Light Pollution

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Light Pollution


UK Skies are getting brighter.

Ever been to an Arizona Desert ...

Over ten years ago I was in Arizona in a desert looking up at the night sky. That's when I discovered the colour of the Universe. Not those white, blurry little pinpoints of light that sometimes pierce the fog of an English winter night. I'm talking full-on technicolor, panoramic, the-angels-are-singing-in-the-background, see-all-the-galaxies-spinning, kind of vista.

Yep, only in America it seems. But not here?

Fast forward to a year later, and my American friends were telling me how much they enjoyed our little island because, and I quote; 'everythin's soo close tagetha'. They said this with some degree of genuine surprise.


If you get the chance to fly over any part of the UK at night you can almost see the five pound notes burning away below you. The problem is very real from up there. It's like an amber map of veins, the almost un-broken southern metropolis known as the South Coast is a 24 hour floodlit Camberwick Green.

Like 'Insecurity' lights. Please turn them off. Sigh.

Using a Sky Quality Meter, I was getting readings of dark sky sites of Mag 20+/Arc second from several locations in and around Hampshire. Though a lot depends on weather, and recently the South has had some really extraordinary clear nights. But in the centre of Portsmouth it's closer to Mag 16.5'ish.

A bit rubbish from a techy point as this figure is not what you can see with your own eyes, it's more for long-exposure imaging, which your eyes are ill-equipped to do. Your pupils are about 5mm across and therefore a bit limiting for gathering photons of light from many light years away.

So, 1 Magnitude is defined as a factor of 100 as a logarithmic scale. I think I'd better explain.

A Magnitude 6 star is quite feint. Tiny. You may just about be able to pick it out in that Arizona desert. On Southsea Seafront with lots of street lighting perhaps a Mag 3 star, which is 15.8 times brighter than that Arizona star, or a Mag 1 that is 100 times brighter, is as good as it gets. Getting brighter, the Moon is about -12.7 when it's full and the Sun -26.75 Mag. Very bright indeed, don't look at it!

The Hubble Telescope can 'see' stars as feint as Magnitude 30. Your 10x50 binoculars can reach about Magnitude 9, and that's a 10,000th of the brightness of a -1 Mag star (say Sirius). See? I hope so.

Why not download a copy of Stellarium, a free open source planetarium software package. Install it and click on some stars, then you'll see what I mean. See what you're missing? Loads.

Binoculars do help you see more, but what about light pollution I hear you cry? Get out of the cities and head for the countryside. Now that's the problem. Not much left that's not blighted by an amber sky. We don't have a cure for light pollution but we do have a way of getting around it, literally.

HantsAstro's search for Dark Skies. It's about getting 'Out There' and using what we have and making the most of it to get the best out of astronomy. That's what we want to do - to see the clear night sky.

There is also the Campaign for Dark Skies - check it out if you want to learn more about dealing with light pollution and doing your bit to combat it.

Sometimes, being kept in the dark would be a good thing, if you're an astronomer that is.

David Woods

Go There

It's a simple plan. Record the night sky across Hampshire, so you know where the darkest skies are. Hampshire is no doubt one of the best places to live, but light pollution threatens to spoil our night sky. There are pockets of dark sky sites that will help you see the night sky better.

If you find any let us know! We use a Sky Quality Meter that measures the magnitude of the night sky so you will be able to compare urban and rural sites. Hampshire's a big county, and we have started this project that is ongoing and will no doubt change over time as more building takes place over the next twenty or so years.

The plan is to get out and see the night sky from some of the best possible vantage points in Hampshire and we will be meeting at different places across the county (and sometimes across the border!) to get the best views of the night sky.

Tell us where you are and we'll add you to our map for review.

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