Swirling through the air in mesmerising saucer-like shapes , these exceptionally rare lenticular clouds are the most common explanation for UFO sightings . The remarkable-looking disc shapes were spotted by amateur photographer Glenn Spencer , 42 , in the sky above Chester in Cheshire . The formations , also known as wave clouds , were scattered over miles , producing a stunning spectacle . Rarely seen in the UK , lenticular clouds are formed when a tall geographic feature , such as the the top of a mountain , obstructs a strong wind . The interruption in airflow creates a wind wave pattern in the atmosphere on one side of the mountain and at the top of these waves , moisture in the air condenses and forms a cloud . As air moves down into the trough of these waves the water evaporates again , leaving behind clouds in a characteristic lenticular shape . Mr Spencer noticed them while driving to the shops and was so amazed that he stopped the car to retrieve his camera from the boot . He said : ' I tried to follow them to higher ground to get a good view . They were just so mesmerising and I thought they looked amazing . It is easy to see why people mistake them for UFOs . They are brilliant . I 've never seen anything like it . ' Scroll down for video . Rare spectacle : These lenticular clouds , also known as altocumulus standing lenticularis , are hardly ever seen in British skies . Stunning : They form when wind blows over high ground and then undulates down in a stream of waves creating a rippled effect as the air cools . Commonly mistaken for UFOs : The clouds are sometimes reported as UFOs , particularly the flying saucer , because of their lens shape . How they form : They occur when the air meets obstructions such as mountains and the clouds ' thickness creates incredible contrasts of light . Mesmerising : Amateur photographer Glenn Spencer , 42 , noticed the flying saucer-shaped clouds as he was driving to the shops in Cheshire . Pilots of powered aircraft tend to avoid flying near lenticular clouds because of the turbulence of the rotor systems that accompany them .
Extraordinary lens shapes are exceptionally rare lenticular clouds and are also known as wave clouds . They are hardly ever seen in the UK but were spotted by an amateur photographer in the sky above Cheshire . The rippling effect is created by cooling air and the clouds are the most common explanation for UFO sightings .