British Astronomical Association
Supporting amateur astronomers since 1890

Secondary menu

Main menu

152 posts / 0 new
Last post
nickjames's picture
Offline
Last seen: 3 hours 25 min ago
Joined: 12/10/2013 - 18:16
David, That is really good. I

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

dgs
dgs's picture
Offline
Last seen: 2 hours 33 min ago
Joined: 15/03/2014 - 23:44
Clear here again tonight!

Clear here again tonight! Also just realised that my Canon has been imaging at f/27! Wondered why I wasn't getting the ion tail recorded, hope to do better now!

David

Grant Privett's picture
Offline
Last seen: 1 day 2 hours ago
Joined: 28/12/2014 - 18:30
Visibility

Is it just me or is the blue ion tail becoming more prominent, or is it merely that the comet is higher in  the sky now?

Attached is a stack from the night of 17/8th July. When the comet spent an hour just above a line of clouds on the northern horizon.

Attachments: 
nickjames's picture
Offline
Last seen: 3 hours 25 min ago
Joined: 12/10/2013 - 18:16
Prominent ion tail

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

mike harlow's picture
Offline
Last seen: 3 hours 24 min ago
Joined: 01/06/2014 - 22:25
NEOWISE spectrum

A quick look at the spectrum from this morning suggests the sodium emission is much weaker now.  Colour images of the dust tail certainly look less 'orange' which maybe why the ion tail looks much more prominent(?).  I initially put all this down to the poor seeing this morning but I think it's real.

Will post images/spectra on my members site when I've had a closer look.  Was also imaging Gyulbudaghian's and Borisov's VNe last night so a lot of images to plough through!!!

Mike.

nickjames's picture
Offline
Last seen: 3 hours 25 min ago
Joined: 12/10/2013 - 18:16
Colour change

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. 

allenhugh10's picture
Offline
Last seen: 3 hours 30 min ago
Joined: 02/08/2016 - 22:43
NEOWISE spectrum 20200716

I captured an Alpy spectrum of the bright coma and adjacent tail on Thursday evening. I removed the sky background from the spectrum but I didn't attempt to subtract the solar spectrum from sunlight reflected off the dust in the coma. So the sodium emission will be weakened a little by that, but I think only by a very small amount. Compared to spectra taken a week or two ago, the yellow sodium emission certainly has weakened considerably relative to the blue-green C₂ emission bands, hence the subtle change in colour I think. In my comparison it can be seen how the sodium emission persists out into the tail whilst the molecular emission bands fall away in intensity. Visually the tail was huge, extending far from the bright nucleus especially in averted vision - a beautiful sight!

Hugh

Robin Leadbeater's picture
Offline
Last seen: 3 hours 3 min ago
Joined: 05/03/2014 - 00:50
directional effect

Hi Hugh,

Interesting. This cross section through the coma appears to show a different story to this vertical section.

https://britastro.org/comment/8942#comment-8942

Perhaps there could be some directional effects in the differences between Dust,Na D and other emission bands with the gas emission moving off the slit to the left relative to the dust.  I have some cross sections across the tail still to analyse  which might shed more light.

Cheers

Robin

allenhugh10's picture
Offline
Last seen: 3 hours 30 min ago
Joined: 02/08/2016 - 22:43
Directional effect

Hi Robin

Here is the stacked spectrum after geometric correction with the slit oriented vertically through the centre of the coma and upwards into the tail region. It is possible to see the sodium emission extending upwards into the tail region

Cheers

Hugh

Robin Leadbeater's picture
Offline
Last seen: 3 hours 3 min ago
Joined: 05/03/2014 - 00:50
long and thin

That's great. There is definitely no Na extending out that far sideways in my image so combining the two images we see just Na near the centre of the coma and streaming out in the tail direction.

Cheers

Robin

nickjames's picture
Offline
Last seen: 3 hours 25 min ago
Joined: 12/10/2013 - 18:16
Long ion tail

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.

