M45 & visual acuity
Speaking of M45, of late I have been able to resolve 8 stars pretty easily and sometimes as many 11. I don't know if it is the skies have becoming increasingly dark and more cleaner, I doubt it, or that my visual acuity is improving.
The integrated brightness of Asterope typically appears soft and easier to detect than Celaeno,which sits almost central and slightly to the west of Taygeta & Electra. It takes a clear steady night to see Pleione just north of Atlas. When I get it, I get it but sometimes it is not as clear and distinct as Asterope or Celaeno. Occasionally, I get other stars that are nearby, especially one that makes a right triangle with Atlas & Alcyone, maybe a degree to the south. Another to the northwest of Asterope can blink or be seen.
Not bad for the city, but as for a transparency indicator it really only makes sense for me.