Hevelian halo

Hevelian halo

[he′vāl·yən ′hā·lō]
(optics)
A faint, white halo with an angular radius of 90°, centered on the sun or moon, and only occasionally seen; it is a member of the class of halos reported but not yet fully explained. Also known as halo of Hevelius; halo of 90°.