FreeLists / az-observing / [AZ-Observing] Re: Photometric Night Definition

[BillFerris@xxxxxxx]

From Brian's montly and annual weather summaries, he defines a photometric  
night as being "cloud-free from dusk to dawn." A night that has "at least  
three-consecutive hours of cloud-free skies" is partial. Thin cirrus causing  
"one 
magnitude or less extinction" puts a night in his spectroscopic category.  
Anything else is cloudy.
 
Hopefully, Brian will chime in with the extinction he would associate with  a 
photometric night. My guess is, he'd consider any night with extinction  of  
0.2 to 1.0 magnitude per airmass to be spectroscopicf. Extinction of  about 
0.15 magnitude per airmass represents a typical cloud-free night in  northern 
Arizona. And extinctions of about 0.11 mag/airmass are seasonally  enjoyed 
during the winter when the atmosphere is virtually free of  aerosols.
 
Bill in Flag
 

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