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Coping with light pollution?


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My city-centre back-garden is typical of most - it is under a light-polluted sky.

What is the best telescope for observing from a light-polluted area?

Have you any tips for reducing the effects of LP – filters, screens, aperture size etc?

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I'm having a few debates on this exact same subject as i live under mag 4 skies and am having aperture fever. I've learnt that aperture is king, the more light from your subject you can gather the better. There is a myth that larger scopes are affected by LP more than small scopes. This is a nonesense if you think of the physics. Depending on budget and your mount get a nice 10" APO refractor :D Failing that a large Fast Newt/schimt newt. The faster the system the better if you plan on taking images. f4/f5 is ideal. No matter what your aperture however you'll never get to see those faint DSO's though unless you can get to dark sites. Your stuck with planets, moon, clusters, doubles and some of the brighter DSO's like M42.

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There is a myth that larger scopes are affected by LP more than small scopes. This is a nonesense if you think of the physics.

I am inclined to agree. Also, larger apertures are less effected by light loss from using light-pollution-reduction filters.

Although.... When observing the comet recently thru moonglow, it showed up better thru the Revelation 80 refractor than the 8" Newtonian. It was the same for M13 globular cluster - there was more contrast.

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I tend to image, more than visual, but even with my modest equipment in a heavily light polluted site, visual observing of m42 is easy, m57 is possible on fairly moonless nights, everything I've tried to image I've managed so far down to the rosetta nebula (which I think is about mag 10, not too bad with a 80mm scope and a digital SLR, whatever scope you use in this light polluted world we live in I think imaging is the future !.

Alan

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Gordon, I was totally convinced that my HEQ5 goto was a load of poo until I stuck a camera on the end of the 'scope. Lo and behold, there was the fuzzy! I was so surprised at the imaging thing that I haven't really looked down the thing since other than for centering the alignment stars. My best kill to date has been M51, a secret type of object visible only to DSLRs and webcams. I have never got even close to seeing it, though I now know that I have looked at it many times.

For us with bright skies, I think that the modern filters are a way forwards in as much as without them, there's nothing to see other than reflected street lighting.

As Alan has said, M42 is easy, my Mum can find it visually now that I told her where its kept, M31 is awesome in scale with a 'scope or a camera or even binoculars.

Best telescope for observing from a light polluted garden? It has to be the one that you have, if you have one, you just need to realise that you have to pick your targets accordingly. Best one to buy? Now that's the toughy.

Moon observing is good if you have really really bad light pollution as its so bright that LP is not really an issue. It can be seen even in broad daylight. Then on to lumps of stars like the Beehive, Subaru (easier to spell than Plieades) and King Cobra.

Planets are between moon brightness and bright star brightness so you might need to spend up to about 50 quid to see Saturn's rings or the stripes on Jupiter visually. 70mm Newtonian reflecter will get you there. Saturn was/is a big wow object, first time up to the last time you look at it. Jupiter is something that I'm not too familiar with as I'm new here, but its bigger than Saturn and brighter so it should be even easier.

I think the next step down in ease of seeing will be the globular clusters which are similar to frogspawn type arrangements of stars. Big piles of them in a small area.

Double stars are just that.

Then on to the faint fuzzies last.

For the 'scope you need to buy, think one for each category. Whatever you buy will do really well in one department and might get close in others.

My experience is that when its moon hunting season I get out the DSLR and either the 200mm Newtonian reflector or the 120mm refractor. Both have a focal length of 1000mm so the image size is identical. The Newtonian gets more shots in the same time as the inlet end is bigger, but the images are sharper with the refractor. For galaxies get a Newtonian, the biggest that you can, as the amount of light coming off these things is quite small and you need as much light collection as you can get. For planets, a long focal length Mak. or SCT. will get you there quicker and with fewer Barlow lenses and stuff.

You will find that, whatever you buy, you will be able to see, or at least image, most of the stuff posted on here. The best advice that I can offer is for you to look at the images posted here, check the kit used (usually listed) then pick a favourite and try to emulate it. If your first choice turns out to be expensive then choose again or save up for the kit. Do not buy some toy scope, as that is likely to put you off for a while.

