[This image is best viewed at full resolution with side to side panning.]

Picture description:

During a 3 week period centred on the summer solstice the northern night skies are in permanent twilight at 54N where I live in the UK. Occasionally a superb noctilucent cloud display makes up for the inability to do regular astrophotography. This was the first display I observed in 2014.

Noctilucent clouds are composed of very small ice crystals and are typically found at an altitude of 80km - on the edge of space. Even though it is night on the ground these clouds are directly lit by the sun. The reflected sunlight gives rise to these "night shining" clouds.

The view is from the north side of the village of Bramhope looking out directly northwards across the Wharfe valley to Norwood on the left and Armscliff Crag on the right (the bump on the horizon). The time was approaching local midnight.

The constellation of Auriga hangs over the center portion of the panorama. Capella is above the local landmark of Armscliff Crag, a prominant gritstone tor at the edge of the Yorkshire Dales.

Science:

Some basic trigonometry will help work out how far north the clouds right on the horizon are and how far away this is by line of sight. It is also possible to work out where the top of the cloud display is by using known stars.

NLCs are about 80 to 82 km above the Earth. Earth's radius is 6371 km.

The increase in latitude from your location to the clouds right down on the horizon is given by:

cos-1 (6371 / (6371 + 80)) = cos-1 (0.9876) = 9 degrees.

The picture was taken close to 54 North so the clouds on the horizon are at latitude 63 North which is 1 degree north of the Faroe Islands.



The direct line of sight distance to the furthest visible clouds is:

tan (9) = distance / 6371

distance = 0.1582 * 6371 = 1009 km

The bright star in the picture is Cappella is very very close to 10 degrees above the northern horizon (measured via Stellarium). In the panorama the top of the clouds are 5 degrees above the horizon. This gives (via the sine rule and angle sum rule ):

@ 5 degrees above horizon (1/2 way to Cappella) - cloud latitude = 59.3 degrees; line of sight distance = 600 km (between Orkney and Shetland Islands)

The visible portion of these clouds cover a vast area. From 5 degrees down to the horizon you are looking at a 400 km distance (hugely foreshortened)

Processing:

This very wide panorama was taken with a 28-80mm Canon lens set at 50mm on a 40D Canon camera. This was a 5 frame overlapping series of images which has been cut down slightly at the left and right edges. It was blended together with Autopano Pro 2.0. Each frame was preprocessed in Photoshop CS2 for noise reduction (Despeckle and Neat Image plugin). Also each frame was preprocessed in Images Plus for a touch of controlled sharpening with Adaptive Richardson-Lucy deconvolution (10 iterations on each frame).

Revision B: Added some chromatic noise reduction and lightened the deep sky

Revision C: Used a masked local contrast enhancement technique to enhance the contrast of features within the noctilucent clouds.