Nick James

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  • in reply to: Wildfire on La Palma #583038
    Nick James
    Participant

    That’s quite close to where I stay when I’m on LP. Hopefully they will get it under control. A local news report here.

    in reply to: Orbital Period of C/2020 F3 (NEOWISE) #582968
    Nick James
    Participant

    I had an email from Graeme Waddington pointing out that the periodic wiggles due to Jupiter and the other planets disappear if you use a barycentric coordinate system rather than heliocentric. This is because, when the comet is far out, it is orbiting around the centre of mass of the Solar System (the barycentre) which is not exactly at the centre of the Sun. Graeme’s plots are attached. The y axis is 1/a which, if you remember from my first post, is equal to (1-e)/q so it has the big advantage that it is well conditioned for orbits where e is near to 1 (i.e. it doesn’t tend to infinity as e tends to 1). Graeme notes “At the ends of the time frame plotted the comet is at 244 au and 250 au from the sun –>  P(orig.) = 4674 yr, P(future) = 7200 yr.  For a similar integration using the JPL15 orbit I get 4434 and 6718 years respectively.”

    in reply to: Nova in Cas #582950
    Nick James
    Participant

    https://britastro.org/node/23563. I get 12.6 unfiltered last night using Gaia DR2 G mags. 

    in reply to: Orbital Period of C/2020 F3 (NEOWISE) #582947
    Nick James
    Participant

    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. 

    in reply to: C/2020 F3 (NEOWISE) #582938
    Nick James
    Participant

    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

    in reply to: C/2020 F3 (NEOWISE) #582936
    Nick James
    Participant

    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.

    in reply to: C/2020 F3 (NEOWISE) #582925
    Nick James
    Participant

    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.

    in reply to: C/2020 F3 (NEOWISE) #582875
    Nick James
    Participant

    There is a lot of detail in the centre of the coma too https://britastro.org/node/23370

    in reply to: C/2020 F3 (NEOWISE) #582857
    Nick James
    Participant

    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.

    in reply to: C/2020 F3 (NEOWISE) #582856
    Nick James
    Participant

    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. 

    in reply to: C/2020 F3 (NEOWISE) #582854
    Nick James
    Participant

    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

    in reply to: C/2020 F3 (NEOWISE) #582845
    Nick James
    Participant

    Very impressive result Robin.

    in reply to: C/2020 F3 (NEOWISE) #582844
    Nick James
    Participant

    David, That is really good. I’m even more amazed that you had clear skies last night! It was raining here in Chelmsford.

    in reply to: C/2020 F3 (NEOWISE) #582834
    Nick James
    Participant

    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.

    in reply to: Fast moving White Dwarf #582832
    Nick James
    Participant

    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.

    in reply to: C/2020 F3 (NEOWISE) #582829
    Nick James
    Participant

    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.

     

    in reply to: Braided structure in F3 NEOWISE dust tail #582825
    Nick James
    Participant

    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. 

    in reply to: C/2020 F3 (NEOWISE) #582814
    Nick James
    Participant

    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.

    in reply to: C/2020 F3 (NEOWISE) #582813
    Nick James
    Participant

    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.

    in reply to: C/2020 F3 (NEOWISE) #582806
    Nick James
    Participant

    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.

Viewing 20 posts - 481 through 500 (of 971 total)