Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

sgl_imaging_challenge_banner_terminator_challenge_winners.thumb.jpg.6becf44442bc7105be59da91b2bee295.jpg

Moonshane

Tell us your sky quality

Recommended Posts

Here's the result for where I observe from - 10mins from my house.  I used to observe from the back garden, but the neighbours put up new extra floodlights - constantly on all night every night, front and back gardens, no PIR detector control ?

The good thing is that it is on the coast- so no light domes looking south :)

20190102_193437.jpg.85f01097cc0f13db01f9228c2279b196.jpg

 

  • Like 1

Share this post


Link to post
Share on other sites

Data below from my site on the Essex/Suffolk border. I don't really know what SQM means but I have imaged objects of mag 20 with my lodestar and 30 second exposures, not sure if this confirms the data in any way? It can get very dark overhead on transparent nights, but there are three massive sources of light pollution 10 miles away in each direction (Colchester, Ipswich and Felixstowe docks) so any mist or vapour in the atmosphere and the sky turns orange. I live on a new build and consider myself very lucky to have the majority of the garden streetlight free, although I live in daily fear of the dreaded 'insecurity' lights being installed.

image.jpeg.08a0c47fa3027a10e8c6529ca06f2d57.jpeg

 

Share this post


Link to post
Share on other sites
Posted (edited)

I’ve got 19.86 at home and 21.38 at my local dark site by that. Both sites have served me well!

21.67 at the campsite I visited during the summer. It’s only about 30 mins drive so may have to investigate observing there more regularly. 

Edited by Littleguy80

Share this post


Link to post
Share on other sites
1 hour ago, jetstream said:

lol!

I agree Iain, while the maps can be accurate it is not necessarily so. One map indicates my current place as quite a bit brighter than my remote dark sites-yeah right... the SQM-L dispelled this (&NELM) and saved me many miles of driving. I have mapped a huge area in my travels and its all the same, including my home.

A very useful thing the SQM-L does is find the edges of darker places, even near towns and cities.

A truly good test of skies is the ability to see M33 IMHO.

Cheers Gerry, I find the map to be overly simplistic, other than perhaps being a rough guide. I have learnt that readings can vary so much with the best, often within the early hours of the morning assuming that transparency is very good. Equally going to the same location on two different nights results in yet further varied readings. For anyone that does stray from their backyard / garden, you quickly become aware and sensitive to the creep of light pollution, not least through expanding towns, villages and roads. It can be quite depressing, so any good pockets of potential dark sky quality are highly valued that will hopefully gain in awareness and protection. Yep using a SQM-L to seek darker places along the edges of Urban areas is useful and a good indicator for determining sky brightness is quite firmly dark adaption and naked eye observing.

  • Like 1

Share this post


Link to post
Share on other sites
Posted (edited)
3 hours ago, scarp15 said:

That online mapping resource is misleading, inaccurate and delusional and certainly should not be used for quoting as a reference in any observers reports. If I was to quote from this map based upon locations I go observing within then I would be implying SQM 21.88.  Whilst I gain 21+ mag skies, this particular reading is quite simply - at least so far - untrue. A Unihedron SQM-L (check FLO) is a highly useful tool for measuring / assessing an average and monitoring sky brightness over a given period during your observing session. Anything else is quite simply for the birds, at least in my opinion.

You know how the saying goes: "one man's trash is another man's treasure"

I found that website to be extremely useful tool once you understand it's limitation and application. Readings with SQM/SQM-L will certainly vary across nights and will be different to map as map probably represents annual average value, or at least average value of recording times (which might or may not be uniformly dispersed throughout the year). VIIRS data is actual recording taken via satellite of ground sources total illumination. Atlas data represents numerical approximation of sky brightness made by integrating ground sources illumination and atmospheric scatter - I think it is very clever that they managed to get it to such level of precision.

One needs to distinguish sky brightness to other things that impact visual astronomy. Transparency, both local and high altitude can have significant impact even in very dark skies - this can make one observing site preferential to another one. SQM readings on particular night might vary significantly to this map. Amount of water vapor in the atmosphere can contribute to light scatter quite a bit, light sources are very dynamic, lights get turned on and off, it even depends on traffic density and road conditions if you have significant road network near by. Dry road and wet road have different reflection properties. Snow increases light pollution quite a bit. So many things impact this that it is quite a miracle that such map works and works so well - within mag 0.5 in most cases - that is up to 63% of base value.

