[Svetlo]Illuminance by the Moon

[Jan Hollan]

Hello everybody,

a comment to the actual lunar illumination, so often mentioned in the
DSLF.

I have offered already my programme planet, which can compute the
illumination by the Moon as well. It could be used for calibrating very
sensitive luxmeters around 0.1 lx, or for calculating illumination of
bedroom windows (lunar light is often strong enough to disturb the sleep)
or natural landscapes. The uncertainty is below 30 per cent, when the Moon
is high in the sky.

The problem has been, that not everybody is familiar in installing a
binary (executable) file into the computer, not speaking about submitting
the needed parameters to it. Today, I've finished a working php script,
which runs the programme for this purpose online from any browser. The
script is at

              http://www.astro.cz/darksky/compute 

If your browser notes the so-called cookies, you can store 
  - your geographical position 
  - the time difference against the Universal Time,
     (a negative one in the US, zero or positive in Europe)  
  - the orientation of your favourite window
 in your computer, so that next time, the programme starts with the proper
data already. 

One value in the programme is a strange astronomical one: the amount of
extinction (of attenuating the direct light) for an object in zenith. The
default one is an extremely low one, for a very clean atmosphere, just 20
centimagnitudes (it is twenty per cent, approximately). A more realistic
would be twice that much, for cities.

Due to extinction, the proportion of direct light diminishes and the
amount of stray light (esp. from the sky near the horizon) rises. The
total amount of moonlight hitting the ground is diminished perhaps twice
less than the amount of direct moonlight.

If you are not shy to read the help file (obtained by supplying a ? on the
command line), you can use the same programme for any planetary ephemeris
(incl. computing illumination by the Sun or any planet).  Supplying just a
parameter like
  k3
 you get a luminous flux density, without considering any interference by
the Earth.

clear skies,
 (needed now, I've not seen myself more than one planet at once since ten
  days...) 

 Jenik

PS. 
 the visit of Bob Gent and the two journalists from the BBC radio in
Czechia, Lucy Ash and Paul Henley, has been a marvelous one, I'm very much
obliged to them. And of course, to the executive director of IDA, David
Crawford, for the award he gave to me. Hope to do much further work for
bringing the beauty of night back to the mankind and the whole nature.