How dark are your skies ?

[slice of heaven]

2 part question

Given you had near perfect seeing and transparency , what magnitude can you see down too with your naked eye from the sites you observe from ?
I know on average I can see down to mag 5 from the backyard, only wishful thinking gets me past this.

What is the accepted method currently of determining the magnitude of stars?
I know it was originally scaled that mag 6 was the limit of stars viewable by the naked eye, yet I've seen people quote they've viewed from mag 7 or better skies?

[ballaratdragons]

Slick,

how can I tell? I haven't got a Mag meter! How do you know what Mag a star is.

Yep, 20 years at this and I still know nothing :rofl:

[slice of heaven]

:lol: BD

Maybe someone can make us one?

I'm just going by the mags printed on star charts when viewing, I start with the stars with a mag I can pick up by eye to align the Telrad,then use the scope to zone in closer.

[ballaratdragons]

Oh!

I suppose it depends on the viewers eyes too.

I suffer from a condition called 'Night Blindness' which means I can't see in near dark!
I do not seem to be affected by it through the scope though, as objects are brighter hence I can see them easily. :shrug:

Aboriginal children have the best eyesight and night vision of any people on Earth. They have been recorded at reading car number plates clearly at over 0.5 k away!!! and can draw the night sky including stars we can only see with knockies! That amazed the specialists.

Fred Hollows mentioned it a couple of times too, and it puzzled him how Aboriginal eyesight deteriated so fast after puberty. (not from disease)

[slice of heaven]

Yeah, I wish I had my kids eyes.Must be the tunnel vision they have. My 4 year old has eagle eyes, she's the first to spot a star or planet as the sun goes down and can pin point a plane while it's just a dot,I've learnt not to doubt what she says she sees.

[ballaratdragons]

Haha! Aaron (Harry) said he could see Jupiter in the afternoon daylight about 3-4 months ago. I told him he must be mistaken but he was adamant! I got the knockies out to show him he is seeing things and . . . there it was! Hmmppphhhh!

[cventer]

if you want to measure it very accurately you can get a SKy Quality Meter from Unihedron www.unihedron.com (http://www.unihedron.com)


I have one and its very cool to measure sky darkness at different locations. Only problem is the old timers hate you becuase next tme they give you the ole "site x is the darkets I have ever seen etc... you now have something to measure their statement by.......

Best regards
Chris Venter

[slice of heaven]

Cool tool Chris :thumbsup:

[dhumpie]

One way to establish your limiting magnitude is to go and get the latest edition of StarWare by Phil Harrington. He has a map of the southern cross and from memory they go down to mag 6 or something. Using that map I determined my suburban sky to have a mag limit of between 5.4 (summer) and 5.6 (highly transparent winter nights). Good enough to bag mag 10 and brighter galaxies ;)

Hope that helps.

Darren

[Striker]

Intersting Post...I dont know what mag I can see...the next clear night I will have a look to see what magnitude star I can see....

[asimov]

The accepted method awhile back was to if you could see any stars with the naked eye in the coal-sack. If you can it's mag 6 & better.

[ving]

have to check... brb!









ok, cant see any stars at all!!! :eek:
(cept sol)

[asimov]

Heres a few links: http://www.go.ednet.ns.ca/~larry/astro/maglimit.html

http://www.go.ednet.ns.ca/~larry/astro/maglimit.html

[rmcpb]

Not really about the dimmest star you can see but this site gives a way of measuring the magnitude of the whole sky from a site:

http://www.saguaroastro.org/content/LimitingMagnitude.htm

Its a bit of fun to brag about your really, really, really dark sky :)

Cheers

[gaa_ian]

I like those charts Rob

[Mick]

Here's a link that maybe of interest. How many stars (http://www.astro.univie.ac.at/~scw/eng.html)

[slice of heaven]

Ya Wally Ving, were all at mag -26 sites when the suns out :lol:
Heres a link for a more simplistic assessment

http://cfa-www.harvard.edu/icq/MagScale.html
The astronomical magnitude scale.