Martin Mobberley's picture
Offline
Last seen: 4 days 5 hours ago
Joined: 05/03/2014 - 09:02
2020 F3 NEOWISE and Bury light pollution

Clear overhead last night but quite a bit of haze/low cloud in the direction of the comet. Unfortunately the comet is now just above the orange/yellow glow of Bury St Edmunds some 6 miles away, the worst place it could possibly be. A couple of fixed tripod 50mm f/1.4 shots and a blurry tracked shot with a much slower (f/5.9) Tak FS60c were taken.

Martin

Robin Leadbeater's picture
Offline
Last seen: 3 hours 3 min ago
Joined: 05/03/2014 - 00:50
spectral cross section through coma

A (sky subtracted but uncorrected for instrument response) spectrum image showing a cross section through the coma, taken 20200713.985 with the ALPY600  (An extreme non linear gamma contrast stretch had been applied to reveal the outer regions while not saturating the inner coma) Full size image attached

Although very intense, the sodium emission is confined to a narrow region of the central coma, particularly compared with the CN band which is visible well beyond the dusty region.

Robin

Richard Miles's picture
Offline
Last seen: 2 weeks 4 days ago
Joined: 07/03/2014 - 16:09
2020 F3 NEOWISE evening of July 16

Imaged July 16 around 22:00UT with a Canon 300mm lens showing detail up to ~3 degrees from the head of the comet. Took some trouble to generate an accurate flatfield before the clouds rolled in and cut short the session. More details on my Members' Page. Most of England was clouded out that evening.

Offline
Last seen: 2 hours 27 min ago
Joined: 22/02/2015 - 22:03
Comet Neowise

Clear   in Crawley after two nights of Cloud  Set up Sky watcher Star adventures  with  Sony 65a slt and  Minolta Rokkor 200mm f4.00 Lens.  . It took some time  to  find the Comet  as the electronic view  finder  struggled. Changed to  Samyang 85 mm  F 1.4 and the  view  finder lit up brilliantly.  Centred   Comet and  replaced  the 200mm  Rokkor.   .  First  results attached   lots of  work to do  to   get an acceptable result  but B/W frame   at 200 mm  shows  the size of the  Tail    The second image is a cropped image  from the 85 mm  lens.  Lots of  work to do to refine images

Stewart Moore's picture
Offline
Last seen: 2 days 4 hours ago
Joined: 08/03/2014 - 13:45
2020 F3 NEOWISE

 A frustrating night (July 17 / 18) for visual observers. Observing from 23:00UT. Comet is buried in low cloud and haze to the north and at times only the nucleus is seen naked eye.  It does not improve as the comet rises. In 10x50B the first 2 degrees of the tail is seen and for a few fleeting seconds the tail extends to at least 5 degrees but then it disappears. It seems that these first couple of degrees are much brighter that the remainder. All this is most disappointing as I got the impression that in a clear sky the comet would be looking superb. When visible the tail is very broad with much detail.  The tail tonight is a very good example of the benefits of averted vision, often 5 degrees seen with AV and zero with DV.

BillW's picture
Offline
Last seen: 2 days 4 hours ago
Joined: 05/03/2014 - 08:50
Hi all,

Hi all,

Even though it is getting a little darker I'm still struggling with bright twilight when it comes to imaging at my lattitude. This is (an un-corrected in any way!)  crop from a shot taken with a FLI KAF39000 camera and a 165 f2.8 lens, 3 x 30 secs through a HMC Y1 Green filter.

The filter helped take out some of the "blue sky" background. The broadening fan of the dust tail is becoming apparent.

