3 Open Clusters and 3 Globulars

31 May 2021, 00:10 – 01:20 (BST)

Seeing: Poor

Transparency: Average – Poor

A mild night to begin with, but cooled gradually over the course of the hour. Also a little breezy. As the temperature dropped, the condensation grew, collecting on the telescope tube and softening the pages of the notebook. The absence of true astronomical darkness was also apparent, making me wonder how I managed to see so much last summer (perhaps the light pollution from the town centre is starting to return to pre-2020 levels).

I started with a look at three open clusters in western Cygnus, two of which I’ve seen before (but only in passing, judging by the brevity of my notes).

NGC 6811, open cluster, Cygnus

133x. Large mass of similarly bright stars near Delta Cygni (and within the Kepler space telescope field of view); shaped vaguely like a fat spinning top, or an arrowhead. Hard to separate from the rich Milky Way background at this magnification; would probably look better in the Ethos.

NGC 6866, open cluster, Cygnus

133x. Compact group of about two dozen bright stars arranged in winding chains, with an underlying haze of fainter members. Quite pretty.

NGC 6819, open cluster, Cygnus

133x. Another compact cluster, shaped a bit like a wishbone or a pair of pliers. Comes alive with averted vision; revealed as a rich spray of faint stars with what looks like a dark lane cutting through the centre of the cluster. The wishbone suddenly becomes a flying squirrel(!), gliding through the Milky Way. Very pretty cluster; worth revisiting at a higher magnification on a better night.

M80, globular cluster, Scorpius

133x. Grainy round glow with a bright core; averted vision appears to expand the size of the cluster. 8th or 9th magnitude field star to the north-east. At 171x the impression remains much the same: a very condensed core and a few “speckles” with averted vision. The most prominent of these speckles (and the only one I was able to hold in view for a significant amount of time) was roughly halfway between the core of M80 and the aforementioned field star.

M12 and M10, globular clusters, Ophiuchus

133x. Both clusters looked a little washed-out tonight, and even increasing the magnification to 171x didn’t make much, if any, improvement to the contrast. (I think to see them at their best you really have to stay up very late on an April night.) Of the two, M10 looked better from an aesthetic point of view, appearing rounder and more condensed. M12 appeared unruly (almost “messy”) by comparison, with 2 particularly bright stars south of the core. As noted last year, the southernmost of the two is so prominent I wonder if it might be a foreground star.

With a waning gibbous moon starting to rise in the southeast, this was always going to be a truncated session, so I rounded off with a quick look at M11, which still looked superb despite the brightening sky. See my article on Love the Night Sky for more on this magnificent cluster.

With a similar forecast for the following night I took the scope out again (31 May, 23:45 to 1 June, 01:00), but, despite the moon rising half an hour later, the sky transparency was even worse. M4 (which looked so good last year) wasn’t even visible above the background glow.

Given the unfavourable conditions, I didn’t bother taking detailed notes, but I did look at M56 in Lyra, plus M80, M12 and M10 again (at 133x). I also looked at M57 and M13 at 333x (9mm Nagler + 2.5x Powermate), but the seeing wasn’t really good enough for such a high magnification.

As usual for this time of year, the sky was alive with satellites, including two bright ones which raced through the field of view while I was looking at M10 and M57.