Important observations by Skylab astronauts

Press, Volume CXIII, Issue 33189, 31 March 1973, Page 19

Important observations by Skylab astronauts

On April 30 a Saturn 5 rocket is due to lift off. from the Kennedy Space Centre, with the Skylab space station. The rocket and unmanned pay load will stand 102 metres high and weigh 3160 metric tons.

The following day three astronauts are due to blast off for a rendezvous with Skylab. in which they will live and work for 28 days. After spending tour weeks in the space station the astronauts will return to Earth Some two months later a second team will be aent up to remain in space for 56 days, and a few weeks after their return a third team will man the space station. This will cover the useful life of the station, which is - expected to be eight months. Many well-designed astronomical projects will be carried out by the astronauts. including solar and planetary observations and special researches in the ultra-violet , and x-ray regions of the spectrum. The instruments have been designed primarily for detailed observations of the Sun. Other astronomical observations will be made since only 100 hours ha/e been scheduled during the first mission for solar observations. Dwarf noval One of the experiments will be concerned with observations of dwarf novae in the ultra-violet portion of the spectrum. This class of stars, numbering just over 200, was referred to in last month’s notes. It so happens that 'he only member of this class that is both bright enough and within the area of observation from Skylab is a far southern star, VW Hydri'. This star usually fluctuates rapidly in a period of 108 minutes around fourteenth

magnitude. At the same time it has oscillations every 25.15 seconds. Superimposed on these small variations are sudden increases in brightness amounting to between three and six magnitudes. The increase to a maximum usually occurs in 24 hours, after which the star fades almost as quickly back to minimum. Such outbursts occur at irregular intervals, which range from four to til days The average interval between successive maxima is 28 days. However, in anv interval of 1000 days, there are the same number of outbursts as in any other interval of the same length. VW Hydri tends to-have a maximum every 179 days, which is not only brighter than other outbursts but lasts longer. The star remains bright for from 10 to 15 days compared to the normal one or two days. These prolonged outbursts are termed “supermaxima” and occur at more regular intervals than the erractic minor outbursts. These facts have been derived from over 50,000 visual observations made by the widely scattered members of the variable star section of the Royal Astronomical Society of New Zealand. There is a .vast difference between the humble part-time astronomer, observing from his backyard, and the advanced technical equipment used in an artificial satellite, such as Sky Lab. Yet the results of the former are proving of the utmost importance to the latter. Predictions The headquarters of the variable star section has supplied the Skylab project with predictions of the dates on

.which VW Hydri is likely toi I have supermaxima. To provide the necessary optical, (observations essential . for] use with the ultra-violet observations from Skylab, the (ground based network of (observers will undertake (intensive monitoring of VW Hydri during late May and early June. Another series of satellites, i the 0.5.0. or Orbiting Solar {Observatories, have since {November, 1971, observed VW Hydri with X-ray detectors. The investigators called ion the New Zealand variable (Star headquarters to provide a complete light curve of the behaviour of VW Hydri . during the last 16 months. , These data were essential

I for a complete understand jing of the observations fron i space and could be obtainei (from no other source. The Orbiting Solar Obser vatories have already pro vided a wealth of new infor I mation on the Sun. The: have shown that tempera tures as high as 30m degree are associated with sola flares. From their result i much has been learnt abou the nuclear reactions prob ably taking place in th accelerated plasma of somi ; flares. Skylab observation will undoubtedly extend thi knowledge and provide ; better understanding of sola phenomena extending ou into the solar corona to a distance of six solar radii.