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Cosmic Challenge: Jonckheere 320

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#1 PhilH


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Posted 01 January 2019 - 06:17 AM

On January 22, 1916, while revisiting some of the stars in his Catalog and Measures of Double Stars discovered visually from 1905 to 1916 within 105° of the North Pole and under 5" Separation, French astronomer Robert Jonckheere returned to a vague double in Orion, which he had previously designated as entry number 320. Jonckheere was later to write of this encounter through the 28-inch refractor at the Royal Greenwich Observatory, "I noticed that the object I have catalogued as J 320 is not a double star, but, like J 475, it appears with the larger instrument to be an extremely small bright elongated nebula. As is the case with J 900, this object also appears to be new as a nebula."

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#2 Astrojensen


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Posted 01 January 2019 - 07:04 AM

A nice little challenge! I've seen it a few times, but that was some years ago. Last time was with a C8, if I'm right. I'll give it a go again, when the weather cooperates, this time with a 6" achromat.


I'll throw out another challenge: What's the smallest scope you can see it with? 



Clear skies!
Thomas, Denmark

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#3 Starman47


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Posted 01 January 2019 - 10:13 AM

It is now on my list for January new moon night, More next week on this.

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#4 Astrojensen


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Posted 03 January 2019 - 03:50 AM

Had a go at it yesterday evening with my 6" f/8 Sky-Watcher achromat. Somewhat hazy, rural skies, drifting clouds, NELM around 5.5, seeing mediocre. 


Not visible in the 16x60 finderscope, but immediately visible as a stellar object in the 150mm at 50x (24mm ES68). A very small, slightly elongated disk visible at 179x (6.7mm ES82). Moderate response to blinking with an O-III filter (it's possible the effect is stronger at lower magnifications). 255x shows the disk clearer and it's bright enough to take more magnification. Best view at 343x (3.5mm no-name long eye relief eyepiece). Tried 858x (3.5mm + 2.5x barlow), but that was too much. 343x showed the planetary much like in the sketch in the article, with the exception that one end was slightly brighter than the other. 



Clear skies!

Thomas, Denmark

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#5 Rudi Bjoern

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Posted 04 January 2019 - 03:19 AM

Thanks for the inspiring challenge...

I tried finding Jonckheere 320 with my 5" f/5 newton, but I couldn't find it.

However, I took an image with my 8" f/4 newton, you can see it here:


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#6 Redbetter



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Posted 10 January 2019 - 05:16 AM

I targeted this one earlier this month after reading Phil's column.  I was using the 20" in poor seeing but dark skies, so it wasn't so much of a challenge for the scope other than overcoming the seeing.  Despite the poor seeing I was detecting two sets of lobes/brightening: the more apparent WNW/ESE components, and a more subtle extension not quite perpendicular to that through the same center.   I used 278x primarily and sometimes 357x which was beyond what the seeing handled decently.


There is a tight, faint, small galaxy pair further north, II Zw 29 (PGC 16724/16725) at roughly 16th magnitude each and not quite stellar.  These must be high surface brightness considering their small apparent size and nearly stellar appearance in poor seeing. 

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#7 Dave Mitsky

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Posted 11 January 2019 - 01:25 AM

I've observed Jonckheere 320 a number of times over the years.  I'll have to take another look at it in the near future.  Here's a report from an observation I made in 1998. 


Observer: Dave Mitsky
Date/time of observation: 1998/12/15 07:18 UT
Location of site: ASH Naylor Observatory, Lewisberry, PA, USA (Lat 40.15 d N, 76.9 d W, Elev 390 m)
Site classification: Exurban
Sky darkness: 5.0 to 5.5 <Limiting magnitude>
Seeing: 6 <1-10 Seeing Scale (10 best)>
Moon presence: None - moon not in sky
Instrument: 17" f/15 classical Cassegrain equatorial mount
Magnification: 118, 144, 202, 259x
Filter(s): O-III
Object(s): Jonckheere 320
Category: Planetary nebula.
Constellation: Orion
Data: mag 11.8  size 7"
Position: RA 05:05.6  DEC 10:42
Description: One of the many deep-sky objects that I observed on this occasion was the tiny planetary nebula Jonckherre 320.  This 7" diameter object was difficult to distinguish from nearby field stars at moderate magnification (118x) without the use of the nebula filter "blinking technique".  J 320 appeared nonstellar (albeit as just a small, circular, colorless, and high surface brightness glow) at higher magnifications, although the use of the O-III filter was a definite plus.  J 320 and J 900, another planetary nebula that I had observed previously, are featured on page 80 of the January 1999 Astronomy.

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