How far away from town lights....

[Dazzyd]

Hi all

Looking on Google Maps to see what locations could be quite decent for observing. How far do you think a location needs to be away from streetlights etc to be a decent observing spot? There's a lot of countryside starting around 15 minutes drive from me so wondering how far into the countryside I need to start looking?

Also, is there a way of drawing a circle in Google Maps or Google Earth that represents say 10 miles? Or does Bing Maps do that maybe?

Thanks guys... actively looking for somewhere possible

[Jim-a]

this may be helpful for looking for a darker site

http://www.avex-asso.org/dossiers/pl/uk/index.html

Jim

[Dazzyd]

Thanks Jim, hadn't seen that site before

[swamp thing]

Hi Daz

Well the simple answer would be, the further the better. Shielding your scope from direct light coming locally helps a bit but sky glow is the real killer of the night sky.

I live in Sutton (south London) this has horrendous LP and I will not observe from home for this reason. So I take my scope about half an hours drive away to use it. This site isn't bad around VLM 5 - 5.25.

But for real dark sky observing I need to travel much further.

It's one of those, the more you put in the more you get out things. The further you are prepared to travel from urban areas the better the night sky will be. It is worth it, trust me on this.

[Dazzyd]

I know what you mean Steve, when I used to spend a lot of time down in Wiltshire (about 110 miles away) the skies used to be amazing! Think I've found a region around 20 miles away, just need to find a location now

[FarSide]

Hi Daz,

Myself and a few friends actually set up on a country track last night only half an hours ride from the town i life in, Reading, and the difference was most certainly worth it. I'm not saying it was dark sky quaility but the star numbers jumped massively. The thing is you're not only looking for LESS sky glow but also a wider horizon. For example i saw scorpius for the first time ever last night because of it's close proximity to the horizon. So you need both less sky glow, and a decent horizon.

[umadog]

Getting away from local light pollution will make a significant difference. e.g. placing 10 miles between yourself and that nasty car dealership. However, the sky glow from a big city can be visible 100 miles away. As Steve says, the further the better, but any distance is good.

[pete_l]

You can also consider the direction the LP is coming from.

Personally, I think the sky to the south is more interesting to observe. The northern "half" of the sky contains lots of good objects, but you can observe them easier by waiting until the time of night (or time of year) when they are more-or-less overhead.

With southern objects, Scorpius as mentioned - Sagittarius too, they never get very high in the sky. So if you want to observe them, it's better to choose a site where the sources of LP are in the north i.e. your site is to the south of the town/city and its LP.

[ollypenrice]

Again, as far as possible. 186,000 miles per second. Damn!

Olly

[acey]

It depends on the size of the light-pollution source (i.e. how many streetlights), the geography of the location, and the atmosphere (moist UK air is terribly good at scattering unwanted light). Garstang did a mathematical model of the problem years ago; the general finding is that you get a big difference initially, then there's a point beyond which further travel yields diminishing returns. For UK, 20 miles should be good in most cases - just as long as you aren't driving towards further light pollution. Going much further than that may give some improvement, but not much.

But that's all assuming you've got one light-pollution source surrounded by empty wilderness, which of course is not at all what UK is like.

Another factor is the extent of light domes on the horizon (as opposed to zenith sky brightness). I go beyond 20 miles in order to reduce the effect of bright light-domes on my horizon, though the zenith limiting magnitude remains pretty much the same.

You've just got to try it for yourself and see. Balance the gain in limiting magnitude against the extra time and petrol.