The ring you sometimes see around the sun or moon is called a halo. it is believed to be caused by the scattering of sunlight by tiny ice crystals very high in the sky. high clouds of ice crystals in the sky are called cirrus clouds or cirrostratus if they form a layer. these often form in front of warm fronts that bring rain. that means a halo around the sun or moon is often a warning that rain may come. the passage is mainly about a. how halos are formed. b. warm fronts that bring rain. c. a warning that rain may come. d. the reasons the sun rises.