1 hour ago, wookie1965 said:

what do the numbers mean?

Brightness and Artificial brightness are probably ground luminosity recorded by satellite. First being just natural sky glow reflected of the atmosphere and ground, and second artificial lights on ground - what we think of when we say light pollution.

SQM is magnitude per arc second squared and can be thought of as: if every arc second x arc second (square with sides 1 arc second) contained a star with apparent magnitude of XX without any other light sources in the sky it would be as bright as sky is now. Just for comparison, Vega is 0 magnitude star, and Jupiter has about 1600 arc seconds squared of "angular surface" when largest. Every 5 magnitudes is x100 less light, so mag20 star is 100,000,000 times fainter than Vega (hope I got number of zeros correct :D ). It should consist from natural sky brightness (zodiac light, milky way, stars ...) + atmospheric scatter of artificial light from the ground. When there is no artificial part, natural brightness is at 22mag.

This number is more meaningful to imagers than observers because it can be used in SNR calculations. It is also useful to guess visibility of some faint objects if you compare that to surface brightness of those objects - this is what Contrast Index in Stellarium for example represents:

image.png.b6f22cc8b02f7a261e58c45c34b8ab7d.png

Ratio of brightness of target to brightness of background sky. Surface brightness in Stellarium is given in magnitudes per arc minute squared, and for conversion one needs to subtract add 8.89 to get magnitudes per arc second squared. Do be careful with surface brightness in stellarium - it is average value and real value can vary quite a bit - think galaxy core vs outer parts - core is way brighter than outer parts.

Ratio from above info represents how many times that particular sky is brighter than natural unpolluted sky in zenith.

Altitude and coordinates are self explanatory, me thinks.

Edited by vlaiv
Magnitudes are positive for faint stuff ...
  • Like 5

Share this post


Link to post
Share on other sites

Yep a Sky Quality Meter should only be used when circumstances are applicable, i.e. periods of good transparency, no stray light etc and in the correct way. The science in this mapping is perhaps impressive, for an actual circumstance concerning an amateur astronomer on a given night, a real time sky brightness reading is more accurate and relevant.

Early on when I first began to go dark sky stargazing, I would head out west from Newcastle and become situated in the middle of Hadrian's Wall. Up at zenith and across north it would be completely dark. Due east was a glow from Tyneside and due west would be a glow from Carlisle. I currently like to venture north into a Northumberland valley or else onto higher ground. North and north east is completely dark, yet south east there is still a glow from the coastal towns and Tyneside. Even at Kielder you cannot fully escape it, although there are verifiable SQM readings taken on exceptional nights of 21.7.  

Perhaps FLO could stockpile Unihedron Sky Quality Meter - L models (that read sky brightness at and near to zenith) and perhaps everyone ought save up for one (especially before Brexit kicks in) and this could stimulate interesting data and debate.   

  • Like 2

Share this post


Link to post
Share on other sites

It's clear that some aspects of the maps are not quite right, at the fine detail level.

The VIRS maps shows a big blob of light pollution north of my 'dark spot' that is a large country hotel, comparable to a village three or four miles away. In practice you can't see any evidence of the hotel.

It seems that a bright 'point source' is causing a large blob of LP.

In contrast two industrial parks that affect me at home don't show on the VIRS maps.

 

The maps are better for finding large dark areas at lower scales.

Share this post


Link to post
Share on other sites

For me it comes out fairly accurately, my best readings are around mag 19.1. I think as long as you know the limitations it is a useful tool for indicating where to explore for dark sites.

20190102_221324.jpg

Share this post


Link to post
Share on other sites

Just thought to check our dark site. This result is almost exactly what we measured on one visit, but to prove the comments Scarp15 made, we have also measured well below mag 21 here in another moon free night.

20190102_225258.jpg

Share this post


Link to post
Share on other sites
1 hour ago, vlaiv said:

You know how the saying goes: "one man's trash is another man's treasure"

I found that website to be extremely useful tool once you understand it's limitation and application. Readings with SQM/SQM-L will certainly vary across nights and will be different to map as map probably represents annual average value, or at least average value of recording times (which might or may not be uniformly dispersed throughout the year). VIIRS data is actual recording taken via satellite of ground sources total illumination. Atlas data represents numerical approximation of sky brightness made by integrating ground sources illumination and atmospheric scatter - I think it is very clever that they managed to get it to such level of precision.

