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Quote:
Originally Posted by mental4astro
There is one thing I don't get about SQM readings - do they take into account the quality of the transparency of the sky too, or just "how dark" it is?
Because an SQM reading can mean bugger all if transparency is stuffed.
I've been to one dark site that is really dark, but transparency is terrible most of the time. Another site I use is much less "dark", but transparency is significantly better than the much "darker" other location, so I can actually see more and fainter stars and objects. I routinely see the Horse of Sagittarius at the brighter site, and next to never at the other darker site, as an example. So will an SQM give me the quality of transparency too?
Sorry if my question is a bit of a digression from Glen's original intentions, but I as the topic has come up now, I felt it necessary to ask here.
Alex.
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The SQM is just a tool that takes the human subjective assessment out of equation. Take fifty people and your likely to get 50 different Bortle ratings from them, regardless of experience. People have different eyes, some good , many bad. As a tool the SQM can be a standard that does not require a human to make an assessment.
Sure transparency is a factor, and the SQM can be somewhat duped by poor transparency, which is why readings made over several night's is a better indicator than one offs. In the case of my location I have years worth of readings to consult. At least the SQM, no matter where it is used around the world, makes exactly the same reading and it is not looking through cataracts, dirty glasses, or the bottom of a Port bottle.
