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Re: (meteorobs) Light Pollution
Glad you enjoyed it. There is a trick that will allow you select an
exact latitude and longitude. Click on the nighttime photo and notice
the URL of the page you get taken to. The ...cgi?xxx,yyy has the x and
y coordinates of where you clicked on the photo. The web page listing
the limiting magnitudes shows the corresponding latitude and longitude
of that location. You can sample a couple of locations on the photo to
determine the relationship between the photo and any latitude and
longitude. You can then figure out the image coordinates of a
particular latitude and longitude, feed those into the URL directly
instead of clicking on the photo, and you've got the magnitude!
Confused yet? 8) We can do an example...
xxx= 21 * longitude + 2626.24385 (approximately)
yyy= -28 * latitude + 1399.7208 (once again, approximately)
(You can double check my calculation of the constants, if you want, by
clicking on a couple of places on the image to get image coordinate and
lat/lon pairs that you can check.)
I live at about 38N 78E.
xxx= 21 * -78 + 2626.24385 = 988 (truncated...)
yyy= -28 * 38 + 1399.7208 = 336 (rounded up...)
The URL http://www.darksky.org/ida-cgi/darksky.cgi?988,336 will take you
to a table for my location. (Pretty dark skies at my house, eh? 8) You
should double check that the lat/lon shown in the table matches what you
were calculating for...
Will
newtonj@ttc.com wrote:
>
> Will wrote
>
> "
> > The IDA has a really cool tool at
> > http://proxima.astro.Virginiadot edu/~ida/darksky/ to estimate light
> > pollution. This lets you check potential viewing sites for light
> > pollution before going there."
>
> This IS a very cool site, only problem I had was managing to pick a spot
> close to home.
> It's the sattelite pic of the US at night, with no boundaries or landmarks
> except the light
> pollution itself. It took me about 20 tries to click about 10 mi. east of
> my home (closer to all
> the worst light pollution sources). But, once I managed to get the right
> spot it seemed
> very helpful. It claims that there are many sites within 45 mi. that would
> give LM's @ 6.7
> (I only get around 5.9 at my "close to home site") maybe I'll try to find
> some new veiwing
> sites this weekend.
>
> John N.
>
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--
Will Marchant
kc6rol@amsat.org http://www.citizen.infidot net/~wmarchan/
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