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Comet C/2015 V2 (Johnson)

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#76 Uwe Pilz

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Posted 19 May 2017 - 01:53 AM

Dear observers,

 

me again.

 

The dust tail of the comet points ti an unusual direction. I have a simulation software for dust tails and analysed the situation with it. 

 

For comparison I used this image from Michael Jäger. The dust tail is 45' long in points to NW.

 

Appending you find my simulation result which is quite similar. From the parameters of the simulation we see what happens:

- The tail consists of very large particles in the range between 30 µm and 100 µm. This is unusual large, normally we find 0,5 µm ... 10 µm.

- The particles left the comet with s rather small velocity, around 50 ms/s. Normally we find around some hundred meters per second. But large particles are harder to accelerate

- Dust particles will be destroyed / fragmented by the solar radiation in some days. These large particles live much longer, around a quarter of a year. This is not surprising because larger particles resist longer to radiation.

 

As you may see in my simulation the dust tail is not symmetric and larger extended to SW. If you look careful at Michael's image you may find a hint of it. The central condensation is positioned slightly above an to the left form the center of the visual coma (which contains parts of the dust tail).

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#77 Tonk

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Posted 19 May 2017 - 07:49 AM

> 25nm wide that is open to OIII and the two main C2 bands @ 501nm, 511nm, 514nm. If you can see anything of the CO+ lines in the tail

 

The Swand band doen't come from CO, but from carbon gas (C2). This is mentioned in the paper "A High Spectral Resolution Atlas...":



Thanks Uwe!! No where did I say that Swan bands come from CO+ smile.gif. If you continue with the rest of my quote I said ...
 

 

... it would have to be a line within this band pass region. Looking at Figure 3 in the paper "A High Spectral Resolution Atlas ..." shows that NONE of the main ionised species found in the ion tail H2O+, CH+, CO+ have lines that coincide with the Swan filter window. So I'm now puzzled why Lumicon claim that their filter enhances tails. Its not an optimal filter for ion tails!

Please don't cut my sentence in half and hence apparently change the meaning.

 

So what I was dealing with is Lumicon's statement that there filter supposedly enhances ion tails (as well as the coma). I was arguing that for this to be true then lines from the principle ion species CO+, H2O+ and CH+ would have to appear in the region covered by the Swan Filter- they dont - so I do not understand Lumicons claim and I was certainly not saying CO+ is responsible for Swan band emissions.

I'm well aware were most spectra lines in comets come from. Its one of my interests as a chemist. If you read post #71 I had already said ...
 

 

Michael, Swan band filters pass a couple of green light lines from C2 molecule fluorescence emissions.

Edited by Tonk, 19 May 2017 - 09:42 AM.


#78 dhawn

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Posted 19 May 2017 - 10:53 AM

Caught the comet again last night from a darker location and could make out what I jotted down as a fan-shaped coma, not long but thick. Also could see much brightening toward the center with my 8" Newt on the coast of CA. Was the best view yet of this guy as it makes its way through Bootes. This is the first time I tried to catch it without referring to any charts. Since I'd observed it a few times in the last week or so, I just traced its path until it swam into view. Back on the 11th it was placed directly between a couple double stars and that was a blast to observe, but it was much brighter and distinct last night, mostly due to my darker location.



#79 Aquarellia

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Posted 20 May 2017 - 10:12 AM

Dear observers,

 

me again.

 

The dust tail of the comet points ti an unusual direction. I have a simulation software for dust tails and analysed the situation with it. 

 

For comparison I used this image from Michael Jäger. The dust tail is 45' long in points to NW.

 

Appending you find my simulation result which is quite similar. From the parameters of the simulation we see what happens:

- The tail consists of very large particles in the range between 30 µm and 100 µm. This is unusual large, normally we find 0,5 µm ... 10 µm.

- The particles left the comet with s rather small velocity, around 50 ms/s. Normally we find around some hundred meters per second. But large particles are harder to accelerate

- Dust particles will be destroyed / fragmented by the solar radiation in some days. These large particles live much longer, around a quarter of a year. This is not surprising because larger particles resist longer to radiation.

 

As you may see in my simulation the dust tail is not symmetric and larger extended to SW. If you look careful at Michael's image you may find a hint of it. The central condensation is positioned slightly above an to the left form the center of the visual coma (which contains parts of the dust tail).

