Top travel destinations 2015 for Coma FIG A sketch of the remarkable coma of Donati’s Comet, One side of the comet’s nucleus was especially active whenever the nucleus’s rotation brought it back into sunlight. It is this that gave rise to the strange haloes, or envelopes, on the sunward side of the coma. Image from George F. Chambers, The Story of the Comets Oxford Clarendon plate fig. opposite page A comet’s coma, or head, is the distinctive blotch of bright light on the sunward side of the comet. Usually it is the brightest part of the comet. A coma is somewhat like an atmosphere around the nucleus, the innermost layer being denser and brighter and the outermost layer less dense and bright. Top travel destinations 2015 2016.