It's just after midnight. There's no moon, and hardly any cloud. A few street lights burn in the village below, but on the hill where I'm standing they have no impact on the brilliance of the night sky. Brilliant, because I'm looking into a canopy of stars too numerous to count, but studded among them are familiar favourites. There's Ursa Major/the Plough/Great Bear/Big Dipper – the first constellation most of us recognise. Sweeping across to the left is the dominant glow of Jupiter, Orion's Belt and sword, there's Venus and the tiny orange blip of Mars. On this dark lane leading into the Snowdonia national park I'm looking into the heavens at stars that could have shone down on these hills for more than 250m years – it's an extraordinary experience, and sadly one denied to half the UK population.
The latest annual star count survey by the Campaign to Protect Rural England (CPRE) and the Campaign for Dark Skies (CfDS) showed 53% of those taking part on a clear night earlier this year could see 10 stars or fewer within the major constellation of Orion. Only 9% could see between 21 and 30 stars within the constellation, and just 2% had really dark skies above them and so were able to see 31 or more stars. Our skies are so "saturated" with glaring light, according to campaigners, that many of us are unnecessarily denied access to the wonders of the night sky.
"Why should we care?" asks astronomer Steve Owens. "Because seeing the stars helps us engage with the universe in a very profound way. It's only been in the last couple of generations that people have grown up without seeing the stars, but when they do, it helps them understand their place in the cosmos. Stars also encourage kids to get interested in science. It's not just a few geeks with telescopes who are interested – there's a massive appetite and enthusiasm for astronomy and space now." Owens is known as Dark Sky Man following his work to get Galloway Forest park in south-west Scotland designated as a "Dark Sky park", making it the only one of its kind in northern Europe. But his concern is that we are "losing the battle for suburbia," where, he says, "pockets of night sky are being swallowed up by orange smog from artificial light".
Campaigners warn the results of the Star Count Survey show that despite action to reduce light pollution in some areas, it's a problem that is largely unchecked. Emma Marrington, CPRE's rural policy campaigner, says: "All too often we hear poor excuses for bad or excessive lighting. Of course we need the right, well-designed lighting in the right places – but there should not be a blanket assumption that glaring lights are needed." Good street lighting should feature a bulb that is encased above and to the sides. This channels light downwards where it is needed and reduces the amount of wasted light. It's known as "cutting off light at the horizontal", which ensures that light is used to illuminate the ground and not the sky.
The "orange smog" isn't just blocking a view of the stars: artificial light causes problems for wildlife, too. In light-polluted areas, birds are continually chirping throughout the night in anticipation of a dawn that won't arrive for many hours. It disrupts the normal routine of many plants, and it affects people's sleeping patterns. It's also costly. Campaigners say that in 2010 local authorities collectively spent more than £500m on street lighting, which in turn accounted for 5% to 10% of each council's carbon emissions.
But, according to the Local Government Association, councils are getting "well ahead of the game". A spokesperson says that "scores of local authorities up and down the country are trialling the switch-off and dimming of street lights late at night in quieter areas, including East and West Sussex, Devon, Dorset, Durham, Monmouthshire, Lincolnshire, Surrey and Hampshire. In Coventry, the city council is replacing 28,000 of its 32,000 street lights. It wants to be able to reduce the brightness of lights when fewer people are around. Exeter city council has just had a plan approved to install remote monitoring technology to turn off 12,000 lights as traffic and pedestrian levels fall, but the lights could also be switched back on in an emergency.
Safety, according to the LGA, has to come top of councils' priorities when it comes to deciding whether to dim or switch off lights. "Councils will not cut lighting if a large number of people are strongly opposed to the idea and there are genuine safety concerns," the LGA spokesperson says.
But turning off street lights can be unpopular, and political. Last year, cuts to street lighting were one of a series of measures highlighted by Labour that, it was alleged, would disproportionately affect women. "With something like street lighting it's not just about the data, but about whether people feel safe, specifically whether women feel they can get the bus back home," shadow home secretary Yvette Cooper told the Guardian.
