sky quality at white horse

Yes, that would be me, perhaps a few others too. I have a narrow angle Unihedron meter which I have probably had for about 7 or 8 years now. Typically when I take it out I let it temperature equalize and then I try to get at least 3 readings straight up or close to straight up unless there is something relatively bright in the sky like Jupiter or Mars or even the northern Milky Way. I usually take 3 readings. I have taken readings going progressively closer to the horizon in most directions, maybe at about 45 degrees up and then just above the tree line. Those readings, of course, are brighter with lower SQM readings and hence not as good NELM (naked eye limiting magnitude) readings.

The best I have recorded from White Horse is a reading at the zenith of SQM 21.76 which equates to a NELM of 6.5 indicating Bortle 3 skies. Having said that I do not think that I have seen the best that White Horse has to offer, a night with excellent transparency and low humidity. A night like that may only be seen a few times per year when all the variables are in our favor.

From west Texas between Marfa and Ft Davis I have had readings indicating 6.7 to 6.8 magnitude stars and those skies are clearly darker - the product of 5000 to 6000 feet of altitude and very low humidity and the absence of offending light. A very noticeable difference from what we can see in the deep south. Our skies, on balance, considering the ammenities we have, including low horizons, are pretty good. Hopefully though we will get at least one or two of those exceptional nights for our area next week.

Here is a helpful calculator to use with your Sky Quality Meter: www.bbastrodesigns.com/SQMandNELMconverter.html

Barry