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Astronomy
Dark skies, warm nights
For astronomers, light pollution is a big issue. In larger population areas it can obscure the stars in the night sky, leaving only the brigtest 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 from population centres
Can you see St. Helena on this picture? Even on the highest resolution version, St. Helena cannot be located. This is one reason why St. Helena is ideal place for astronomy. The other is that, even at night, the temperature rarely falls below 10° Celcius.
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.
St. Helena now keenly awaits the formal verdict from the committee.
The following photograph was taken by Steve during his visit{1}.
Sky view by Steve Owens, for the St Helena Tourism Association
The picture clearly shows the extent of the visible stars from St. Helena.
Walking in the footsteps ...
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 astronomer Neville Maskelyne (who was Astronomer Royal from 1765 until his death in 1811) came to observe the Transit of Venus in 1761. The site of Edmund Halley’s observatory is regularly on the itinerary of island tour operators (Halley was also an Astronomer Royal). Other astronomers who have visited the island include: John MacDonald (1796), Henry Foster (1828-31), Admiral Duperry (1832), 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).
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{1} 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)
For an interactive map of St. Helena click here.