Today marks the start of International Dark Sky Week, a global initiative to get people out of towns and cities and seeing a night sky as it’s meant to be seen, unspoiled by light pollution.
Most of us live in urban environments these days, with the ever-present orange glow lighting the night sky. From my garden in Glasgow I can see only a few hundred start on a clear night. But if I traveled south by car for an hour down to Galloway Forest Dark Sky Park, or north by the same distance to Loch Lomond National Park, I’d count thousands of stars.
And then if I made more of an effort to get to the very darkest parts of our country (the heart of Galloway Forest, or Northumberland Dark Sky Park, or up to Coll Dark Sky Island) the number of stars would be overwhelming, too many to count.
At this time of year in the UK (especially in Scotland) you’ve got to wait until quite late to see the sky free of twilight (2230 in Exmoor Dark Sky Reserve for example, 2330 in Coll, and after midnight up in the Orkney Islands), but it’s worth making the effort if it’s clear.
If you do head out tonight here are a few things to watch for:
2150-2155 on Sunday 20 April only: The International Space Station passes overhead, the last pass of this run and your last chance to see it until June. Look SW to see it rising before it brightens to magnitude -1.1 in the S
The Lyrids meteor shower will reach its peak in a couple of days (21/22 April), but you might catch some early Lyrids tonight; the darker your skies the more you’ll see.
Cygnus the Swan, and the other stars of the Summer triangle will be rising high in the east after midnight. In the right wing of the swan is the star Kepler-186, with the new-found twin Earth, known as Kepler-186f. The star is far, far too faint to see, even with a very powerful telescope, but you can still look in that direction and give a little wave.
There are only two International Dark Sky Islands in the world, and both of them are in the British Isles: Sark in the Channel Islands; and Coll in the Inner Hebrides.
These beautiful short films show what you’ll see on a clear night:
I’ve visited both islands several times, and they’re beautiful places, and not just at night when the stars come out. They’re very different: Sark is lush, with hedgerows and country lanes, and at 49°25′N latitude its climate is very continental. Coll on the other hand is almost entirely treeless, it’s rugged, boasts long sandy beaches, and lies at 56°38′N. Contrary to common impressions of the weather on the west of Scotland, Coll is one of the sunniest parts of Scotland and so has, like Sark, a high number of clear dark nights.
And it’s on dark nights when these islands are at their most stunning. Now that summer’s on its way though the dark nights will shorten and eventually disappear altogether until autumn, so you’ve plenty of time to plan your visit. Sark has a longer dark sky season, running from August till mid-May, as opposed to Coll’s which runs from September till mid-April, but the nights are longer on Coll than on Sark during the darkest winter months, the best time for stargazing.
Make sure that if you’re going to Sark or Coll for stargazing that you avoid the bright moon. Ideally you would be there during a new moon or thin crescent; at the very least you should avoid the week on either side of the full moon. To maximise your chances of seeing the wonderful dark skies make sure you stay for several nights!
The negative effect of light pollution on wildlife has long been known, specifically – but not exclusively – its effect on bats, bugs, and sea turtles. Now the British Trust for Ornithology (BTO) are running an Early Bird Survey, asking people in the UK to monitor the pre-dawn feeding times of garden birds to see what – if any – effect light pollution is having.
To take part you need to get up before dawn* on 9** January 2014 (tomorrow, as I write this), watch your garden bird feeders, and record the times that the first ten species arrive to feed. You can download the full instructions here (pdf), and submit your observations here.
* dawn occurs at different times around the UK, so you should find your sunrise time and get up half an hour earlier than that, during civil twilight.
** observations on 10, 11, and 12 January are welcome too.
As the BTO website says:
Winter is not an easy time for birds. They need extra energy to keep warm, especially during long winter nights. To cope with this, they lay down extra fat reserves, though small birds quite often only lay down enough for a single night. Longer nights not only affect the amount of energy a bird uses, they also reduce the amount of time that birds can feed in. Birds, therefore, have to make the most of the daylight hours to replenish their energy reserves before it gets dark.
The 2004 BTO Shortest Day Survey, run in association with BBC Radio 4, investigated the patterns behind birds arriving at garden bird feeders first thing on a winter’s morning. Building on observations from the Shortest Day Survey, the Early Bird Survey will investigate what effect, if any, light and heat pollution have on the feeding patterns of birds during a cold winter’s morning.
The International Dark-Sky Association (IDA) announced today it has designated two new International Dark Sky Places in the UK, including one representing the largest land area of protected night skies in all of Europe. This brings to six the total number of IDA International Dark Sky Places in the UK, second only to the United States.
IDA is proud to recognise Northumberland Dark Sky Park and Coll Dark Sky Island for their exceptional efforts in helping preserve and promote dark night skies over Britain. I have worked with both of these areas as a dark skies consultant, advising them on the process of achieving dark sky status. To date this puts the number of dark sky places that I have been heavily involved in to five; more than anyone else in the world, I think!
The reasons for these areas seeking dark sky status are many and varied. Off-season winter astronomy tourism is one main driver, while for councils the economic and environmental benefits of night-sky-friendly zero-waste lighting are paramount. Northumberland County Council have recently announced an investment of £24million to refit all public street lights in the county to energy efficient LED lights, fittings which pay back the initial investment within 6-8 years through reduced operating costs, and which have a significantly reduced carbon footprint, due to their efficiency and the fact that no light is wasted – it all shines down to the ground where it’s meant to be, rather than into the sky.
