Funding for Telescope

Press, 28 January 1988, Page 40

Funding for Telescope

On December 8, the Council of the European Southern Observatory (E. 5.0. authorised the funding of the Very Large telescope (V.L.T.). This, with an aperture of 16 metres, will be the world’s largest optical telescope. E.S.O. was formed 25 years ago with the aim of providing European astronomers with the most modern observational facilities at the best possible site. E.S.O. now comprises eight European member states with headquarters at Garching, West Germany. Its extensive collection of telescopes are at La Silla in Chile. It was obvious when E.S.O. was first formed that Europe did not have a suitable site for large telescopes, because of its climatic conditions and pollution. At the same time southern skies were then largely, unexplored with large instruments, yet they offered the opportunity of studying many unique and important objects inaccessible to northern telescopes. A southern site would also provide the opportunity of examining the centre of the galaxy in greater detail since this would pass directly overhead. An extensive site survey was undertaken with the result that it was found that Chile offered suitable sites that had the maximum freedom from clouds and good steady seeing conditions. That was why E.S.O. established its main observational complex in that

country. The first generation of large telescopes came into operation in the 19705. The discoveries made with these caused astronomers to think how much more could be accomplished with even larger instruments. Designs for larger instruments were drawn up in Europe, the U.S.A, and U.S.S.R. They were required to provide greater light grasp and better resolution. This would enable objects to be studied in greater detail and, at the same time, bring within range even more distant galaxies. It was realised at E.S.O. that any large telescope must be located at the best possible site. Several years ago they began the search for a site that, if possible, would be even superior to La Silla and the other major observatories in Chile. This has resulted in finding that other sites in northern Chile will provide such conditions. Ten years ago a start was made on considering the most suitable design for a large instrument. Numerous options were considered for the V.L.T. These finally came under two broad designs. One visualised a large mirror, built in segments. The other suggested that an array of smaller apertures would be best, so arranged that they could bring any object to the same focus. In the meantime interferometric methods had been developed. Finally

E.S.O. decided that an aperture of 16 metres would be suitable, provided by an array of four four-metre telescopes. This could be operated in the conventional manner or used as an interfere meter for which purpose two additional movable telescopes of two metre aperture were included in the array. The advantage of use in the interferometer mode is that it becomes possible to measure very small objects such as the cores of galaxies and quasars. It also becomes possible to examine in much greater detail objects such as prototype stars (those in the process of formation) and to better understanding how close binary systems exchange mass between the components. Normally any large telescope is housed in a very large and costly building which is supported by a huge dome. A completely new technique for covering telescopes was seen in the inflated radomes widely used to cover antennas. The domes will consist of a double-wall fabric hemisphere, supported by rigid hoops that open and close in two symmetrical parts. Each side of the double-wall cover is made of seven lenticular ribs, which are inflated over the dome when closed. The interior is pressurized so that the cover is stiff. This pressure can be automatically increased by over-pressure in strong winds. A prototype dome, 15

metres in diameter, has already been tested in Holland. This is about half the size of the final dome. This month it is being erected at La Silla on a specially prepared base. There it will undergo additional testing and be used in experimental setups during the development of the V.L.T. An advantage of an inflatable dome is that, during fine spells, it can be completely collapsed, leaving the telescope in the open air. E.S.O. is already in the forefront of astronomical research. The addition of the V.L.T. will enable their astronomers to maintain this position for many years. Throughout February Venus will be a brilliant object in the western evening sky during twilight. It will be setting about two hours after the sun. Jupiter, in Pisces, will also be prominent in the north-western evening sky. It will set around midnight on February 1, and 10 p.m. on February 29. This month Mars moves from Ophiuchus into Sagittarius, where it joins Saturn. The two planets will be very close together on the morning of February 24. Saturn with a magnitude of 0.6 will be the brighter of the two planets. However, as they do not rise till well after midnight they will be of little interest except to early risers.

The supernova in the Large Magellanic Cloud, SN 1987 A, continues to be the main soure of astronomical research. It has now faded steadily to reach magnitude 7.0 at the time of writing. Instruments on the Soviet Mir station and on the Japanese Ginga satellite have recorded hard X-rays from this source. It is unclear as to whether this emission came from the expanding shell or from a neutron star at the core of the exploding star. It is suggested that Cobalt-56 has been the main energy source during the recent fading phase. The rate of fading gives a decay time of between 106 and 115 days, which is very close to the mean life of Cobalt-56. Spectral observations of SN 1987 A have yielded some unexpected results. Such observations have sampled the interstelar at medium over a light path of about 165,000 light years. Along this path lie clouds of gas in the disc and halo of the Galaxy as well as in the Large Magellanic Cloud. These clouds appear to be non-turbulent and cold with a temperature below 170 degrees Kelvin. One cloud is thought to be in the galactic halo about 15,000 light years below the plane of the Galaxy. These observations, if confirmed, appear to disagree with present theories of the galaxy and may prove to be an interesting by-product of investigations of SN 1987 A.