Rich wrote,

Is the data from the SBig device different from that being reported by the Clear Sky Clock?

Yes, it is different in quality from the Clear Sky Clock. The Clear Sky Clock is based on a mathmetical model on the macro (+300 miles) and meso scale (10-300 miles) and has no "time memory". A micro site seeing study is on a micro scale (<10 miles) and gives continuous readings that identify probable hours during the night of excellent seeing. The Clear Sky Clock seeing index is a further abstracted index of a northern hemisphere seeing model maintained by the Canadian Meterological Service. The Clear Sky Index is a number 1 to 5 ranging from good to bad. The CMS model is based on satellite photographs. http://www.weatheroffice.gc.ca/astro/seeing_e.html The CMS model operates on the macro (+300 miles) and meso scale (10-300 miles). As the Clear Sky Clock website says of their index: "It's an experimental forecast." The type of data you get from continuous seeing monitoring is on the micro-scale - less than 10 miles. Characterizing the seeing at a particular site using continuous monitoring produces an average hourly turbulence measurement in terms of arcsecs. The SBIG website has a sample graph. Typically, we use 1 arcsec as a nominal aveage turbulence and as a seeing limit. So, once your scope has a resolution performance below 1 arcsec (e.g. about 10 inches of ap and above), telescope's resolution performance does not get used (absent adaptive optics that professionals use or by lucky imaging). 10 to 16 inch DOBs have a better resolution than this average - they will resolve down to 0.5 or 0.6 arcsecs. Contrast that value with the best sites in the world - like Mauna Kea - that has an average 0.5-0.6 arcsec seeing. While 1 arcsec of turbulence is the usual average value for "average" or "good" seeing, there are times of calm where turbulence can fall lower. A seeing monitoring study helps characterize those hours of the night when, at a particular site, those times of atmospheric calm below the 1 arcsec limit are most probable. Intuitively, you SPOC old-timers know when those times are (the early morning hours) based on years of observing experience at SPOC and other favored sites. The seeing monitor just puts an objective number to what you already know in your gut. - Kurt _______________________________________________ Sent via CSolutions - http://www.csolutions.net