Maybe get to try again in another couple of weeks!

djswan2002's picture
Offline
Last seen: 2 hours 4 min ago
Joined: 20/04/2017 - 19:58
F3 obs continues

A fascinating object. Friends and passers-by have been out for a look and have been most impressed. I have found that non-regular stargazers, with just help to point them in the right direction, are able to pick it up with the naked eye and notice the fuzziness reaching upwards. Most people favour the view through binoculars (10 x 50s) rather than the telescope (200mm SCT, 32mm Plossl). I am pleased to have been able to pick up the ion tail with just single frames with a DSLR! A greenish tint is also appearing in the coma, as highlighted by Nick James in a recent email.

Attachments: 
Robin Leadbeater's picture
Offline
Last seen: 3 hours 3 min ago
Joined: 05/03/2014 - 00:50
A Spectrum from the comet tail

A spectrum of the emission lines from the comet tail.

It is very different to those of the coma usually seen in amateur spectra and is dominated by CO+ emission lines  (the absolute intensity in the spectrum is only ~1% of that in the coma spectrum)

Cheers

Robin

allenhugh10's picture
Offline
Last seen: 3 hours 30 min ago
Joined: 02/08/2016 - 22:43
Comet tail spectrum

Hi Robin,

How do you approach the dust subtraction? It's a very nice tail spectrum. It inspired me to re-check my rather noisy tail spectrum just beyond the brightest part of the coma. I realise that I could pick out the three most intense double-peaked CO+ bands in the spectrum

Cheers

Hugh

James John Fraser's picture
Offline
Last seen: 1 month 1 week ago
Joined: 05/03/2014 - 10:40
C/2020 F3 (Neowise)

Not had much luck seeing this comet for the last two weeks. I got a brief view last night July 18-19. Still have strong twilight in north Scotland. Images taken from the bedroom window due to a neighbouring weeping willow.

Apologies to Allen and Hugh - I hit the wrong 'reply' button.

Robin Leadbeater's picture
Offline
Last seen: 3 hours 3 min ago
Joined: 05/03/2014 - 00:50
deleted

deleted

(The reply to posts is not working correctly. I replied to #121, not #122 !)

Robin Leadbeater's picture
Offline
Last seen: 3 hours 3 min ago
Joined: 05/03/2014 - 00:50
Dust subtraction

Hi Hugh,

It was done rather crudely in this example. The spectra are flux calibrated using a nearby reference as normal. I then just subtracted the Pickles G2v spectrum scaled relative to the comet spectrum in a region where there is just the dust continuum. It is pretty good at removing  the solar absorption lines and most of the dust continuum but leaves a residual shape in the continuum dependent on the broad reflectance spectrum of the dust so not good for quantitative measurements. It would be better to modify the G2v spectrum first to better fit the dust continuum leaving just the emission.

Cheers

Robin

dgs
dgs's picture
Offline
Last seen: 2 hours 33 min ago
Joined: 15/03/2014 - 23:44
This is a comparison of raw

This is a comparison of raw spectra taken 8 days apart showing depletion of sodium emission but increase in C2 and CN.The comet looks like it has now lost its golden colour and images are picking up more blue/green in the coma perhaps due to this increase?

David

https://britastro.org/node/23385

John Coffin's picture
Offline
Last seen: 1 day 1 hour ago
Joined: 24/10/2017 - 13:58
Spectrum of tail of comet NEOWISE

Hi Robin, What exposure time did you need to capture the spectrum of the tail and what scope and camera did you use?

Thanks

John 

Robin Leadbeater's picture
Offline
Last seen: 3 hours 3 min ago
Joined: 05/03/2014 - 00:50
exposure

Hi John

C11 + ALPY600 + ATIK428. Total exposure time was 45min (9x 300s)

Cheers

Robin

nickjames's picture
Offline
Last seen: 3 hours 25 min ago
Joined: 12/10/2013 - 18:16
Lots of detail at small scales too

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

zen32156's picture
Offline
Last seen: 6 hours 40 min ago
Joined: 04/05/2016 - 20:59
Comet processing problems with Deep Sky Stacker

I've just posted a picture of the comet I took the other day. The problem I have is in the processing stage when I use Deep Sky Stacker to try and track on the comet and stars to produce an image in which both look sharp. I can get either an image tracked on the stars or the comet but it crashes when I try to do both.