Stella Creasy, Labour's shadow Home Office minister, wants a national audit before our streets get any darker. She believes local authorities "are in the dark themselves about the impact of cutting lighting on crime, fear of crime and accidents".
"Given the anxiety these proposals are causing, and the concerns about the impact of light pollution as well, it's not acceptable to leave councils without a proper evidence base for their decisions and hope for the best." She added: "The government should conduct an urgent audit into the impact of these changes, so that we can all have confidence that the needs of communities are being met, and what seems like a short-term cut won't be a long-term cost to communities across the country."
Are we, though, denying ourselves the wonder of the cosmos out of a misplaced sense of safety? There's been relatively little research into whether crime goes up when the lights go down. One American study suggested crime went up rather than down when lighting in Chicago alleyways was increased, and a recent police review into part-time street lighting in Hertfordshire concluded that there's no evidence of an increase in crime when lights are turned off.
Rob Smith, from Hertfordshire county council's transport management team, said they had looked at research from elsewhere that suggested turning off or dimming the lights wouldn't lead to higher levels of crime or accidents, and that their review reinforces those findings.
Of course, living on the edge of the Snowdonia national park, I'm far less likely to become a crime statistic than women in many other areas of the UK – and less likely to walk home at night in fear of an attacker. Standing alone in the dark on my Welsh hill, I realise I am one of the fortunate ones, for I can appreciate the night sky in all of its infinite magnificence. What's saddening is that in our towns and cities, the light from deep outer space, which has travelled for many millions of years from the distant stars and galaxies above me, ends it journey to most of us blocked high above the ground as a result of the light from humans.
What to look for
When the late American astronomer Carl Sagan wrote the first paragraph to the book that accompanied his landmark 1980 television series Cosmos, he got straight to the nub of why staring up at the sky at night is – and will always be – a belittling, yet wondrous, experience for us humans.
"The cosmos is all that is or ever was or ever will be," he said. "Our feeblest contemplations of the cosmos stir us … We know we are approaching the greatest of mysteries."
The most recognisable part of the cosmos is, of course, the closest celestial body to us – our moon. Even binoculars will greatly enhance the view, allowing you to see shadows being cast inside the largest craters on its surface.
Arguably, one of the best times (and easiest for children) to look up at the night sky is the period just after dusk. The fast-fading influence of the sun's rays can light up satellites as they pass overhead, or even the International Space Station. They can be distinguished from planes because the light will be constant, not flashing.
It is also the period when some of the solar system's planets are easiest to spot. This month, for example, look to the west and you will be able to spot the bright "stars" of Venus and Jupiter. Venus will be brighter because, even though it is far smaller, it is much closer to us (and the sun) than Jupiter. If you have a good pair of binoculars, or a modest telescope, you might be able to see Saturn's rings, and some of Jupiter's many moons.
Harder to make out, but still visible higher up in the east to south-east sky, will be Mars. Meanwhile, a couple of hours later, as true darkness sets in, Saturn will begin to rise from the horizon in the east.
By this time, if you are lucky enough to live in a light-pollution-free area, one of the greatest wonders will be visible. Look directly overhead and you will see a thick band of luminosity stretching across the sky. This is the Milky Way, the millions of stars that make up our galaxy. If you're extra lucky, you might catch the fleeting, long streak of a meteorite entering the atmosphere.
Lastly, try to identify some easy-to-find stars. The Big Dipper, or Plough (formally known as Ursa Major), is a cluster of stars called an asterism that together look like a big saucepan with a long handle. Use the two stars on the far right of the "saucepan" – the "pointers" – as guides to point you up towards the next brightest star, the North Star (Polaris), which sailors used to use for navigation at sea.
• This article was amended on 20 April 2012 because the original said Jupiter's rings could be seen with binoculars or a modest telescope. This has been corrected.