31 August 2016, Zeiss Cas 150/2250 Large planetary nebulae - Jones 1 and Helix

Telescope: Zeiss Cassegrain 150/2250 Eyepieces: ATC53P - ATC Plossl, f=53mm, (42×, 530) ATC40K - ATC Kellner, f=40mm, (56×, 440) A-16 - Zeiss Abbe Ortho, f=16mm, (141×, 200) O-15 - Vintage Zeiss Ortho, f=15mm, (150×, 170) A-10 - Zeiss Abbe Ortho, f=10mm, (225×, 130) Time: 2016/08/31 20:10-21:45UT Location: Konojedy Weather: Very clear sky. Good seeing. Mount: Zeiss 1b Accessories: Baader/Zeiss T2 prism

This was the last night in an unprecedent nificantly larger than my refractors. It is series of seven azure days and clear nights still quite compact and manageable to ob- interrupted only with one rainy day. I was serve with it on light equatorial mount as already tired after that many nights spent is Zeiss 1b. I love its DSO performance. outside. The next day was also the very It seems to be very well baffled and it pro- first day in school for our oldest kid and I vides quite dark sky background with good had to get up early in the morning. Despite contrast even from our light polluted back- of this, I made an effort and I drove 20 min- yard. The hate is coming from the poor high utes east, further away from Prague, to the power performance. The view is soft already place where we were holding small observ- at 225× which limits the performance both ing party couple of days ago. I have realized on planets and DSO. In particular, details in this might be the last good, pleasant sum- small planetary nebulae suffer and the faint mer DSO night in this year. It would be a stars reach is limited. shame to miss it. The plan for the night was to take an ad- I took with me my largest telescope, vantage of darker sky and larger telescope about 50 years old 150mm Zeiss Cassegrain. and to find some globular clusters that I I did not wanted this telescope in the be- had failed to see so far. I had in mind two ginning. I just wanted to get a hand on of them: Djorgovski 2 and IC 1476. And I Zeiss 1b mount and the Cassegrain came wanted to try some brighter Abell planetary with it. It was not in top conditions. nebulae. Finally, I planned to study in more All optical surfaces were pristine clear but detail two large planetary nebulae Jones 1 it came badly miscollimated and with re- and NGC 7293. painted tube. This is my first Cassegrain It was not yet completely dark at my ar- and I have yet to master the collimation pro- rival and I decided to start with Saturn. cedure for this type of reflector. A week ago, It was quite low above horizon and my ex- I had made a serious attempt to collimate pectations were low as well. I was sur- it using borrowed artificial star. The result prised pleasantly. The seeing was good and was much better but clearly still not perfect. I had found out that the image was quite This is the reason for current love/hate sharp at 141× at one spot near the edge relation with the scope. I like the larger of the field. This gives a hope that the power provided by the 150mm mirror, sig- telescope can be further collimated to per- form at high powers as well. Cassini division was practically invisible at this magnifica- was well visible, I could notice even brown- tion. Power of 141× revealed slightly irreg- ish NEB and nice pastel-like colors around ular shape of NGC 6558. My estimate of its the north pole. The view was quite close size was 20. to what I experience in my small refractors, Now, it was dark enough to go for tough although not there yet. Switching to 225×, targets. Djorgovski 2 is located close to the planet got quite soft. I checked quickly open cluster NGC 6520 (V=7.6, 60) and the view through vintage 15mm Zeiss or- dark nebula B86 (50). This pair was my thoscopic eyepiece. In small refractors, the starting point and I enjoyed it for a while. performance is very similar to top modern Low power of 42× showed nice dense star eyepieces, like Zeiss ZAO-I 16mm or TMB cluster with milky background which was in Monocentric 16mm. In this case, there was striking contrast with dark area east of it. surprisingly large and bright halo around Cluster was elongated in north-south direc- Saturn. A feature I have not noticed in tion. In addition, there was lovely bright smaller refractors. This was probably due orange star in the same field of view. I liked to combination of lack of coatings and more the view at 141× even more as B86 became light collected with larger aperture. more pronounced and patchy with some ar- Waiting for darker sky, I decided to eas becoming strikingly dark. check some Sagittarius globuar clusters be- As for Djorgovski 2 (V=9.9, 9.90), I was fore jumping to the difficult targets. Bright thrilled when very faint, about 10 rounded NGC 6656 (M22) (V=5.2, 240) never dis- glow started to show at 42× in short mo- appoints in any aperture. Larger 150mm ments with averted vision. I sketched care- mirror was decomposing the cluster into fully its position, it was located almost in many hundreds of stars already at 42×. the center of a square made out of medium Power of 141× was showing beautiful com- bright stars. The observed position was in- plex star cluster with many features in its deed cofirmed later using DSS image. I must bright center. In short and dirt look, I have have seen