Does anyone know a way round this? Or are there any recommended alternatives to DSS for this. 

Any help would be great! 

dgs
dgs's picture
Offline
Last seen: 2 hours 33 min ago
Joined: 15/03/2014 - 23:44
NLO doing its bit for Comet outreach!

Norman Lockyer Observatory members gather for the first time since lockdown for a news bulletin on Comet Neowise for ITV's News at Ten.

https://m.youtube.com/watch?v=2ciG0yTR6Q4

David

Grant Privett's picture
Offline
Last seen: 1 day 2 hours ago
Joined: 28/12/2014 - 18:30
Visibility

For me the comet is still naked eye and about 5-6 degrees long. It was a bit hazy last night so tougher to see by direct vision but still there: https://britastro.org/node/23435

No obvious sign of banding in the dust tail but when using Live View the coma was clearly green.

Its been a real treat to have some tolerable weather and a comet with two bright tails.

We should start to see some images from Aus in about 10 days time... Hope its stays bright for them.

Offline
Last seen: 1 month 4 weeks ago
Joined: 07/07/2014 - 01:00
#127 Comet processing problems with Deep Sky Tracker

A response to zen32156

I wonder if stacking images taken over a shorter time period may help.

There is an interesting video on Youtube by Peter Zelinka entitled "Editing Comet Neowise with Photoshop".  He mentions Deep Sky Stacker and not using sigma clipping average method to process images.  Unfortunately I have only ever used an old version of Photoshop Elements so am unfamiliar with the software in the video which looks way above my area of expertise.  However, if you look at the video starting at about 9 minutes in it may answer your questions or at least give you a few ideas.  Others may also find the video of interest.

John Coffin's picture
Offline
Last seen: 1 day 1 hour ago
Joined: 24/10/2017 - 13:58
Alpy spectrum of comet C/2020F3 (Neowise)

Hi, I live on the Essex marshes with views almost to the horizon, so managed to get a spectrum of the coma of this comet on Tuesday am. Didn't try for the tail. The Swan Bands are stunningly beautiful (to a spectroscopist). The image is the raw unprocessed spectrum.

This is an annotated plot of the spectrum, the relative intensity of the emission lines is not reliable because the instrument response was calibrated using Merak which was at an altitude of 20 deg but the comet was at only 10 deg. Neither the sky background or the solar spectrum was subtracted when processing the spectrum. The emission lines were labelled according to data in Richard Walker's Spectral Atlas and on the following website http://web.gps.caltech.edu/~mbrown/comet/all.txt

The full size images are attached.

Robin can advise on whether the annotations are reasonable. John.

Robin Leadbeater's picture
Offline
Last seen: 3 hours 3 min ago
Joined: 05/03/2014 - 00:50
Stunning indeed

Stunning indeed.  The sodium emission is dropping away fast now. I wonder how far out from the sun we will be able to detect it? Here is a quick raw spectrum image (yet to be reduced) of the NaD line region from 2020-07-20. 

Compared with the same 10 days earlier, the sodium lines are now almost superimposed on the sky lines here as the Doppler shift drops to zero as the comet passes us.

Cheers

Robin

Offline
Last seen: 1 month 4 weeks ago
Joined: 14/08/2014 - 11:43
From Birmingham

Whilst the comet is invisible here to the naked eye, due Birmingham's light pollution, I immediately found it on July 20, in 10x50 bins and thanks to the chart Nick had posted, at 01:30 BST and again at 23:15 BST. (My brother in Maidenhead reports a similar experience.) Mostly cloudy here since.

