I recently gathered several observations of M 51, made during the years 2016 and 2017, in order to have a deep and detailed report of the features which can be seen with a 25*'', and in particular the HII regions of the galaxy. All observations have been done with the same scope, 25'' dobson Obsession, same eyepieces, Nagler ans Ethos, at the same place, southern Alps.
During these nights, the SQM varied beetwen 21,6 and 22,00 (verified by two different guys with two different devices), the NELM about 6,7v, up to 7,0v at the zenith, and the seeing beetween 4'' and 2,0*''. Of course, the halo has been drawn during the darkest nights and the spiral and HII regions when the seeing was better (but unfortunately not extremely good).
Here are what I could see.
First, stars in and out the halo. On the hereunder sketch, one yellow line means the star is seen in direct vision, two lines with adverted vision, three lines at the limit, and a cross means that it has not been seen. 17 stars have been individualized on the halo.
On another hand, IC 4278 is difficult but sure, but IC 4277 not seen, even knowing its position and shape perfectly.
The spiral*:
The most luminuous , and also darkest parts, are detailed on the follwing sketch. Luminous areas are noted in a scale from 0 (black zone) to 9 (for example nucleus of brightest galaxies), and dark zones according to the Lynd's scale, from 1 to 6 (totally opaque).
It is interesting to note that I saw not only the bridge, but also the dark lane in the middle of it.
The HII regions*:
They are taken from two catalogs*:
HK83 : Hodge – Kennicut, catalogue des régions HII dans 125 galaxies, 1983
CCM : Carrenza – Crillon – Monet, 1969, A & A, 1: 479C (M 51, catalogue de 162 régions HII).
Overall, I saw also 17 HII regions, some of them with details in their shape an brightness*; I think that I should be able to see more regions with a better seeing. Fore those of you who read french, you have a very detailed report at*: http://www.deepsky-drawings.com/m-05...alo/dsdlang/en
Very nice, and I like the presentation. As far as the quasi-starlike HII regions, I have so far seen and identified only CCM 71 and 72 (16", 300x with ZAOII, blue-zone site). Looking at your sketch, they are the same as HK 76/78 and 80. I too have seen the dust lane in the "bridge", and a few other segments (same scope and site, lower mag).
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