Northumberland International Dark Sky Park
A UK National Park and adjacent forestry plantation encompassing nearly 580 square miles (1500 km2) of public lands in northern England, Northumberland National Park and Kielder Water & Forest Park are the first IDA-recognized International Dark Sky Park consisting of two independent parkland units.
Once at the frontier of Roman Britain where Hadrian’s Wall repelled Pictish invaders, Northumberland International Dark Sky Park now serves as a bulwark against the incursion of harmful light pollution into one of the darkest locations in England.
With today’s IDA announcement, National Parks UK and Forestry Commission England adds dark skies to their portfolio of protected natural resources including the largest manmade woodland and reservoir in northern Europe. Kielder Forest provides Britain with 200 million board feet (475,000 m3) of timber annually.
The dark night sky attracts an increasing number of visitors to the region. Kielder Observatory, the UK’s largest and most active public observatory, widely promotes local astronomy events and activities. “Dark skies and astronomy have become a passion in the area,” according to Heidi Mottram, Chair of the Kielder Water and Forest Park Development Trust and Chief Executive of Northumbrian Water.
As both Northumberland National Park and Kielder Water & Forest Park began to vie independently for IDA recognition, it quickly became evident that two heads were better than one. “It made perfect sense to work together to protect one of our greatest assets and make it available to more people,” Mottram said.
Park officials hope that protecting dark skies through the promotion of responsible outdoor lighting will increase the allure of Northumberland as a tourism destination.
“Becoming a Dark Sky Park will reinforce the status of Northumberland as an unspoiled destination offering a true sense of tranquility and wildness – a tonic in this day and age,” said Tony Gates, Chief Executive of Northumberland National Park.
Coll International Dark Sky Island
A sparse population and geographic isolation make the night skies over the Isle of Coll among the darkest in Europe. The island adopted a quality outdoor lighting management plan to ensure Coll remains dark for many future generations of residents and visitors.
Coll lies about six miles (10 km) west of coastal Argyll and hosts just over 200 residents. It attracts dozens of bird species according to the Royal Society for the Protection of Birds, which owns an extensive reserve at the west end of the island and hosts one of Coll’s recognized night sky viewing sites on its land. Nature tourism in part draws thousands of visitors to the island each year.
“Achieving dark skies status will be great for the island in many ways,” Julie Oliphant, hotelier at the Coll Hotel, explained. “Not only will it ensure that any future development on the island is done in a way that protects Coll’s natural and unspoiled beauty, but it will also help promote winter tourism.”
Fred Hall of the Argyll and Bute Council echoed the sentiment. “The Isle of Coll is a unique island in many ways, not least of which is its beautiful countryside and sea views but also the lack of light pollution,” he said. “I can think of no better island in the inner Hebrides to gain the Dark Skies accolade.”
Northumberland is IDA’s thirteenth International Dark Sky Park, while the Isle of Coll becomes the world’s fifth International Dark Sky Community. They join four existing International Dark Sky Places in Britain: Galloway Forest Park in Scotland, Isle of Sark in the Channel Islands, Exmoor National Park in England, and Brecon Beacons National Park in Wales.
If you’re interested in gaining dark sky status for your area, then get in touch!
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.
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|
Spring in the northern hemisphere is the best time to view the elusive, faint astronomical phenomenon known as Zodiacal Light.
This light – literally “light from the zodiac” – appears only just at the end of evening twilight or just before morning twilight, and is seen as a cone of very faint light stretching up from the horizon, narrowing as it does so, following an imaginary line in the sky known as the zodiac, or to give it its more astronomically correct name, the ecliptic.
The angle which this line makes with the horizon varies throughout the year, and the steeper the angle the more evident the zodiacal light will be. The steepest angle for observers in the northern hemisphere occurs in the evening sky in March and April, or the morning sky in October and November.
How best to see Zodiacal Light
You will need to be as far as possible from any sources of light pollution. In fact the Zodiacal Light is one of the benchmarks of the Bortle Dark Sky Scale, which says that it is only visible in skies with Bortle Class 5 or better, and even in suburban/rural transition sites it is not striking. Under rural skies it is “striking”, while in a truly dark sky site it is bright enough to cast a shadow. Under exceptionally dark skies it might appear as a band stretching from horizon to horizon.
Once you’ve found your dark sky site, you need to find somewhere with as clear a western horizon as possible, and wait until the end of evening astronomical twilight (assuming you’re viewing it in the spring – if it’s the autumn then you need to start observing before the start of morning astronomical twilight). You can find your twilight times using timeanddate.com or the excellent Velaclock app for smartphones. As a general rule, for observers in the UK, you need to wait until two hours after sunset before you skies get dark enough to see this elusive light. But wait too long and the bulk of the cone of light may have set, so sunset+2hours is really the perfect time.
What Zodiacal Light looks like
As mentioned above, Zodiacal Light is a faint grey cone of light stretching up from the horizon. The darker your observing site the larger this cone will appear, and the higher into the sky it will stretch. From the very darkest sites on Earth it can stretch overhead and down to the far horizon.
What’s Zodiacal Light made of?
Zodiacal Light is sunlight reflecting off particles of dust and rock orbiting the Sun. This dust is in a lens-shaped cloud with the Sun at the centre, and the cloud lies in the same plane as the planets in the solar system (which is why it’s visible along the ecliptic). The particles in the Zodiacal Light are around 0.15mm in diameter (some smaller, some a little bigger) and probably come from shattered comets and asteroids.
Photographing the Zodiacal Light
As tricky as it is to see with your naked eyes, it’s even harder to catch on camera. Harald Edens has a great page about how best to photograph it.
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.