Shining Halo cloud mystery :

Above is a still from video taken last October and uploaded onto YouTube of a giant halo in an overcast sky over Moscow. The unusual sight ignited UFO rumors, but was easily explained by meteorologists. The "clouds" was just an optical illusion caused by sunlight hitting a cloud at just the right angle. The cloud's round shape is likely what is known as a hole-punch cloud. These clouds occur within cirrostratus clouds, which are often composed of ice crystals and drops of water that are below freezing temperature but still in liquid form. When cirrostratus clouds are disturbed by planes or strong winds, the droplets can freeze instantly or evaporate, the latter of which will form the hole.

Photo Credits : Source