Circumhorizontal arcsWe are all familiar with the haloes around sun or moon formed by light interact

Circumhorizontal arcsWe are all familiar with the haloes around sun or moon formed by light interacting with ice crystals or water droplets in the atmosphere. We usually have to be looking up at the sky in order to see them, but sometimes a similar phenomenon takes place on the horizontal plane. The light is encountering minute prisms of ice in the distant cirrus clouds creating a fiery rainbow effect parallel to the horizon. The sun must be over 53 degrees up in order for this to happen, and icy high altitude cirrus clouds need to be in the sky. The hexagonal prisms of ice also need to be aligned horizontally to refract the light in the necessary manner, so the phenomenon is quite rare.LozImage credit: Todd Sladoje via APOD -- source link

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