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How dark is your sky on a moonless night?

Piero

By Piero
in Observing - Discussion

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Piero

Piero

Posted
Posted

Here we go! SQM measurements are more than welcome of course. If you don't have a SQM meter, feel free to put an approximated NELM measure and description of what can be seen. As sky darkness is not always the same, I guess it makes sense to give an average measure. Record measures are also welcome (Gerry, you are also allowed to post! :D) but please specify that that is just occasional. :) 

From my typical observing location here in Cambridge it's about 19.60. In Venice area it's about 18.20. I don't know exactly how dark is in Lorenzago (Alps, North Italy). The milky way is well defined and visible throughout the sky but M33 is not visible naked eye. I think it is about 6-6.3 mag NELM. :rolleyes: 

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Stu

Stu

Posted
Posted

Great idea Piero!

From my report last night and other sessions I would say my sky is around mag 19.1 on a good moonless night. 6 stars visible in Ursa Minor, the seventh usually visible with AV which puts me at around Mag 5 at the zenith.

Best ever so far was a one off reading of 19.28 last night.

EDIT After John's excellent post, I'll add the following. On the best nights here M31 and the Double Cluster are just visible with averted vision. I've never caught the Milky Way here at all though.

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pipnina

pipnina

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Posted

From the dark site, the beehive cluster was a naked eye object. Darkest star I can confirm seeing was around mag 5.5 though dimmer stars were briefly detectable. I once could have sworn I saw glimpses the rosette without a filter in the 10".

From home I'm not so lucky. Most of the stars I used to star-hop with from the dark site are washed out in the telescope, the dimmest star I can recall seeing from home is mag 4.2. But because I'm in the suburbs that's in the best part of the sky, 180 degrees the other way and it's closer to mag 3. I did manage to just about detect the flame from home, though. But It definitely was not an easy spot. From the dark site the Flame is quite a lot better. 

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John

John

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Posted

My skies vary a lot depending on the direction you are looking in !

Overhead I reckon I can get mag 5.5 or therabouts with the naked eye. On a decent night I can see a good stretch of the Milky Way and M31 is visible with direct vision as is the double cluster in Perseus.

So far, the faintest point source I've managed to see with my 12" scope is around mag 14.2 I think.

 

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DRT

DRT

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Like John, I get a lot of variability depending on which direction I am looking. It is much darker to the north as I have clear countryside between us and Sheffield which is around 12 miles away. Chesterfield is less than half that distance away to the south west so anything low in that direction is very difficult to get a good view of. I can't see low down to the east or west due to rooftops and trees but at relatively high altitudes east is much darker than west, again due to clear countryside to the east. The zenith is quite dark.

I've just downloaded the SQM app onto my iPhone so will post my numbers tonight :smile:

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jetstream

jetstream

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Posted

There are times that the conditions here just come together and last night was one of them unexpectedly. There are many that know the SQM can be affected by transparency- and it can go either way a bit. Supporting the SQM with NELM is a great idea, but can take up precious observing time.

I warmed up the SQM by taking many readings- over twenty- to ensure no errors and this SQM-L has been calibrated from the factory.

I am at 1100 ft and in a relatively remote area with my SE to SW views overlooking Voyageurs National Park in Minnesota a few miles away.

My typical SQM reading is around 21.6 mag/arcsec with an NELM of 6.3 ish, last night the sky gave up 21.9 mag/arcsec and an NELM of 6.6 using HIP 74818. Here is a poor picture of my SQM-L after taking one of the readings, using my Canon T3i.

 

sqm 019.JPG

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Joe12345

Joe12345

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Posted

I think my skies are okay, not brilliant though. Last night I was using starhops with M5.5 stars, but I doubt I could go much fainter. In the summer on the best nights I can sometimes glimpse the milky way through Cygnus.

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ollypenrice

ollypenrice

Posted
Posted
1 hour ago, Beulah said:

Mr Jetstream wins the thread, awesome :D

 

Isn't that the highest these gadgets read under starlit skies?  :)

Awe, you've made me reluctant to post, now! :icon_mrgreen:

In fact my range is the same as Gerry's. 21.6 is common, with a best of 21.9. The devices do read higher, though. We had an Australian astronomer stay a couple of years ago and in the outback at his preferred site he said 22.1 or 22.2 were possible. Another of our guests goes regularly to Tivoli in Nambia and he said that, to his surprise, the zentih readings were the same as here. Where Namibia scored, predictably, was closer to the horizon. In mainland Europe you are never going to get desert-like horizons.

Olly

(SE France, pre-Alpine 'Baronnies' range, alt. 900 metres.)

