The term 'astronomical ring' refers to two distinct phenomena in astronomy. The first is a HALO, which is a circular or elliptical region of diffuse light around a celestial object, such as a star or planet. Halos are caused by the scattering of light by dust particles in the atmosphere. The second phenomenon is coronae, which are rings of gas and dust that form around stars and planets. Coronae are created when material from the star or planet is ejected into space, forming a ring-like structure.