Now, the US government can add another shape to its list – and it's like nothing we've ever seen.
A photographer in Chicago has shared his stunning shot of a spooky object that was changing colour while it was stationary in the night's sky.
he remarkable shot was taken by Dietrich Zeigler, a photographer in Chicago, and shared exclusively to MailOnline.
'It was around evening just as the sun dipped below the horizon,' he said.
'I noticed some colorful shimmering and took out my 70-200 MM lens and shot this.
'The object's appearance was striking, with a palette of purple, gold and green.
'It seemed to be changing colours, but the shape remained the same which looks like a mask.
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