Ordinary Meeting, 2003 November 29
Deep Sky Observation from Australia, July 2002
The speaker subtitled his talk Confessions of an Astronomical Twitcher, which he explained was a reference to the habit of travelling considerable distance, often with expensive equipment, to view elusive objects. In this instance, the habit had impelled Mr Johnston to relive the excitement of his youth in undertaking an off-road Landrover tour of Australia. It was explained that there were many attractions to this particular location: the southern sky could be viewed at reasonable altitude and comparatively cheaply, and without braving such inhospitable conditions as the Antarctic offered.
Mr Johnston's tour had started in Sydney, and whilst skyscrapers prohibited much practical observation here, there was at least one treat for the astronomer: the Sydney Observatory, which was home to a 19th century time-ball tower. Moving north, the forests of northern Queensland were also not good observing sites, but the tops of dividing mountain ranges provided clear open skies, and the speaker soon set about putting his Meade ETX to use. Driving conditions proved rather tricky in places, and the speaker illustrated a few of those feats of which he was most proud.
From a practical point-of-view, the speaker recommended to any future travellers that the southern sky should be learnt before setting out, as he had found it particularly difficult to navigate, with a vast array of very faint stars washed out by the dark skies. Mr Johnston had found a 35° south planisphere particularly invaluable in this respect. His targets were primarily open and globular clusters, as an ETX was not ideally suited to galaxy observation. Where possible, a description was written of each object, a magnitude estimated, and a Shapley classification assigned (1 = point-like, 12 = very loose). The results are recorded in table 1. The speaker commented that his classifications deviated quite considerably from some of the textbook values, but felt that writing such descriptions had been a highly educational experience.
Mr Johnston continued his observation programme from around Darwin, in the Northern Territory. Here, the seeing conditions are renown for being invariably excellent, and the speaker's visit passed without a cloud in sight. Of those objects he observed, the speaker gave special mention to 47 Tuc (NGC 104), the second brightest globular cluster in the sky, and Ω-Centauri (NGC 5139), the largest globular cluster in the Milky Way, and the sight of which had for him made the trip seem worthwhile in itself. With Sagittarius virtually overhead, the Lagoon Nebula (M8) was an easy binocular object. However, the real treats of the southern sky were the Megellanic Clouds, and the Galactic Centre in Sagittarius. Also worthy of mention was the naked-eye dark coal-sack nebula, obscuring a region of the Milky Way just south of Crux. The speaker closed his account with an image of the Moon, vertically flipped from its familiar northern hemisphere orientation, and a long-exposure star-trail image of the southern celestial pole.
Following the applause for Mr Johnston's lively account, the President thanked him, before adjourning the afternoon's proceedings until the Christmas Meeting, to be held at the same location on January 10.