As the crow flies, I live 33km south of Sydney in Engadine. 1.5km either East or West of me is National Park, and to the South there is one small suburb and then very little till you hit Wollongong 50-odd km away.
Mine varies a bit according to humidity and how long it has been since the last southerly change gave the sky a good clean out.
Over the last few months I've been measuring the backyard sky quite a bit with my SQM-L meter and was surprised to find it a little better than I expected.
With the Moon at least 10 degrees below the horizon on all occasions, the worst reading I've got in the last 2 months has been 19.45 which equates to a ZLM of +5.1. The best reading was 20.02 just after midnight about 8 weeks ago which equates to a ZLM of +5.5.
The median reading is around 19.82 which equates to +5.39. By eye, I'd have estimated the average to be about the +5.2 mark.
Where I occasionally observe near Darkes Forest, 20km away South I've taken two readings both at 20.55 equates to a ZLM of +5.85.
At our Southern Highlands site 90km away near Bargo, it is usually between 20.95 and 21.25 equating to ZLMs of +6.1 and +6.24 -- so it can vary a bit too. This site is what I'd call "nearly dark".
The best readings I've had at Mudgee (a true dark site) were 21.95 which equate to +6.61. I've only used the SQM-L there on one trip so far. I reckon I've seen slightly better nights at Mudgee than those tested, so on the best nights the ZLM there is about +6.65 to +6.7.
I've seen better though on the few nights I've spent at Siding Spring Mountain. At significant altitude there it is probably approaching, though not quite +7.0.
A recent development by a neighbour has pretty much put an end to my backyard observing (6 Kms west of Sydney).
The neighbour to the rear of me built a garage about 18 months ago, not a problem in itself, but about 2 weeks ago, he decided that a light was necessary to illuminate the 1 metre or so between the garage and my fence.
I've now idea why this was necessary as there is no door through the back of the garage nor is there anything stored there.
Perhaps he decided that I'm a shifty looking character as I spend time in the backyard with binoculars.
On a brighter note, I was recently in Tasmania, about 40 Kms south of Hobart and the skies were magnificent!
Pity baggage restrictions prevented me from taking my binoculars with me
In a random one-night summer experiment(I was curious) star hopping around Crux and using CDC for magnitudes, It worked out approx +6.0 direct, and approx +6.22 averted.
Obviously different night different results, so no idea what could be considered an average...
Approx 40km from Perth, 5km from Rockingham (2nd largest WA city, pop. ~ 90k)
Tonight, transparency looking good, bit of twinkle, I reckon my suburban backyard at 9pm was about +4.6, direct not averted, my eyes/glasses, 20 min dark adaption, in the direction of CRU and TRA.
Ok using Erics star counting method, (thanks Eric), Area 27 near Crux, I got 15 stars, that makes it 6.8 for me. I tried doing area 26 to confirm, but kept losing count.
Ok using Erics star counting method, (thanks Eric), Area 27 near Crux, I got 15 stars, that makes it 6.8 for me. I tried doing area 26 to confirm, but kept losing count.
G'day Y'all
Hmmm a bit over the top from your light poluted location more likely 5.8 - 6.0
Take a read here for a better view
Well Robert I don't know, I just used the counting method described in Erics post on this site to establish this figure. For the record I don't actually live in Townsville, I live on 24 acres about 30Km north of Townsville, and our property backs onto native scrub. The only bit of light polution visible in our sky is for about 5 degrees from the north eastern horizon. I am not arguing the point, because as my avatar suggests, I am a newby, just clarifying my location. Thanks for your help.
You can easily confirm the figure, pick a +6.8 mag star from a star atlas that will be as close as possible to zenith(directly overhead) and see if you can spot it.
If not, try a +6.7, then a +6.6....
I found that even on nights of apparently perfect seeing, I can see a +6.0 as a steady point, and then a +6.1 as fading from visible for a few seconds to gone for a few secs to visible again and took that as my threshold.
Hi guys, i have made visual limiting mag estimates of 6.9 during W1 Boattini's brightening stages in June.
I can confidently call it LM= 6.9 from my backyard and at the local aerodrome.
I don't have an SQM, which i hope to purchase one day.
I've seen better though on the few nights I've spent at Siding Spring Mountain. At significant altitude there it is probably approaching, though not quite +7.0.
Is there some way of separating the numbers that appear to be on top of each other??
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