Re: Three sets of charts for GaN

[Jan Hollan <jhollan@amper....muni.cz>]

> Connie and Mark,
>
> a public directory
>
> http://amper.ped.muni.cz/jenik/astro/maps/GaN-Orion/2012/
  contains everything indispensable now.

> ...(allall.zip contains but the assembled charts for all latitudes, i.e. 
> the all.pdf files). Two alternative zenith extinctions are there, 40 
> cmag and 25 cmag. Of course, I'll add some description to the directory 
> later etc., like for 2011.
 -- a new one will be a primer on photometric quantities, like luminance 
etc.

As I wrote, at 0 degrees, people can observe Crux at 01 h on January 18, 
this is the sidereal time of Apr 15, 21 h, so they have a proper map 
available for using Crux. But they should watch Orion earlier in the 
evening, and this late again. Difference of such luminance proxies for 
varying altitudes is another indicator of the amount of light pollution -- 
natural sky has almost uniform luminance, unlike a polluted one.

For situations, when the target area of the sky is above 40 degrees, the 
difference between maps for zenith extinction 25 cmag and those for 40 
cmag, can be neglected. But when comparing sky at lower altitudes with 
maps, a set with a corresponding transparency of the air should be chosen. 
I think most people can distinguish days with good long-range visibility 
and deep blue sky from those with whitish sky and pick up the proper set.

Write me if anything more is needed urgently (like if you find any 
errors).

yours,
 Jenik

(I had to add a new feature to map_bsc, to switch off a label for Mars for 
some southern gray maps in April, as it would melt with Regulus. Should 
describe it now and put the new programme versions where they belong.)

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                             Jan Hollan, Ph.D.
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