Might have to recheck mine if the moons of Jupiter are visible at mag5.

That chart goes down to mag 7 for naked eye limits, below the original mag6 limit of the original charts. Have the skies become darker in the last 2000 years, or who changed it?

[fringe_dweller]

Due to doing a lot of meteor obs reports i got to know how to tell at a glance without even looking for specific stars roughly what the LM at Zenith is at my familiar sites - ie backyard ect. Slice i am surprised that you only see down to mag 5 at MB! In my backyard in suburbia near ttg plaza I can see down to nearly mag 6 in certain darker areas of my overall sky in the east and S/E - but in the north and west it is very bad - rarely more than 4.5 - 5. At our dark site near Mt Pleasant i have noted stars down to 7.2 at zenith (with effort) at times. Depends if you are talking about wether you can see them easily or with effort see them come in and out of view. I find the visual appearances of the Magellenic clouds to be great rough guide to conditions for us in the s.hemis.
I used to use this site http://www.namnmeteors.org/lm_calc.html for meteor obs before I started printing out charts with snp to the mag i wanted and in the fields i wanted (I re-use them over and over forever now) - and then marking/numbering stars at various relevant mags and writing them down on a seperate page for reference.
Also the bortle scale is a great scale - wish it was more popular - I have read people can see down to mag 8 at extreme sites on top of 5000 mtr chilean mountains ect. in perfect conditions :-) wish there was a southern hemisphere specific version of the bortle scale.
http://www.frostydrew.org/observatory/columns/essays/bortle.htm
Kearn

[slice of heaven]

My assessment was only on an average its mag5 across the sky Kearn. When starhopping I will use mag5 or brighter in the Telrad so I'm only taking into account the stars I dont need to struggle to see.
All the factors you've listed come into play in how to actually calculate a sites darkness, and with so many variables it seems hard to actually determine how dark a site truly is.
Does 1 mag6 star at zenith thats barely recognizable make it a mag6 site?
There doesnt seem to be a true definitive measure of a sites darkness, unless of course you have Chris' cool tool.

[fringe_dweller]

technically, yes mate - if you are making a conventional report and that is the accepted criteria for the format, then yes than it is a mag 6 sky.
Kearn

[slice of heaven]

So basically dark skies are like beauty..."There in the eyes of the beholder"
I might have to buy a lazer pointer and put my 4yr old girl to the test and see if she can reach mag7 or better in the backyard. :)

[fringe_dweller]

"So basically dark skies are like beauty..."There in the eyes of the beholder"
LOL yep! :)
Dark skies depend on a few other variants too i guess - i find with my 25mw lazer pointer in the suburbs - you see an awful lot of dust particles in the beams path (looks like they are burning as some people say) but in the country I struggle to see many dust particles in the beams path, normally, which makes the beam a bit dimmer of course. Even during a full moon I find country skies are much better for observing due to the lack of pollution/dust particles being lit up (yes i have gone out for meteor showers during full moons!)
Kearn

[acropolite]

I can see the LMC and SMC and 47 Tuc on an average night and the milky way is just that (from Home), what that equates to I'm not sure.

[fringe_dweller]

Phil, that equates to skies i am seriously jealous of! on the envy scale of one to 5 - it would be a 3.5? :D
When I say the mag's are a personal guide for me, if I was to see a southern latitudes specific bortle scale, i would envisage the two madge's and the two mega globs would figure largely. Because they are diffuse objects first, and in the case of the mag's VERY LARGE diffuse objects, which makes them ideal, i would think, for true visual 'unaided eye' quick rough estimations. The level of stucture and detail you see in the SMC and the LMC varies a lot, with conditions and the site, as you all know. At really dark skies, to us, the LMC takes on a more rectangular solid barred stucture and the apparent 3Dness can be wild of course with both of them at truly dark skies when they are crossing the meridian particularly - I would include the 3D factor in any scale too. Also with the SMC being around mag 3 but very diffuse and large - i find it diffucult too see at all naked eye in most suburban situations, if at all most times. i would say if you can easily see the SMC low or at nadir for mid latitudes you would have at least 6th mag, or close to, skies. With some obs you have to state the LM in the same area of the sky you observed the object in, and thats what really matters in most cases i guess.
Kearn