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Mr Spock

Mr Spock

Posted
Posted

I can see all of Ursa Minor but the milky way is a distant memory. It used to be visible here but the sky has gotten more polluted over the years. I though the LED lighting being installed would help but it's made it worse.

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Scott

Scott

Posted
Posted
3 hours ago, Stu said:

Great idea Piero!

From my report last night and other sessions I would say my sky is around mag 19.1 on a good moonless night. 6 stars visible in Ursa Minor, the seventh usually visible with AV which puts me at around Mag 5 at the zenith.

Best ever so far was a one off reading of 19.28 last night.

EDIT After John's excellent post, I'll add the following. On the best nights here M31 and the Double Cluster are just visible with averted vision. I've never caught the Milky Way here at all though.

I wonder how much experience has to do with what we can see. Stu is far more experienced than I and he can see M31 with averted vision but not the milky way. I on the other hand don't think I've seen M31 (unless I'm assuming it's HIP3881) yet the summer milky way is easily visable. I have no idea what this means. I just thought it was an odd observation. I also don't know what is concidered bad with these meter readings. I get that 21.6 is very good :)

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Stu

Stu

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Posted
Just now, Scott said:

I wonder how much experience has to do with what we can see. Stu is far more experienced than I and he can see M31 with averted vision but not the milky way. I on the other hand don't think I've seen M31 (unless I'm assuming it's HIP3881) yet the summer milky way is easily visable. I have no idea what this means. I just thought it was an odd observation. I also don't know what is concidered bad with these meter readings. I get that 21.6 is very good :)

That's a very good point Scott. I think in theory they are around the same surface brightness but I'm not sure. Perhaps I just concentrate specifically on using AV to see M31, but if I can't see the Milky Way fairly obviously I don't spend time looking for it. Either way it's either invisible or so dim as to be not worth looking at!! ?

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Beulah

Beulah

Posted
Posted
2 hours ago, ollypenrice said:

Awe, you've made me reluctant to post, now! :icon_mrgreen:

In fact my range is the same as Gerry's. 21.6 is common, with a best of 21.9. The devices do read higher, though. We had an Australian astronomer stay a couple of years ago and in the outback at his preferred site he said 22.1 or 22.2 were possible. Another of our guests goes regularly to Tivoli in Nambia and he said that, to his surprise, the zentih readings were the same as here. Where Namibia scored, predictably, was closer to the horizon. In mainland Europe you are never going to get desert-like horizons.

Olly

(SE France, pre-Alpine 'Baronnies' range, alt. 900 metres.)

Thanks Olly for that. :) I did read sometime back that 22 MPSAS was pretty much the maximum; I may have been mistaken:

 

http://www.unihedron.com/projects/darksky/faqsqm.php

Quote

What is the range of the Sky Quality Meters?

There is no specific limit on the range of the SQM because the calibration step fixes the maximum and minimum frequencies to intermediate values. For normal night-time viewing, the meter should accurately read from about 16 to 23 mpsas.

 

I managed 23 MPSAS in a blacked out room on a cloudy winter night... :D (took 50 seconds)

 

 

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YKSE

YKSE

Posted
Posted

My backyard is SQM 18.6 to 19.1(NELM 4.5 to 4.9) at moonless nights, darkest at autumn, parly of Milky Way between Vega and Altair visible sometimes when it is dark. My dark site is 20.8 to 21.3 (NELM 6.0 to 6.3). With a SQM in dark site, you'll notice how bright a SQM 18.6 sky is.

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Uranium235

Uranium235

Posted
Posted

On a good night I get a hint of the MW at the zenith, but living in a town centre location and right next to a hospital doesnt do me any favours. But if I were to travel a couple of miles out beyond Bewdley, past the Wyre Forest it can get very dark indeed.

No meters as such here, I judge the quality by what I can see on the southern horizon.

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DRT

DRT

Posted
Posted
10 hours ago, DRT said:

Like John, I get a lot of variability depending on which direction I am looking. It is much darker to the north as I have clear countryside between us and Sheffield which is around 12 miles away. Chesterfield is less than half that distance away to the south west so anything low in that direction is very difficult to get a good view of. I can't see low down to the east or west due to rooftops and trees but at relatively high altitudes east is much darker than west, again due to clear countryside to the east. The zenith is quite dark.

I've just downloaded the SQM app onto my iPhone so will post my numbers tonight :smile:

17.33 :sad:

 

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Stu

Stu

Posted
Posted
3 hours ago, DRT said:

17.33 :sad:

 

I reckon that must be wrong Derek. I'm sure your skies would at least be as good as mine, probably better. What's your NELM?

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