Sunday, 28 February 2010

Sky Quality

I borrowed Vectis AS' Unihedron Sky Quality Meter a couple of weeks ago, to see what the sky in the back garden is like. I live in a rural area, although light domes are apparent in the distance from Newport, Sandown and Shanklin, and during nights when the Moon is not about I often get skies of NELM (Naked Eye Limiting Magnitude) 6.5, although usually it's anything between 6.0 and 6.5. Someone mentioned the SQM at one of our observatory nights a couple of weeks ago so I asked if I could borrow it. Unfortunately, I have only been able to use it on one occasion, due to the awful weather just recently. However, I took several readings over the course of the evening, which I'd describe as a very average evening, and got readings of 20.9 which correspond to NELM 6.1. I need to take the SQM back in time for the IW Star Party but I'll borrow it again and try it on a very dark night after midnight, which is when I suspect I'll get even better readings.

A couple of weeks ago, I was asked if I could step into the breach and do a talk on visual deep sky observing at the February VAS monthly meeting this Friday just past. I agreed, as I don't mind public speaking, and I'm pleased to say that, despite me forgetting I was doing the talk until Wednesday and therefore not doing any practice with it at all, it went well, with no inadvertent swearwords, no collapsing into giggles and no stuttering! I think I managed to convince at least a couple of people that visual observing is a viable alternative to imaging.
I mentioned my clear night spreadsheet and eyebrows certainly were raised when I mentioned that, in January and up to 25th February we'd had a decent proportion of nights - apart from a long cloudy spell between 9th and 24th January, then another seven nights of clouds between 11th and 17th February - when some observing was possible, corresponding to 33% of all 56 available nights to date. I pointed out that it is a far from scientific method and it only highlights observationally usable nights, where you can get any observing in from a long session with the big dob to an hour with a pair of binoculars - if I was only including totally clear nights, then that total would easily be cut by half to two thirds. However, I have still not managed any observing since 4th January (the night before the snow), mostly due to laziness and cold - we got some nice nights when the snow was on the ground but sheet ice and compact snow made conditions that were bordering on lethal and it was just not safe to lug the scope out.

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