The city) by the Saracens, Notabile (locale notabile, et insigne coronae regiae, as it is called in a charter by Alphonso, 1428) under the Sicilian rule, and Citta Vecchia (old city) by the knights.
The most interesting members are: a Coronae, a binary consisting of a yellow star of the 6th magnitude, and a bluish star of the 7th magnitude; R Coronae, an irregular variable star; and T Coronae or Nova Coronae, a temporary or new star, first observed in 1866.
Prior to Young, halos and coronae had not been clearly differentiated; they were both regarded as caused by the refraction of light by atmospheric moisture and ice, although observation had shown that important distinctions existed between these phenomena.
It has now been firmly established, both experimentally and mathematically, that coronae are due to diffraction by the minute particles of moisture and dust suspended in the atmosphere, and the radii of the rings depend on the size of the diffracting particles.
These appear ancos differ from halos and coronae inasmuch as their centres are at the anti-solar point; they thus resemble the rainbow.