The distance from Sun to the edge of the ring of light is equivalent to the outstretched span of a hand held up at arm’s length. The effect is caused by the cloud's ice crystals acting as tiny prisms that refract the sunlight passing through.
Full classification: Cirrostratus, showing the optical effect: 22-degree halo
Other examples of 22-degree halo:
 Cirrostratus, 22-degree halo |
