How dark are my skies?? (or yours)

[kalasinman]

An easy method to measure your sites sky darkness with a DSLR.

http://www.pbase.com/samirkharusi/image/37608572&exif=Y

In my village I get 12 mins to half histogram, or a Visual Limiting Magnitude around 6.4 or Mag/sq arc" = 21.

At least this is what it was tonight, which looks pretty average for a clear night before moonrise and with street lights going.

--Jack

[nicoscy]

I use the DSM application for the iPhone and I get SQM readings of 18.02 in the center of my city. 

But the dark sites I frequent (50 minute drive) are all between 21.0 - 21.4

[kalasinman]

That's great! I wish we all had darker skies.

[Kriss Craik]

Thanks for the info, will see what get were I live

[SteveNickolls]

Thanks for this. The night sky around here is poor, I have previously estimated it at around Mag 4.3 against various stars. Will try the method out first clear night I get.

Cheers,

Steve

[RichM63]

An interesting read, but not for me I'm afraid, although thanks for the article.

As I am not planning to move house I use the simplified version.

When I look up if I can see lots of stars = good, if my glasses get covered by rain = not good.

[Macavity]

http://under-a-dark-sky.com/how-dark.html

Has a plot relating limiting naked eye magnitude to sky brightness.

But I am still motivated to buy / make a sky quality meter. I would just

like something "reproducible" to record re. my observing sessions.

Maybe even decide to give up before the frustrations really set in? 

[ronin]

I follow Rich, I take a look and decide.

Am in a place where there is light pollution, but they conveniently switch off some of the lights at midnight. My road is plunged into darkness of a sort in about half a second. I cannot see Lovejoy before they go off but it is easy when they are switched off.

Not every light goes so there is LP bouncing around and that depends on the atmosphere and what is in it.

LP is not the only factor. If you had a site so dark you were afraid to walk as you could see in front or around you but 365 days of cloud you are not going to see a star or nebula. To me dark is secondary, clear is primary. They build observatories where it is most likely to be clear, not necessarily where it is dark. It is the number of clear nights that are important to them.

Consider can you see more under a dark clouded sky or under a clear light polluted sky?

Problem with the UK is the dark and the cloudy bits tend to be the same.

[Double Star]

Very useful thanks! I will open the DSLR up at f1.8 ISO 1600, do the maths and see what I get.

I can see the milky way well on a clear night from our garden, but as a newbie, that's about all I know.

[Charic]

As I write this during my lunch break, i dont remember the numerical scale ( it varies ) but I go outside, observe the sky, then adjust Stellarium to match what I see visually. I can then take a measurement from Stellarium if needed.

I'll have to try a measurement with my DSLR after I have studied the link. See if the Nikon is up to it ?

[rwg]

So, tonight I get 15s @ ISO 12800, f/4, which caculates out as 240s @ISO 800 and a sky brightness of about 19.9, visual limiting magnitude about 5.4.

That seems around right to me - it's not great but not bad in terms of transparency tonight. The milky way isn't really visible (maybe it would be if completely dark adapted). I'll have to try to remember to do this again when we next have a crystal clear night.

Thanks for the link

Robin

[kalasinman]

I'm not confident of the results with this method, but it seemed easy, and available to many so why not?