Interesting Uwe!

I did a special sketch this morning, I used a 10mm Delos with a 152mm refractor to got another image. Here the tail was supposed to take the NW direction and I saw a kind of shockwave to E-NE.  in my sketch the size of the "pseudonucleus area" is only 3' wide, anyway that seems to confirm your statment.

 

C2015V2-20170520_l.jpg

 

Michel


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#80 Special Ed

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Posted 20 May 2017 - 02:58 PM

Michel,

 

Why does the comet look so different from your previous sketch?  Were you just concentrating on one part of it?



#81 Thomas Ashcraft

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Posted 20 May 2017 - 11:19 PM

Comet C/2015 V2 Johnson  May 21 2017 c.0400 UT. Canon modified 6D and Samyang 135 mm lens. - Thomas - New Mexico

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#82 Aquarellia

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Posted 21 May 2017 - 02:35 AM

Michel,

 

Why does the comet look so different from your previous sketch?  Were you just concentrating on one part of it?

Indeed I concentrate my sketch just on the pseudo nuclei.

For this last sketch I used my 1m25 refractor 6" with high magnification, the previous one was done with my short reflector 12" f5 with a low magnification, that makes the difference.

Michel



#83 Special Ed

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Posted 21 May 2017 - 07:16 AM

OK, gotcha.

 

Here is an image posted in the DSLR forum that shows the offset of the coma to the SW very well.  smile.gif

 

Here is another one.


Edited by Special Ed, 21 May 2017 - 08:06 AM.


#84 astrocy

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Posted 23 May 2017 - 01:38 PM

I searched again for C/2015 V2 (Johnson) early this evening of May 23th using 20x80 binoculars. By sweeping its general position in Bootes I could not find it, but after checking its exact position, it was easy to spot almost immediately about 4 degrees from Delta Bootis. It seemed larger in the diameter than the previous time I saw it and its coma stood out more easily. I did not notice much difference in its brightness which I estimated near +8.


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#85 caheaton

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Posted 23 May 2017 - 07:33 PM

I was able to catch this again last night at Calhoun Park during a short diminishing of the light fog that developed over the entire park (and increased as the night wore on making Monday a literal wash out).  It wasn't visible in the 50mm finder, but in the 120ST it was obvious, with an oblong almost rectangular shape that was brighter on one end.  No color noted...just gray.


Edited by caheaton, 23 May 2017 - 07:33 PM.

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#86 checcocpb

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Posted 25 May 2017 - 06:19 AM

This shot was taken with an 80mm f/6 apo  and an unmodified eos 650d 3200 iso for 66". the biggest double star in the lower left corner is µ Boo.

Regards

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#87 Thomas Ashcraft

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Posted 25 May 2017 - 09:46 AM

Comet C/2015 V2 ( Johnson ) May 25 2017 0325 UT. 30 second single exposure. 25600 ISO.  Thomas - New Mexico

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  • COMETV2JOHNSONTIMED_cn10100LIGHT_30s_25600iso_+26c_20170524-21h25m20s822ms.jpg

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#88 Thomas Ashcraft

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Posted 25 May 2017 - 10:41 AM

Tail a little more visible in this version. - Thomas

 

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#89 Thomas Ashcraft

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Posted 26 May 2017 - 06:57 PM

May 25 2017 Seventeen minute time lapse from 0314 UT to 0331 UT. Just experimenting. Comet is moving quite noticeably. - Thomas

https://vimeo.com/219168446


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#90 Special Ed

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Posted 27 May 2017 - 09:10 PM

Here is an observation of Comet Johnson from overnight has it passed ~2* east of episilon Boo (Izar).  The comet had a short, fan shaped tail and a stellar central condensation.  I detected it moving to the SW relative to a mag 12.3 star.  This was first light for my 40mm ES 68 ep.

 

I also made these estimates with my binoculars.

 

C/2015 V2 (Johnson)  2017 05 27.08  m1= 8.0  DC= 3  Dia= 10'  Alt: 75*  No Moon  12x36 B

 

C_2015_V2_Johnson_2017.05.27.composite.JPG


Edited by Special Ed, 27 May 2017 - 09:43 PM.

