Technology: Cut-price telescope takes a clear view of the northern sky

时间:2019-03-04 10:15:08166网络整理admin

By NIGEL HENBEST SCANDINAVIAN astronomers have opened an ‘intelligent’ telescope in the Canary Islands that automatically adjusts itself to produce the sharpest possible images of the sky. And they have done it at little more than half the cost of a conventional telescope of the same size. The Nordic Optical Telescope is the result of a collaboration between Denmark, Finland, Norway and Sweden. Until now, astronomers in these countries have been able to use some telescopes in the southern hemisphere, but their only instruments to look at the northern sky were in Scandinavia. There, they experience problems with the weather and with turbulence in the atmosphere, which blurs the images of stars and other astronomical objects. In 1981, the Scandinavian astronomers decided to take advantage of the much better conditions on the Spanish island of La Palma, at an observatory site already opened up by British and Spanish astronomers. With a budget of only Pounds sterling 4.5 million, the astronomers could not design a large telescope. Instead, they chose a medium-sized instrument, designed to produce the sharpest possible images. The Nordic Optical Telescope has a mirror 2.56 metres in diameter, making it the twentieth largest in the world. It can gather only 25 per cent as much light as the largest instruments, such as the neighbouring William Herschel Telescope on La Palma. A small team designed the telescope to weigh as little as possible, but sufficiently rigid to ensure it does not shake and blur the images of the sky. This makes it economical to build and operate. The telescope’s mirror also has an extremely short focal length, only twice its diameter. As a result, the telescope is only half the length of a more conventional instrument. The designers came up with a protective dome that was very small, fitting snugly around the short telescope. They tested the system in wind tunnels to ensure that the wind blowing around and into the dome would not stir up the air and so distort the incoming starlight. They also analysed the way that heat from the ground disturbed the air, and decided to put the telescope 8 metres above the ground. A computer constantly checks the positions and alignments of the main and a second mirror, to ensure the sharpest images. Paul Murdin, who was in charge of the British telescopes on La Palma for several years, acknowledges the team’s achievement but also points out they have had to pay some penalties. In particular, light can come to only one focus, behind the main mirror. With most large telescopes, astronomers can also examine the light at the focal point of the main mirror, at the top of the tube, or with the use of extra mirrors at other positions. The director of the new telescope, Arne Ardeberg, of the Lund Observatory in Sweden, says that the sharp images will provide clearer views of distant galaxies, so telling us how galaxies change as they grow older. The sharpness of the images will also help astronomers to see planets going around other stars. The telescope is designed to make accurate measurements of the polarisation of light from stars, nebulae and quasars,