[RAJAH235]

From another point of view,(sorry about pun), if you pick a constellation with mags ranging from say, -1/0, to 8 or 9 & below, from your charts, then on your observing night, count how many stars you can see in it. This gives a 'rough' indication of seeing/mag. etc.....It's surprising how much it varies by..... :D L.

[janoskiss]

I overlayed a desaturated version of the light pollution map with the current Iceinspace member map. I think you can count on one hand the members under unpolluted skies.

[[1ponders]]

Nice Steve. Slight scale mismatch, ya get that, but a great idea.

[Starkler]

I live on the edge of the yellow and green I think.
On good nights I can just detect the LMC , SMC when they are placed high, but to the north and west I would be lucky to make mag 4 :(

http://gar.customer.netspace.net.au/scope2/Auslight.jpg

[janoskiss]

As good as I could get it without spending too much time on it. :P The white border line from the light pollution map matches the border of Oz & NZ to within a pixel, which is probably better than the resolution of the data anyway.

[slice of heaven]

Nice maps guys

[cometcatcher]

Mag 6.5 at the zenith here but the horizon especially to the south where the city lies is horrible. But I'm getting old and going dim anyway.

I remember when I was a kid, doing astronomy then at Eimeo 32 years ago the skies were very dark.

Seen big changes where I presently live over 25 years. Andergrove has literally exploded with a population increase along with the lighting.

[asimov]

After reading more info on this subject, I realize I "under exaggerated" my skies as being 5.5-6. I'm thinking now it's more like 6.5-7 mag.

[slice of heaven]

Your skies should be Ideal John, apart from your local streetlights youve no major centres apart from Pt Lincoln. Any skyglow from there?
I'll have to reassess my skies the next chance I get.

[ving]

so can i on a good night, but faintly :)
nor do i know what this equates to...

[slice of heaven]

Probably that your skies are darker than someone elses that cant see them :)
AND that we need a darksky table that relates to the Southern Hemisphere so people can gain a perspective of what type of skies others are viewing and imaging in.

[ving]

yes thats what i thought too :poke:
:P

[slice of heaven]

Is anybody/bodies up to the challenge of creating a Southern Hemisphere darksky table using selected easy to distinguish objects that are visible across the Southern Hemisphere?

[asimov]

Hi Slice. No, I don't get affected from the lights of Port Lincoln luckily. The street lights are a nuisance naturally. I ended up making 2 big frames 10'X8' & covering them with black plastic to over-come the street lights & the wind if it does happen to spring up while I'm observing. I need to make 2 more screens & then I'll have like a mini removeable observatory.

[ballaratdragons]

From my back paddock with unaided eyes on any given clear night (except from mooning) I can see the full Milky Way as a fairly bright band of white and all the stretches of dark matter running through it stand out including the Coal Sack (very obvious).

I can also see 47Tuc, Omaga Cent, just make out Tarantula and the Magellanic Clouds are obviously very easy.

When I went to the Star Camp sight one night (only 2k away) I was amazed at how much more I could see with unaided eyes! Everything is so bright I actually had trouble differentiating the Crux from all the other stars! There are almost too many!

[asimov]

Hi Ken! Long-time-no-see mate! Yup. You have mag 7 skies by your description?

[ballaratdragons]

Yeah, I'm still around John. Been VERY busy! Storms created havoc around here!!

I would like to do a Star Mag check but haven't had any sky for quite a while.

I will pick a section of sky and draw exactly what I see (every star), then I will compare it to a star map. Easiest way I can think of.

[asimov]

From what I've been reading, If you can see stars in the coalsack naked eye, you've got mag 7 easy..