I received an SQM sky quality meter last week, generously loaned to me by Eric Kingston (Erick on IIS), and tonight I put it to work assessing the darkness of the Eagleview night sky. I measured the sky brightness at the zenith (or as close to without pointing directly at the bright Milky Way) and took 8 readings, pointing in very slightly different directions overhead, one after another, over a 10min period at 7:20pm, 9:00pm, 10:00pm, 11:00pm, 11:45pm and 1:00am. I then discarded the highest and lowest readings in each set and averaged the other 6 readings. The results in magnitudes/square arc sec, were as follows (the bigger the number the darker the sky):
(I also did a set pointing at about 25-30 deg above the northern horizon and directly toward the Canberra light dome and the average reading was 21.79 so even that ain't too bad)
You can see the effect of the Milky Way being directly overhead at 730 and as it moved away from near the zenith and it got darker, the numbers improved. Maybe they could have improved further after 1am but I decided to finish up, as although the numbers had improved a lot with successive sets of measurements, by 1am the Milky Way was nowhere near the zenith so I didn't think there would be much improvement...? Plus I was buggered
Anyway, anything higher than 22 indicates really dark skies, so pretty happy with these results as they empirically confirm that the skies over Eagleview are indeed exceptionally dark and explain the great contrasty views I've had through my 12" Dob
I have posted the last 1am set of measurements, along with the best reading of 22.32 (which was discarded), just to show the numbers were real
I knew tonight was dark as, for only the second time in my life, I was able to detect the extremely faint Zodiacal Bridge, the very faint band of light, a result of sunlight being scattered of the tenuous disc of tiny dust particles that fill the plain of our Solar System and it is visible as a super faint band following the ecliptic and running almost perpendicular to the Milky Way. The last time I saw this phenomena was in far north QLD from my friend Tim Curruthers, Savanah Skies Observatory, near Chillagoe, which is located under dry and very dark skies 3hrs drive West of Cairns inbetween cooee and nowhere
Seems this assessment above was a little inaccurate
It turns out that the SQM meter I had borrowed for these measurements, needs calibration. The IR filter that covers the sensor in the SQM meter, was frosted over, so this blocks some light from entering and causes higher than normal readings. So, if you own an SQM-L meter yourself, check that the IR filter over your sensor isn't a cloudy/creamy even blue clour (see attached photo), if it is, you have frosting inside it and it will give inaccurate readings, ie darker than reality.
I have since purchased another (second hand) SQM meter that is not frosted and in a couple of side by side comparisons so far, all be they (so far) not under quit as exceptional conditions as the magnificent night I enjoyed above, the unfrosted SQM meter returns readings on average about 0.3 mag/squ arc sec lower, give or take. As luck would have it..the second meter however has shown some intermittent issues too that has lead me to believe it too may also be faulty but in a different way, Maama Mia!
I will do some more quantitative/comparison tests with fresh batteries but at this stage this revelation would suggest that on the beautifully dark, transparent sky I had on the night mentioned in my post above, the average reading at 1am that night, was probably closer to 21.90 with several readings hitting 22.00 or just over.
So while not quite as ridiculously incredible as first thought and who knows if the second SQM meter is even reading properly..?..this is still pretty awesome, so I am still over the Moon
This revelation sparked me to investigate properly just how one can accurately quantify their sky darkness, or is it indeed possible at all?...and it is clearly not that easy. There are many interpretations and descriptions of subjective analysis of the sky darkness available on the Net
On the night in question, after a snow front had passed through and it was obviously crystal clear and transparent, the main features that struck me and that stood out naked eye and suggested a truly dark sky was above me, were:
1) A bright Zodiacal Light triangle after sunset and before sunrise that reached all the way up to the Zenith
2) The full very faint Zodiacal bridge (see attached), following the entire ecliptic, was faintly visible, as was the Gegenschein.
3) The Milky Way was full of many and intricate high contrast dark lanes
4) The Milky Way was strikingly broad across its centre (a real wow factor), with an outer gossamer glow easily 45deg wide or more across its core
5) When overhead Milky Way cast an obvious shadow when I put out my hand
6) The sky had so many stars it was breathtaking
7) I could see globular clusters M22 and M4 and two stars in the Coal Sack, naked eye, comfortably.
8) The one light dome (Canberra) was subdued and its upper faintest extension low in the north
9) Once they had risen to the meridian, M31 and M33 were both visible.
