Today marks the 175th anniversary of the birth of John Muir, the Scottish-born American naturalist, writer, and advocate for the preservation of wild land.
The protection of our wildernesses landscapes (defined as anywhere you cannot see the intrusion of human activity) is more important than ever, with the spread of suburbia and the urbanisation of more than 50% of the world’s population.
But one measure of what makes a wilderness has to-date been largely ignored: that of the darkness of the night sky. After all, if you can see the sky glowing orange at night then you are seeing the intrusion of human activity, and you can’t consider the land you’re in a true wilderness.
John Muir’s legacy as the founding father of the conservation movement lives on today, in part in the organisation The John Muir Trust.
The JMT estimates that the amount of Scotland’s landscape that is wilderness is rapidly diminishing, dropping from 31% of Scotland to 28% between 2008 and 2009, but I think if you added in the spread of man-made light pollution the situation would be decidedly worse.
I am fortunate to have been awarded the JMT’s Bill Wallace award to help fund a trip later this year (once the skies get dark again after the bright summer nights) to map light pollution in one of Scotland’s most wild landscapes, between the JMT properties of Quinag and Sandwood Bay.
Hopefully this project – the first of its kind in this remote area – will shed some light on the problem of the loss of our wilderness nightscapes.
With summer coming to an end in the British Isles we start the return to the dark skies of autumn and winter. Depending on where you are in the country you will have been without truly dark skies for many weeks, maybe even months, as summer evening twilight lasts throughout the night during the summer.
This all-night-long twilight is almost gone throughout the UK, indeed anywhere on the mainland UK can see astronomically dark skies around 1am at the moment. Only the furthest north outpost of the British Isles still doesn’t have that opportunity.
On the island of Unst, the furthest north of the Shetland islands, lies the UK’s furthest-north town, Skaw, at 60°49′N and 00°47′W. This tiny village will see astronomical darkness return at 0043 on 24 August, lasting only 46 minutes until at 0129 the sun’s light begins to creep into the sky again.
The last time that astronomical darkness was seen at Skaw was on 18 April, over four months ago! Indeed this settlement is so far north that between around 13 and 29 June each year they never get out of civil twilight, meaning that the sky’s bright all night long!
Compare this with the furthest south town in the British Isles, Saint Clement in Jersey, in the Channel Islands. Astronomical darkness returned to Saint Clement on 4 July this year, having been absent since 8 June; only four weeks without true darkness!
Such is the effect of differences in latitude that these two settlements, separated by 1299 km, have such hugely different seasonal swings between summer and winter.
Last Saturday night I visited the site of the soon-to-be-open Scottish Dark Sky Observatory. Sitting on a hill top in Craigengillan Estate near Loch Doon, this stunning new public observatory lies on the edge of Galloway Forest Dark Sky Park, under some of the darkest skies in the UK.
At the moment the observatory is still under construction, and is due to open in a few months time, at the start of this winter dark sky season. It will be open to the public and school groups for day-time and night-time visits.
The site itself is wonderful, and the observatory is nestled amongst the graggy hill tops east of Ness Glen, just south of the small town of Dalmellington on the A713.
The observatory will include a fully robotic 20” Corrected Dall Kirkham telescope in a 5m dome, operated from either of two control rooms; a roll-off-roof observatory with a 10” SCT for a more hands-on, out in the open observing experience; a multi-purpose lecture room served by a toilet and kitchen and an “outdoor classroom” in the form of an elevated observing deck from which to enjoy the experience of naked-eye observation. Facilities will be provided for amateur astronomers to set up their own equipment and have access to the toilet and kitchen facilities. It will be open to the public, amateur astronomers and to schools and universities, with the aim of inspiring people of all ages and all backgrounds with a sense of wonder at the vastness and beauty of the heavens and the revelation of man’s place within the universe.
The Observatory was the brain child of Craigengillan Estate owner Mark Gibson and the Renfrewshire Astronomical Society (RAS). A member of the RAS, Colin Anderson, is an architect and he designed the buildings. It’s a tribute to Mark, Colin, and others in the RAS that this project is even possible, and I for one cannot wait to observe from their incredible new observatory.
The global family of International Dark Sky Places – areas with stunning night skies and exemplary lighting controls to preserve those skies – has grown again recently, with the addition of some huge parks and reserves. There are currently (as of June 2012) 18 places around the world that satisfy the International Dark-sky Association‘s (IDA) requirements.
I’ve been lucky enough to visit 12 out of these 18 incredible places, including the two most recent additions to the IDA family, NamibRand Nature Reserve in Namibia, and Aoraki Mackenzie in New Zealand, both of which have been awarded International Dark Sky Reserve status this year.
The IDA has three different designations: International Dark Sky Park (IDSP), International Dark Sky Reserve (IDSR), and International Dark Sky Community (IDSC).
