Comets' antitails

What is the current "accepted" explanation of a comet's antitail?

The antitail is not an opticial illusion or an illusiont by
perspective. It's a real spike towards the sun. Some astronomers
mumble "old dust ejected some weeks before", which it cannot be,
as the antitail is very thin and only occurs near perihelion.

Some pictures of this:
http://history.nasa.gov/SP-404/ch4.htm#54
http://history.nasa.gov/SP-404/ch4.htm#56
http://www.star.ucl.ac.uk/~idh/solar/cap/comet/hb12.htm

--
Holger Isenberg

http://mars-news.de

"Holger Isenberg" wrote in message
...

What is the current "accepted" explanation of a comet's antitail?

The antitail is not an opticial illusion or an illusiont by
perspective. It's a real spike towards the sun. Some astronomers
mumble "old dust ejected some weeks before", which it cannot be,
as the antitail is very thin and only occurs near perihelion.

Some pictures of this:
http://history.nasa.gov/SP-404/ch4.htm#54
http://history.nasa.gov/SP-404/ch4.htm#56
http://www.star.ucl.ac.uk/~idh/solar/cap/comet/hb12.htm


If it occurs at perihelion, and the observer (on Earth)
happens to be near the plane of the comet's orbit, then
heavy particles left behind in the comet's orbit will
be seen edge-on. The Sun will illuminate them, and the
ones close enough to the Sun will reflect enough light
to be seen from Earth. A perspective effect would make
the older material behind the comet seem to be a sunward
spike.

Heavy particles would be left behind in a thin trail,
as they would not be moved much by light pressure.

In alt.sci.planetary Greg Neill wrote:

The Sun will illuminate them, and the
ones close enough to the Sun will reflect enough light
to be seen from Earth.

And why then is the spike directly connected to the comet's head and
not visible later at the very same position when the comet head moves on?

--
Holger Isenberg

http://mars-news.de

"Holger Isenberg" wrote in message
...
In alt.sci.planetary Greg Neill wrote:

The Sun will illuminate them, and the
ones close enough to the Sun will reflect enough light
to be seen from Earth.

And why then is the spike directly connected to the comet's head and
not visible later at the very same position when the comet head moves on?

The particles behind the comet eventually drift away,
their density falling to the point where the surface
magnitude drops below seeing threshold. So only the
"fresh" portion of the arc is seen.

Bas ASCII art follows:

In alt.sci.planetary Greg Neill wrote:
The particles behind the comet eventually drift away,

Does not explaint the very sharp tip of the spike towards the sun.
With your theory the spike would widen towards the sun, like the
normal comet's tail does.

--
Holger Isenberg

http://mars-news.de

"Holger Isenberg" wrote in message
...
In alt.sci.planetary Greg Neill wrote:
The particles behind the comet eventually drift away,

Does not explaint the very sharp tip of the spike towards the sun.
With your theory the spike would widen towards the sun, like the
normal comet's tail does.

The tip consists of the more distant section. It
will subtend a narrower angle, despite the widening
of the track as it dissipates.

In article ,
Holger Isenberg wrote:
What is the current "accepted" explanation of a comet's antitail?

They are made of relatively large particles shed by the comet, which
remain very near the comet's own orbit (they are not strongly affected by
radiation pressure or the solar wind) and are seen in perspective when
Earth is very near the comet's orbital plane.

(Comet Kohoutek showed a strong anti-tail, bright enough for spectroscopy,
and several different lines of spectral evidence agreed that the particles
in the anti-tail were much bigger than those in the main tail.)

The antitail is not an opticial illusion or an illusiont by
perspective. It's a real spike towards the sun.

Evidence? Please be specific.

Why is it seen only when Earth is almost exactly in the plane of the
comet's orbit, and why does its width depend on *how close* Earth is to
the orbital plane? (It's narrowest when Earth passes through the plane,
broader both before and after, which is exactly what you would expect.)
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

Holger Isenberg wrote:
What is the current "accepted" explanation of a comet's antitail?

The antitail is not an opticial illusion or an illusiont by
perspective. It's a real spike towards the sun. Some astronomers
mumble "old dust ejected some weeks before", which it cannot be,
as the antitail is very thin and only occurs near perihelion.

Some pictures of this:
http://history.nasa.gov/SP-404/ch4.htm#54
http://history.nasa.gov/SP-404/ch4.htm#56
http://www.star.ucl.ac.uk/~idh/solar/cap/comet/hb12.htm

I'm curious about something. You seem interested in comets. You have
found something that you don't understand. Why the attitude? I mean,
why the a priori assumption that the professional astronomers must be
wrong and you have stumbled across some mystery that everyone else has
missed? This is what all the nutters on usenet do: they equate their
own limits of understanding with that of everyone else, assuming that if
they don't get it then nobody does. And if a reasonable solution is
suggested the nutter always clings to his misconceptions... I'm not
saying you are a nutter, but your *attitute* and utter lack of humility
bear all the hallmarks of one. You may wish to think about that.

Personally, I've been burned so many times by ignorant people with your
attitude that I'm not about to waste my time answering your question. Pity.

--
Greg Crinklaw
Astronomical Software Developer
Cloudcroft, New Mexico, USA (33N, 106W, 2700m)

SkyTools Software for the Observer:
http://www.skyhound.com/cs.html

Skyhound Observing Pages:
http://www.skyhound.com/sh/skyhound.html

To reply remove spleen

Holger Isenberg posted:

What is the current "accepted" explanation of a comet's antitail?

It is caused when dust particles released by the comet and trailing roughly
behind in the plane of the comet's orbit are all seen "edge-on" as our line of
sight passes through the plane of the comet's orbit. Dust particles are
relased when the comet's surface is heated by sunlight. The solar wind and
radiation pressure from the sunlight move these particles outward roughly away
from the sun and from the nucleus. The finer ones are blown well away from
the sun and form the comet's dust tail, but more massive ones are a little
less affected. As they move away from the sun, they travel slower than the
comet's nucleus, since their orbits are now slightly larger than that of the
comet. This causes the dust particles to seem to trail behind the nucleus in
a broad band which is in the same orbital plane as the comet's nucleus is.
When our line of sight passes through this plane, instead of looking through a
mass of only a few particle as we do above and below the orbital plane we see
some of the larger the particles effectively all at once, since our line of
sight passes through most of the locations of these larger dust particles. If
the comet is post-perhelion and the geometry is right, these trailing
particles may form the "anti-tail". It may seem to be pointing at the sun,
but it really is just the direction which the comet is traveling away from in
its orbit. Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

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