Ordinary Meeting, 2006 March 22

 

Seven Nights on a Bare Mountain

Dr Moore reported that he had recently travelled to Tenerife with Owen Brazell to spend seven days observing in the Teide National Park between 2005 October 30 and November 6. He started by outlining some of the island's attractions for prospective astro-tourists. Being a popular tourist destination, it had cheap and abundant transport links; low-cost airline Ryan Air served it, for example, albeit not directly from the UK. At 3,718 m above sea level, the island's volcanic mountain, Teide, yielded very clear skies. And, being situated 23° to the south of the UK's latitude brought further attractions to the island. Many more of the southern constellations were visible from Tenerife as compared to our native skies, and in the summer, the skies were considerably darker: even in June, Tenerife saw 90 minutes of true astronomical darkness each night, whilst the UK saw none between mid-May and late July.

The attractions to the astro-tourist extended beyond the astronomical, the speaker added – the island's volcanic geology was truly fascinating to see. Geographically, Tenerife was the largest of the seven Canary Islands, an archipelago off the north-western coast of Africa, owned by Spain. The islands remained actively volcanic to this day, and Tenerife's landscape was dominated by the towering heights of one of the volcanos: Mount Teide. Though presently dormant, it had erupted as recently as 1909.

Teide's attractions as an observing site had long been recognised by the professional as well as amateur communities; the history of its use by astronomers could be traced back to the 1856 expedition by Charles Piazzi Smyth, then Astronomer Royal for Scotland, to make experimental observations to test the supposed benefits of mountain-top observing. Smyth had tested the seeing conditions that he found using double stars, and over the three months of his investigation, had concluded that observations were possible in Tenerife which were quite incomparable to anything he had ever achieved in Edinburgh. Systems which he had found utterly irresolvable in Edinburgh became trivially separable in Tenerife. Smyth had gone on to assert that the limiting magnitude of his 18 cm refractor had been extended from mag 10 in Edinburgh to mag 14 in Tenerife. Ever since Smyth had returned his favourable reports, astronomy had continued in the Canaries; Tenerife was now home to the extensive Observatorio del Teide, meanwhile the neighbouring island of La Palma hosted the better-known Isaac Newton Group (ING) of Telescopes.

Turning to describe his own trip, the speaker explained that he had stayed at the Parador Hotel, at an altitude of 2,000 m above sea level, which had a selection of telescopes in a back shed, which the owners allowed experienced observers among their clients to use on occasion (contact details would be given at the end of the talk). The hotel presently housed a 24½" f/4.4 Dobsonian with high quality optics by AE Optics / Jim Hysom, and a 10" f/6 Newtonian; there were plans to extend this collection. The Dobsonian was a huge instrument, but had no drives or setting circles, and so required a user who could star-hop. A large stepladder was required to remove the lens cap, and some care was required; it had been unusable on one of the nights of the speaker's visit due to high winds making it impossible to use the ladder. A second night had been lost to cloud, but five nights of very fine observing had been possible. Dr Moore's only other gripe about the instrument had been that it had been kept in a rather warm shed in the daytime, and the optics had taken a long time to cool to a stable temperature.

Seeing the observing site, the speaker had initially been rather concerned to see the peak of Teide towering above him to the east; it seemed to block a substantial portion of the sky. In the event this had not been much of a problem; being in the east, one simply had to wait for objects to rise over the obstruction. Light pollution had been minimal, bar a few car headlights coming up the mountain pass. Low altitude cloud layers forming below the hotel were helpful in blocking out any light from the sea-level tourist resorts below. Generally, the most annoying source of light pollution was Sirius, appearing as a giant beacon in the sky. The speaker had placed the naked-eye limiting magnitude at ~6.0 on most of the nights of his stay, sufficient for Uranus to be a naked-eye object, though a bit disappointing in contrast to the mag 6.7-6.8 limits which he had experienced on past trips to La Palma.

Dr Moore than turned to describe the range of objects which he had been able to observe. Giving an overview of the parts of the sky accessible from Tenerife in November, Scorpius, Sagittarius and Corona Australis had all been early evening constellations, meanwhile Leo and Hydra had been among those which rose later in the night, as dawn approached. He remarked that Sagittarius was not a constellation that one associated with northern November skies, but it had been quite observable at a latitude of 28°N; this rich part of the Milky Way had been an exceptional sight in such dark, steady skies.

Of the 83 objects which he had observed, a few stood out especially, perhaps the Orion Nebula (M42) most of all. Through such a fine telescope, it had possibly appeared even more beautiful to the eye than John Herschel's drawings of it. The detail accessible in the Veil Nebula (NGC 6960, 6979, 6992, 6995) had been stunning; sweeping the telescope around, nebulosity had appeared everywhere. The speaker wished he had been able to sketch its whole extent, but that would have proven very time consuming.

The Horsehead Nebula (Barnard 33) had also stood out as a remarkable sight, especially with the use of an Hβ filter. Turning the Dobsonian to the Fornax galaxy cluster, eleven galaxies had simultaneously fitted into its field of view; the speaker never recalled having seen so many galaxies in a single field before.

To sum up, Dr Moore concluded that his had been a very rewarding trip, albeit not especially cheap – the final cost had been £734 per person. He felt on balance, though, that this had not been an unreasonable price to pay for the observations he had been able to make. He thus recommended the Parador Hotel to any members who might be interested in following in his footsteps; the 14½" Dobsonian was potentially available to experienced observers on application to Rod Greening3, though some evidence would be required that users knew how to handle such an instrument. The speaker's observations had, out of preference, been entirely visual, but those wishing to bring their own photographic equipment would also be welcome.

The President thanked Dr Moore for his account, and then introduced the evening's final speaker, Dr Serena Viti of University College, London. Dr Viti's research interests included astrochemistry, the modelling of the clumpy nature of inter-stellar gas, and ultimately, the formation of stars from those clumps. Tonight, she would be talking about recent ground-breaking observations of low-mass stars.

Ashburn

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39.04°N
77.49°W
EDT

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