Though not quite apparent in this picture, cirrostratus clouds will often create a "halo" around the sun or moon. Cirrostratus clouds are strato type clouds at the high level so they are composed of ice crystals. Ice crystals are hexagonal shaped so when sun or moonlight passes through the ice crystals of a cirrostratus cloud, the light is dispersed (much the same way as light is dispersed in a prism) in such a way that a familiar ring will form. Cirrostratus clouds are commonly an indication that a warm front is approaching. Cirrostratus clouds will often thicken and lower into altostratus, then stratus, and eventually nimbostratus. There is an old proverb that says "A ring around the sun or moon brings rain or snow upon you soon." The situation being described here is a cirrostratus layer overhead and they frequently do indeed signal an approaching precipitation event.
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