One needs to distinguish sky brightness to other things that impact visual astronomy. Transparency, both local and high altitude can have significant impact even in very dark skies - this can make one observing site preferential to another one. SQM readings on particular night might vary significantly to this map. Amount of water vapor in the atmosphere can contribute to light scatter quite a bit, light sources are very dynamic, lights get turned on and off, it even depends on traffic density and road conditions if you have significant road network near by. Dry road and wet road have different reflection properties. Snow increases light pollution quite a bit. So many things impact this that it is quite a miracle that such map works and works so well - within mag 0.5 in most cases - that is up to 63% of base value.

Brightness and Artificial brightness are probably ground luminosity recorded by satellite. First being just natural sky glow reflected of the atmosphere and ground, and second artificial lights on ground - what we think of when we say light pollution.

SQM is magnitude per arc second squared and can be thought of as: if every arc second x arc second (square with sides 1 arc second) contained a star with apparent magnitude of XX without any other light sources in the sky it would be as bright as sky is now. Just for comparison, Vega is 0 magnitude star, and Jupiter has about 1600 arc seconds squared of "angular surface" when largest. Every 5 magnitudes is x100 less light, so mag20 star is 100,000,000 times fainter than Vega (hope I got number of zeros correct :D ). It should consist from natural sky brightness (zodiac light, milky way, stars ...) + atmospheric scatter of artificial light from the ground. When there is no artificial part, natural brightness is at 22mag.

This number is more meaningful to imagers than observers because it can be used in SNR calculations. It is also useful to guess visibility of some faint objects if you compare that to surface brightness of those objects - this is what Contrast Index in Stellarium for example represents:

image.png.b6f22cc8b02f7a261e58c45c34b8ab7d.png

Ratio of brightness of target to brightness of background sky. Surface brightness in Stellarium is given in magnitudes per arc minute squared, and for conversion one needs to subtract add 8.89 to get magnitudes per arc second squared. Do be careful with surface brightness in stellarium - it is average value and real value can vary quite a bit - think galaxy core vs outer parts - core is way brighter than outer parts.

Ratio from above info represents how many times that particular sky is brighter than natural unpolluted sky in zenith.

Altitude and coordinates are self explanatory, me thinks.

Thank you for the explanation looking at it means ive got pretty shoddy skys.

Share this post


Link to post
Share on other sites
Posted (edited)

My skies are Bortle 7 according to the site, which would mean M31 would be possible naked eye, which hasn't been my experience.

Regardless of what the map says, there is a lot of variation. Some nights feel like Bortle 6 and a lot feel like Bortle 8.

Edited by Ags

Share this post


Link to post
Share on other sites
3 minutes ago, Ags said:

My skies are Bortle 7 according to the site, which would mean M31 would be possible naked eye, which hasn't been my experience.

I think that M31 would be very challenging from a Bortle 7 sky - maybe just visible with AV when fully dark adapted and with excellent transparency, but I wouldn’t hold my breath....

  • Like 1

Share this post


Link to post
Share on other sites
Posted (edited)

Well I am not convinced by my home location which reads as Bortle 7 and SQM of 18.78 because from the Bortle Scales descriptions as far as I am concerned we are Bortle 8 can only see the very brightest stars and not all of them.  I took a reading last year with an SQM meter and it read 17.45.

Bromley Bortle scale.jpg

Fortunately me and a few others go to a darker location in East Sussex on a regular basis where the reading is more accurate at Bortle 4 and also matches our SQM meter reading. 

Cairds Bortle scale.jpg

Edited by carastro

Share this post


Link to post
Share on other sites
Posted (edited)

A middle of of the road reading for me. Dark enough to enjoy myself!

NELM@Zenith is 5.5 on a good night.

E65ED062-202D-4D4E-AE11-30A343D5DFDC.jpeg.ed35af7a02c3ccec6fd22ef6771aba18.jpeg

I wish that my gear was more portable....

Paul

 

 

Edited by Paul73

Share this post


Link to post
Share on other sites
25 minutes ago, Ags said:

My skies are Bortle 7 according to the site, which would mean M31 would be possible naked eye, which hasn't been my experience.

