International Dark Skies Week 13-19 April 2015

This week is International Dark Skies Week, 13-19 April 2015.

Created in 2003 by high-school student Jennifer Barlow, International Dark Sky Week has grown to become a worldwide event and a key component of Global Astronomy Month.

“I want people to be able to see the wonder of the night sky without the effects of light pollution. The universe is our view into our past and our vision into the future . . . I want to help preserve its wonder.” – Jennifer Barlow

This year’s International Dark Skies Week coincides with the International Year of Light, which makes it particularly appropriate.

Why not head outside at night and explore dark skies? You could head to any International Dark Sky Places. In the UK we have six:

• Galloway Forest Dark Sky Park
• Exmoor Dark Sky Reserve
• Sark Dark Sky Island
• Brecon Beacons Dark Sky Reserve
• Northumberland Dark Sky Park
• Coll Dark Sky Island

Any of these sites will provide excellent views (weather permitting!) of a real dark sky.

If none of these are convenient why not visit a Dark Sky Discovery Site near you. These are sites that have been identified by local communities as being convenient for stargazing, although they don’t have the light pollution control measures that the International Dark Sky Places do.

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Perseids Meteor Shower 2014

This month sees the most reliable meteor shower of the year; the Perseids. However this year the near-full Moon will be in the sky too, brightening the sky so much that only the brightest Perseid meteors will be visible. It’s still worth looking up over the next week if you have clear skies, in case you might spot a bright Perseid.

You can begin watching for Perseid meteors now, and the shower will last until late-August, but the peak of the shower occurs on Tuesday 12 August 2014, which means that the nights on either side of this will be best for meteorwatching, albeit with interference from the moon.

Perseus at 0200 13 August 2014

The best time of night to watch the meteor shower is from around 2200 onwards on both 11 and 12 August 2014, once the radiant, the point from where the meteors appear to originate, rises above the horizon.

The number of meteors that you will observe every hour depends on a number of factors:

• the density of the cloud of dust that the Earth is moving through, that is causing the shower in the first place;
• the height above the horizon of the radiant of the shower, the point from which the meteors appear to radiate;
• the fraction of your sky that is obscured by cloud;
• the naked-eye limiting magnitude of the sky, that is a measure of the faintest object you can see.

The Perseid meteor shower has a zenith hourly rate (ZHR) of between 50 and 200. This is the number of meteors that you can expect to see if the radiant is directly overhead (the point in the sky called the zenith), and you are observing under a cloudless sky with no trace of light pollution.

However conditions are rarely that perfect. In the UK, for example, the radiant of the shower will not be at the zenith; it will be around 30° above the horizon at midnight, and 45° above the eastern horizon at 2am.

Assuming a clear night, the other factor is the limiting magnitude of the sky, a measure of the faintest object you can see. Man-made light pollution will be an issue for most people. From suburbia the limiting magnitude of the sky is ~4.5 (around 500 stars visible), so you will only be able to see meteors that are at least this bright; the fainter ones wouldn’t be visible through the orange glow. In a big city centre your limiting magnitude might be ~3 (only around 50 stars visible); in a very dark site like Galloway Forest Dark Sky Park the limiting magnitude is ~6.5 (many thousands of stars visible), limited only by the sensitivity of your eye. So in most cases it’s best to try and get somewhere nice and dark, away from man-made light pollution.

This year though the full Moon is a great leveller, giving everyone a limiting magnitude of around 3.

The calculation that you need to make in order to determine your actual hourly rate is:

Actual Hourly Rate = (ZHR x sin(h))/((1/(1-k)) x 2^(6.5-m)) where

h = the height of the radiant above the horizon

k = fraction of the sky covered in cloud

m = limiting magnitude

Let’s plug the numbers in for the Persieds 2014.

ZHR = 100 at the peak, say.

h = 30° at 0001, 45° at 0200, 60° at 0400

k = 0 (let’s hope!)

m = 3 (pesky moon!)

So your actual hourly rate at 0200 under clear dark skies is

(100 x sin(30))/((1/(1-0) x 2^(6.5-3) = 4.4 meteors per hour at 0001
(100 x sin(45))/((1/(1-0) x 2^(6.5-3) = 6.2 meteors per hour at 0200
(100 x sin(60))/((1/(1-0) x 2^(6.5-6.5) = 7.6 meteors per hour at 0400

Remember though that these numbers might be lower if the ZHR drops off after the peak.

It is of course worthwhile having a look on the days leading up to the peak, when the numbers of meteors will be gradually increasing towards this rate.

*UT = Universal Time = GMT, so for UK times (BST) add one hour to these

Shedding Light: a Survey of Local Authority Approaches to Lighting in England

Last Friday 25 April 2014 the Campaign to Protect Rural England (CPRE) released a report (pdf) entitled “Shedding Light: a Survey of Local Authority Approaches to Lighting in England”, that addresses the growing problem of light pollution in rural areas.