John Coffin's picture
Offline
Last seen: 1 day 1 hour ago
Joined: 24/10/2017 - 13:58
Comet C 2020 F3 (NEOWISE) image

This is a photo taken with an astro-modified Canon 350D on a tripod on 13th July at 0100. Exposure 3 secs, F4, ISO 6400, focal length 55mm.

Attachments: 
alanbthomas's picture
Offline
Last seen: 2 hours 49 min ago
Joined: 17/01/2019 - 11:49
Still trying . . .

I must say I am a little (OK, a lot!) envious of members down in places like Devon, Somerset, Dorset etc. as I have been out on three occasions so far at unearthly hours here in Warrington and been thwarted by cloud each time. As I write, a leaden sky is pouring rain over my observatory (the back lawn). But I am enjoying the many superb images of NEOWISE that have appeared here - and I'm still hoping to get a glimpse before the month's end. Upwards and onwards!

Xilman's picture
Offline
Last seen: 5 hours 9 min ago
Joined: 24/03/2018 - 15:17
Sighting from La Palma

Now that I´m back in Tacande I've been able to see the comet for the first time. In the UK I had an obstructed northern sky which is brightly lit by Cambridge city. Here (at latitude 28 degrees north) UMa sets behind the mountains around midnight or so but was well above the horizon at about 2100 local time (circa 18:45 UTC).

The comet was an easy naked-eye object. I guesstimated a roughly 3-degree tail when viewed through 7x50B. The sky was slightly hazy so perhaps more could have been seen under ideal conditions.

Far too big for me to photograph much more than the coma, so I won't even try.

BillW's picture
Offline
Last seen: 2 days 4 hours ago
Joined: 05/03/2014 - 08:50
Hi,

Hi,

An alternative look at the comet.

The polarisation of sunlight being reflected and scattered by dust particles around the nucleus and in the tail can be easily mapped.

Image one is from a sequence centred on 0050UT 19/7/20.

The lines represent the orientation and magnitude of polarisation. The light in the tail is polarised ~4%. There is other stronger polarisation, ~6% across the nucleus, possibly due to a much greater density of particles. additionally there is quite strong polarisation oriented ~60  degrees from the tail polarisation closer to the nucleus.

Initially I wasn't sure if this was real or an artifact....

Image two is from a sequence centred on 2358UT 23/7/20.

Interestingly, is the stronger polarisation is again seen around the nucleus but with a different orientation and location. It still could be an artifact but it may suggest possible Mie scattering from larger particles. The change in position may be due the rotation of the comet, from a jet or other active area.

Cheers,

Bill.

nickjames's picture
Offline
Last seen: 3 hours 25 min ago
Joined: 12/10/2013 - 18:16
Polarisation maps

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.

Grant Privett's picture
Offline
Last seen: 1 day 2 hours ago
Joined: 28/12/2014 - 18:30
Polarisation

Really nice to see this.

The comet is approx 30 degrees from the sun, so the background should display Rayleigh scattering induced polarisation of a few percent. From memory, the orientation in the first image looks roughly right given the suns position pretty much below the north horizon. The comet should have its own dust response - as the Zodiacal light does - and certainly appears to here. I'm a bit perplexed by the orientation of the background polarisation in the second image though. Was the amplitude the same?

Your amplitude measure, was that a Stokes parameter or the degree of total linear polarisation or similar?

I imagine perfect alignment of the 4 polariser images is essential to the values measured when the target has fast changes in brightness. I have always had greatest problems getting good results in parts of the image with steep gradients - subpixel registration is important (I found to my cost).

I assume you only used linear polarisers.

BillW's picture
Offline
Last seen: 2 days 4 hours ago
Joined: 05/03/2014 - 08:50
No, it was done with a

No, it was done with a circular polariser in front of the lens, I don't have a large enough linear polariser for those lenses.

Anyway, one image is taken as the zero degree image, then the pol is rotated through 45 deg, then another 45 deg, then one more. Giving 0, 45, 90 and 135 degree images. Even that's not going to be very accurate!

