Quote:
Originally Posted by JohnD
We're seeing this as a globular cloud, because the tail of the receding comet happens to point away from the Earth. But cocmets can have two tails, one dusty and straight while the other is charged (?) and curved.
A curved tail would be visible, I presume as a pear-shaped extension of the cloud but it isn't there. What does this tell us about Holmes? Or rather, what is known about comets that have, or don't have, curved tails?
John
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I think you have them backward. An ion tail, swept away at high speed by the solar wind, is nearly straight and points almost directly away from the Sun. The particles of a dust tail move much more slowly from solar wind and light pressure, and generally lag behind the ion tail in a curved pattern such as that of McNaught.
At Holmes' distance from the Sun, the light and wind pressure are relatively weak, and we are seeing a colossal amount of dust that was expelled in a roughly spherical pattern and is slowly being pushed back. An ion tail would be faint and pointing almost directly away from us. The dust would make it hard to see from this angle.