August sees the return of the most reliable meteor shower of the year; the Perseids, with rates of shooting stars possibly increasing to over 100 per hour under perfect conditions.
Read my previous blog post Meteor Showers: The What, How, Where, When, Why for general advice on how best to observe meteor showers.
A shooting star – otherwise known as a meteor – is a tiny piece of space dust that burns up in our atmosphere, forming a bright, brief streak of light in the sky. Many people have never seen a shooting star, and think they’re rare events, but given dark skies you can expect to see a few every hour on a clear night. From cities, under light polluted skies, you can’t see most of the faint ones, and so only the rarer bright ones are visible.
However at regular times each year the Earth moves through thick clouds of space dust – left behind by comets – and we get a dramatically increased rate of meteors. On the night of 12/13 August we’ll pass through the densest part of a dust cloud left behind by Comet 109P/Swift-Tuttle, and will see the rate of meteors increase by a factor of 20!
You can begin watching for Perseid meteors now, and the shower will last until late-August, but the peak of the shower occurs overnight on 12/13 August 2016, which means that the nights on either side of this will be best for meteorwatching.
The best time of night to watch the meteor shower is from around 2200 onwards on 12 August, once the radiant, the point from where the meteors appear to originate, rises above the horizon. However the moon will be in the sky until after midnight, and will interfere slightly for observers in dark sites. The later you observe the higher the radiant will be, and the more meteors you’ll see.
The number of meteors that you will observe every hour depends on a number of factors:
•the density of the dust cloud 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 darkness of your sky, measured using naked-eye limiting magnitude, a measure of the faintest object you can see.
This year the Perseid meteor shower has an expected zenith hourly rate (ZHR) of around 150. 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 2200, 40° high at midnight, and 50° high at 0200.
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.
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 2016.
ZHR = 150 at the peak, say.
h = 30° at 2200, 40° at 0000, 50° at 0200, 65° at 0400
k = 0 (let’s hope!)
m = 6.5 (if you’re observing under skies free from light pollution)
So your actual hourly rate under clear dark skies is
(150 x sin(30))/((1/(1-0) x 2^(6.5-6.5) = 75 meteors per hour at 2200
(150 x sin(40))/((1/(1-0) x 2^(6.5-6.5) = 96 meteors per hour at 0000
(150 x sin(50))/((1/(1-0) x 2^(6.5-6.5) = 115 meteors per hour at 0200
(150 x sin(65))/((1/(1-0) x 2^(6.5-6.5) = 135 meteors per hour at 0400
Remember though that these numbers apply only to the peak of the Perseid occuring at these times. If the peak happens at 0400 on 13 August (and we’re not sure exactly when it’ll occur) then you might see 135 meteors per hour, but “only” 75 per hour if the peak occurs at 2200 on 12 August.
Remember that these rates are for perfectly dark skies. If you live in suburbia then divide these numbers by 4 or 5; if you live in a bright city divide these numbers by 10. Take home message: get somewhere dark!
It is worthwhile having a look on the days leading up to the peak, when the numbers of meteors will be gradually increasing towards this rate.
Live in or near Glasgow? Come and join me for the Perseids #Meteorwatch at Whitelee Wind Farm!
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.
Join me this Thursday night / Friday morning (18/19 September 2014) for some Twitter-based stargazing!
Many people will be staying up late or even overnight to watch the results of the Scottish Independence Referendum come in. To while away the wee small hours I thought it’d be fun to do a bit of stargazing too!
If you find yourself staying up late then join in by following me on Twitter @darkskyman, and using the hashtag #indyrefstargazing. I’ll kick things off around 9pm on Thursday as the sky darkens, and throughout the night I’ll be describing what’s up in the sky, and how best to see it, winding up around 6am as the dawn breaks. By then we’ll be eagerly awaiting the result of the referendum, which is estimated to be around 7am.
Join in, it’ll be fun! You can send me questions via Twitter too, or just say hello. You don’t need any equipment to take part: just your eyes and clear skies. If you’ve got binoculars, dig them out, as you’ll be amazed how much more you can see.
Sunday marked the start of International Dark Sky Week 20-26 April 2014, 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 this week here are a few things to watch for:
The Lyrids meteor shower will reach its peak on 21/22 April but you might catch some early Lyrids in the days beforehand, and some after the peak; 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.
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!
Yesterday Comet ISON (C/2012 S1) brightened suddenly, meaning that it’s now visible to the naked eye – just.
According to astronomer John Bortle Comet ISON brightened from magnitude +8.5 on Monday and +7.3 on Wednesday, to +5.4 on Thursday, meaning that it is now visible to stargazers without the aid of binoculars or telescopes – although those devices will help!
You’ll have to be determined to see it, as it rises in the east just before dawn, so an early start is required. At the moment it’s not spectacular, although some astronomers are still holding out hope that it might become the Comet of the Century as was predicted earlier this year. We’ll need to wait and see whether it continues to dramatically brighten. If it does then it may be visible high in the night sky in December.
How Best to See Comet ISON
Here are three simple steps you can take to maximise you chances of seeing this comet.
1. Find somewhere dark with a clear eastern horizon
Although it is now a naked-eye object, any light pollution in the sky will make it next to impossible to see, so head to your local dark sky site. If you don’t know how to find one then have a look at this light pollution map of the UK to give you an idea. In general you want to make sure that any nearby town or city is behind you, so head to the east of any populated are. You’ll need a flat horizon too – east coast is ideal – as hills and trees will block your view. At the moment the comet is still low in the sky when twilight brightens the sky making it impossible to see.
2. Keep an eye on the weather forecast
There’s no point heading out if it’s cloudy towards the east, but just because it’s raining when you go to bed doesn’t mean that it will still be raining at 6am. Check local weather forecasts for predicted cloud cover before dawn.
3. Find Mercury and Spica
The planet Mercury rises around 6am, and at that point the star Spica, in the constellation of Virgo, will be only a few degrees above the horizon. Comet ISON lies above and to the right of, approx. 10° higher than Mercury in the sky. Here’s a simple finder chart for approx. 6am.
There’s a great piece in Guardian Travel today about stargazing breaks in and around Galloway Forest Dark Sky Park. The article was written by Kevin Rushby, who visited the park earlier this year, and who I took out stargazing on a beautiful night.
It really is an amazing place, and on a clear winter’s night you can see thousands of stars, the Milky Way, shooting stars, nebula, galaxies, satellites… and much more.
But for most people the night sky is a confusing place, and having a guide to lead you around is an ideal way to begin stargazing. (Ahem! A good guide book is handy too…) I run regular stargazing weekends and evenings at a number of hotels near Galloway Forest Dark Sky Park (and one down in Exmoor!) over the course of the winter. Here are the dates for the weekends I have planned for this coming winter:
1-3 November 2013 Selkirk Arms Hotel, Kirkcudbright
29 November – 1 December 2013 Kirroughtree House Hotel, Newton Stewart (SOLD OUT)
6-8 December 2013 Kirroughtree House Hotel, Newton Stewart
31 January 2013 – 2 February 2014 Yarn Market Hotel, Exmoor
28 February – 1 March 2014 Kirroughtree House Hotel, Newton Stewart
28-30 March 2014 Selkirk Arms Hotel, Kirkcudbright
I also run bespoke stargazing nights at Glenapp Castle, Ballantrae.