A comet's tail does not stream behind it
Comet tails point roughly away from the Sun. A comet on its way out of the inner solar system can travel tail-first.
Established2 min read
Dust in a comet's coma feels radiation pressure. Ionised gas feels the solar wind, a stream of charged particles leaving the Sun at hundreds of kilometres a second. Both forces point generally anti-sunward. The ion tail is the straighter one. The dust tail curves, because the grains also keep the orbital motion they had when they were released.
On the inbound leg the tail trails behind, more or less, since behind and anti-sunward roughly agree. After perihelion the comet flies away from the Sun and the tail leads. Photographs of comets in the evening sky sometimes show this, if you remember which way the Sun is.
Caveats
- Two tails are common, and they do not point in exactly the same direction.
- Very close to the Sun, other effects — fragmentation, outbursts — can throw material in odd directions. The steady rule is the one in the claim.
Sources
- 1Biermann L.. Kometenschweife und solare Korpuskularstrahlung. Zeitschrift für Astrophysik 29, 1951.