Light pollution

[Broadymike]

Hi all.

I live in a bit of a strange place as far as light pollution goes. Apparently the town I live in is a 5 on the bortle scale. I live on the coast though and my house is literally 50 yards at most from the sea.  I have uninterrupted views across the English channel so to the east the only light pollution I get is a very very faint glow from France 30 odd miles away. Unfortunately there is also a well lit road between my place and the cliff. 😒Although if I make a bit of effort I can nip down to the beach and have 80ft cliffs behind me for blocking out a lot of the light from the actual town. 

 

Basically within any reasonable travelling distance I'm mostly always going to be surrounded by towns within a few miles causing some light pollution if I go inland. If I stick to the coast the worse case scenario is it could only come from 50% of the surrounding area. Does this mean that certainly observing eastwards I can consider it a darker sky? I'm not really sure on the science of how light pollution works as far as using telescopes goes. Is it a directional thing so keeping it behind you is good, or an ambient over all light level at your location? 

I know this may seem a bit of a rookie question but thats exactly what I am really. Very new but super enthusiastic. So thanks in advance for any info you may be able to help me with.

 

Clear skies and good times! 🤩

[vlaiv]

Light pollution is very difficult to predict and explain because it varies with many parameters.

It is both directional and omnidirectional thing.

You'll notice that most of the time - sky is better over the sea because there are no light sources to be scattered around in that area. Turning your back on street lighting or having cliffs blocking direct light is good thing as far as your night vision is concerned but won't help with scattered light.

Even if you don't see street lights directly - you'll notice that sky is brighter in that general direction. Ground light reflects of the atmosphere and creates a glow.

How much light is scattered in atmosphere depends on several factors - first of course is how much light there is in the first place, and I don't mean moving around and going further away from light sources - even if you stay put, level of light changes during the night. Traffic will change intensity and all those car lights contribute. People go to sleep at some time and they turn of their lights - I noticed that it usually gets darker after about 1am here where I am.

Humidity in air is major factor for how much light is scattered. Transparent nights - which are good for observing of faint stuff also lower light pollution as light does not scatter as much in atmosphere. If there is haze - then it deals you a "double damage" - it attenuates faint light of your target and helps scatter light pollution making sky look brighter.

If you spend some time at night shielded from direct sources of light and just get dark adapted - you'll be able to judge which parts of the sky are darker than others. Best place will probably be near zenith and a bit to opposite side of those ground lights. You should wait for targets to be in that zone for best observing.

[Broadymike]

Thanks. Pretty much sums up what I thought might be the case. Have to say that up until last night the previous 3 nights I managed to get some great views of Saturn and jupiter. They are obviously in the east at the moment and I do have more problems certainly finding naked eye objects to the west. That was with the small 70mm refractor that I have.

Unfortunately it clouded over last night which was a real bummer as I acquired a 114mm f8 reflector yesterday from fb marketplace for a bite your hand off bargain. Wasnt planning on upgrading yet but couldn't really turn it down for £35. It isn't ideally what I'd like but it's a very cheap step up from what I already had and may well make for a more portable rig in the future.  

[Nyctimene]

Consulting lightpollutionmap, you've described your observing situation quite adequate:

https://www.lightpollutionmap.info/#zoom=8.74&lat=51.2076&lon=1.8402&layers=B0FFFFFFTFFFFFFFFFF

The only rather dark sky seems to be located to the east - the view over the English channel. I'd try to find a sheltered place  between the cliffs and the sea, not too exposed to (salty) spray and mist, and start observing from there. A portable rig will be essential, so your tripod plans are sensible; later a travel dob, e.g. the Skywatcher Heritage 130 P Flextube (or the 150 P variant) would be an upgrade. When observing near the beach, salt will be the enemy of optics and (metal) mechanics, so protecting the optics (closed OTA; e.g. a light shroud) and some cleanup and wiping (not the optics!) will be relevant.

Stephan

[Pixies]

I live on the coast in a Bortle 6 zone. To the south and west is a significant amount of light pollution which heavily restricts what I can see lower down in those directions. However, to the North and East, towards the sea and some more open countryside, it is noticeably darker. On a good night, I can just make out the milky way closer to the horizon in that direction.

I've been tempted to take the scopes down to the beach, but I know what happens to the cars parked outside - so I refrain from doing so.

[Broadymike]

Thanks for your replies. 

Luckily it only takes me about 2 min to walk down to the beach so for me it's a no brainer to go down there if I'm observing in that direction. As far as salty spray etc shouldn't need to worry too much about that this time of year as the sea is quite calm and there's nothing in the air. To be honest if it got to the point of being an issue the conditions wouldn't be good for getting the scope out anyway. Either too windy for the scope or miserable for me lol. 

Managed to get my new scope out for a quick test last night before the clouds came in and was really happy with the results so far. The forecast is looking hopeful for a nice clear night on Sat. If that is the case I think I'll be down the beach for a late one so I can pick up jupiter and Saturn. Nice and handy that they are in the east lol.  I feel for me at the moment they are nice objects to get a good judgement of the scope. 

