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On December 24, 1968, astronaut William Anders aboard the Apollo 8 reconnaissance mission took what has been called arguably the greatest environmental photograph of the Earth.
The crew had been photographing details on the moon's surface from orbit when, looking up, they spotted the Earth rising.
They marvelled at the vivid blue of the oceans, the brown and green of the land masses, the bright white swirls of weather systems, all so clear from 380,000km away.
That famous "Earthrise'' photo has been superseded by the International Space Station images many of us have seen of the Earth at night with cities and large swathes of Europe, North America and Asia illuminated brightly.
What also grabs the attention are the dark patches where electricity is a luxury, such as in North Korea and much of Africa, or the cities are smaller and the population is much lower, including New Zealand.
Ironic, then, that while those in space are able to see night-time on Earth ever more clearly, down here it is getting harder to see out into space.
In recent years, New Zealand has been in the vanguard of efforts to keep our skies as dark as possible.
Anyone who has spent time in Central Otago or the Mackenzie Country will understand why - on a cloud-free night, twinkling stars in their millions offer a dazzling spectacle.
Free of a great deal of the light pollution that afflicts much of the globe, and with an atmosphere blessedly absent of the haze seen elsewhere, we have a direct connection with the universe and, for those in the South, incredible chances to view the shimmering Aurora Australis when it comes out to play.
As the Dunedin City Council starts replacing the city's 15,000 ageing high-pressure sodium streetlights with new LED lights, it is easy to see why there is concern that progress might affect the night sky.
Earlier this year, the council confirmed its plans to install white 3000 Kelvin (K) LED street lighting, starting with outer areas of the city, including the Taieri, Saddle Hill and Strath Taieri, before moving on to the inner-city next year.
The intention is to have the $15million project, of which the NZ Transport Agency is paying about 85%, finished in Waikouaiti and Port Chalmers about the middle of 2021.
At a public city council forum last week, Kyra Xavia, of the Lightwise Guild, pleaded with councillors to think again about installing the 3000K LED lights.
She said those white lights were "unsafe'' for people and wildlife, and promoted instead the use of warmer, amber 2200K lighting right across the city.
Ms Xavia previously said the less intense 2200K lights had a much lower impact on the environment, emitting less green- and blue-wavelength light, and cut light pollution by generating less glare and contrast.
In September, council asset and funding manager Merrin Dougherty said lower-intensity lights would indeed be installed at the end of the project in ecologically sensitive areas because research showed they caused less disruption to nocturnal life.
These would be at Aramoana, on the Otago Peninsula, in Waikouaiti, Waitati, Karitane and the Town Belt.
While a certain level of brightness is obviously needed for public and road safety, there is plenty of research showing light at night can affect the circadian rhythms of animals and disrupt their foraging habits, reproduction and migration. Blue light in LEDs can suppress the production of melatonin, which helps with sleep.
The Scientist reports that 80% of humanity, and more than 99% of people in the United States and Europe, now live under light-polluted night skies.
Light pollution is recognised as a major anthropogenic pressure on the environment.
We must not be afraid of a little more darkness.
The alternative is the potential loss of wildlife and the forfeiture of the sight of the Southern Lights and the majesty of our universe.