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FeatureWatching the SkiesTake a tour through New Zealand's major research observatory. Lyndon Watson Sharp-eyed travellers passing through the Lake Tekapo village on their way between Christchurch and Mt Cook or Queenstown might notice a scattering of white roofs on the hill which rises 100 metres behind the village. The hill is Mt John, and the roofs belong to the Mt John University Observatory, the premier site for astronomical research in New Zealand. The observatory is not staffed and equipped, except on special occasions, to entertain the visiting public, but we know what a visitor who drives or climbs up the steep, winding access road would find. Passing the resident superintendent's house on the north side of the hill, the visitor would come to the top of the hill and a cluster of buildings housing the observatory's two 61-cm telescopes, two different sky-mapping cameras, and the observatory's office and maintenance workshop. Beyond the buildings, the sky-mapping cameras of the Harvard Sky Survey sit out in the open, protected by covers which make them look like anti-submarine mortars mysteriously transported from the deck of a frigate to the tussocky hill. Over the top and down a little to the southern side of the hill, the last building is the former US satellite-tracking station which now houses the observatory's one-metre telescope and the well-equipped observers' living quarters and library, as well as some atmospheric research instruments. The building overlooks Tekapo village, and visiting astronomers are always impressed by the beautiful views of the highest part of the Southern Alps and the lake with the homesteads of high-country sheep stations spaced around its shore. The observatory was founded in 1965 as a collaboration between the University of Canterbury and the University of Pennsylvania. The University of Florida was later involved as well, but nowadays the observatory is run by Canterbury University alone. The site in the dry Mackenzie Basin provides many nights of clear sky, especially in the autumn and winter months, but its major attraction for professional astronomers is that it is the most southerly fully-equipped research observatory in the world. Many of the most interesting objects in the sky are near the celestial south pole, and the Mt John observatory is uniquely well-placed to observe them. Astronomical AnalysisThese days astronomers don't use their naked eyes for anything other than aiming their telescopes -- and even that's usually done by video screen now. Instead, they use instruments to do various kinds of analysis of starlight. There are three fundamental kinds of analysis and they are all performed at Mt John. Photometry and spectroscopy together give astrophysicists all the information that they have about the structure, composition, and evolution of stars. The Mt John observatory is equipped with high-quality instruments for a wide range of astrophysical research, including:
All of those instruments except the single-channel photometers, were built in Canterbury University workshops. In addition, visiting astronomers from other universities and observatories bring their own instruments suited to their particular research projects. The TelescopesAll of the observatory's telescopes are Cassegrain reflectors. Light from a star is captured by a large, concave mirror (the "primary" mirror) at the base of the telescope and reflected back up to a small mirror (the "secondary" mirror) at the top. The primary mirror has a hole in its centre and the secondary mirror reflects the starlight back through the hole to a focus beyond the primary mirror where it can be captured by a camera or one of the observatory's instruments mounted on the base of the telescope. There are, at present, two 61-cm (24-inch) telescopes and the 1-metre McLellan telescope. The viewing conditions at Mt John would be good enough for a telescope in the 2-metre or 2.5-metre class, but present funding does not run that far. The installation of a larger telescope ought, however, to be on the long-term agenda when economic considerations are more favourable. The first of the present telescopes was imported from the US in 1970. It is a 61-cm (24-inch) Optical Craftsmen reflecting telescope. In its original form, the telescope was not rigid enough for professional work, and the University of Canterbury has completely rebuilt it, replacing everything except the mirrors, which are optically excellent, and installing a computer-controlled driving system. The "OC", as it is called at the observatory, is now in constant use for photometry. The other 61-cm telescope is a Boller & Chivens instrument which was installed at the observatory in 1975 and is still in its original form. When the US satellite-tracking station closed in 1983, Canterbury University seized the opportunity and acquired the building for use as accommodation and to house a new, larger telescope. The McLellan telescope, named after the then permanent head of the Physics and Astronomy Department, was entirely built in the workshops of the department using lessons learnt from the rebuilding of the OC telescope. With its open truss construction, the McLellan looks like a giant relative of the OC. The mechanical and electronic parts of the telescope were entirely made in the department; the 1-metre diameter primary mirror and two secondary mirrors (for wide and narrow angles of view) were made by the DSIR in Lower Hutt. The electric drive system has a built-in computer which calculates celestial coordinates and keeps the telescope pointed at the target star as the stars move around the sky, and an auxiliary computer rotates the dome so that the shutter opening is always aligned with the telescope and provides automatic setting of the telescope onto coordinates given to it by the astronomer. It is not possible to look through the McLellan telescope, and observers work in an adjoining data room, setting and guiding the telescope using video screens and remote controls, and controlling the instruments using computers. The instruments which use the CCD chip -- the photometer module and the chelle spectrograph -- as well as the LUCIFERS spectrometer and instruments belonging to visiting astronomers, are used with the McLellan telescope. For some kinds of research, where some sensitivity must be sacrificed for the sake of greater precision, the chelle spectrograph is dismounted from the telescope and housed in a thermally-stabilised cabinet with the light being fed to it from the telescope by an optical fibre. The UsersSince Mt John is a university observatory, its primary users are the academic staff and research students of the University of Canterbury. The three astrophysicists at Canterbury, Dr John Hearnshaw, Dr Peter Cottrell and Dr William Tobin, all have their own research projects, sometimes more than one at a time, and they all supervise MSc and PhD students who use the observatory. The astrophysicist at Victoria University in Wellington, Dr Denis Sullivan, and his research students are also given time at the observatory on an equal basis. Another frequent user is Dr Richard Dodd of the Carter National Observatory. Photometric and radial-velocity work often requires repeated observations of the same stars -- even every night or more than once per night. Such "service" observations are carried out at Mt John by resident observers, even when the academic staff and students are back in Christchurch. Mike Clark as resident superintendent of the observatory lives on the site and assists with observations as well as being responsible for the running of the observatory. Alan Gilmore and Pam Kilmartin live in Tekapo village and spend every suitable night collecting astrometric and photometric data, both for their own research and for the staff and students in Christchurch. International astronomy is highly collaborative and astronomers travel all over the world to use the observatories which are best suited to their research projects. Staff and PhD students from Canterbury University are sent when necessary to work in observatories overseas, and foreign astronomers come to Mt John to take advantage of its position and the high quality of its telescopes and instruments. In the early days at Mt John, students were sent from the collaborating universities in the US and, more recently, a student from Argentina has been using the Mt John facilities to gather data for his research. An astronomer from France has been a recent regular winter visitor to observe planetary nebulae in the southern sky, and the southerly position of Jupiter in the sky brought astronomers from overseas to observe the impact of Comet Shoemaker-Levy last year. Not many universities around the world have astronomical observing facilities to rival those of Canterbury, and very few can give their astronomy research students so much time on high-quality instruments. The Mt John observatory constitutes one of the relatively few contributions that New Zealand makes to fundamental scientific research. Astronomy is an advancing science, and a working observatory must constantly keep up with advances in instrument design and techniques: it is to be hoped that future policy and funding will allow Mt John to keep its place in international astronomy, if not advance it. Lyndon Watson is a PhD student in the University of Canterbury's Department of Physics and Astronomy, researching active chromosphere stars at Mt John. |
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