On the issue of Light Pollution

[JRWASTRO]

Greetings All,

I was on Kangaroo Island south of the city of Adelaide and took the opportunity to investigate locations on the island from which to take long exposure DS images. The weather was terrible,  the fishing hopeless and manual focussing followed this theme.

I wanted to look at the colour cast that was caused by the lights of Adelaide. To do this I set up my trusty Canon 5D and hooked up an 85mm f1.2 lens. This lens is notoriously difficult to focus and I did not care too much for accurate focus and was more interested in the colour cast.

The exposure was 30s at iso 1250 and this is the result:

As you can see, if you neglect the bad focus, the colour cast is prominent. The CBD is 125km away and to the right of centre in the image. The image spans about 25 degrees at this range the city lights are 4000 feet below the horizon !! FYI the location is Emu Bay .

The relative darkness of the site may be gauged by examining the following picture of the bay. The moon is well below the horizon  and the bay is illuminated by starlight. The colour cast in the sky is evident but the scene is illuminated by "hot" (colour temp = 5000K  ??) starlight hence the natural looking colours on the ground.  Camera kit: Canon EOS 5D, Lens 85mm F1.2, exposure 30s at iso 1250:

Conclusion:

To escape the effects of LP due to the city of Adelaide one must travel at least 250km away with no other cities in between. At a range of 250km the city lights will be about 16,000 feet below the horizon and the LP should be about 1/4 of that on the island.

Cheers all,

Jeremy.

Finally, I took a single exposure, to the south, of the LMC and SMC. This is a single exposure of 30s at iso 1250. The lens is 40mm f4.  The light gradient is depressingly obvious.

[JRWASTRO]

Please can some body show me how to edit a post after the fact.

Jeremy.

[FunkyKoval35]

Hi JRWASTRO

You need to drop down ISO to around 800.

Adam

 

[Carina Lass]

That's worse than looking at Brisbane from 50 k away.

Adelaide shoudl turn off the lights!

[Thalestris24]

Hi Jeremy

I can sympathise and empathise... Probably the best strategy is to image in the opposite direction.... As the lp is very yellow maybe a lp filter might help. I live near a city centre and the lp is beyond fixing. Nebulae and galaxies are pretty much off the menu. I have a future plan to try to image in a Northerly direction since that will be pointing away from most of the city lights.  Narrowband filters can be helpful but I can't always get enough long exposures because the weather here is awful too!

Louise

ps you have to do a number of posts (I forget how many) before you can edit. Likewise to access the classified section (should you want to!)

Edit: editing via the buttons bottom right. However, they are only available for a limited time post post...

[JRWASTRO]

Many thanks for all the replies much appreciated.

1. Thank you for the empathy and the sympathy Thalestris24 . Firstly it is embarassing when one makes a mess of the formatting and can't do anything about it.

2. Next about the LP : I do not mind travelling to get a half decent image but I get quite dejected to find that the image is spoiled due to LP. I will be making another trip to the island and this time I will be taking my portable imaging kit. This last location was at the shack loaned to be by my brother in law and next time I'll try to image from the centre of the  island.  I wanted to buy a piece of useless scrub land to set up a small observastory but it looks as if I'll have to look at getting some in the centre of the island.

Carina Lass, Hello.

Brisbane ? never imaged from that vicinity. I'll be driving to Brissy for Christmas as two of my 3 sons live there. I'll check out the LP. Further I'll be checking out the hinterland as we  (she who must be obeyed and I) will be driving to Rockhampton via the distillary at Bundaberg !!

Adam, about dropping the iso to 800 ... very good call. Perhaps the overall performance will increase. Advice taken.

Regards to all,

Jeremy

[ronin]

You need 250 posts to edit, and that excudes any in The Lounge - they don't count.

Sounds like a bad night, what were you fishing for? :grin:

Must remember to avoid Aus: Fishing bad, light pollution bad, :rolleyes:

[IanL]

I had the good fortune to do an epic road trip around that part of the world 20 years ago, when presumably there would have been slightly less LP from the city. We drove from Melbourne to Adelaide in one very long day and during a quick break somewhere a bit north of Mount Gambier took a look at the Milky Way and SMC/LMC.

There was no local light pollution as there were very few towns in that area. The skies were inky black and stunning to behold. Nonetheless there was a distinct dome of LP low on the horizon from Adelaide which I guess was approximately 300km distant. I really do wonder how far one needs to go to escape it?

[ollypenrice]

Well, there are places in the outback which beat 22 on the Sky Quality Meter but they might be quite a trek! Maybe your own light aircraft?? 

I have an extremely dark site, best of 21.9 on the SQM, but the cities of Aix en Provence and Marseille are really fairly close to our south, about 170 Km by road, so less in a straight line. However, a series of east-west orientated mountain ranges do a stunning job in baffling the light.

Olly

[Thalestris24]

Well, there are places in the outback which beat 22 on the Sky Quality Meter but they might be quite a trek! Maybe your own light aircraft?? 

I have an extremely dark site, best of 21.9 on the SQM, but the cities of Aix en Provence and Marseille are really fairly close to our south, about 170 Km by road, so less in a straight line. However, a series of east-west orientated mountain ranges do a stunning job in baffling the light.

Olly

 About 4 - 4.5 here...

