You know, every time I look at the Sombrero galaxy (M104) it looks different. Malcolm is spot on- transparency is everything.
Thru a 10" it's an easy spot with street lights around and lots of light pollution. After 3 years of observing it regularly (isn't it an object we always include on our lists?) I've only had two memorable nights where it looked amazing. I'd agree with what's commonly said of the rarity of only getting about four nights of the year with amazing seeing conditions. Funnily enough, the first occasion was only at 8pm when everyone had there lights on. It was fairly high in the sky at around 55 degrees. The dark lane cut a striking black line- I've never seen it look so good since. A couple of hours later, I was back out there again and couldn't wait to get more goodness from it. Alas, it looked like every other session observed on it and showed nothing outstanding. Just a greyish fuzzy spindle with brighter halo in the middle. So the transparency at that moment must have been amazing.
The second time was a doozy. Embarrassingly funny story here.... It was late at night around 1am- many people had turned off their lights (esp. next door!) so the sky was noticeably darker.
I thought I'd stumbled across a galaxy I'd never observed before. It was the most amazing thing I'd ever seen. It was a ridiculously bright spindle. The core was so bright that it was easily visible in my finder as a star. The core was easily distinguished, sitting above the galaxy plane with it's round shape so prominent it looked a tennis ball lit up. And oh my gosh- the colour of the galaxy- it was a vivid golden colour. I couldn't take my eyes off it for a long time. Had the galaxy remained a fuzzy grey colour as is a normal observation from my site, with a soft whitish glow around the core and a dark lane that's just there- then it would've been easy to identify as it. The Scorpion shaped asterism sitting next to it in my finder (commonly called "jaws") is a popular guide for star hopping so you think this would have been the clue that I was on M104 now wouldn't you lol. I spent a good week trying to find this new galaxy I'd observed. Along with the Scorpion asterism, the star Porrima was used as a guide for where it sat & then I measured the sky using my hand to where my red dot finder was pointing- so it was a fairly small patch of sky. From his dark sky site, I had poor Ron observing every galaxy within that area so we could find out what this magnificent spindle shaped galaxy was that I'd seen. As a seasoned observer, it had him scratching his head over it despite saying to me, "now are you sure it's not M104?!" My insistence to the contrary became his determination lol. There was nothing there except M104. I had to surrender.
I was mightily embarrassed. And there taught me a valuable lesson on how different a galaxy can look upon each viewing. This is why every time I observe these days- if M104 is in the sky, it will always get observed!
I hope my story will inspire new people to observing to keep re-looking at it, that includes through the course of the night. The same applies to DSO's in general actually, but as M104 is a fairly bright object, I'm guessing it's changes are more noticeable. This galaxy takes high magnification well btw. In my 10" dob I observe it using a 10mm (120x) or a 7mm (170x) eyepiece very successfully.
This thread
HERE is a highly educational thread for observing galaxies and Michael's post- refer post #35 has valuable information on how to observe it successfully- probably one of the best posts I've seen around.
For anyone needing helping finding M104, take a look at posts #36 & #37 in the above link for an awesome explanation & map on how to find M104 using the Jaws/Stargate asterism (that Scorpion looking asterism that I mentioned earlier).
That link is a worthy bookmark!