Dark skies - any indicators / scale

[davidpretorius]

Hi Guys.

down here at my shack, apart from two lighthouses on the horizon and a minute amount of sky glow from a town of 2000 people 30 km away, the sky is dark, very dark.

I took the scope out last night and the jaw dropped.

For those at snake valley, the view of the LMC and SMC was the same as my house back in lton, but down here, breathtaking!!!

I had trouble finding eta carina, due to the extra stars visible!!! But once viewed throught the ultrawide, WOW! Sculptor galaxy, easily spotted with the guide scope!

One thing i had not seen before was the companion to Alnitak (bottom right star of the three in orion). This was with the 2" 80 degree ultrawide. It stood out so much, but i had never come across it before.

Starry night indicates an apparent magnitude of 9.53.

As this will be a future site for dragging my mates from IIS to when they visit me in tassie, i would like to convey the "darkness".

Is there a scale ie apparent magnitude at a rough magnification, or a rough rule of thumb that the more travelled guys use to indicate darkness, a certain star or galaxy???. I have a 10" x fl1250 scope.

Remember this to me was a jaw dropper and I am used to snake valley darkness!!!

Once the wind drops, i am going to have an all nighter. Jupiter and Saturn rising over the ocean will be magic!

[fringe_dweller]

David, get your SN and print out a map for a small patch at zenith, and one at say 45º altitude, then one for say within 5-10º or closer to horizon, for all around the same time (well after sunset, say 2 hours at least) get the chart to go down to 8th mag at least (this is for a naked eye test) - and then find and clearly mark a number of stars at intervals of .1 of a mag at around the 7th mag - 8th mag for zenith - so close to 7.1, 7.2 ish and so on - I use a seperate piece of paper for details of stars mag/name/ and just number the stars on the printed chart as it gets confusing otherwise. The stars at 45º wouldnt be as high a mag as zenith so go down to around 6th mag - for the horizon even less -
also the bortle scale evn tho it is for northern hemisphere is still useful for describing to others the conditions of your observing location - it makes it very easy to picture for a person familiar with the scale :-)
http://www.frostydrew.org/observatory/columns/essays/bortle.htm
atmospheric phenonema like the gegenschien, zodiacal light, skyglow are very good indicators
for instance we were on a comet imaging trip in outback SA once and a quarter moon came up later on - just as it was rising we saw these highly defined fingers of light creep very slowly along both horizons simultaneously from the east/moons direction - they were about maybe 3-5º in thickness - they were very dense and strongly defined milky white and quite seperated from the inky black - they eventually met on the western horizon and then the moon came up - i think that lasted about 10 - 15 minutes or so from memory - one of the bizarest things I have ever seen :) I think it was airglow - not sure
heres an exert from my notes
" We have never seen a moonrise like that either!!, amazing thing from a really dark place, with fingers of light stealthily encircling the dark horizons till they met in the west with sharply clear lines of distinction between light and dark - not unlike some aurora a bit - very nice - felt like we were on the moon almost, not surprising though with that sort of outback country. Would go to see just that again anyway!"

[acropolite]

Sounds good Dave, BTW north islanders don't call them shacks, they're weekenders or holiday homes. Where is it, on the east or west coast. My shack's the same, no street lights or light pollution; the milky way has to be seen to be believed; I haven't been there since I got my LX. I'm envious, I should be there at the moment, keep the reports coming and make sure you catch a few fish.

[davidpretorius]

thanks fringe dweller, makes sense. i haven't got a printer with me, but will take out the laptop and pick a bit of the sky and compare.

i will play with starry night to bring up only mag 8 stars.


phil,

go to st helens and head to binallong bay and keep going to "the gardens" we are the last shack before 10km of beaches north of us.

Mate, the 4 of us lton boys must set aside a winter long weekend and come down here. Heaps of room for us!

[acropolite]

My shack's at Ansons, a few K's further north. Aside from the west coast it's probably as dark as it gets.

[fringe_dweller]

I only suggested printouts as the laptop will ruin your night vision even with the red screen mode in SN -
another very simple but telling test is how well you can see your hand right in front of your face - as the old saying goes :P - if you cant see it all when dark adapted even very close - then brother you are somewhere VERY dark :) unless the winter milky way is casting shadows then your in astro heavan.
I/we used to go on holiday all the time to Coles Bay and St Helens, feycinet peninsula (sic?) as a kid when we lived there - it was totally undeveloped then - had it to ourselves quite often :-))) still one of my favourite places have ever been.
have a good one dude.

[Photon]

Hi Dave, Your on re that weekend away, its in my diary!!! I visit Musselroe Bay during the summer for a bit of Cray diving and apart from the Swan Is and Eddystone Pt lighthouses and the occasional sea mist, its as you describe! I only use binoculars for viewing though. (need a stainless scope in that environment!).