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Ray,
The change is mainly due to the gravitational perturbations of the major planets. The orbital period is very sensitive to the eccentricity so a small change in e has a big effect on the period since a = q / (1 – e) and P = a^(3/2). The attached plots show the results you get if you integrate the current orbit forwards and backwards including the gravitational effects of all the planets and the biggest asteroids. There is a clear 12 year signature which is Jupiter but you can also see the large change in period corresponding to the small change in eccentricity.
Thanks to Hazel for pointing out that we need a new chart for this comet. Here it is: https://britastro.org/wp-content/uploads/sites/2020f3_Aug.pdf
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 33×22 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.
Bill, this is very interesting. Can you give a bit of an explanation of how you got these maps. Did you take images in two orthogonal polarizations and then difference them? If so, how do you calibrate them unless they were taken at the same time.
There is a lot of detail in the centre of the coma too https://britastro.org/node/23370
Attached is the blue channel of my widefield image last night (Sony A7s, 50mm f/1.8 lens). The FoV is around 40 x 27 deg and the subs are stacked on the comet’s motion. It was hazy last night and I have horrible gradients to get rid of. Also my flat field hasn’t worked properly. This shows up as concentric rings in the sky background. I need to redo the flat and do some more fiddling to get an image but this shows an ion tail around 25 deg long.
I’d noticed the colour change too. That’s very interesting. I should have been flying off to La Palma this weekend but that was cancelled due to C19. That comet would have been a great target from the top of the mountain.
It certainly looks more prominent and the dust tail close to the nucleus doesn’t have the prominent dark band any more. Here’s my take from this morning. https://britastro.org/node/23324
David, That is really good. I’m even more amazed that you had clear skies last night! It was raining here in Chelmsford.
John Mason and the South Downs Planetarium crew have done a great video for the general public on comets in general and C/2020 F3 in particular. You can find it here.
David, I hold you personally responsible that I now have to hoover out my keyboard after reading that Daily Mail article while eating my lunchtime sandwich. Do they actually pay their astrologer to write this stuff? I have to admit though that “Comet Neowise” is certainly having a significant influence on my life at the moment.
It cleared up for a while after midnight last night in Chelmsford but I was asleep. This is a picture from a cheap north-facing IP video camera showing just how bright the comet is. This is a stack of 100 video frames, so about 4s total exposure.
That’s a really good page. Unfortunately fake images like this are common. At least this one was blatant, some are more subtle and harder to identify for what they are. A good maxim is that if you see any astro image that shows something no one else is showing from someone you have never heard of, be suspicious and dig around a bit to get some idea of the authenticity. It is a shame that social media is overrun by this kind of stuff. A faked comet picture is pretty minor compared to some of the other, sometimes very convincing, fake messages out there.
I shouldn’t say this but I’m pleased it is cloudy tonight with a prospect of rain so I can get some sleep. I was a bit of a zombie in work today after three consecutive all night sessions.
ffmpeg doesn’t handle FITS directly but convert (one of the command line utilities in the Imagemagick suite) will convert from FITS to any common graphic format and can stretch, crop, etc. in the process. Being command line programs they are easy to script in bash or whatever and mean that you can make timelapses very easily from raws or FITS.
Hi Andy, Welcome to the forum. That looks like a fantastic image. Could you post a higher resolution version please with technical details (when, where, exposure, equipment, field of view etc.). You can submit it to the Comet Section via cometobs@britastro.org. Details of how to submit are here. Thanks.
The real detail in the comet is spectacular. I really don’t understand why anyone would want to make stuff up like that.
