Bernd Brinkmann just wrote:

> I have a question concerning the position angle (or angel ?) of comets. Up to
> now all cases I found were correct. But with C/1999 J2 (Skiff) I encountered a
> problem. See the image at my homepage (URL below).
>
> At top of the frame is the galaxy PGC 55322 and the chain of three stars to
> the lower left is clearly to identify. The image is rotated by 180 deg (south is
> up, east is right) deg.
>
> Guide gives a PA of 166 deg. My image shows a PA of about 10 deg. Does
> anybody have an explanation for this behaviour? The distance from earth to
> the comet is nearly 6.7 AU.

Guide indicates basically the antisolar direction. While ion tails
normally point in this direction, dust tails do not. In extreme
cases, if we view onto the dust accumulated in the orbital plane
of the comet edge-on, there may be the phenomenon of an
antitail, pointing to the opposite of the antisolar direction.

This appears to be the case in Bernds CCD image. The comet node
is about 50 degs, whereas the solar longitude at the moment the
image was taken was 52 degs, indicating that we were about
precisely in the orbital plane of the comet at the time of the
photograph. Thus it is a beautiful example of an antitail.

Other nice comets with antitails were comet Arend Roland
1956 R, and comet Bradfield 1987 P1


Hartwig

H. Luethen
h.luthen@...-hamburg.de
priv: Behnstr. 13, D-22767 Hamburg
lab: Institut fuer Allgemeine Botanik, Ohnhorststr. 18
D-22609 Hamburg, Germany
Tel: 0049 (0)40-3800551 priv
0049 (0)40-428-16-346