Measurement of The Universe (A Survey of the universe)
In everyday life, when we cannot directly pace off a distance we confidently go beyond the metre stick and employ the tried and true methods of geometry and trigonometry. These become our new tools. But the way in which we use these tools is governed By completely different,”more subtle principle our belief in the.Uniformity of nature. This belief allows us to draw parallels between the properties of objects near and far. In the context of the scale of the Universe we call this underlying principle, ‘distance by analogy
Our methods are not foolproof and as such we must be prepare for a range of errors of many types. The methods and mathematics of surveying are well defined and can be modified to accommodate the measuring of a field, a city, a planet or distances to the stars. The methods of trigonometry are not concerned with the objects they measure, and the random errors we make in applying these methods of surveying depend strictly on how well we do our work. In astronomy this usually amounts to how accurately we can measure small angles. Analogy, on the other hand requires a new step, in fact, a leap. In it we assume that some critical quality (height or brightness, for example) of a distant object is the same as some nearby object. The nearby object is familiar to us and we have measured its properties directly. Subsequently, using these assumed properties, we can employ the principles of geometry to calculate an appropriate distance.
Our calculations may be well done, but if our assumptions are wrong, our answers will be systematically in error. While random errors in measurement quickly reach overwhelming proportions in frontier astronomy, where the limits of every experiment are pushed to their furthest, their effects are predictable However, systematic errors in our assumptions loom, unknown, at every turn. Astronomers must make many assumptions and draw many analogies about objects far outside our normal experience. To appreciate the consequences of this necessary fact is to understand a frailty of every model of the Universe.