Big haul of Messiers on First Trip to a Dark Site

[Zermelo]

The forecasts were unanimously good for Friday night, so for the first time we decided to head out to a “dark site”, Trinity Hill Nature Reserve , which is listed on https://www.darkskydiscovery.org.uk/dark-sky-discovery-sites/map.html .

To be honest I wasn’t expecting a significant improvement in the sky; on the light pollution map website both this site and our back garden are assessed as Bortle 4, although it gives SQM values (2015) as 21.50 and 21.16 respectively (I know those maps are based on satellite-based ground luminosity measurements rather than more accurate skyward meter readings). Oddly, the dark sites website gives an SQM value of 19.82 for Trinity Hill. The motivation for the trip was more to get away from neighbours’ searchlights, and to be less constrained with making a little noise past midnight. The other reason was that, from our back garden, the southern horizon is largely inaccessible. I wanted a decent session to try to locate as many as possible of the summer delights low down in Sagittarius, Ophiuchus and Scorpius. I’d never even seen Sagittarius from home.

We arrive early as it was the first time, to find that the entrance to the main car park was padlocked – not very welcoming for stargazers; perhaps it’s COVID-related. There is still room to park outside the barrier, and we do a reconnoitre of the immediate area. There are paths that are reasonably flat but we decide to set up just off to the side (taking care to check for ground-nesting birds) to avoid obstructing any late dog-walkers (but we saw none).

At first, it doesn’t look promising. The ground is very uneven; we are immediately assailed by flies and midges (addition to the Dark Site Checklist: insect repellent); and the equipment starts to attract dew even before the sun goes down. I manage to level the scope, align on Vega and Arcturus as soon as they show, and we sit down and watch the sky for further appearances. I normally start with doubles to make the most of the light evenings; there are several on the observing list but most were a bit challenging in twilight, or else not yet risen. I do find Theta Sagittae, which is a comfortable split at 112x.

As the sky darkens, I switch to some other targets. M29, a modest open cluster in Cygnus, is found easily. NGC 6830 in Vulpecula is similar. Globular M80 in Scorpius had been previously unresolved from the back garden and is the same here. It is now getting towards midnight, and I'm starting to think that the new location would prove no better. I decide to point upwards to a known quantity, M13, to make a more direct comparison. It looks good, but I’ve seen it as good before at home.

The horizons still look murky and nothing can be seen by eye. We had set up with the aim of looking south, but I can’t make out anything low down. Most of my target list is there, and I’m not hopeful. But the scope’s GoTo is doing well tonight so I dial in the globular M4 in Scorpius, and find it immediately. It looks good in a Starguider 5mm at 150x – I can see some hints of structure, and several stars are resolved. This is more promising. What about a diffuse nebula? I try for M16 in Serpens with the BST 12mm. The finder says I’m located exactly, but I see nothing. But adding a UHC filter shows traces of nebulosity – faint, but definitely there. OK then, down into Sagittarius for the Swan Nebula, M17.  It’s really clear, and the shape is very distinctive. On to the Trifid Nebula (M20). The central star is bright, and the surrounding nebulosity is visible, but not very clear. But averted vision is dramatically successful here, even showing the segmentation from darker lanes. And I know where I’m going next, because I could see it even in the 6x30 finder while lining up the Trifid’s star - the Lagoon Nebula (M8). It doesn’t disappoint. Large and irregular, the dark band crossing its centre is very obvious.

Off with the filter and back to the clusters. M23 shows dozens of stars; M18 is smaller but still pleasant. M21 is more modest. M24 is awash with stars in the 18mm BST. Then comes M25, and globulars M28, M19, M62. The smaller globs are just unresolved patches, but I’m amazed we can see them at all, being less than ten degrees above the horizon at the time. It’s now well past 1 a.m. but we can’t go without seeing the Big Daddy. M22 is superb at 150x, appearing extended and a little uneven.

I’ve been concentrating so much in the eyepiece that I haven’t looked up for quite a while. The sky has been transformed in a couple of hours. There are many more stars visible than I’ve ever seen at home, and the milky way stretches from Cassiopeia in the north all the way to the southern horizon, with brighter and darker structures very obvious. And at its southern end, appearing to sit directly on the ground, is at last the teapot of Sagittarius.

It’s now very obvious that this location is darker than home, and worth the journey. The flies seemed to go away after sunset, and while there is damp everywhere by the end, it did not affect the observations – possibly because the scope was nearly horizontal for so much of the session.

The final tally is 22 observations, including 15 new Messiers.     

 

Edited June 6, 2021 by Zermelo
Forgot to identify the target following on from M20

[John]

Excellent report. Thanks for posting it

Last night was a cracking night for observing. Tonight =

 

 

[Pixies]

Excellent result. Like you, I don't have a low view to the southerly horizon, so many of these targets are not available. Also, my primary dark site is a little hilly and again the southerly horizon is obscured.

However, I've been informed of a quiet darkish site nearby that has low fields all the way to the south and I'll be heading there one night soon, but probably need to wait a little until darker skies return. It's not as dark as the above site (21.75 vs 21.55) but sounds similar to yours.

 

 

[Whistlin Bob]

Excellent report. I have the same problem from home. I must try the same thing.

[Pixies]

@ZermeloWest Bexington is quite near you and looks to be pretty dark

 

[Zermelo]

8 minutes ago, Pixies said:

West Bexington is quite near you and looks to be pretty dark

That's right!
That little bit of coast (and another one between Lyme and Seaton) is the only place east of Exmoor that the website puts into Bortle 3. (I spent a distracted hour clicking on the map when I first came across it).
I'm not aware of any specific observing sites there, though.