IDSPs are areas of public land that are near-empty wildernesses, and which have enacted strict controls of outside artificial lighting throughout the entire park. There are currently ten IDSPs.
IDSRs are large areas centred on a dark sky core, a significant area – an observatory, say – in need of protection against light pollution, and a 15km-minimum buffer zone around that core, encompassing surrounding communities. The communities in the buffer zone have lighting controls that help minimise light pollution in the core area. There are currently four IDSRs.
IDSCs are communities – cities, towns, villages, islands – that have enacted exemplary lighting controls to limit the spread of light pollution into their night skies. There are currently four IDSCs.
The following table has some information about the various International Dark Sky Places:
|Name||Location||Park Area||Designation||Year Designated|
|Aoraki Mackenzie||New Zealand||4300 km2||Reserve||2012|
|Big Bend National Park||Texas, USA||3242 km2||Park||2012|
|Borrego Springs||California, USA||110 km2||Community||2009|
|Cherry Springs State Park||Pennsylvania, USA||4.3 km2||Park||2008|
|Clayton Lake State Park||New Mexico, USA||1.9 km2||Park||2010|
|Exmoor National Park||England, UK||692 km2||Reserve||2011|
|Flagstaff||Arizona, USA||255 km2||Community||2000|
|Galloway Forest Park||Scotland, UK||780 km2||Park||2009|
|Geauga Observatory Park||Ohio, USA||4.5 km2||Park||2011|
|Goldendale Observatory State Park||Washington, USA||0.2 km2||Park||2010, provisional|
|The Headlands of Emmet County||Michigan, USA||2.2 km2||Park||2011|
|Homer Glen||Illinois, USA||58 km2||Community||2011|
|Hortobagy National Park||Hungary||800 km2||Park||2011|
|Mont Megantic||Quebec, Canada||5000 km2||Reserve||2008|
|NamibRand Nature Reserve||Namibia||1722 km2||Reserve||2012|
|Natural Bridges National Monument||Utah, USA||31 km2||Park||2006|
|Sark||Channel Islands, UK||5.4 km2||Community||2011|
|Zselic Landscape Protection Area||Hungary||90.4 km2||Park||2009|
I recently attended the Third International Starlight Conference held by the Starlight Initiative near Lake Tekapo, New Zealand. The conference brought together a huge range of specialists who seek to limit the excesses of light at night, and the venue sat in the recently-announced Aoraki / Mount Cook International Dark Sky Reserve (IDSR) in New Zealand’s stunning south island.
The beauty of the night sky from somewhere like Tekapo is astounding, and the IDSR status will help keep it that way, limiting the amount of lighting that can spill into the sky from the surrounding communities. Under such starry skies it’s easy to understand why we’d want to protect them, but for most of the population of the planet starlight is becoming increasingly more elusive.
To help emphasise the importance of a dark starry sky the conference looked to build upon a document written at the first Starlight Conference in La Palma, in 2007, the Starlight Declaration in Defence of the Night Sky and the Right to See the Stars.
The Starlight Declaration states:
a. An unpolluted night sky that allows the enjoyment and contemplation of the firmament should be considered an inalienable right equivalent to all other socio-cultural and environmental rights. Hence the progressive degradation of the night sky must be regarded as a fundamental loss.
b. Knowledge—armed with education—is a powerful vector that can heal the growing rift between today’s society and science and contribute to the advancement of mankind as a whole. The dissemination of astronomy and of the scientific and associated cultural values should be considered as basic contents to be included in educational activities.
d. Control of obtrusive light must be a basic element of nature conservation policies since they impact on several species, habitats, ecosystems, and landscapes.
c. Protection of the astronomical quality of areas suitable for the scientific observation of the Universe must be given priority in national and international scientific and environmental policies.
e. The intelligent use of artificial lighting that minimizes sky glow and avoids obtrusive visual impact on both humans and wildlife should be promoted. This strategy would involve a more efficient use of energy so as to meet the wider commitments made on climate change, and for the protection of the environment.
f. Tourism, among other players, can become a major instrument for a new alliance in defence of the quality of the nocturnal skyscape. Responsible tourism, in its many forms, can and should take on board the night sky as a resource to protect and value in all destinations.
Necessary measures should be implemented to involve all parties related to skyscape protection to raise public awareness—be it at local, regional, national, or international level—about the contents and objectives of the International Conference in Defense of the Quality of the Night Sky and the Right to Observe Stars, held in the Island of la Palma.
Dated 20 April 2007, La Palma, Canary Islands, Spain
This blog post is a copy of one which I wrote for the Guardian Science blog, posted there on 13 April 2012.
The small South Atlantic island of Saint Helena is about as remote as any place on Earth gets. It lies 2000km from Africa and 3000km from South America, and I’m heading there for eight days this month to carry out a dark sky survey.