[oscar_camilleri]

You are lucky to be in a bortle 5 area, where I live currently its bortle 8 ( think of the 20th century fox animation with those search lights lighting up the sky, that's how my sky is looking at the moment 😭 ). Luckily I'm planning a camping trip to Brecon Beacon in August where I plan to gorge myself to exhaustion. 

[Starwatcher2001]

23 hours ago, Broadymike said:

Unfortunately it clouded over last night which was a real bummer as I acquired a 114mm f8 reflector yesterday

This phenomena is a well known astronomers curse - welcome aboard Mike! The board sponsor (FLO - First Light Optics) even puts stickers on the boxes of astronomy kit they sell

Avoiding the beach might be wise for another reason too - sand. I don't think it plays well with optics. (Just noticed Stephan mentioned this earlier). The beach sand probably looks at the fine optics in your scope and eyepieces and feels like an under-achiever. 🤣

Edited June 4, 2021 by Starwatcher2001
added a bit

[Broadymike]

1 hour ago, Starwatcher2001 said:

This phenomena is a well known astronomers curse - welcome aboard Mike! The board sponsor (FLO - First Light Optics) even puts stickers on the boxes of astronomy kit they sell

Avoiding the beach might be wise for another reason too - sand. I don't think it plays well with optics. (Just noticed Stephan mentioned this earlier). The beach sand probably looks at the fine optics in your scope and eyepieces and feels like an under-achiever. 🤣

I get what you mean about sand and optics. I spose I never really explained it that well. At the bottom of the steps/slope to the beach there is promenade with beach huts that's about 30ft wide and is raised up a few feet from the actual beach. Yes there is a bit of sand around but I wouldn't go down there if it was windy enough for that to cause a problem. 

What's quite good where I am is that depending on which beach I go to I can also get quite good northerly views about 2 min away and also to the south but that's a whole 15 min drive lol. There's always somewhere by the sea where you can avoid all the downsides like sand lol. 

 

[mikemarotta]

On 03/06/2021 at 11:10, Broadymike said:

... That was with the small 70mm refractor that I have. ... as I acquired a 114mm f8 reflector yesterday ...  .  

I was wondering about the portability as I read over your posts a bit too quickly. I went back to catch the salient details of size and weight. I also chose my instruments specifically because I can carry them. You say that you walk to the beach. I mean, even with a little extra kit and gear, you need a lot of pockets if you are walking. Even a mere 14 lbs can get heavy after a while. 

Anyway, the best telescope is the one that gets used. I have viewed quite a bit with my 70mm. My skies did not permit several attempts at epsilon Lyrae (famous double-double) and I had to go up to the 102mm to catch that. However, other people have been successful with 80 and 70 mm refractors. So, the seeing is important. Also, on that score, some people will tell you that the sea is a terrible place to view from because the air is all moist and salty, compared to dry land (like the Sahara, I suppose).  

I am just curious about your impressions and look forwarding to reading more of your reports.

 

Edited July 5, 2021 by mikemarotta

[Broadymike]

6 hours ago, mikemarotta said:

Also, on that score, some people will tell you that the sea is a terrible place to view from because the air is all moist and salty, compared to dry lan

There I also the other way of looking at it that open bodies of water don't retain heat anywhere near as well as well as concrete, bricks, tarmac and land generally. Also with water being flat and featureless any wind isn't affected causing updrafts etc. This mean that the seeing will generally be better over water due to less turbulent air.  As for moist and salty air the air may have slightly higher humidity near the sea in the UK but nowhere near as bad as it is in hotter climates. We just don't have the temperatures needed to make a significant difference plus the UK is generally damp everywhere not just by the sea lol. The air only really gets salty when the sea is rough. If the sea is rough that will mean it would be at least windy but probably horrible outside meaning I wouldn't have the scope out anyway. 

Where I live compared to the beach is pretty much the same distance to parking a car and walking to block out the street lights. I live about 50 yards from the steps to the beach, so not really a huge consideration. I've found that with careful packing that my reflector and all that's needed to observe for a night all fits into my camping rucksack so it's also easy to move. 

Reports are hard to come by at the moment as I haven't had any clear skies for over a week now. I partly blame FLO as my new rigel quickfinder turned up and haven't had a clear night since, but it is Wimbledon fortnight so that means it usually rains a lot so got a double whammy there. You mentioned epsilon lyrae that was one of the objects I looked at last time I managed to get the scope out. I had just collimated the 4.5" for the first time did a quick star test and all seemed good. When I had looked at it before the initial split was easy enough but I just couldn't seem to get any separation on either of the 2 pairs. This time though the easier pair split fairly easily and the harder of the two had moments of definite separation. Saturn and jupiter looked amazingly clear too. Cassini division could easily be seen and some nice bands coming through on jupiter. 

Can't wait for another cloudless night.