How dark is my sky?

[Bart]

Hello All,

I've always wondered how dark is the sky from my back garden. I'm fairly rural but with some LP to the west. However, looking at Ursa Minor I can definitely make out a Mag 5 star and with averted vision I can just make out a Mag 5.55 star between the handle and the pot, I think!

Would this be considered a reasonably dark sky?

Thanks

Bart

[umadog]

Ursa major is quite low in the sky now, so the limiting magnitude at the zenith should be better. I find the Bortle scale useful, because it doesn't only cite limiting magnitude but also other sky features. Different people can have different abilities to pick out faint stars and that makes limiting magnitude hard to translate. According to the Bortle scale, you would be in a "Suburban Sky" with weak Milky Way Bortle Dark-Sky Scale - Wikipedia, the free encyclopedia That may be a little off, though, it all depends on how you estimate limiting magnitude.

The "dark site" I go to often is about mag 5.5 (by my reckoning). I can see M31 naked eye but the milky was is washed out at the horizons. I certainly can't see M33 naked eye. Your sky could be similar. Personally, I'm content with observing under such skies. I can see dust-lanes in M31, the N. America nebula, crescent nebula, etc. Stephan's quintet is usually invisible, however, which reminds me that these skies are actually very light polluted. Bortle 1 and 2 is definitely a completely difference experience. You have such skies within driving distance so go for it!

[Bart]

Thanks Umadog ,

Yes M31 is almost always a naked eye object, milky way visible but like you,d it gets washed out down at the horizon, but saying that, M8 would still almost be naked eye in the south. M33 eludes me naked eye.

Must find a true dark sky site that isn't perched on the side of the road!

Thanks again

Bart

[rory]

i watched a clip from "sky at night" when they looked at the amount of stars visible within the square of pegasus . they had london on none at all,and from the site where they were ( slightly rural countryside /village) they could see 4 .

so the night i found m33, i looked at the square and counted 2,this was after 30/40 mins of eye adaptation.

is this quite a common rule of thumb for many ? or is this an old way ? lol.

[Bart]

thanks Rory

Haven't tried the Pegasus test or assessed on the Bortle scale. I imagine there is an element of subjective assessment here as it would somewhat depend on you vision quality. When I said I could make out a 5.5 star, it was'just' make it out..

People comment on how dark our sky is but that's only relevant to their 'townie' eyes, I'd like to know what an experienced astronomer might think.

Bart

[Astronut1982]

Hey,

I use this website to work out how dark my sites are & to find decent new dark sites :-

need-less light pollution

Hopefully that'll help. it will tell you where on the bortle scale your site is & an fairly accurate estimate of what the faintest magnitutde objects you will be able to see.

Jeff

[umadog]

Yeah, the square of pegasus is another way to do it. Again, though, it depends on whether the asterism is near the zenith or not. Bart, it certainly sounds like you can get some good observing in but if you have the ability to try for darker skies once in a while then you'll find it worth the effort.

[rory]

thanks for the bortle link umadog. reading that id say im around 6 to 7 .

not great, but i think a 5 is possible with a short 20 min drive.