When a strange ‘highway’ was spotted in the skies in China, few people knew what had caused the unusual astronomical phenomenon.
After investigating, meteorological experts think the bizarre pathway was created by a combination of sunbeams ‘cast from over the horizon,’ clouds high in the sky and shadows.
The striking photos of the unusual astronomical phenomena were spotted in the sky above Boao Town of Qionghai City in Hainan Province, South China.
Mark Selzer, forecaster at the Met Office, told MailOnline: ‘It’s hard to be completely sure from a picture, but it’s likely this [sight] is due to a phenomenon known as crepuscular rays – or sunbeams – being cast from over the horizon.
‘The sun is dim but still shining on parts of the cirrus cloud high up, but the dark blue section is due to shadows being cast.
‘The shadows are most likely caused by clouds which can’t be seen from the observer’s point of view due to the curvature of the earth,’ he explained.
Cirrus clouds are a type of atmospheric cloud generally characterised by thin, wispy strands, giving the clouds their Latin name, meaning a ringlet or curling lock of hair.
The cloud strands sometimes appear in tufts of a distinctive form and are referred to by the common name of ‘mares’ tails’.
However, a spokesman for the Met Office said the type of cloud ‘isn’t too important’ but it is the height of the clouds that really matters.
He said: ‘Cirrus is a high level cloud – normally with a cloud base at around 18,000to 40,000ft – and that’s reflecting the light from the sun.’
The meteorological experts believe that lower level cloud – perhaps a cumulonimbus, which has a cloud base of about 1,200 to 6,500ft – is possibly causing a shadow, which is seen as the darker band or ‘highway’.
Crespular rays play a key role in this strange sight and occur when the sun is behind irregular cloud which cast shadows.
The Met Office’s spokesman explained: ‘Where there are no shadows, you get the effect of well defined sunbeams.
‘In the case of the picture, there is only one shadow, which creates the dark patch across the sky.’
However, the experts could not rule out the unlikely possibility that high mountains could have cast the shadow instead of a cloud without an in-depth knowledge of the region’s geography.
Gavin Pretor-Pinney, founder of the Cloud Appreciation Society, agreed with the Met Office’s explanation and added that the optical effects caused by the shadow cast by convection clouds are coming from behind the photographer, as is the light from the sun.
He said: ‘The shadows that these tall clouds are casting onto the layer of cloud ahead appear to converge towards a point on the horizon due to the effect of perspective. It is similar to the way that train tracks appear to converge off in the distance.’
Mr Pretor-Pinner that the effect could actually be described as ‘anti-crespular rays’ as they converge as they recede into the distance.
‘Anti-crepuscular rays are not common, especially rare and dramatic examples like these,’ he added.
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