So, reading the various descriptions in this detailed interpretation and this one of the dark sky Bortle scale levels and taking only theoretically perfect skies as Bortle level 1, I would probably put the sky that night at Eagleview comfortably into the Bortle scale at level 2 with a couple of elements of a level 1 site and certainly one of the very best skies (probably second best..?) I have ever observed under, in my 40 years of active astronomy I think the extra altitude helps a tad too?
Now, while fun to do (and I may do a little more analysis yet), t'is time to just enjoy the fantastic environment rather than trying to measure just how good it is
Mike
Last edited by strongmanmike; 03-11-2021 at 12:15 PM.
lak of photoMike,
In your sketch of your observatory I see the base for your dob is shown as rectangular.
Might I suggest as follows
:-cut the top out of a 44 gallon drum and then cut on third of the drum (top removed third
:- dig a circular trench, say 4 inches deep to receive the cut end of the drum
:-pack the trench to locate the drum so that the top is level
:- fill the drum nearly to the top with stones
:-top with cement and screed it to the drum rim
This size neatly fits Skywatcher dobs.
The photo just shows our drum in place
Chris
Bother the photo was too large
Last edited by muletopia; 02-11-2021 at 11:19 PM.
Reason: lack of photo
lak of photoMike,
In your sketch of your observatory I see the base for your dob is shown as rectangular.
Might I suggest as follows
:-cut the top out of a 44 gallon drum and then cut on third of the drum (top removed third
:- dig a circular trench, say 4 inches deep to receive the cut end of the drum
:-pack the trench to locate the drum so that the top is level
:- fill the drum nearly to the top with stones
:-top with cement and screed it to the drum rim
This size neatly fits Skywatcher dobs.
The photo just shows our drum in place
Chris
Bother the photo was too large
A cool idea there Chris, thanks I was considering pouring a small round slab actually...but because I am secretly hoping to get a larger Dob someday soon (maybe) , thought I'd wait and see if that is just a pipe dream or not
That zodiacal bridge pic is really nice. I saw the Gegenschein at Coona one year but never seen a bright picture of it. You should start the "EagleFest" star party to finance "iEagle" telescope services in the near future.
That zodiacal bridge pic is really nice. I saw the Gegenschein at Coona one year but never seen a bright picture of it. You should start the "EagleFest" star party to finance "iEagle" telescope services in the near future.
Yeah its a top shot taken from the Mangaia islands (Cook archipelago) by Petr Horálek.
I had vaguely identified the Gegenschein once before from around Adaminaby up in the snow high country as a teenager but I didn't see the full stretch of the Zodiacal bridge or band until I visited Tim Carruthers observatory, in way out, inland far north QLD, near Chilagoe, back in 2019. His skies are well and truly Bortle 1 there and the best I have ever been under, both features were very clear and obvious from there, just like the photo but minus the colour! I wasn't really expecting to be able to see them from Eagleview but on a couple of excellent transparent nights, as described above, I was indeed able to make them both out in the wee hours when they were overhead, it's like looking up and seeing two Milky Ways in the sky (one bright one faint), almost perpendicular to each other. From Chilagoe it was utterly spectacular and easy to see, from Eagleview not quite as obvious but certainly visible.
I imagine these features might be visible from Wiruna on good nights too..?
I imagine these features might be visible from Wiruna on good nights too..?
Not sure about that. I saw it in 2012 at Coona only because Lachlan who was there with some dude from the Texas Star Party exchange pointed it out to me. It was a milky patch at the zenith. Not obvious but you could see it with averted vision. I recall the milkyway though that was wrapped all around the horizon 360 degrees and you could still see it. That was pretty cool. Like a ring. Saw the zodiacal light after sunset out west a couple of time but never saw the zodiacal bridge either. I did see my hands and arm shadow though with the milkyway up ahead one cold winter at Wiruna in 2008. Not defined outline but you can certainly see the blurry shade. I don't think I'd see it now. My eyes aren't as good anymore.
I recall the milkyway though that was wrapped all around the horizon 360 degrees and you could still see it. That was pretty cool. Like a ring.
Yeah I've been lucky enough to see that at Eagleview too, its really quite amazing to see, huh?! One needs an unobstructed horizon under good dark and clean skies though. One day I will attempt a panorama/mozaic of it from the attached spot
Here is the picture. Importantly the "stand" can be relocated, just lift it out and roll to a new location and place it as before. In the photo it is in its second location.