My penchant for buying toys means that I now have three 'scopes, but I find myself using them for different jobs. Moon = refractor, sun = Maksutov and DSO = Newtonian. BUT I like to play with the toys in ways that are "wrong", and I get a kick out of that, but that's just me. Light pollution filters are the way to go and they really work both for visual observing as well as imaging.

The bottom line is the best 'scope is the one that you can afford, the only real question here is the 'scope design, as this has a bearing on image scale. Get a previously cherished 'scope and have a go so that you candraw up a target list, that way you can trade it in when the need arises.

This started out as clever, witty and informative, until I re-read it and fixed it, I hope that it still works after being mended.

Captain Chaos

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I must admit i've not tried "trusting the GOTO" yet. I've aimed my scope at M51 but couldn't see a damn thing. I guess taking a long exposure photo with my DSLR will (may) show something. but visually i doubt i'll ever see it.

Hi Gordon.

I've seen M51 from my light polluted site (mag. 4 skies), in Newcastle- under -Lyme using a 105mm apo refractor. I also think I've spotted it with a 20x80 binoc. Wait for a good clear night with no moon give it another go.

Ian.

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Well Ian if you've seen M51 from newcastle-under-lyme then i should have no problems as i live in clayton :D

When you say you've SEEN m51, do you mean visually or via long exposure photography? I'll have to wait for this rain and clouds to pass and try again. I'll report my progress!

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Well Ian if you've seen M51 from newcastle-under-lyme then i should have no problems as i live in clayton :D

When you say you've SEEN m51, do you mean visually or via long exposure photography? I'll have to wait for this rain and clouds to pass and try again. I'll report my progress!

Hi Gordon.

We must be near neighbours, I live in Clayton also, just off Cambridge Drive.

As to your question, yes it was visually.

Mind you, in a week or so it's the time of unending astronomical twilight, so that 'll add to the light pollution we're saddled with to make it more difficult to pick up.

Ian.

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Lp with a large scope... I read up alot on this and the myth does hold truth!. You can increase the LP with a larger scope (light grab).. Its also down to individual nights of seeing quality as well. One LP night can vary to another - this I know living close to the sea (i.e less than a mile).

:?

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My city-centre back-garden is typical of most - it is under a light-polluted sky.

Have you any tips for reducing the effects of LP – filters, screens, aperture size etc?

I would go with the most aperture I can afford. The view only gets better, and occasionally you get to go to a dark sky site.

I move the scope to a well shadowed area in my back yard, and I have sometimes hung my patio umbrella in strategic locations to block neighbour's porch lights and street lights, and have found that I can get almost ten minutes of relief from the street lamp nearby by hitting the sensor on it with a good powerful laser. For difficult targets, on a good night, I have hung a towel over my head to block stray light. It works.

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I move the scope to a well shadowed area in my back yard, and I have sometimes hung my patio umbrella in strategic locations to block neighbour's porch lights and street lights...

I have been thinking of making a fold-out screen that shields me and the scope.

... have found that I can get almost ten minutes of relief from the street lamp nearby by hitting the sensor on it with a good powerful laser.

:silent: :D

For difficult targets, on a good night, I have hung a towel over my head to block stray light. It works.

Good idea 8)

I also like the idea of the Astro-Engineering Observing hood. I saw one at a show and it looked good - a heavy black cloth with metal weights sewn into the hem to help it stay put.

image.jpg

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Seriously, what's the hole for?

Your head,

You wear it with the longest part hanging behind you like a cloak, then you pull it up and over your head when viewing.

I know it looks ridiclious but it does work and is well made.

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Has anyone tried these?

image.jpg

They come in two sizes and are...

'made of padded Terry towelling and can be hand-washed and air-dried. Both seal out light and make very comfortable eye surrounds. They are great for solar observation where extraneous light can spoil the view so easily. An ideal aid to combat light pollution, improves the view by minimising the effects of local environment glare'.

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