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Astronomy

Dark skies, warm nights

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Astronomy compels the soul to look upwards and leads us from this world to another.
Plato, The Republic. Book VII. 529

Want to really see the stars? And not freeze while doing so?

This page is in indexes: Island Activity, Island Detail

Milky Way from St Helena [Saint Helena Island Info:Astronomy]
Milky Way from St Helena{a}{1}

Go to: The issue: light pollutionNo light pollution here!Walking in the footsteps…Read More

The issue: light pollution

For astronomers, light pollution is a big issue. In larger population areas it can obscure the stars in the night sky, leaving only the brightest visible. Meaningful observations become impossible. Two specific problems affect the observer. In high ambient light levels the human eye cannot reach its full sensitivity, so observing fainter objects is much harder. And with high levels of generated light the sky exibits a phenomenon known as ‘Skyglow’, whereby the sky itself seems to become illuminated.

As the following photograph shows, considerable amounts of light radiate upwards from the world’s major population centres. Even small islands - the Hawaii chain, for example, is clearly identifiable:

The world at night, photographed from space, showing upward light radiation [Saint Helena Island Info:Astronomy]
The world at night, photographed from space, showing upward light radiation

No light pollution here!

Can you see St Helena on this picture? Even on the highest resolution version, St Helena cannot be located{2}. This is one reason why St Helena is an ideal place for astronomy. The other is that, even at night, the temperature never falls below 10°C.

Stars over the Farm Lodge Hotel [Saint Helena Island Info:Astronomy]
Stars over the Farm Lodge Hotel{3}
When you experience the soft blackness of a tropical night on isolated St Helena, with the Southern Cross surrounded by a million bright pinpricks of light, it’s easy to imagine yourself on an asteroid sweeping through space.{b}

To quote from a blog{4}{5}:

The thin atmosphere and non-existent light pollution means the moon is bright, very very bright, the likes of which I have never seen before. Stepping outside in the middle of the night one would imagine it is early morning, and driving is possible in the dead of night without the use of headlights, such is the illumination provided by the moon beams. (I only tried this for a short distance!). Looking out at the moon and the false daylight makes me grateful for the shared experience with my family. It is not possible to describe the night sky here, you may read this blog, I could post pictures, and when we return home I will doubtless tell friends and family of the crisp dark shadows cast by the midnight sun. But it is only Bev and the boys who will truly understand when we return home, just what it is to step out at night to see the earth bathed in this white glow.

In 2012 the St Helena Tourism Association invited Steve Owens, a freelance science communicator and astronomer, Fellow of the Royal Astronomical Society and Chairman of the International Dark Sky Association’s Dark Sky Places Development Committee, to visit St Helena and assess the darkness of our skies. The International Dark Sky Association is based in Arizona and is authorised by the international astronomy associations and societies to give accreditation to locations and communities who pass the audit for being an exceptionally good place for anyone to pursue their interest in astronomy.

When Steve Owens sailed away from St Helena on 30th April he was able to tell us that:

  • He had collected enough data for the audit;

  • The darkness of the St Helena night sky qualifies for ‘Gold Tier’ status - the highest rating;

  • From his initial observations he thinks the majority of our public lighting complies with the standard required by the audit, and there are already several, and maybe sufficient, plans in place to improve street and public lighting to satisfy the audit requirements.

There is more on this story in the 4th May 2012 edition of The Independent and his blog posting is reproduced below{6}.

St Helena now keenly awaits the formal verdict from the committee.

The following photograph was taken by Steve during his visit{7}.

Sky view [Saint Helena Island Info:Astronomy]
Sky view{c}

The picture clearly shows the extent of the visible stars from St Helena.

Top Twenty things to do [Saint Helena Island Info:Astronomy]

Stargazing is one of our Top Twenty things to do during a visit to St Helena.

Top Twenty things to do [Saint Helena Island Info:Astronomy]

Walking in the footsteps…

Nevil Maskelyne [Saint Helena Island Info:Astronomy]
Maskelyne

Edmond Halley [Saint Helena Island Info:Astronomy]
Halley

In addition to the exceptional quality of our night sky St Helena has several historical links with eminent astronomers and a long connection to the Royal Astronomical Society.

The site of Edmond Halley’s observatory is regularly on the itinerary of island tour operators (Halley was the 2nd Astronomer Royal). While here he observed the positions of 341 stars in the Southern hemisphere, publishing his results in Catalogus Stellarum Australium.

The astronomer Nevil Maskelyne (who was Astronomer Royal from 1765 until his death in 1811) came to observe the Transit of Venus in 1761, accompanied by Mr Robert Waddington, also an astronomer.

Other astronomers who have visited the island include: Charles Mason & Jeremiah_Dixon, who joined Maskelyne here in 1761; John MacDonald (1796); Henry Foster (1828-31); Admiral Duperry (1832); Manuel Johnson (1834) - his observatory was at the top of Ladder Hill, from where he compiled his ‘Catalogue of 606 principal fixed stars in the southern hemisphere’ published in 1835; Sir James Clark Ross (1840); Lt. Edmund Palmer (1850-52); Lt. Washington (1852); Capt. Oliver (1869); Dr. David Gill (1877); Prof David Todd; and Cleveland Abbe (1890). And to this list we must now include Steve Owens (2012).

Astronomers sites (from Tourist Office map 2014) [Saint Helena Island Info:Astronomy]
Astronomers sites (from Tourist Office map 2014)

Read More

Article: “Saint Helena Dark Sky Island

Dark Sky Diary 13thApril 13, 2012 by Steve Owens{6}

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.

Saint Helena, 1815 [Saint Helena Island Info:Astronomy]
Saint Helena, 1815

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.

Small and Large Magellanic Clouds, Akira Fujii/Davidmalin.com [Saint Helena Island Info:Astronomy]
Small and Large Magellanic Clouds, Akira Fujii/Davidmalin.com

Saint Helena’s Astronomy Heritage

Saint Helena has long been used by astronomers as a site for making important observations. Edmond 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 Nevil 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 Meter (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.

More stories [Saint Helena Island Info:Astronomy]

More stories on our page Read articles about St Helena.

closinghumourimage [Saint Helena Island Info:Astronomy]

Laugh at funny astronomy humour - LOL [Saint Helena Island Info:Astronomy]


Credits:

{a} Paul Tyson

{b} John Vigor, ‘Small Boat to Freedom’, 2005{6}

{c} Steve Owens, for the St Helena Tourism Association



Footnotes:

{1} Canon EOS 500D, 30s, ISO-1600, 13/10/2014 21:44h

{2} Conveniently, we are almost in the middle of the image, just a little down - go west from the bulge in Africa and there we are[’nt!] You can find Ascension Island, up and to the left, probably because of the USAF air base there

{3} Photograph taken by a participant in the island’s first ‘Dark Sky Tour’ in May 2015

{4} twoyearsintheatlantic.com, posted 7th November 2014

{5} See more blogs.

{6} Reproduced for educational non-commercial use only; all copyrights are acknowledged

{7} Taken on 27th April 2012 at 23:12h with a Canon EOS 5D camera using an 8mm ‘fisheye’ lens at F3.5 over a 190s exposure (ISO 1000)



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