This survey will allow me to determine the quality of the night sky above Saint Helena – the darkness of the sky, but also the clarity of the stars – in anticipation of the island becoming an International Dark Sky Place, a designation awarded by the International Dark-sky Association (IDA).
Light pollution is a common problem for astronomers living near cities; a familiar orange glow drowning out the light from all but the brightest stars in the night sky. With the spread of suburbia there are increasingly fewer places where stargazers can enjoy an unspoiled dark sky, but the further you travel from urban areas the more stars you will see, and Saint Helena as about as far as it’s possible to be from the next town.
Under such dark skies the Milky Way can be seen stretching from horizon to horizon in an arc overhead, and the heavens are studded with thousands of stars and many nebulae, including the dramatic Magellanic clouds not visible from far northern latitudes. Indeed its location at 16° south of the equator means that virtually every constellation is on display at some time throughout the year.
Saint Helena’s Astronomy Heritage
Saint Helena has long been used by astronomers as a site for making important observations. Edmund Halley – he of comet fame – visited the island in 1677 to catalogue the southern stars and observe a Transit of Mercury. The following century, in 1761 Neville Maskelyne, later to become Astronomer Royal, came to observe a much rarer Transit of Venus. (Incidentally, a Transit of Venus occurs this year on 5/6 June, only the fifth to occur since 1761, and the last for over 100 years).
The Dark Sky Survey
During the survey I’ll be using a Sky Quality Metre (SQM) to assess the brightness overhead. This device measures sky brightness in units of magnitudes per square arcsecond (magnitudes are a measure of brightness, the lower the number the brighter the sky; square arcseconds are a measure of area, where one arcsecond is 1/3600 of a degree).
In my back garden in the suburbs of Glasgow the SQM reads around 18 magnitudes per square arcsecond; in the centre of Glasgow it might read 16. The darkest readings come from remote places like Galloway Forest Dark Sky Park where 21.7 isn’t uncommon. In the very darkest places the limit of the device comes from the brightness of the stars overhead, and so you can’t expect readings much darker than 22.0 even in sites free of light pollution.
As well as these SQM readings I’ll be estimating the naked-eye limiting magnitude (NELM) of the night sky above Saint Helena. This basically involves looking for the faintest star I can see and reading its magnitude from a star atlas. In a city the NELM might be 3 or 4; in Galloway Forest Dark Sky Park it might reach 6.5 or even 7, where the only limit to what you can see is your eyesight.
Dark Sky Tourism
So why go to all this trouble? Well, an extensive dark sky survey is just one of the criteria expected of an International Dark Sky Place. Once this survey work is carried out, along with a lighting audit and adoption of new lighting codes on the island, the IDA might confer this status on Saint Helena. And the drive for all this work? Tourism. At the moment Saint Helena’s tourism is based almost exclusively on Napoleon’s exile there between 1815 and 1821. The Island also has several hundred species of flora and fauna which only found on this remote Island and is steeped in history from the Age of Discovery when it was a crucial staging post for sailing ships. The island attracts around 1000 visitors per year.
The main difficulty for the prospective visitor is travel to the island. The only way of getting there right now is on the RMS Saint Helena, on a six-day ocean voyage from Cape Town, something that may deter all but the most determined traveller. Come 2015 however, the island will have its own air strip, making it more accessible and tourism visits more regular.
The Saint Helena Tourism Association hopes to attract visitors with the prospect of the stunningly dark skies above the island. The concept of dark sky tourism has been growing over the past few years. There are currently 16 International Dark Sky Places recognised by the IDA, including three in the UK: Galloway Forest Dark Sky Park, Sark Dark Sky Island, and Exmoor Dark Sky Reserve. These sites are seeing an increase in visitor numbers in the dark winter season as keen stargazers, inspired perhaps by Prof Cox, flee the bright city lights for darker skies.
VisitScotland, our national tourism agency, has just released this splendid radio advert to entice people to visit the beautiful Dumfries and Galloway this spring, home to Galloway Forest Dark Sky Park.
It’s a perfect time of year for stargazing, if you’re happy to stay up a bit later into the night.
If you’re planning a stargazing visit you’ll need to time your visit well. At night you have to wait until the Sun is far below the horizon (the end of astronomical twilight) and also wait until the Moon has set. The perfect nights for dark sky stargazing in D&G in April 2012 are between 9 and 23 April. On 9 April the skies will be pitch dark between 10:30pm and midnight, when the Moon rises. The hours of darkness grow each night as the Moon rises later and later, until 15 April when darkness lasts from 11pm until 4am. As we’re approaching midsummer the nights are shortening, and so by 23 April it will be properly dark between 11:15pm and 3:15am.
