When people visit my Studio, and see the images I have taken of the Northern Lights, they ask “Are they really that green colour and can you see it?” to find out the answer, please read on…
"Are they really that green colour and can you see it?”
The short answer to this question is yes, but our eyes can see only see the Northern Lights as a grey or bluish grey dancing light shapes in the sky. This is because of how our eyes work in the dark compared to how they work in daylight.
You see, the retina in the human eye contains two types of photoreceptors, rods and cones. It has about 6 to 7 million cones and they provide the eye with the ability to distinguish colour. However, these cones only work effectively when it is light. On the other hand, the eye has about 120 million rods and these are far more effective at helping us to see in low light and near dark conditions, but they cannot distinguish colour. So, as it gets dark and the cones stop working, our eyes move from enabling us to see in full colour to enabling us to only see in black and white. This means that anything we look at in the dark, including the Northern Lights will only be seen in black and white and shades of grey.
On the other hand, the sensors that you find in digital cameras do not suffer from this limitation and are extremely effective at picking up both light and colour in the dark. This means that they pick up the colours in the Northern Lights that were present at the time meaning that the colours you see in the images produced by a camera are not a result of any photo editing.
The auroral colours that are present are actually a result of collisions between gaseous particles in the Earth's atmosphere and charged particles released from the sun's atmosphere. Three colours tend to be present in the aurora, with each colour depending on the type of gas particles that are colliding. Green is the most common as most solar particles typically collide with our atmosphere at an altitude of around 60 to 150 miles where there are high concentrations of oxygen and it is particle collisions involving oxygen that produce a pale yellowish-green colour.
Blue and purple can also be present, but far less frequently than green as they tend to only appear when solar activity is high enough to cause particle collisions in our atmosphere at an altitude of 60 miles or less. At these heights, it is a reaction with nitrogen that causes the aurora to be tinged with purple or blue.
Finally, on rare occasions, red can be present in the aurora, but only when intense solar activity causes solar particles to react with oxygen at altitudes above around 150 miles. At this height the oxygen is less concentrated and is “excited” at a higher frequency or wavelength than the denser oxygen lower down in the atmosphere and produces a purely red aurora.
So, what the digital camera sees is exactly what is happening, colours and all, whereas the human eye will perceive the aurora as a grey or bluish grey dancing light. To give you an idea of what this would look like I’ve prepared two images of a fantastic Northern Light Show that happened at Castle Tioram in September of last year. The one on the left is what the camera saw and the one on the right is what I saw as I was taking the photograph.
You will find the images featured in this blog, along with many more, in the “Our Night Sky” photo gallery. If you’d like a print of any one of them, please feel free to get in touch. Also get in touch if you’d like to arrange some night photography tuition.
Hi, I’m Steven Marshall, a Scottish landscape photographer based at Rockpool House in the heart of the beautiful West Highland Peninsulas of Sunart, Morvern, Moidart, Ardgour and Ardnamurchan. Get in touch for photography tuition, tours and print sales.