The polarisation functions in IRIS are used to produce the various maps. 

Oddly enough on the second night, you could easily see the difference in the various frames due to the sky pol on the camera LCD display. IRIS offers several pol functions but I don't know how it's actually determining the various vectors to produce the images.

Everybody seems to get obsessed taking images I just wanted to try something different and see if it would work! The fact that the Rayleigh scattering/polarisation is perpendicular to the solar direction would seem to suggest it was successful after a fashion... but how accurate, who knows! That's why I say the stronger pol nearer the nucleus could still be an artifact.

Perhaps someone else can try it...?, the comet is still around!

Grant Privett's picture
Offline
Last seen: 1 day 2 hours ago
Joined: 28/12/2014 - 18:30
Circular polariser

Could you tell me what sort of circular polariser it was please? Am sort of surprised it was so successful against the linear signal from the comet.

Is it one that normally fits on a DSLR camera lens?

dgs
dgs's picture
Offline
Last seen: 2 hours 33 min ago
Joined: 15/03/2014 - 23:44
Compilation of C/2020 F3 images taken in July

Compiled from images using 28mm - 300mm lens, 100mm f/6 refractor, 50cm f/4 newtonian from Salcombe Regis & NLO, Sidmouth.

https://www.youtube.com/watch?v=Q35MKbjnWZM

David

Offline
Last seen: 2 weeks 6 days ago
Joined: 03/09/2013 - 15:17
Fabulous sequence David!

Fabulous sequence David!

dgs
dgs's picture
Offline
Last seen: 2 hours 33 min ago
Joined: 15/03/2014 - 23:44
Thanks Hazel, cloudy here for

Thanks Hazel, cloudy here for the next few days as well.

David

Offline
Last seen: 2 weeks 6 days ago
Joined: 03/09/2013 - 15:17
Comet still visible!

Brief gap in clouds last night (25/07/2020) at around 23:00 (BST). At present we can just catch it (sideways) through our west-facing bedroom window. Not naked eye from here (Surrey) at this time, although we saw it clearly naked eye at about 02:30 in a crisply clear but brightening NNE sky on July 11. But last night it was still good in binoculars (8x50) and very easy to locate beneath the Plough. Faint and fairly diffuse dust tail, better with averted vision, but any ion tail not seen.

nickjames's picture
Offline
Last seen: 3 hours 25 min ago
Joined: 12/10/2013 - 18:16
Animation of motion in the coma and tail

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.

nickjames's picture
Offline
Last seen: 3 hours 25 min ago
Joined: 12/10/2013 - 18:16
New chart

Thanks to Hazel for pointing out that we need a new chart for this comet. Here it is: https://britastro.org/sites/default/files/2020f3_Aug.pdf

Robin Leadbeater's picture
Offline
Last seen: 3 hours 3 min ago
Joined: 05/03/2014 - 00:50
the spatial distribution of the dust and chemical components

I have finally completed the analysis of my spectroscopic cross sections through coma and tail taken 2020-07-13 and added a poster to my members page

https://britastro.org/node/23655

It shows some interesting differences in the distribution of the various components which make up the cometary material.

The CN and Sodium components are seen in both coma and tail but the C2 component which dominates the  coma emission spectrum  is absent in the tail, replaced by the CO+ component. 

The spatial distributions are significantly different for the various components. In particular the sodium emission in the coma is confined to a narrow central region but the CN component is widespread in both the coma and tail. The Sodium distribution in the tail is skewed anticlockwise relative to the dust, consistent with the presence of a separate sodium tail.

Cheers

Robin

 

djswan2002's picture
Offline
Last seen: 2 hours 4 min ago
Joined: 20/04/2017 - 19:58
Na tail

Very nice, Robin. Is there very much in the literature on the spatial distribution of the various components in comets longitudinally through an apparition? If only bright-ish comets coming close-ish to Earth were more frequent...

Pages