🚀 go-pugleaf

In a previous article, hughes@twostep.cs.uiuc.edu (Eric Hughes) wrote:
>bcarpent@sun.cis.smu.edu (Bryan Carpenter) writes:
> 
>>Additionally, astronomists have found Earth bound celestial viewing
>>increasingly difficult as more of the planet is urbanized.  That means
>>that astronomists are forced to make only "guesstimations" when dealing
>>with astronomical matters.  
> 
>Yes, but if the lighting is constant, computers can be used to "subtract"
>the ground light sources (up to a point).  Besides, astronomers have to
>deal with lots of other problems, like clouds, ground movement, earth
>rotation, ...

I think filters are used more commonly than computers to deal with 
this problem.  (The best solution of course is to locate the telescope
in an area far from settlements....still not that hard even today).  
A filter can be designed to block specific wavelengths of light while 
being mostly transparent to most other wavelenghts.  For things like low
pressure sodium lights the light comes from only one or two narrow 
light bands so can be blocked without interfering with most of the
light spectrum (ie most starlight makes it through the filter).  
But for things like mercury vapour lights the light
is emitted over many bands and is pretty hard to block.

As for problems like earth rotation....this is very easily solved,
even on inexpensive amateur telescopes.  Clouds are avoided by 
situating large telescopes in areas that are generally cloud free...
a lot of study goes into finding good sites for major telescopes.
I believe Chile is one of the most favoured locations right now
because there are mountain sites there (near the Atacama desert I think)
that are very dry, have very steady air, and are hundreds of kilometers
from any artificial light sources.

Don