This short entry will discuss observing NGC objects near the horizon; in my case, towards the south and east. My latitude is 42 degrees N, so that limits how far south I can see on a good night (it is next to useless to attempt low objects on a less-than decent night). The fainter the object, the more difficult it is to see when it is down low. A few objects recently attempted in Cetus have seen my scope pointed nearly horizontal. If I were attempting to split a bright, wide double star, this would not pose too much of a problem. Neither would locating a large, bright open cluster, or a large and bright globular cluster. M 7 is way down there at -35 degrees, though it usually looks pretty fair from my site. I have successfully observed down to -42 degrees, glimpsing oc 6231 in Scorpius one time with my 8". That time the scope was flat out horizontal, and the cluster was at its highest point. Omega Centauri, the globular cluster everyone wants to see at least once in their lifetime, has reportedly been seen from Point Pelee National Park by a member of our club, just a few miles from my location. It lies below -47 degrees!! Our local club (Windsor RASC) sponsors dark sky nights there once a month, and the south horizon view over Lake Erie can be very good. This is the southern-most tip of mainland Canada, and lies at 41 degrees 55 minutes N latitude.
So those are the extremes. For me, -42 degrees. From my county (and country), -47 degrees. But what about "normal" low horizon deep sky observing? As mentioned, M 7 is getting pretty low, at -35 degrees. Everything above that can be seen on a good night, with exceptions. Below that, views can get very unsettled. Very faint globulars are a problem, and then there are galaxies. I have been researching my lowest easily obtained galaxies of late, and find that I must be pointing up pretty high to see the really faint ones. Using Cetus as my example, here are some interesting tidbits.
Cetus drops to nearly -25 degrees. I am not happy when I am observing galaxies down there, faint or otherwise. Not only am I looking through a lot of atmosphere when my scope is pointed down that far, but southern sky light pollution turns that part of the sky a milky hue, making it impossible to see galaxies. I have glimpsed eg 253, the Sculptor Galaxy, which lies just below -25 degrees. It was not a showpiece sight, but it was viewable. I have (barely) glimpsed eg 45 in Cetus. This would be a tough object even if overhead, but its position at -23 degrees makes it a formidable task, even for a 12". I have tried for years to glimpse this object, finally having success last month on a truly spectacular night. My life is now nearly complete.
On that same night I also had my first really satisfactory view of pn 246. It has a low surface brightness and lies at -12 degrees. However, despite seeing perhaps a dozen brighter galaxies down there, it is hardly worth it. It usually takes several attempts, and not much is seen except a ghostly haze. Things begin to get more comfortable for me at around -8 degrees. From here on up, even the dim galaxies begin to pop out. From -6 degrees up, I am finally back to 100% certainty of locating almost any NGC object!
Finding out my low sky limitations has been enormously helpful. I no longer waste precious time on cold nights trying to locate objects that are all but impossible from my location. I have not given up on the more southerly objects, but will save them for a planned expedition to New Mexico next autumn. Observing from 32 degrees N should make the job reasonably promising, along with darker skies. Do you know your low sky limitations? Try some brighter objects down there, and then slowly try for fainter and fainter, until there is... nothing. Like me, you just might learn something!
Mapman Mike
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