Why do the aurora look better through a camera? And how do you spot a fake image? Q&A with an astrophotographer

Thanks to modern cameras, the phenomenon was all over social media. It seems almost everyone knew someone who managed to snap vivid images of the night sky illuminated in pink, purple and green.

To understand why camera phones were able to pick out colours and details invisible to the naked eye, The Conversation spoke to Darren Baskill, an astrophysicist and photographer – an astrophotographer – at the University of Sussex.

For those who missed them, were the lights really as spectacular as they looked in photos?

The short answer is: no. I was lucky enough to see the aurora in person, in the dark skies of the South Downs National Park. But even there, I could only faintly see the colours with my own eyes. The difference between the green and red hues were particularly striking, even with the naked eye, but those colours were certainly enhanced when viewed through a camera.

However, there were also lots of fake images, often where two completely different photos had been merged together to form one. Be particularly wary of any photo claiming to show the aurora amid a starry sky above a large city.

Even on a perfectly clear night you wouldn’t see many stars due to light pollution. For instance, London’s Tower Bridge has been superimposed on a photo of the aurora possibly taken from a remote, dark location in a Nordic country.

Note the lack of stars in this – very believable – photo of Battersea Power Station.

Why are cameras able to see the colours more vividly?

The technology behind modern digital cameras is rapidly improving, with every generation of camera being far superior to the last. Advancements in mobile phone cameras have been driven partly by people wanting to take photographs in dimly lit night clubs and bars, and that sensitivity to low light levels allows modern phone cameras to also see the northern lights so clearly.

Inside the human eye, there are two types of cells used for seeing. The “cone” cells are sensitive to colour but need plenty of light in order to function, whereas the “rods” cells are sensitive to low light levels but cannot distinguish colour.

When it’s dark, the cone cells don’t work and the rods take over. This is why, when you stumble to the bathroom in the middle of the night, everything appears grey as the cones aren’t receiving enough light to recognise colours. But that’s when the rods come into their own, allowing to see your way in grey scale.

Cameras don’t have this problem when taking a photograph. To compensate for the dark conditions, a camera can just take a longer exposure and collect light for longer, building up a picture of the scene and collecting colours that the rods in the human eye cannot detect.

Can you give us an example?

Sure. Here are three versions of the same photo I took in my back garden on the outskirts of Brighton, on England’s south coast. The first is the original unprocessed photo, while the second has been processed – I changed the brightness and contrast and upped the saturation. The third version has been processed to represent more or less what I saw with my eyes.

What about light pollution?

Another problem is inefficient lights that shine into the sky where it is neither needed nor wanted. This reflects off the atmosphere and drowns out our view of the stars and aurora. The pupils in our eyes shrink to prevent us from being blinded by light, whether it be sunlight or a neighbour’s floodlight – but this also prevents us from seeing the fainter aurora.

For the best views of the aurora, you need to go somewhere dark so that the pupils in your eyes can relax and open up to allow as much light into your eyes as possible, which also allows you to see some of the colours.

Are some auroras more photogenic than others?

Auroras form a wide variety of different patterns and colours, depending on several factors including how the magnetic fields of the Earth and Sun are interacting with each other, the gases in our atmosphere that are emitting the light, and how energetic the auroral activity is.

Some of these aurora can be quite static, such as a green glow caused by oxygen in our atmosphere, while others can be colourful and dynamic.

Are some phones and cameras better than others?

All cameras are different, but usually the more you spend the better the camera. I personally have a relatively cheap mobile phone, so I was unable to capture any of the aurora using that. However, I also have a relatively expensive DSLR camera, and I was able to capture some stunning views using that.

For next time, what are some tips for taking good photos of the aurora?

To get great photos of the aurora and the night sky in general, aim for dark skies. The further away you can get from the inefficient lights of towns and cities, the better. Also the more you can spend on your camera, the better your results will be.

When photographing aurora, you want your camera to be collecting as much light as possible. Automatic camera modes find it difficult to judge this, but in manual mode have the aperture of your camera wide open (f/4, for example), make your camera chip amplify the image by using a higher ISO setting, and use exposure times of a few seconds.

Personally, I found four second exposures at f/3.5 and ISO 2500 worked well for me on Friday night. But the beauty of digital photography is that you can experiment with different settings as you go along, and see the results for yourself in real time.

Darren Baskill, Lecturer, Physics and Astronomy, University of Sussex

This article is republished from The Conversation under a Creative Commons license. Read the original article.