Astronaut Thomas Pesquet, whose photos we’ve featured before, recently captured photos of the Aurora Australis, otherwise known as the southern lights (the counterpart to northern lights for the southern hemisphere). While photographing the brilliant night sky spectacle from Earth is interesting enough, to do so from outer space like Pesquet is even cooler.
Further distinguishing Pesquet’s image is the blue color of the southern lights, a rare hue for the phenomenon. Blue Aurora Australis only occurs with specific, unusual geomagnetic conditions. It’s typical to see a green or pink display, but blue and yellow are also possible, among other colors. The moon added additional illumination to the display.
Une aurore polaire bleue 💙 ! Je me demande ce que Mère Nature nous réserve pour la suite : une aurore boréale 🟡 ou 🔴 vif ? Un immense 🌈 ?.A blue aurora! What’s next Mother Nature? A giant rainbow?🌈 There are no complaints from me 💙 #MissionAlphahttps://t.co/BpJDnaFckx pic.twitter.com/DnWxMRw6JP
— Thomas Pesquet (@Thom_astro) August 26, 2021
On Facebook, Pesquet shared additional photos and information. He writes, ‘I don’t know why we’ve seen so many in a few days when I barely noticed one during Proxima, but this one comes with a little something extra. The moon was high and very bright, it lit the clouds creating a very special atmosphere… and it made this aurora polar… almost blue. For the pros of the photo, no it’s not the white balance, the devices were set exactly as with the previous pictures.’
During Pesquet’s first mission in space, he didn’t see many auroral displays. However, during his ongoing mission aboard the International Space Station (ISS), aurorae have been regular.
Image credit: Thomas Pesquet / ESA
On the topic of blue aurora, Aurora Borealis Observatory writes, ‘The main entities responsible for the aurora are monoatomic oxygen (O), diatomic nitrogen (N2) and ionized diatomic nitrogen (N2+). Oxygen emits either a red-orange or a lemon-green glow. N2 emits a deep red glow while its ionized form emits a deep blue/purple glow. As a rule the colors are set and never change but the three parameters stated above make the colors vary. Sometimes the color limits are quite defined but most of the time the entities mix with currents at different altitudes and create other colors like pink, yellow, emerald-blue, magenta and purple. During periods of intense geomagnetic storms you can potentially get a lot of different colors at once. Blue is synonymous with high geomagnetic activity. It happens in very precise conditions. It is quite rare and happens under very specific conditions.’
However, the article points out that you can also get a visibly blue aurora when the display is lit by moonlight, which can happen even if you don’t see the moon in the sky, as aurora occurs at the edge of space. Green aurorae can look more turquoise when affected by moonlight. ‘The top of the aurora tends to turn magenta, purple, violet and blue as the moon gets brighter. During full moon, it is not rare to actually see a blue auroral canopy on top of the green. Remember that it is not the actual color blue that is produced but it is more as if you were putting a filter in front of the moon.’
Is what Pesquet saw blue southern lights or a more typical green display that appears bluer because of strong moonlight? It could be both. Pesquet’s altitude makes it more likely for him to see N2+ molecules being excited and emitting blue photons. But, on the other hand, the moonlight is certainly having an impact. Either way, the images are stunning.