Louise

[Gina]

I've no idea what it is here but it's certainly not bad.  Some LP from the small town of Honiton about 5 miles SW of here but little local LP.  Mayb sometime I can borrow an SQM

[Thalestris24]

Useful map here: http://www.lightpollutionmap.info/#zoom=4&lat=6446067.20803&lon=57385.66938&layers=B0TFFTTT

Funnily enough, there are no user SQMs for Glasgow city centre... I got my value of 4.0 - 4.5 from http://en.wikipedia.org/wiki/Bortle_scale which is obviously not the same as SQM values. In my case, it really makes no difference!

Louise

[JB80]

Kangaroo Island is one of my favourite places on this planet, we would love to have a property there if we could. One day maybe if we work to it.

That is a good representation of Adelaide's glow if not a bit sad to see how bright it is.

I spent many nights on the Murray in various areas and as long as you were away from a town the skies were always great but the best I have ever seen was in Port Campbell on the Great Ocean Rd.

[JRWASTRO]

Most Important:

Re: Must remember to avoid Aus: Fishing bad, light pollution bad

The fishing in Aus is excellent I just did not do too well this time. Light pollution around the developments and cities is certainly very bad due to very poor design by the electric authorities and the complete  indifference of the local councils. But away from the cities (300 to 500km away) the conditions for AP are second to none.

What sought of fish?

Mainly Australian Salmon and some Mulloway ( http://en.wikipedia.org/wiki/Argyrosomus_japonicus ) off the rocks at Stokes Bay and Snellings beach. But when I visit my sons I'll take my light game (20kg class) gear to go for Spanish Mackeral , Cobia, Travalley and Tuna.

Yes Jarrod KI is very nice. Scrub blocks are relatively cheap but one must remember that bush fires are a reality so one needs to clear a "reasonable" area in the block to have a chance of surviving. I was looking at a block on the south coast of about 622 acres and clearing about 5 acres in the centre of the block.

Port Campbell and the great ocean road ? Rugged area that. Facing Bass strait.

Greetings Olly,

Re: Well, there are places in the outback which beat 22 on the Sky Quality Meter but they might be quite a trek! Maybe your own light aircraft??

Light aircraft?  My brother in law has an aircraft and hanger and runway on his property. I'll talk nicely with him and see how I go!!   My place at Cockatoo Valley use to register 18 to 20 on the SQM but not any more. But the ( really dark skies of the Flinders Ranges are not far away (1/2 days drive) and our astronomical society organises imaging trips twice a year.

Kind Regards to all,

Jeremy.

[JRWASTRO]

What is a Mulloway ?

[pyrasanth]

I just say "Thank God for narrow band filters"

[Thalestris24]

 About 4 - 4.5 here...

Louise

Just realised I misquoted - I'm actually 9 on the Bortle scale with naked eye limited magnitude of 4.0 or even less, I'd say

Anyone want to buy me a car so I can escape it?

Louise

[DaveS]

I'm just in Avex-Asso's pink zone for London (Having moved out from deep in the white zone), NELM of about 4.5, but I have very little direct LP. Since moving here there have been a couple of very clear nights where I've glimpsed the Milky Way as a faint band at the zenith. Pretty good considering both A-A and Stellariun say Bortle 8-9, I would say 6.5-7.5 depending on the level of clag. LP in London is very dependent on the air pollution.

[JRWASTRO]

Yes Dave The amount of LP we see is due to air pollution and is mainly due to scattering of the light in the atmosphere. There are times when the humidity is high and the LP looks very bad but when the local atmosphere is dry I see much less LP.

[DaveS]

I find the best nights often occur after rain, especially if there's been a bit of wind. Clears the clag out of the air, but then it gradually accumulates again. The worst is if there's a prolonged high with little wind in summer (What passes for summer here). Then the sky can be an orange fog, even though it's supposedly clear, and nothing is visible below mg 2.5..

Something I have noticed since moving out here, the cars aren't covered with a film of dust after rain like I was used to further in, and the trees along the main road show a nice collection of lichens, so I guess the air is a bit cleaner.

[Moonshane]

Living 10 miles from Manchester uk I am struggling to fire up much sympathy...........

[DaveS]

Useful map here: http://www.lightpollutionmap.info/#zoom=4&lat=6446067.20803&lon=57385.66938&layers=B0TFFTTT

Funnily enough, there are no user SQMs for Glasgow city centre... I got my value of 4.0 - 4.5 from http://en.wikipedia.org/wiki/Bortle_scale which is obviously not the same as SQM values. In my case, it really makes no difference!

Louise

Thanks for that link, very interesting. Looks to be more detailed than the Avex-Asso site, and with somewhat different levels of LP. It shows my location has slightly darker skies than where I was which I find "on the ground".

[Thalestris24]

Thanks for that link, very interesting. Looks to be more detailed than the Avex-Asso site, and with somewhat different levels of LP. It shows my location has slightly darker skies than where I was which I find "on the ground".

Hi

I suppose doing one's own sqm measurements would be definitive - not worth it for Glasgow city!

Louise

[lensman57]

Living 10 miles from Manchester uk I am struggling to fire up much sympathy...........

I live less than 3 miles from the airport, can't think what it would be like when expansion is completed.

A.G

[Moonshane]

Ouch