Light pollution from towns and cities spreads a long way, lighting the sky up and spoiling the view of the stars even in areas with few or no lights of their own. However that’s only the tip of the iceberg. According to CPRE:

Street lighting in England costs councils approximately £616m per year and can account for up to 30% of their carbon emissions so tackling light pollution will have a triple benefit – cutting costs and carbon too.

Although around one third of councils surveyed were switching lights off between midnight and 5am, when they aren’t needed, and around one half of councils dimming lights at similar times, there is still much more to be done.

Image from the CPRE report: Light pollution of Eastbourne, from Warren Hill

According to Emma Marrington, CPRE Dark Skies Campaigner:

‘The results of our survey show that many local authorities are taking steps in the right direction to manage lighting more effectively. But much more can be done to encourage all authorities to take this issue more seriously.

‘We urge councils to do more to control lighting in their areas, and ensure that the right lighting is used only where and when it is needed. We often hear concerns that changing street lighting can impact on public safety but our research revealed no evidence to support this. We’re not advocating changes where they’re not appropriate, but why shine bright lights on residential streets, quiet roads and open countryside throughout the night when it’s not needed?

‘Genuine dark starry nights are becoming harder and harder to find which is why councils should take action to control it now. Light pollution blurs the distinction between town and country, ruins the countryside’s tranquil character and denies us the experience of a truly starry sky.’

CPRE ends the report by making nine recommendations:

1. Light pollution policy All local authorities should have a policy to control light pollution in their Local Plan, in line with the National Planning Policy Framework and the associated National Planning Practice Guidance on light pollution. This should include identifying existing dark areas that need protecting.
2. Street lighting policy Local authorities should consider  preparing a Street Lighting Policy, which could include Environmental Lighting Zones to ensure that the  appropriate lighting levels are  used in each zone, with very strict requirements applying in identified dark areas.
3. Part-night lighting schemes We encourage local authorities to investigate how part-night lighting schemes (e.g. switching off between midnight and 5am) or dimming could work in their areas, including examining the cost, energy and carbon savings. This should be done in full consultation with the local community.
4. LANTERNS research project All local authorities who are switching off or dimming street lighting should monitor crime and accident statistics and consider taking part in the Institution of Lighting Professionals/LANTERNS research project which aims to quantify any effects of changes to street lighting on road traffic accidents and crime.
5. LED lighting Local authorities should give careful consideration to the type of Light Emitting Diode (LED) lighting they use and consider the potential impacts that higher temperature blue-rich lighting has on ecology and human health.
6. Targets for replacing lights Local authorities with responsibility for street lighting could set targets for replacing all their street and road lights with less light polluting types, such as full cut off flat glass lamps.
7. Testing new street lighting New street lighting should be  tested ‘in situ’ before a lighting scheme is rolled out across a wider area to ensure that it is the minimum required for the task and does not cause a nuisance to residents.
8. Preserving dark skies Local authorities should have a strong presumption against new  lighting in existing dark areas,  unless essential as part of a new development or for public safety reasons that have been clearly demonstrated.
9. Highways Agency guidance The Highways Agency should review the lighting section of the Design Manual for Roads and Bridges, which is used to design motorway and trunk road lighting, to ensure it remains relevant for local authorities.

The whole report makes for interesting reading, but a few things stand out:

• only 65% of councils in England have a policy on lighting
• 87% of these councils said it was a continuation of an existing policy; only 13% had adopted a new policy as a result of the 2012 National Planning Policy Framework (NPPF).
• The top three reasons that councils were switching off  lights at night are:

1. 95%: Energy Saving
2. 91%: Cost Saving
3. 43%: Reduced Light Pollution

• The top three reasons that councils were switching off  lights at night are:

1. 97%: Energy Saving
2. 78%: Cost Saving
3. 54%: Reduced Light Pollution

• 11 councils said that dimming schemes had gone largely unnoticed by the community
• 91% of councils that are switching off lights are continuing to work with local police to monitor local crime statistics

Dark Sky Islands

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.

Sark

Coll

They were designated by the IDA (the International Dark-sky Association) under their International Dark Sky Communities programme, Sark in 2011 and Coll in 2013.

These beautiful short films show what you’ll see on a clear night:

The Starry Skies of Sark from Sue Daly on Vimeo.

Isle of Coll – IDA Dark Sky Community from Ewan Miles on Vimeo.

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!

Light Pollution and Birds: Early Bird Survey

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.

Northumberland and Coll: The Newest International Dark Sky Places

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.

Stargazers at Cawfields, Northumberland Dark Sky Park

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!

Light Pollution and the Loss of Wilderness

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.

International Dark Sky Places

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.

The Church of the Good Shepherd, Aoraki Mackenzie IDSR Image by Fraser Gunn

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

 

The Starlight Declaration

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

Zodiacal Light

Spring in the northern hemisphere is the best time to view the elusive, faint astronomical phenomenon known as Zodiacal Light.

Daniel López, IAC Zodiacal Light on the left and (false colour) Milky Way on the right

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.