As a comet nears the Sun, ice sublimates explosively, and solar radiation pressure sweeps the released gas and dust into a tail that always points away from the Sun.
outgassing ~ 1/distance^2
tail always points away from Sun (radiation pressure + solar wind)
- Orbit eccentricity — how elongated the comet's ellipse is — higher means a sharper close pass by the Sun.
- Orbital speed — how fast the comet completes each lap of its orbit.
- Outgassing/ejection rate — how vigorously ice sublimates into gas and dust as solar heating increases near perihelion.
- Tail particle lifetime — how long ejected dust and ion particles remain visible before dispersing.
Comet tails are a direct, visible record of solar wind direction — this is literally how 19th-century astronomers first inferred the solar wind existed.