the cluster as there were no faint noticed several narrow dark lines and whiter stars in the area that could mimic it. patches. The most prominent was at NE A little bit east of NGC 6520, there edge. Careful look revealed that the bright- is another Djorgovski’s globular cluster ening consisted of several brighter stars. NGC 6540 (Djorgovski 3) (V=10, 10). It I had to look again at two gloular clusters was found by W. Herschel in 1784 who clas- NGC 6522 (V=8.3, 5.60) and NGC 6528 sified it as a faint nebula. Later, Collinder (V=9.6, 3.70). Desipte their location near changed the classification to open cluster the Galaxy’s center, they are still visible (Cr 364). As was the case of Djorgov- due to presence of a small, clear window ski 2, Djorgovski discovered it in 1987 inde- (Baade’s Window) relatively free of gas pendently when looking for obscured glob- and dust. NGC 6522 is also the oldest ular clusters in IRAS infrared data. Bica known cluster in Galaxy and it was probably and his colleagues finally confirmed in 1994 formed together with our galaxy. Both clus- that Djorgovski 3 is indeed a globular clus- ters were visible at 42×. Brighter NGC 6522 ter. They also identified it with Herschel’s was easy to notice, NGC 6528 required some NGC 6540. Some catalogues list the clus- concentration with averted vision. Power of ter as 15th magnitude object, clearly a mis- 141× showed the targets clearly, however I take, as I was able to find it even in 63mm could not notice any further details. refractor (see my report “Magical midsum- With the following two globular clusters, mer night” from June 22, 2012). NGC 6558 (V=8.6, 3.70) and NGC 6569 This night, I was able to see the cluster al- (V=8.4, 5.80), I went even further south, ready at 42×. Averted vision was showing almost touching the horizon. NGC 6569 tiny elongated nebular patch. The cluster was easy to notice at 42× while NGC 6558 was faint at 141× but still clearly visible. It was small nebular patch strongly elongated (3:1) at PA∼ 100◦. North of it, I have no- ticed very faint star separated from the neb- ulosity by a narrow dark line. It was hard to ignore the large bright emission nebulae in the area. I could not help and I had to look at Laguna (M8) and Trifid (M20) at least briefly. In particular, I was curious, if I would be able to detect the characteristic dark lines in M20. I could not see them at 42×, while there were clearly there at 141×. My time was limited, and I could not to spent more time in there. I had a different target in mind for sketching this night. The second tough globular cluster on my ulae from the Abell’s list. There was noth- list was IC 1454 (Palomar 7) (V=10.3, ing at place of Abell 72 (V=12.7, 13400), 70). The cluster was discovered in 1889 vi- either at 42× or 56× with OIII filter. I sually by Lewis Swift in 16-in refractor and had more luck with IC 1454 (Abell 81) independently rediscovered by George Abell (V=14.0, 3900) and NGC 7076 (Abell 75) in 1952 during survey of Palomar plates. I (V=13.5, 5600). Both were extremely hard could guess at 42× a presence of small, very to notice at 56× with OIII. Averted vision faint glow. There was medium bright star showed them only for short moments. With- just north of it. The cluster was still ex- out DSS images that I took with me, I would tremely difficult at 141×. I could hold it not be able to localize them at all. IC 1454 with averted vision only for a second or two. was small rounded nebular patch preceding It was very faint and rounded glow. Its size a bright star. NGC 7076 was another tiny was about 1/4 of the distance to the brighter nebular patch. It seemed slightly elongated star at north, i.e. about 10. I have noticed in north-south direction. another very faint star (V=13.19) just pre- The final target of the night was plane- ceding the nebular patch. A check of the tary nebula NGC 7293 (Helix Nebula) DSS image at home confirmed that I local- (V=7.3, 180). Again, from its look through ized the cluster properly. 180mm apochromat in one of the previous Now it was time to switch to planetary nights, I knew that this would be an inter- nebulae. I have started with Jones 1 esting target for sketching. I was not turned 0 (V=12.1, 5.5 ) which I saw for the first time down. Power of 42× was showing com- couple of nights ago from the same place. plex ring-like structure with several brighter First in small 95mm apochromat and later patches even without OIII filter. The view in 180mm apochromat. I could even suspect got even more patchy at 56× with OIII, see its bubble like character in larger telescope the rough sketch made directly in the field. equipped with OIII filter (unfortunately, I It was a wonderful and well spent night. don’t know the used magnification). Alas, I I’m glad I overcame my tiredness and took could not see the bubble in 150mm at 42× the large telescope under the dark sky. I can with OIII filter. Most of the time, the neb- only wish for more nights like this. ula was extremely faint rounded glow at my threshold of detection. Occasionally, I had Alexander Kupˇco a feeling that the glow is quite elongated in E-W direction. I was picking out probably one of the two bright arcs visible on images. Then I checked three faint planetary neb-