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#91 Mike Harvey

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Posted 29 May 2017 - 01:12 AM

I observed it, visually, with 120mm binoculars last night and it looked very much like your sketch'. Well done!

 

I was completely unprepared for imaging it because I expected it to be smaller and fainter than it actually is.



#92 canukLX90

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Posted 29 May 2017 - 02:25 AM

Nice sketch and observation there Special Ed.  Had a couple of nights of clear sky now cloudy again so catching up on some

image processing.  Here is my comet image from the early morning hours of the 23rd.  Anti-tail just visible in the image and

getting close to 180 degrees from the dust tail.

 

PJ

Attached Thumbnails

  • C2015V2_final_02.JPG

Edited by canukLX90, 29 May 2017 - 02:27 AM.

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#93 R Botero

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Posted 29 May 2017 - 02:42 AM

My attempts from South East London. Very nicely located comet but our nights are too short now! 

 

get.jpg

 

get.jpg


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#94 Aquarellia

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Posted 29 May 2017 - 03:49 AM

Here my yesterday night contribution as in the sketch forum:

 

C2015V2-20170528_l.jpg

 

My estimations : m 8.3 DC 4 dia 12' Tail NW 25' The tail looks longer than 3 days before and I suspected to see the ion tail but I'm really not sure.

Michel


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#95 andrew hampton

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Posted 29 May 2017 - 08:54 AM

Up until last week the comet appeared to be steadily brightening, as heading for closest approach in June, around 7.5 mag. in 10x50s to me. It seems to have dipped a bit over the last few days, would this be a temporary fluctuation ?

 

andrew



#96 Special Ed

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Posted 29 May 2017 - 10:57 AM

@Mike Harvey--thanks!  I'll bet the comet looked good in your 120mm binoculars.  smile.gif 

 

@ PJ--thank you--and I like your latest image.  Can you post an inverted version?  That can help bring out faint detail.  I can just ​make out the ion tail on my monitor.

 

@ Roberto--nice images.  The first one clearly shows the comet passing between those stars I labeled on my sketch.  cool.gif 

 

@ Michel--another great observational sketch from you--you have quite a series on Comet Johnson now.  smile.gif   Your

magnitude estimate is inline with what Andrew says he has observed.  I thought it looked dimmer than when I last saw it, too. 



#97 stevecoe

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Posted 29 May 2017 - 06:24 PM

Howdy all;

 

My RV is parked about 8 miles from Wickenburg, Arizona.  That is 60 miles from the lights of Phoenix.  There is Milky Way out my door.  Last night I was using my 8X42 binoculars around midnight and Comet Johnson was rather obvious, being near the zenith.  It was about 15 arc minutes in size with direct vision and little elongated, I would estimate 1.2X1.  Averted vision makes it larger and more prominent in the binoculars.

 

Clear skies;

Steve Coe


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#98 andrew hampton

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Posted 31 May 2017 - 04:12 AM

I caught a few brief glimpses of the comet between the clouds last night around midnight UK time. In a 4" F5 refractor at 38x I felt the comet was a bit brighter than 8 mag. and the coma looked a bit larger also. Then the clouds rolled in...

 

andrew


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#99 SpaceConqueror3

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Posted 31 May 2017 - 09:11 AM

I agree with you Andrew. I viewed it three nights over last weekend and I thought it brighter than 8th mag as well. I could easily see it in my 8 X 50 finder.



#100 canukLX90

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Posted 31 May 2017 - 06:48 PM

Special Ed as requested here is an inverted image.  I really had to stretch the previous posted image to show the very faint ion tail so that it was "visible" in the inverted image.  Those who are posting drawings/sketches of what they see at the eyepiece is the real reality of what can be "seen".  Computers, CCDs, and software are great at bringing out the faintest details but it can mislead people as to eyepiece expectations.  Many posted images of Johnson show fairly prominent ion tails but those images must be heavily stretched...the comet nucleus is blown out and large...I try to keep my stretching within reasonable reason to show the nucleus and as much of the tail as possible.  Good data and large primary optics at fast f ratios certainly helps but it only gets one so far before the software processing takes over.  Thanks to all who have sent me "likes" on my postings.

 

PJ

 

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  • C2015V2_invert_1.JPG

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