I don't think that a caste base can be moved that easily.
Chris
PS the trees are not close, this is the crop from the central portion of a telephoto shot.
From the ob I set a horizon file at uniform 30 degrees, all well
Ok cool thanks for that. Hmmm? I have 44gal drum too... Might get a disc ready to pour when the concrete truck comes to do my support pier, there is always left overs
Hi Mike,
I am watching your progress and waiting for a seeing report.
I want to know whether sub 1 arc second seeing is possible in Australia?
It might only happen between say 2am and 5am on a few lucky nights
but I think it's possible at your site.
If so there will likely be many astro imagers wanting to use your site.
I really hope so.
Hi Mike,
I am watching your progress and waiting for a seeing report.
I want to know whether sub 1 arc second seeing is possible in Australia?
It might only happen between say 2am and 5am on a few lucky nights
but I think it's possible at your site.
If so there will likely be many astro imagers wanting to use your site.
I really hope so.
cheers
Allan
Hi big Al
Well with this rain the start of observatory construction has been delayed ..aaaand due to interruptions and delays within the international container shipping network, I'm pretty sure my new 3M Scopedome won't be ready for delivery to site until perhaps late January at best but more likely sometime in Feb..? but I am patient, besides, I have to get the support pier constructed and then the deck built before then anyway
My many nights of visual observing over winter, certainly give me hope that it is a steady site there were no nights where I thought, nah, the seeing is not good tonight (so that's promising) had some of the best views of Saturn and Jupiter I have ever had. Darkness, contrast and transparency are certainly most excellent, as was the frequency of clear sky time at night (not so good right now in all of SE Aus)
Anyway, it is first and foremost my intention to setup a working observatory for myself , then, if I am successful with all this new fangled computerisation and automation palava then, sometime down the track, if some others are lucky enough to be able to share and utilise these magnificent sub-alpine skies, well and good
Photos from last weekend and this weekend, my sons Perentie 4X4, setup camp in a lovely clearing right at the top of our property, at 1450m ASL...very cool
Mike
Last edited by strongmanmike; 08-11-2021 at 10:44 AM.
Perhaps get a secondary hobby to help you cope...rebuilding pre 1930 cars maybe.
Good luck and thanks for keeping your story in front of us..I love it.
Alex
He he...at the moment just being on site is enough to make me happy, it is a magnificent location and there is plenty to do...PLENTY! ..especially since I just completed a chainsaw course last weekend rev, rev cut cut cut...everything! Mu hu hu hu ha ha haaaaa
Well with this rain the start of observatory construction has been delayed ..aaaand due to interruptions and delays within the international container shipping network, I'm pretty sure my new 3M Scopedome won't be ready for delivery to site until perhaps late January at best but more likely sometime in Feb..? but I am patient, besides, I have to get the support pier constructed and then the deck built before then anyway
My many nights of visual observing over winter, certainly give me hope that it is a steady site there were no nights where I thought, nah, the seeing is not good tonight (so that's promising) had some of the best views of Saturn and Jupiter I have ever had. Darkness, contrast and transparency are certainly most excellent, as was the frequency of clear sky time at night (not so good right now in all of SE Aus)
Anyway, it is first and foremost my intention to setup a working observatory for myself , then, if I am successful with all this new fangled computerisation and automation palava then, sometime down the track, if some others are lucky enough to be able to share and utilise these magnificent sub-alpine skies, well and good
Photos from last weekend and this weekend, my sons Perentie 4X4, setup camp in a lovely clearing right at the top of our property, at 1450m ASL...very cool
Mike
Thanks for the update Mike.
I am really hoping it will go well and
that we'll all see some magnificent images at
a quality not seen before posted on Ice in Space
and maybe even some APODs.
Thanks for the update Mike.
I am really hoping it will go well and
that we'll all see some magnificent images at
a quality not seen before posted on Ice in Space
and maybe even some APODs.
that has lead me to believe it too may also be faulty but in a different way, Maama Mia! 
, thought I'd wait and see if that is just a pipe dream or not 
Might get a disc ready to pour when the concrete truck comes to do my support pier, there is always left overs 
in all of SE Aus)
, then, if I am successful with all this new fangled computerisation and automation palava 
