[KarlInOhio]

if the comet is streaking through the galaxy... then what is the green stuff IN FRONT of it? wouldn’t the mass of the comet be in the body and moving the fastest? is there some form of gas or some other substance being pushed out ahead of the body of the comet that is diffusing the light?

You're used to how things work with atmospheric drag. Since there is no atmosphere in space the results of the ice in the comet sublimating tends to hang around the comet until the solar wind pushes it away from the sun. Anything on the sun's side of the comet will initially move forward of the comet.

When the comet is traveling away from the sun, the tail leads the comet on the way away from the sun. When it is closet to the sun, the tail generally perpendicular to the travel path.

[sten]

if that’s the case, then when a comet is in the middle of deep space, wouldn’t it look like a sphere and be dark, since there would be nothing to light it up

of course, the stuff being pushed outwards might not happen as the mass itself isn’t being heated