You can see the full range of dark sky stargazing activities on offer in and around D&G on the VisitScotland Stargazing Spectacular website
Having just tried to assess Naked Eye Limiting Magnitude from a dark site, I realised that my previous post on the subject merited some amendments.
Rather than using the whole constellation of Ursa Minor to carry out your NELM estimate, it’s much simpler to use just part of it, that part around the “body” of UMi, roughly bounded by and immediately surrounding β, γ, ζ, and η UMi. Here’s a more detailed star chart of that part of the sky, with all 34 stars brighter than magnitude 7.2 labelled.
And here’s a list of the magnitudes of each of these stars:
| Star Number (Name)
||Magnitude|| Star Number (Name)
|1 (β UMi)||2.05||18||6.55|
|2 (γ UMi)||3.00||19||6.60|
|3 (ζ UMi)||4.25||20||6.60|
|4 (5 UMi)||4.25||21||6.65|
|5 (4 UMi)||4.80||22||6.70|
|6 (η UMi)||4.95||23||6.80|
|7 (θ UMi)||5.00||24||6.85|
|8 (11 UMi)||5.00||25||6.85|
|9 (19 UMi)||5.45||26||6.85|
|15 (20 UMi)||6.35||32||7.10|
|17 (3 UMi)||6.40||34||7.20|
As you can see, it’s much easier to fine-tune your NELM estimate using this chart compared to the previous one, as there are not such big jumps between brightnesses from one star to the next.
Colours in this table correspond to the Bortle Scale colour key.
Crucially, one thing I omitted to note in the previous post was that this process should be carried out when your target stars are high above the horizon. The stars of Ursa Minor, when observed from the UK, vary in altitude between 40° and 70° roughly speaking, so ideally you’d wait until they were higher than 60° above the northern horizon.
|Month||Times when Kocab (β UMi) alt > 60°|
|mid Jan||0300 till start astronomical twilight (~0600)|
|mid Feb||0100 till start astronomical twilight (~0530)|
|mid Mar||2330 till start astronomical twilight (~0430)|
|mid Apr||2230 till start astronomical twilight (~0400)|
|mid May||end astronomical twilight till start astronomical twilight|
|mid Jun||no hours of darkness|
|mid Jul||no hours of darkness|
|mid Aug||never > 60° during hours of darkness|
|mid Sep||never > 60° during hours of darkness|
|mid Oct||never > 60° during hours of darkness|
|mid Nov||never > 60° during hours of darkness|
|mid Dec||0500 till start astronomical twilight (~0630)|
UPDATE: Here’s the chart with the magnitudes written directly beside each star.
There are a variety of ways of measuring your night sky quality, and one of the most effective ways is by looking for the faintest star you can find with your naked eye, and noting its brightness, or magnitude. This provides what is known as Naked Eye Limiting Magnitude, NELM.
Of course just randomly casting about the sky for faint stars can lead you on a merry chase, and so a very useful method is to use one specific constellation – one you can always see, no matter what time of year – and look only at stars within that one constellation. This narrows the field somewhat, and makes your task that much easier.
For observers in Europe and North America the constellation of Ursa Minor, the Little Bear, provides an excellent choice for estimating NELM.
The overall shape of Ursa Minor is made up of seven bright-ish stars, but around and amongst these are many more fainter stars.
|Bright Star Name
|Ahfa al Farkadain (ζ)||4.25|
|Anwar al Farkadain (η)||4.95|
Even some of these “brighter” stars might not be visible from city centres. For example, if you are observing from a site with Bortle Class 8 you would not see η-UMi, while those unhappy stargazers under a Bortle Class 9 sky would only be able to pick out the three brightest stars, α-, β-, and γ-UMi. Only at Bortle Class 7 and darker will you make out all seven of the main stars of Ursa Minor.
But what if you’re at a good dark sky site? Well, you’re going to need a longer list of magnitudes, and a more detailed map of Ursa Minor.
|Star Number on
|Star Name||Visual Magnitude||Bortle Class
The stars in the map and table above have been numbered (by me – these aren’t official designations) from 1 to 19, with 1 (Polaris) being the brightest, and 19 (14 UMi) being the dimmest. You will only be able to see all 19 numbered stars from exceptionally dark places, virtually free of light pollution, what Bortle called “typical truly dark sky sites”. From my garden in the outskirts of a major city I can see numbers 11 and 12, but not number 13, giving me an NELM of 5.45.
The Bortle Scale is a useful way of estimating your sky brightness, i.e. to what extent light pollution affects your view of the night sky. By going outside on a clear moonless night and recording what astronomical objects you can see you can assign a Bortle Class rating to your observing site.
I have used the Bortle Scale to assess night sky quality many times, and always felt the lack of a handy flow chart to lead me through it. So I made one. Enjoy. (You can also download the pdf version.)
PS The content of this chart assumes some prior knowledge of astronomy, but any of the terms used are easily google-able.