college. If you’re lucky (and sufficiently convincing), you might also be able to have your college porter escort you to the roof, where you can capture the skyline and easily adjust your angle of capture no matter where the aurorae decide to appear.
