Quality dobs? / Light Pollution

[Solanum]

Due to my workplace being used as a political football in a spat between government and the management of the government agency I work for, there is a 99% chance I will be moving to Adelaide next year (0.2% chance of being made redundant, 0.8% chance of our site being reinstated).

My choice of home is unlikely to have usefulness for amateur astronomy as the deciding factor, therefore I wondering how my 10" GSO Dob will go with the Adelaide light pollution.

So my questions:
1) do I need to increase aperture?
2) If so, will a 12" in Adelaide be the equivalent to my 10" in Mildura, in terms of fuzzies etc.?
3) If I get a new dob next year, do I go for another GSO (been pretty happy with it), something a bit more upmarket (e.g. Saxon with pyrex mirror etc.), or are there more premium dobs with better mirrors I can get 'off the shelf'?

[madtuna (Steve)]

I'd be inclinded to take the 10" you have and try it out.
You may be pleasantly suprised. Also a good skyglow filter might help?

[Starkler (Geoff)]

I'm sorry to inform you that there is no compensating for light pollution.

In dark rural skies I can see things in my 50mm finder scope that I have trouble seeing in suburban skies with 10" of aperture.

I would stick with the 10 that you've got, as another 2 inches wont make up for what you lose.

[Solanum]

Originally Posted by Starkler

In dark rural skies I can see things in my 50mm finder scope that I have trouble seeing in suburban skies with 10" of aperture.

That's pretty depressing..... I do some work at a field site about 30 minutes from here (Mildura) and when I'm out there before dawn, the milky way literally goes from horizon to horizon, I would never have believed it if I hadn't seen it (multiple times) with my own eyes. Haven't had the scope out there though.

Still, I know from visiting family that my own backyard in Mildura has darker skies than anywhere within quite a distance of Adelaide....

So do any of the 'light pollution' filters actually work? I would have thought it wouldn't be too difficult to create a filter that blocks the sodium lines alone.

[Screwdriverone (Chris)]

Yes, get a Ba'ader Moon and skyglow filter ($85 for 1.25" version from Andrews comms) this really helps with artificial light and moon glow.

Nowhere near as good as dark skies but it does make a big difference in blocking sodium skyglow, its the only filter I have and I think its the only one you will need to eliminate light pollution (or at least minimise it properly)

Cheers

Chris

[Starkler (Geoff)]

Originally Posted by Solanum

That's pretty depressing..... I do some work at a field site about 30 minutes from here (Mildura) and when I'm out there before dawn, the milky way literally goes from horizon to horizon, I would never have believed it if I hadn't seen it (multiple times) with my own eyes. Haven't had the scope out there though.

Once you have experienced dark skies, suburban dso viewing pales in comparison and just doesn't seem worth the effort. That's my experience. Sorry!

On the upside, having a bit of aperture helps in enabling one to crank up the power to mitigate light pollution with smaller targets of high surface brightness. You can still get reasonable views of the brighter planetary nebs for example. Small scopes I find virtually useless in this context as you run out of light before getting a good amount of magnification.

So do any of the 'light pollution' filters actually work? I would have thought it wouldn't be too difficult to create a filter that blocks the sodium lines alone.

The problem is that not all artificial light is sodium lighting. Where I live I'm plagued with mercury vapour "flower pot" lights which have a broad spectrum that cannot be filtered out. The usefulness of light pollution filters is related to the amount of extraneous light of a nature that can be filtered.

In practical best case terms, the contrast gained by using a broadband LP filter could be emulated by a small increase in magnification, eg swapping a 12mm for a 10mm eyepiece.

There is no substitute for dark skies

Heres an Adelaide based page on LP http://astronomy.concreteairship.com...i/lpgallry.htm

[tnott]

Hi Solanum,

I live the southern part of Adelaide. There is a lot you can see even in the city - double stars, planets,moon that are completely unaffected by light pollution.

If you are living in the outer fringes then many of the brighter DSO are visible as well, though not as nice as in dark skies.

If you have a bit more aperture (like my 16") then the narrowband UHC and OIII filters work really well to bring out nebulae , which make up almost half the interesting objects in the skies. Don't waste your time with a general light pollution filter as they will make a subtle difference on emission nebulae only. Also, the larger the aperture,the better the narrowband filters will work, especially with the OIII.

For galaxies and fainter clusters you will need to get out of Adelaide I'm afraid, but the good thing about Adelaide is that you don't need to drive too far to get pretty dark skies.

When at home, I tend to use my ETX 125 mostly and view the moon,planets, doubles etc - but can also see many of the main DSO's like the Swan, Orion, Globs and Open Clusters. If I use the 16" I can still see much more detail than the 5", and the UHC/OIII filters in the big scope bring out emission nebula like nothing else. I have a Moon and Skyglow filter but don't use it as the difference it makes is minimal.

Once or twice a month, I usually travel 40 mins to Tooperang or 60 mins to Stockport for an ASSA viewing night in dark skies. The 3/4 of the sky away from Adelaide is just about as dark as anywhere else. I usually spend most of my time hunting down faint fuzzies I can't see from home.

So there is still plenty to see if you move to Adelaide!

[monoxide]

Hey Solanum,
i've got a 12" dob that your more than welcome to come take a look through if/when you move here, if you bring the 10" you could make the comparison for yourself. i'd be interested to see the difference too

[Solanum]

Thanks for the replies folks, much appreciated.

Originally Posted by tnott

I live the southern part of Adelaide. There is a lot you can see even in the city - double stars, planets,moon that are completely unaffected by light pollution.

If you are living in the outer fringes then many of the brighter DSO are visible as well, though not as nice as in dark skies.

Once or twice a month, I usually travel 40 mins to Tooperang or 60 mins to Stockport for an ASSA viewing night in dark skies. The 3/4 of the sky away from Adelaide is just about as dark as anywhere else. I usually spend most of my time hunting down faint fuzzies I can't see from home.

So there is still plenty to see if you move to Adelaide!

We will most likely move to the Blackwood/Belair area, or around there. I'm not sure how the sky glow would compare to down in the city? My in-laws live out at Nairne and they have a pretty good half sky (perhaps three-quarters to be fair), the other side isn't so great though!

I didn't know there was a Stockport near Adelaide - the original Stockport is where I lived as a kid. Stockport County is still my team!

Originally Posted by monoxide

Hey Solanum,
i've got a 12" dob that your more than welcome to come take a look through if/when you move here, if you bring the 10" you could make the comparison for yourself. i'd be interested to see the difference too

Thanks for the offer, it will probably be around April that we move, so plenty of time to consider all the options. I'm working on getting my father-in-law to build an observatory and buy an RCOS, don't think my mother-in-law will let him though!!

[tnott]

Originally Posted by Solanum

Thanks for the replies folks, much appreciated.

We will most likely move to the Blackwood/Belair area, or around there.

That's where I'm at. Near the city, the Milky Way and the Magellenic Clouds are invisible, but around here they are faint but there.

[toyos]

The extra contrast & sharpness of a good larger refractor can help too with the light pollution, that's if you may consider switching to a refractor