Loch Ainort, Isle of Skye

Exploring the edges of darkness, Pete Bridgwood takes us on a journey through the stages of twilight, that magical time before sunrise and after sunset when beautiful and subtle colours creep across the sky

Once the bleary-eyed fatigue of an early morning alarm has waned, there can be few spectacles more magical than the psychedelic sprawl of colour gracing a pre-dawn cloudscape. While darkness still envelops us, the rotation of earth to the point where the centre of the sun is 18 degrees below the horizon marks the official beginning of morning twilight.      
Twilight is defined in three stages, as the sun appears to rise up below the horizon. The first stage is known as astronomical twilight, and to our naked eye it is barely discernible from the darkness of night. When the centre of the sun's disc reaches 12 degrees below the horizon it becomes possible to discern the position of the horizon, but it remains too dark to walk around without the aid of a torch and we're not yet able to discern any pre-glow from the rising sun along the horizon.      
The onset of the second phase, known as nautical twilight, is an indication to landscape photographers that we need to start preparing for the ‘performance'. The first hints of colour are often invisible to our naked eye, because we don't perceive colour very well in relative darkness, but during the later parts of nautical twilight our cameras can sometimes record what we're unable to see, and the resultant images can look surprisingly colourful. The dull light still demands a long exposure, so there's no need for filters to blur the surface of water or smear the clouds.      
Civil twilight begins when the sun reaches six degrees below the horizon. As a general rule, we should ensure that we're on location before the start of civil twilight because this also heralds the start of the ‘blue hour', when the sky becomes awash with the more strongly scattered blue, indigo and violet wavelengths. The ‘blue hour' is a misnomer, it actually only lasts for around 10 to 15 minutes at the start of morning civil twilight and then blends seamlessly into the ‘golden hour', when the yellows, oranges and reds start to steal the show. At dusk, all these phases repeat themselves, but in the opposite direction.      
My image of Loch Ainort was made from the roadside at the very start of the ‘blue hour' on a cold morning in March. The violet reflections in the loch were unusually vivid and even at this earliest stage of twilight I could sense something special was about to follow. The sunrise that morning was nothing short of spectacular: an explosion of crimson. But sometimes less is more, and perhaps this calmer splash of indigo has a more enduring appeal.

Canon EOS 1Ds MkII with 17-40mm lens at 17mm, ISO 100, 25sec at f/13, Manfrotto tripod and head

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