Regardless of what the map says, there is a lot of variation. Some nights feel like Bortle 6 and a lot feel like Bortle 8.

Same here, and it says M31 difficult with averted vision and MW invisible.

I managed to see M31 on few occasions with averted vision (maybe twice or three times at the most), but I was also able to see hints of MW at zenith, probably more times than M31. Only once have I managed to see M31 dust lane with 8" scope from my location.

These things vary with transparency, so LP is not the only factor. Aerosol optical depth extincts light quite a bit, and for my location I get variations from below 0.1 to above 0.5 - when southern wind blows it can lift Sahara sands and carry them all the way across Mediterranean Sea. More than once we had "muddy" rain because of this in past few years.

This is why it is useful to check out aerosol optical depth forecast (finally managed to find the page, they kept changing it lately):

https://atmosphere.copernicus.eu/charts/cams/aerosol-forecasts?facets=undefined&time=2019010200,3,2019010203&projection=classical_europe&layer_name=composition_aod550

  • Like 1

Share this post


Link to post
Share on other sites
8 hours ago, Moonshane said:

Just a bit of advice. Make sure you obscure your detailed coordinates. Don't want to advertise expensive kit in gardens unecessarily ?

There are some lucky people ?

I am hoping I can build an observatory at the end of the garden and hide myself away from lights / face East which should give me a shot ?

 

My skies are so bad, my scope has been collecting dust for years so zero chance of it ever being in the garden haha.

  • Like 1

Share this post


Link to post
Share on other sites
23 minutes ago, Paul73 said:

A middle of of the road reading for me. Dark enough to enjoy myself!

NELM@Zenith is 5.5 on a good night.

E65ED062-202D-4D4E-AE11-30A343D5DFDC.jpeg.ed35af7a02c3ccec6fd22ef6771aba18.jpeg

I wish that my gear was more portable....

Paul

 

 

Paul,  you have very similar conditions to Kelling Heath - can't be bad!

image.jpeg.e35a4c65d0fb748d22a6ee3a08f36594.jpeg

Share this post


Link to post
Share on other sites
1 hour ago, RobertI said:

Paul,  you have very similar conditions to Kelling Heath - can't be bad!

Yes. I’m luckier than most. But there is always darker sky somewhere. ?

I’m jealous of Dave’s NR Bridport,Dorset sky. Dark sky and a lovely part of the world.

The numbers only tell half the story!

Paul

 

Share this post


Link to post
Share on other sites

Location info is correct as I live on a 20,000 acre wildlife refuge there is little concern of finding much more than a chipmunk or deer at these coordinates, the light pollution map seems quite hot for this area so I'm tending to believe its quite a bit better than stated but a broad calculus gives one result and local field tests likely would provide more accurate information. Clear/Skies Everyone ?

WEBPAGE_20190102_184249-01.jpeg

Share this post


Link to post
Share on other sites

Just checked

Home Site SQM 20.59

New Forest Site SQM 21.21

Rob

Share this post


Link to post
Share on other sites

Whilst it's never going to be as accurate as single or multiple SQM readings at specific times I actually think it's a fairly usable estimate as for most it seems to reflect average conditions or be just a little off. If you live in say a Bortle 7 zone and want to use it to try and find somewhere accessible and darker than where you are, I doubt a small difference in readings will matter. If you want to get serious about levels then I agree a meter reader would be a useful investment but as this is free and you can get a rough idea of 'the world's' light pollution from the comfort of your armchair I think it does pretty much what it says on the tin.

  • Like 4

Share this post


Link to post
Share on other sites
20 minutes ago, Moonshane said:

Whilst it's never going to be as accurate as single or multiple SQM readings at specific times I actually think it's a fairly usable estimate as for most it seems to reflect average conditions or be just a little off. If you live in say a Bortle 7 zone and want to use it to try and find somewhere accessible and darker than where you are, I doubt a small difference in readings will matter. If you want to get serious about levels then I agree a meter reader would be a useful investment but as this is free and you can get a rough idea of 'the world's' light pollution from the comfort of your armchair I think it does pretty much what it says on the tin.

For me it has gone a bit further than described on the tin, it has provoked an interest in owning metering equipment. Likely it has done this to others as well ?

  • Like 1

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.