The supplied sources do not present a mythological origin story. In the modern scientific framing reflected by the sources, a great comet is not created by supernatural agency but is a comet — a small Solar System body with a nucleus of ices and dust — whose physical properties and orbital circumstances (large, active nucleus; close approach to the Sun and/or Earth) combine to produce exceptional brightness visible to casual observers.
Great comets are exceptionally bright comets visible to the naked eye, typically as bright as or brighter than a second-magnitude star, often exhibiting conspicuous tails that under dark skies can extend 10 degrees or more. Brightness can be temporary and may increase dramatically during sudden outbursts (for example Comet Holmes brightened from magnitude ~17 to ~2.8 in 42 hours).
As physical astronomical objects, great comets 'do' the things comets do: they eject large amounts of gas and dust when heated by the Sun, producing coma and tails that reflect sunlight (and can fluoresce), and their observed brightness varies strongly with distance to the Sun and Earth. Abrupt outbursts of activity can cause rapid increases in brightness; a comet's chance of becoming 'great' depends on nucleus activity, perihelion distance (closer approaches to the Sun increase activity), and closeness to Earth (which increases apparent brightness). The sources specify no agency, intention, or direct supernatural interaction with humans.
Community Record
- [1]Great comet. "A great comet is a comet that becomes exceptionally bright and easily observable to the naked eye... There is no official definition; the term is often attached to comets such as Halley's Comet... Typically, they are as bright or brighter than a second-magnitude star and have tails that are 10 degrees or longer under dark skies... Great comets appear at irregular, unpredictable intervals, on average about once per decade... The requirements for this to occur are: a large and active nucleus, a close approach to the Sun, and a close approach to the Earth... Comet Holmes ... unexpectedly brightened from an apparent magnitude of about 17 to about 2.8 in a period of only 42 hours, making it visible to the naked eye."wiki
- [2]Wikidata: Exceptionally bright comets (Q140464). Wikidata label and description: 'Exceptionally bright comets' (entry Q140464).other