Re: [CFDS] filters

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

> My answer to anyone suggesting that there is no problem with LPS skyglow
> since it can be filtered out is that 99.9% of ten-year-olds do not possess
> such filters - and neither does anyone else who would like to see the beauty
> of the night sky (apart from a few astronomers).
> Cheers
> Bob

Excellent answer, Bob, I'd go further. Nobody at all possesses such a
filter.

D1 and D2 are never ``filtered out''.

The advantage of LPS for research lies just in the fact that measurement
in some filters is least affected by such light. And that that its
contribution to spectral radiance of the sky is low for most of the
spectrum, what is favourable for spectroscopy (however, the very sodium
D doublet is an important tool for studying the universe).

A comprehensive info on LPS is at Chris Luginbuhl's page,

http://www.nofs.navy.mil/about_NOFS/staff/cbl

and its advantage for astronomy is explained excellently in the 2-page
document

http://www.nofs.navy.mil/about_NOFS/staff/cbl/LPSnet/whyastronomyneedsLPS.pdf


I can add one more advantage, for deep-sky experts: it affects scotopic
vision little, so when trying to glimpse something with averted vision,
the contrast is better with no other pollution than those by LPS. However,
for most tasks, foveal vision is used, where LPS performs unbeatably...


As filtering is concerned, I can imagine the only way how it could be
made without losing a lot of natural light as well: looking through a
cavity filled with a sodium vapour, but with no discharge inside. It has
to be almost at the usual operational temperature of LPS, 260 degrees
Celsius, to keep sodium vapourised. It has to be large enough to enable a
good view through it, perhaps as a window in an otherwise opaque roof.

A challenge for NASA... to be attacked, with little hope to succeed, in a
hypothetical world with LPS dominance.


Thanks for a good question, Tom!

jenik




------------------------ Yahoo! Groups Sponsor --------------------~--> 
$4.98 domain names from Yahoo!. Register anything.
http://us.click.yahoo.com/Q7_YsB/neXJAA/yQLSAA/1.XolB/TM
--------------------------------------------------------------------~-> 

<sb>Campaign for Dark Skies Mailing List
Please don't post HTML and don't crosspost to the list.
When replying to list messages trim ALL unnecessary material including THIS footer and any egroup advertisements.
 
Yahoo! Groups Links

<*> To visit your group on the web, go to:
    http://groups.yahoo.com/group/CFDS/

<*> To unsubscribe from this group, send an email to:
    CFDS-unsubscribe@yahoogroups...

<*> Your use of Yahoo! Groups is subject to:
    http://docs.yahoo.com/info/terms/