Astronomical term for the nebulous envelope around a comet's nucleus.
coma; comatic aberration
Optical aberration causing off-axis points to appear as comet-shaped blurs.
This lens has little coma, so star images are sharp.
As the comet approaches the sun, a coma forms around it.
A comet's coma shines brightly as it approaches the sun.
Comatic aberration tends to occur in cheap lenses.
齣 (a frame of film or a panel in a comic strip) is a homophone of コマ but denotes a segment of a sequence, unlike the astronomical or optical コマ.
Borrowed from English 'coma', ultimately from Latin 'coma' (hair), via Greek 'kómē'.