How far does light pollution reach?

[Bart]

Hello everyone,

I wondered if there is a general rule about how far LP reaches. For instance, my view to the West isn't great due to LP. Now, there is a town of 10,000 people about 10ish miles to the west,but also a city of about 120,000 to the west about 20miles away. Which one is giving me the LP?

I realise this is kind of a 'how long is s piece of string' question but I wondered if i went in search of dark skies, how far away from a town should i be thinking of?

Any help would be appreciated.

Bart

[SamAndrew]

I found this interesting, useful, and depressing at the same time,

need-less light pollution

there's a map half way down that generates a night sky view from where ever you place the cursor over UK (not great for Ireland)

It looks like you really need to be 50 miles from anything to get good skys

[Peter Drew]

My experience has been that as soon as you are far enough from one LP source, you're getting too near to the next.

[Bart]

I found this interesting, useful, and depressing at the same time,

need-less light pollution

there's a map half way down that generates a night sky view from where ever you place the cursor over UK (not great for Ireland)

It looks like you really need to be 50 miles from anything to get good skys

Thanks SamAndrew,

The map just about makes it as far as my location. Thats a good program, have you found it accurate?

50 miles! Does anyone have any chance? I'm guessing 50 miles will get you pristine skys but hopefully less than that will get you very good skies.

Thanks again.

Bart

[swamp thing]

Hi

I remember reading you need to be at least 100 miles from any major city with a population of over a million to escape it's light pollution entirely.

Not easy in the UK.

Regards Steve

[pete_l]

It also depends on how much dust, pollution and other particulate matter there is, hanging in the air. That's what reflects the light from a source. So if you have "clean" air, possibly blown in off the sea, then you'll see much less backscattered light from anywhere than if the local atmosphere is moist and dusty. Of course, then you'll be more likely to be under clouds or fog.

Nearby sources of light is only one factor - the amount of cloud/mist and "seeing" is just as important.

[Beulah]

Hi

I remember reading you need to be at least 100 miles from any major city with a population of over a million to escape it's light pollution entirely.

Not easy in the UK.

Regards Steve

*sigh*

I can't think of anywhere that would fit that description.

[glowjet]

I think you may find that if you can head out into the country, where villages are well scattered, hilly and wooded areas help, but in some 15 to 20 miles you should notice a big difference, than being sat on the outskirts of a city, from own experience I live on the outskirts of large city to the North East, I can`t see the Milky Way from my garden, but if I travel to my friends, who is located something over 15 miles to the North and in the country, with almost an acre of land, with a large wood on one side and no neighbours, the Milky way is clearly visible along with a lot of other sky detail, especially on a Moonless night. But that is no comparison to the Black mountains area of Wales, where the skies are so full of bright pinpoints of light they are like Diamonds on black velvet, and the Milky Way is so bright it casts its own illumination, happy memories from sea trout fishing at night, many years ago

[Chris H]

I live in a pretty dark location on the north coast of Anglesey there are no street lights and few neighbours the sky is pretty dark but to the east there is a large light dome that extends about 35 degrees above the horizon from the lights of Llandudno, Rhos, Colwyn Bay along the north wales coast and probably Liverpool beyond that. It's over 20 miles from here to Llandudno and 55 miles to Liverpool. Dublin is 80 miles to the west you can't see anything from that, so I'd agree that you need to be around 100 miles from a city of over a million.

My inlaws live in Llanidloes, mid Wales and the skies there are much better and they are 60 miles away from the west midlands but the hills and valleys must help to screen distant light pollution.

[umadog]

It'll follow some sort of inverse square law with the zenith becoming good much earlier than the horizon. Obviously, how bad it is depends both on the distance and the intensity of the source. In practice, a little light pollution near the horizon is a pain but you can still have wonderful dark skies at the zenith. So, whilst it's nice to have zero LP, you can pretty damn happy with skies that have just a touch of it near the horizon.

I was at Bryce Canyon in July, where skies must be darker than mag 7, and from there I could very clearly seen the lights on the cooling towers of a power station 100 km away. They made their own little light dome. In the opposite direction to those lights was a horizon glow about the intensity of the zodiacal light, which could have been Las Vegas, 300 km away. Then again, it could also have been the zodiacal light, which I've only seen once before and so don't have much experience of. I don't think it was that, though, because it looked the wrong shape. So LP may spread further than 100 miles.

[hemihaggis]

*sigh*

I can't think of anywhere that would fit that description.

eh... ??? the whole of scotland north and west of glasgow .... maybe looking at a map would help lol that includes just about the whole of the scottish highlands , the inner hebrides , the western isles , orkny isles and the shetland isles , thousands and thousands of square miles .... the most space and the least people in just about the whole of europe ...

[Chris H]

It'll follow some sort of inverse square law with the zenith becoming good much earlier than the horizon. Obviously, how bad it is depends both on the distance and the intensity of the source. In practice, a little light pollution near the horizon is a pain but you can still have wonderful dark skies at the zenith. So, whilst it's nice to have zero LP, you can pretty damn happy with skies that have just a touch of it near the horizon.

