Observational astronomy holds a special place in science in that, except for a very few instances, all the knowledge and information has been collected simply by measuring the radiation which arrives from space. It is not like the other laboratory sciences where the experimentalist is able to vary and control the environment or the conditions of the material under investigation. The 'experiment' is going on out in space and the astronomer collects the information by pointing the telescope in a particular direction and then analysing the radiation which is collected.
In interpreting the accumulated data, the reasonable assumption is made that the same physical laws discovered in the laboratory can be applied to matter wherever it is assembled in space. Many of the astronomical measurements, in fact, provide us with means of observing material under a range of conditions which are unattainable in the laboratory. In order to understand these conditions, it is sometimes necessary to provide an extension to the laboratory laws or even consider invoking new laws to describe the observed phenomena.
Laboratory analysis is practised on meteorite samples which are picked up from the surface of the
Earth and on micrometeoritic material which is scooped up by rocket probes in the upper atmosphere. Some thirty years ago the Apollo and Lunakhod missions brought back our first samples of lunar material for laboratory study. Interplanetary space probes have sent and still are sending back new data from the experiments which they carry. They are able to transmit information about the planets that could not have been gained in any other way. Astronomers have also gleaned information about the planets by using radar beams. However, all these active experiments and observations are limited to the inner parts of the Solar System, to distances from the Earth which are extremely small in relation to distances between the stars.
When it comes to stellar work, the experiments, whether on board space vehicles or Earth satellites, or at the bottom of the Earth's atmosphere, are more passive. They involve the measurement and analysis of radiation which happens to come from a particular direction at a particular time. It is very true to say that practically the whole of the information and knowledge which has been built up of the outside Universe has been obtained in this way, by the patient analysis of the energy which arrives constantly from space.
As yet, the greater part of this knowledge has been built up by the observer using ground-based telescopes though in recent years a wide variety of artificial satellite-based telescopes such as the Hubble Space Telescope and Hipparcos have added greatly to our knowledge. The incoming radiation is measured in terms of its direction of arrival, its intensity, its polarization and their changes with time by appending analysing equipment to the radiation collector and recording the information by using suitable devices. The eye no longer plays a primary role here. If the radiation has passed through the Earth's atmosphere, the measurements are likely to have reduced quality, in that they are subject to distortions and may be more uncertain or exhibit an increase of noise. In most cases, however, these effects can be allowed for, or compensated for, at least to some degree.
The task of the observer might be summarized as being one where the aim is to collect data with maximum efficiency, over the widest spectral range, so that the greatest amount of information is collected accurately in the shortest possible time, all performed with the highest possible signal-to-noise ratio. Before the data can be assessed, allowances must be made for the effects of the radiation's passage through the Earth's atmosphere and corrections must be applied because of the particular position of the observer's site and the individual properties of the observing equipment.
It may be noted here also that with the advent of computers, more and more observational work is automated, taking the astronomer away from the 'hands-on' control of the telescope and the interface of the data collection. This certainly takes away some of the physical demands made of the observer who formally operated in the open air environment of the telescope dome sometimes in sub-zero temperatures. Accruing data can also be assessed in real time so providing instant estimates as to its quality and allowing informed decisions to be made as to how the measurements should proceed. In several regards, the application of computers to the overall observational schemes have made the data more objective—but some subtleties associated with operational subjectivity do remain, as every computer technologist knows.
We cannot end this chapter without mentioning the role of the theoretical astronomers. Part of their tasks is to take the data gathered by the observers and use them to enlarge and clarify our picture of the Universe. Their deductions may lead to new observational programmes which will then support their theories or cast doubt upon their validity.
It goes without saying that an astronomer may be both theoretician and observer, though many workers tend to specialize in one field or the other. Again, it has been estimated that for each hour of data collecting, many hours are spent reducing the observations, gleaning the last iota of information from them and pondering their relevance in our efforts to understand the Universe. The development of astronomical theories often involves long and complicated mathematics, in areas such as celestial mechanics (the theory of orbits), stellar atmospheres and interiors and cosmology. Happily in recent years, the use of the ubiquitous computer has aided tremendously the theoretician working in these fields.
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