I recently created a visualisation of comet ISON's orbit. However, I received a critique that the dust tail of the comet should be pointing away from the Sun after perihelion.

As far as I know, the ion tail of the comet definitely points away from the Sun as it is blown away by the solar wind.

I want to know what is the direction of the dust-tail of the comet, before and after the perihelion. Is it always trailing the path of the comet (to a fair degree of approximation) or are there other significant effects?


1 Answer 1


Comet tail always aims away from the sun, as it's torn from the comet's gas cloud by solar wind. It trails slightly behind, as the comet moves along its orbit while the gas travels directly away, but that's relatively minor - the speed at which the gas and particles are pulled away forming the tail is much higher than the comet's orbital velocity.

Your visualisation shows it trailing behind the comet as if it was moving in some gaseous/liquid medium that stops the lighter particles while letting the heavy comet head travel ahead. This is not the case - as the comet is far away from the sun, the gas cloud just forms its atmosphere and travels with the comet. As it approaches though, the intensity of solar wind increases and it pulls away the atmosphere which can't be protected against it by magnetic field or strong gravity, as the comet has neither.

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    $\begingroup$ There's more than a single comet tail, for example one of dust particles and the other of gas molecules (the easiest to observe them separately is by using narrowband filters in the visible part of the electromagnetic spectrum, or even RGB filtering by camera's CCD sensor), and sometimes even the third tail can be observed, e.g. with comet Hale-Bopp's sodium tail. All of these of course on top of the coma (exosphere surrounding the comet due to gassing). $\endgroup$
    – TildalWave
    Commented Nov 4, 2013 at 18:23
  • $\begingroup$ Although the visualisation appears like you described (liquid medium), it is an emergent pattern. Actually, I have modelled it as: older particles in the tail getting dispersed while comet is emitting newer particles. Aside, does your answer take into account the different types of comet tails? $\endgroup$
    – HRJ
    Commented Nov 4, 2013 at 18:39
  • $\begingroup$ @HRJ: Then change parameters, much stronger influence on the particles - faster movement and more of them - relative to the comet movement. Different fractions of the tail may be scattered at various speeds and form various cones, and the visible/observed angle of the cone may depend on our viewing angle from Earth (it may be even an ellipse if Earth is within the cone as the comet approaches the Sun) but despite differences in angles, intensities, the cones are always directed by solar wind, away from the Sun. Not necessarily exactly away but absolutely not "sideways". $\endgroup$
    – SF.
    Commented Nov 4, 2013 at 19:40

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