That's quite a lot of work, Nick, but well worth it - I was surprised to see
knots of material flowing down the tail in your animation.

I agree that a Theta of 10 degrees is a good choice with the L-S filter.
Your 1.3" pixels means that 2 pixels is about 2.6", so that translates to 4
pixels radius or so on my system. I'll go with 3.5 pixels radius
(0.68"/pixel).

I have about 46 minutes worth of i filter imaging (~300 frames) from the day
before (July 21) and 97 minutes  (~700 frames) from July 20. Not sure when
I'll be able to tackle these! The comparison of 3 animations over 3 days
might also show up something new.

Cheers,
Richard

----- Original Message -----
From: "Nick James" <ndj@nickdjames.com>
To: <baa-comet@simplelists.com>
Sent: Monday, July 27, 2020 1:55 PM
Subject: Re: [BAA Comets] NEOWISE close-up

> I've only just got around to processing my images of C/2020 F3 (NEOWISE)
> from July 22. An animation is here:
>
> http://www.nickdjames.com/Comets/2020/2020f3_20200722_ndj.gif
>
> This shows a field of view of 33x22 arcmin processed using a
> Larson-Sekanina filter with r=2, th=10 deg. There are 9 frames each of
> around 330s duration (from 2143 - 2228). You can clearly see motion in the
> tail and material spiraling out from the centre of the coma. The small
> black dot at the centre of the coma is the reference pixel for the filter.
>
> I have done quite a few experiments with this data and I think the
> parameters I have chosen are the best compromise to show detail and motion
> (i.e. around 300s integrations and L-S with r=2, th=10).
>
> It always amazes me that so much relative motion is visible in active
> comets over such a short period of time.
>
> Nick.
>
>
> On 21/07/2020 12:51, Richard Miles - rmiles.btee at btinternet.com (via
> baa-comet list) wrote:
>> Thanks Nick.
>> I wonder what the rotation period of the nucleus is?
>>
>> My 10' x 7' close-up image processed first with the Larson-Sekanina
>> filter, the second using a rotational gradient filter is here on my BAA
>> Members' Page:
>> https://britastro.org/node/23409
>>
>> The frames spanned from 21:50-22:14 UT on 2020 July 20.
>>
>> Richard
>>
>> ----- Original Message ----- From: "Nick James" <ndj@nickdjames.com>
>> To: <baa-comet@simplelists.com>
>> Sent: Tuesday, July 21, 2020 7:11 AM
>> Subject: Re: [BAA Comets] NEOWISE close-up
>>
>>
>>> C/2020 F3 (NEOWISE) is now high enough that I can image it using my
>>> telescope. I start imaging when the sky is bright since any more than
>>> 10s exposure currently saturates the central part of the coma. There is
>>> a lot of detail in the inner coma and tail and this is an unsharp masked
>>> image of the central 0.5 degree showing streamers in the tail and
>>> multiple shells in the coma.
>>>
>>> http://www.nickdjames.com/Comets/2020/2020f3_20200720_2126_ndj.jpg
>>>
>>> I remember back in 1997 that Terry Platt produced timelapse movies of
>>> the inner coma of C/1995 O1 Hale-Bopp showing the shells spiraling out
>>> from the centre. Here are the stills from that movie:
>>>
>>> https://britastro.org/cometobs/1995o1/1995o1_19970328a_platt.html
>>>
>>> I also attempted a wide-field image last night using a Sony A7s + Canon
>>> 85mm, f/1.2L lens but the light pollution here makes processing it very
>>> difficult. It does show the ion tail stretching back to Merak and Dubhe
>>> which are the two bright stars in the upper right of this image:
>>>
>>> http://www.nickdjames.com/Comets/2020/2020f3_20200720_2242_ndj.jpg
>>>
>>> Nick.
>>>
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