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Re: (meteorobs) RE:Hale/bopp ion tail missing
Hi George and everyone,
----------
> De : GeoZay@aol.com
> Objet : (meteorobs) RE:Hale/bopp ion tail missing
> Date : jeudi 27 mars 1997 02:17
>
> Okay,
> After last nights posting that I didn't see the ion tail on hale/bopp in
the
> negative from last nights exposure...I've had a closer look at the
negative
> this morning. I can just barely see a trace of the ion tail...a lot
thinner
> than what it has been in the past for the same kind of exposure. It's
still
> there...but very ghostly.
> George Zay
There may be a solar wind calm as an explanation from the faint look of the
ion tail but I have another one:
have a look at the last NASA ephemeris of Hale-Bopp (that the only thing I
can do at the moment because I am located 22S):
you will find that
- HB was at its closest from Earth during the last few days and the closer
we look at a comet, the fainter the tail will be.
- the Beta angle (Sun-Object-Earth) is at its maximum and as the ion tail
is in the opposite direction from the sun as seen from the comet, the
greater this angle is, the wider the span of the comet's tail is from the
Earth
Let us try with a sketch:
S is the Sun, C the Comet, ---------- its tail and E the Earth
Wide Beta angle (around 50 deg) Low Beta angle (around 25 deg)
S C---------- S C----------
E
E
The angular size of the tail as seen from Earth is greater on the left
sketch and the as the angle is more important, the tail appears less
condensated and by the way less bright.
Sorry for the 'English' but french is my usual language and I tried to make
my explanations as clear as possible.
Jean-Christophe from New Caledonia (22S, 166E)