International Dark Sky Reserve in Dorset

Why is Cranborne Chase AONB Dark Sky Reserve so unique?

Areas of Outstanding Natural Beauty are designated as such because of the exceptional qualities of their landscape, which is safeguarded in the national interest. Cranborne Chase is unique in that it is the only one of the 46 AONBs that is also an International Dark Sky Reserve, a recognition that the half of the environment that is above the horizon is also of exceptional quality and is worthy of protection.

From the dawn of civilisation until very recently, the one thing that every sighted human has had in common is a view of the starry constellations of the night sky. It’s a sobering thought that this shared heritage is now denied to most of the world’s people: 90% of the population of the United Kingdom has never seen a dark night sky. It has become such an alien experience that some city-dwellers have even been frightened by it the first time they have seen it. Clearly, something needed to be done.

International Dark Sky Places Project

In 1988, an astronomer at the Kitt Peak Observatory in Tucson, Arizona, decided that enough was enough: Dr David Crawford and a colleague founded the International Dark-Sky Association (IDA). One of his first tasks was to demonstrate that a dark sky did not mean a dark ground, and it is a testament to his work that the Milky Way is visible from the well-lit streets of Tucson, a city of more than half a million people.

The IDA’s International Dark Sky Places programme aims to promote the IDA’s ideals world-wide. Cranborne Chase AONB’s director, Linda Nunn, was convinced that the AONB could be one of these Dark Sky Places, so together with Bob Mizon, a Dorset astronomer and the Director of the Commission for Dark Skies (the British equivalent, and affiliate, of the IDA), she set about the task. Her dream was realised in October 2019, when Cranborne Chase AONB was awarded the prestigious status of International Dark Sky Reserve (IDSR), then only the 14th in the world (there are now 17).

The benefits to our natural environment 

Although many of us came to dark skies advocacy through astronomy, simply because astronomers were the first to notice adverse effects of artificial light at night (ALAN), what we didn’t know is that this was merely first inkling of a much greater web of harm to the environment, to wildlife, and even to human health. If you drive, you will have noticed that your windscreen and numberplate collect far fewer insects than they did even five years ago. This is indicative of a specific aspect of the biodiversity crisis that is sometimes called the “insectageddon”; according to recent research, we are on course to lose 40% of our insects by 2050. Along with climate change and habitat loss, artificial light at night (ALAN) is a significant driver of this decline and is the one that is easiest to remedy.

It is not only insects that are adversely affected by ALAN. Nature needs the night, and many animal species are primarily or exclusively nocturnal. For example, Cranborne Chase is one of the few places where Bechstein’s bat (Myotis bechsteinii), one of Britain’s rarest and most threatened mammals, can still be found. Bats of the Myotis genus shun light, which makes them more vulnerable to predation. Migrating birds are another victim of light pollution: worldwide, between three and ten billion migrating birds die annually as a direct consequence of ALAN.

The benefits to our health

We humans are not immune either. ALAN can affect the “sleep hormone” melatonin, and its suppression has been linked to a range of disorders ranging from loss of concentration to cancers.

The most harmful light is that from the blue end of the spectrum, a major component of “bright white” LED lighting. Not only does the atmosphere scatter it more than reddish light, exacerbating skyglow, but at night it is directly harmful to vegetation, insects, birds and mammals. This should not surprise us; as the Sun sets, the natural light reddens and becomes golden. This is the crepuscular light that every living thing evolved with; we have simply not evolved to cope with blue-rich light at night.

What can be done?

The good news is that we not only know what the solutions are, but that they are easy to implement, and there are no losers except those who sell energy or bad lighting. We can encapsulate these solutions in the phrase “Right Light, Right Place, Right Time”.

  • The right light is the minimum amount of light necessary for the lighting task. Using more light than is necessary is always wasteful and – well – unnecessary. It should also be the minimum colour temperature (CCT). We aim for “warm white” light, i.e. that with a CCT of 3000K or below; this excludes the harmful “bright white” or “blue rich” light.
  • The right place is simply where it is actually needed, i.e. not illuminating the underbellies of nocturnal flying fauna, shining through a neighbour’s window, or causing glare for drivers.
  • The right time is when and only when it is needed. You can achieve this by using timers or PIR motion-detector switches.

Here on Cranborne Chase AONB, we are committed to restoring the once-universal starry heritage that ALAN has stolen from us.

If you would like to contribute to this endeavour, either in the AONB or elsewhere, you can come to one of our Dark Skies events,  together, we can make an enormous, beneficial difference.

Steve Tonkin FRAS, Dark Sky Advisor 

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