I was at Bryce Canyon in July, where skies must be darker than mag 7, and from there I could very clearly seen the lights on the cooling towers of a power station 100 km away. They made their own little light dome. In the opposite direction to those lights was a horizon glow about the intensity of the zodiacal light, which could have been Las Vegas, 300 km away. Then again, it could also have been the zodiacal light, which I've only seen once before and so don't have much experience of. I don't think it was that, though, because it looked the wrong shape. So LP may spread further than 100 miles.

Vegas probably has more lights than the average city.

[umadog]

Oh, yes, indeed. It must produce more light pollution than most cities of its size. This is the chief reason why I think I may have been able to see the glow from that distance.

[Bart]

It's over 20 miles from here to Llandudno and 55 miles to Liverpool. Dublin is 80 miles to the west you can't see anything from that, so I'd agree that you need to be around 100 miles from a city of over a million.

Well, I live over 100 miles from Dublin and thankfully thats the only place with > 1 mill peeps on this island. However, Midleton 10,000 @ 7 miles or Cork 130,000ish @ 20ish does appear to cast a fair amount of LP. My guess is that its Midleton, so my plan is to head 20ish miles NW to a better dark spot and see what the difference is. Thanks all

Regards

Barry

[Beulah]

eh... ??? the whole of scotland north and west of glasgow .... maybe looking at a map would help lol that includes just about the whole of the scottish highlands , the inner hebrides , the western isles , orkny isles and the shetland isles , thousands and thousands of square miles .... the most space and the least people in just about the whole of europe ...

I don't live anywhere near Scotland and can't think of anywhere within a reasonable driving distance.

[arbacia]

That image is The Cuenca Mountais Natural Park, one dark place in central Spain, where every year I organize a Star party. The place is at 170km Western Madrid. The background light is not a sunset, is the light dome of Madrid (5 million people). In oposite direction, towards the East, the horizon is in the same way because of the lights of the mediterranean cities such as Castellon, Valencia and Alicante.

Patricio

[kirkster501]

Great website.

We can't expect the whole of society to change so we can practice our hobby more effectively though can we? Anymore than forcing all cars of the road so cyclists can have a better time.

No harm wishing though and making the case.... I am East of Nottingham and my Western sky is a write off.

Sorry for my contentious tone but just looking at it from the other side as well.

Steve

[umadog]

More sensible lighting strategies would save money, reduce pollution, and very likely improve safety. Those are changes that are good for society as a whole. Nobody is suggesting that society should change simply for the sake of a minority hobby. LP may well also harm wild life, you can find texts about this on-line. I notice that the new brighter street lamps have led to songbirds singing all night at my parent's North London home. Such abnormal behaviour can't be good for them.

[Bart]

Great website.

Sorry for my contentious tone but just looking at it from the other side as well.

Steve

Why?

Only joking..

Seriously, I work in utilities and the amount of money wasted by local authorities is shocking. Urban lighting can be done more efficiently.

I'm only thankful here in Ireland we've a relatively sparsely populated island, Dublin excluded.

Bart

[Smudgeypoo]

I think in the NE England cloud is our main enemy. I live not far from Darlington but far enough, MW easily visible on a very good seeing night. As soon as there are any mist/clouds the reflected lights from the conurbations is dreadful.

Still, I am not too far away from some very good sites so should count myself blessed!

[glowjet]

If the government introduced an energy saving Bill, to the effect that all councils must reduce side road lighting ( all residential areas ) midnight to dawn and all major roads cut by half during this time ( illuminate every other light ) the effect would be dramatic, both in terms of money saved and the LP.

[Mercury]

I live on the NE outskirts of a NE City with its own river and the Humber estuary. My zenith and northern aspects are not too bad considering a large village 1.5km and a market town 8km to the North. The East, South and Western aspects are very bad with most short exposures showing orange background and long ones yellow.

There is also the problem of air born water vapour from all the water surrounding us. It's a nightmare for reflecting light and dewing all my equipment up.

If I go over the Humber to Lincolnshire for about 30km the Milky Way shines bright and I have to look carefully for the constellations because I'm not used to seeing so many stars.

Yes light pollution bothers me but it doesn't stop me enjoying my favourite past time.

David

[chiltonstar]

I would agree with many of the comments about distance and atmospheric conditions. I live out in the sticks, but in the directions of London (50 miles) and Reading (20 miles), I can certainly see quite bright skyglow when there is cloud or haze at the right altitude.

In France at a very rural site in October, I couldn't see the skyglow from Paris (100 miles north) on clear nights, but 10 sec exposures with a DSLR and a 300mm lens started to reveal a bright patch in the right direction.

Still, as we look like running out of electrical power as the nukes are shut down and we rely more and more on windmills, we may be able to look forward to some fabulous, LP-free evenings....!

Chris

[Mercury]

That's a good thought Chris.

David