Astronomy

Dark skies, warm nights

Astronomy compels the soul to look upwards and leads us from this world to another.{g}

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

SEE ALSO: Dark Sky Tourism is not the same as Dark Tourism. For the latter see our page Dark Tourism. You may also be interested in St Helena’s role in Space Exploration .

Light Pollution

{h}

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 exhibits 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. St Helena is highlighted on this picture with the red circle. Even on the highest resolution version, St Helena registers only a faint glow. This is one reason why St Helena is an ideal place for astronomy. Enlarge the image on the right to see how many stars you can see from St Helena…{2}

Maybe try the full-sized version…Ⓘ{d}

According to the statistics published on www.lightpollutionmap.info, which cover 250 countries, St Helena is the 16th smallest source of light pollution, behind places such as Tokelau, the Pitcairn Islands, Tuvalu and Montserrat. America, unsurprisingly is #250, China is #249 and the UK is #229 (just below South Africa, #228). The full list is reproduced below or you can download the full list hereⒾ.

Other advantages

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.{i}

As indicated in the quote above, other advantages of St Helena for star-gazing are that:

• Even at night, the temperature never falls below 10°C;

• Our exceptionally high air-quality means you are looking up through clean air; and

• Because we are in the Southern Hemisphere, but close to the equator, you can see stars that are not visible from Europe and North America or more southerly latitudes (e.g. the Southern Cross).

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.{j}

Dark Sky Status

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.

St Helena now keenly awaits the formal verdict from the Dark Sky Places Development Committee (which, at the time of writing has still not been received).

The photograph below was taken by Steve during his visit{3}. 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.

Halley’s Mount, 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 a Transit of Venus in 1761, accompanied by Mr Robert Waddington, also an astronomer. He also set up an observatory close to Halley’s. Maskelyne’s Observatory is less visited than Halley’s.

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). For more about visiting astronomers read the paper ‘Astronomers and other scientists on St HelenaⒾ’ by W.G. Tatham & K.A. Harwood (1974){4}. More recently, from 2019 to 2021 Mark Westmoquette lived here and founded the St Helena Astronomy Club.

Our Night Sky

Here are some photographs of the night sky, taken from St Helena:

The Southern Cross

Southern Cross{h}

St Helena is in the Southern Hemisphere so a feature of our night sky is the Southern Cross, Crux.

As the diagram shows, it comprises four stars:

Interestingly, Crux used to be a Northern Hemisphere constellation. It was recorded by the Ancient Greeks and around 4,000 years ago was seen as far north as Britain, but due to natural changes in the night sky it drifted southwards and by 400 CE it was never seen in Europe. Crux was first shown in its correct position on the celestial globes of Petrus Plancius and Jodocus Hondius in 1598 and 1600, and would have been observed from St Helena by Halley in 1677.

Eclipses, Comets, etc.

Great Comet, 1843{k}

Eclipses (solar and lunar), Comets, Transits and other astronomical events are all seen from St Helena, as they are from everywhere else on the planet, though our unpolluted air, dark sky and good weather mean there is a much greater chance of actually seeing the event.☺

Edmond Halley visited the island in 1677 inter alia to observe a Transit of Mercury and Nevil Maskelyne came in 1761 to observe a Transit of Venus.

The Great Comet of 1843 was studied from St Helena from 6th to 23rd March and observations were made with an altitude and azimuth instrument by Gilbert.{l}

According to the Records, in the 43 years from 1843 to 1886 a total of nine comets were observed in the skies above St Helena; in 1843, 1858, 1860, 1861, 1880, 1881, 1882, 1884 (‘Pons Comet’) & 1886. Halley’s Comet is not included - not seen until 1910. There was also in the period a cluster of Lunar Eclipses in 1884, 1888 & 1891.

What was then the longest duration Lunar Eclipse of the 21st Century was clearly seen and photographed on St Helena on 27th July 2018 (below).

I am discounting reports of UFOs. Why would they appear only to cranks and weirdos?{m}

Astronomical Data

You can see a pretty diagram of where it is currently daylight and nighttime here: www.timeanddate.com/‌worldclock/‌sunearth.html.

The Weather and the Moon

Just before dark

St Helena gets spectacular sunsets, for you to admire while on your way to your viewing location.

Read More

Below: Astronomy Day Transit of… Article: Saint Helena Dark Sky Island Weblink: Astronomy for Kids VIIRS Country statistics

Astronomy Day

Astronomy Day probably should be celebrated on St Helena, but isn’t - possibly because the system for fixing the dates (there are two ‘Astronomy Days’ each year) is obtuse and so has to be declared (by whom?) each year.

Transit of…

Venus, 1761

A Transit is where a planet - either Mercury or Venus - passes between the Earth and the Sun{5}, and can be seen as a tiny dot passing across the Sun’s face.

Please Note a Transit MUST be viewed with special equipment because looking directly at the sun will damage your eyesight.

The significance of observing a Transit is that, by timing how long it takes the planet to cross the Sun’s face and using some rather clever maths it is possible to calculate the distance between the Sun and the Earth.

Astronomers Halley and Maskelyne both came to St Helena to observe a Transit of… - Venus in the case of Maskelyne and Mercury in the case of Halley. Interestingly, the values calculated by Halley and Maskelyne after their St Helena observations differ only slightly from current calculated values.

If you want to know more see the Wikipedia: Transit of Mercury or Transit of Venus.

Article: Saint Helena Dark Sky Island

Dark Sky Diary 13th April 2012 by Steve Owens{4}

Saint Helena, 1815

Small and Large Magellanic Clouds, Akira Fujii/Davidmalin.com

The small South Atlantic island of Saint Helena is about as remote as any place on Earth gets. It lies 2,000km from Africa and 3,000km from South America, and I’m heading there for eight days this month to carry out a dark sky survey.

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.

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 5/6th 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 St Helena (1990-2018), 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.

Weblink: Astronomy for Kids

There’s a useful introduction to astronomy, aimed at kids but actually quite useful for adults too, at job-prices.co.uk/‌astronomy-for-kids.

VIIRS Country statistics

Here are theVIIRS Country statistics, published on www.lightpollutionmap.info: