Thanks for the feedback. The L-S filter is the best I believe for conveying
a fairly true-to-life image - certainly much better than the rotational
gradient processing filter.

I have an animation of three Sloan-i images taken at 22:00, 22:18 and 22:32
(mid-times) yesterday. Am amazed at how much the tail and coma changes over
this short time interval, as there appears to be an increase in the solar
wind hitting the comet that modifies the tails pretty markedly. It shows
that the solar wind does its best to blur out tail detail in images spanning
more than 10 minutes or so.

Have uploaded to my BAA Members' Page some detailed images of the central
60" region of the coma as seen on July 20 and 21:
https://britastro.org/node/23443

No observing for me tonight - good luck with yours,
Richard

----- Original Message -----
From: "Nick James" <ndj@nickdjames.com>
To: <baa-comet@simplelists.com>
Sent: Wednesday, July 22, 2020 9:35 PM
Subject: Re: [BAA Comets] Inner dust and gas comae of Comet NEOWISE from
2020 July 21

> Richard,
>
> Thanks for those. I'm having trouble keeping up with the processing of
> my images but I do have a stack using the C11 taken about 30 mins before
> your I Band image. Mine are unfiltered so the tails merge but you can
> see a lot of common features in the attached. This is L-S filtered with
> r=4, theta=15deg. The L-S filter is very powerful but can often
> introduce artefacts if you are not careful. It is good to see similar
> results from two different systems with, presumably, two different L-S
> settings. What parameters did you use?
>
> It looks like another clear night here tonight so that will be three
> nights in a row. It will be instructive to look at changes
> night-to-night. We also need imaging from other longitudes to fill in
> the gaps.
>
> Nick.
>
>
> On 22/07/2020 15:54, Richard Miles - rmiles.btee at btinternet.com (via
> baa-comet list) wrote:
>> Imaging with two filters, a B filter having a passband of 370-510 nm and
>> a Sloan i passing 700-850 nm allows a comparison of the dust and gas in
>> the inner coma.
>>
>> The two images from observations made last night, which have been
>> subjected to the same Larson-Sekanina processing, are remarkably
>> different in several aspects.
>>
>> The dust image shows a short spiralling jet beginning somewhere around
>> p.a. 0° and spiralling anticlockwise through an angle of about 210°.
>> The same feature in the gas coma appears to move outwards about 2x
>> faster than the dust one and spirals anticlockwise more than 400°.
>>
>> Notice also the two prominent tails that emanate from either side of the
>> pseudonucleus, whereas the dust is a much more mixed feature.
>>
>> The dust envelopes are at different distances from the nucleus than the
>> gas ones. Also the dust envelopes are sort of parabolic in shape whereas
>> the gas are generally circular centred on the nucleus. This circular
>> symmetry extends much further outwards than shown here when seen in the
>> ordinary light image
>>
>> At a solar elongation of 35°, phase angle of 103° and a distance from
>> Earth of 0.69au, we are having a favourable apparition of Comet NEOWISE.
>> That we see distinct spirals in the inner coma means that we must be
>> seeing the nucleus relatively close to 'pole-on' and that there is one
>> active region on the nucleus that is producing a large fraction of the
>> outflowing material in a continuous fashion lasting perhaps many days.
>>
>> Richard
>
> To unsubscribe from this list please go to
> http://www.simplelists.com/confirm.php?u=aR5jVcAm0PpxqWzIIDZTQWdURWgNdCOC