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Different ways to perceive the Universe

The figure shows three drawings that seem to represent three completely different celestial bodies. In actual fact, it is the galaxy NGC 300 seen with instruments that are capable of perceiving the different types of electromagnetic radiation, that is with different wavelengths. Why does the Galaxy appear so different to each of the three instruments?

To answer this question we must continue from where we left off on the previous page: we said that electromagnetic waves have very different wavelengths; the human eye cannot perceive all the waves only those where the wave length falls within a small interval: these waves make up what we call visible light. The other electromagnetic waves, with wavelengths that are either below or above that interval, are not perceivable and make up a sort of invisible light. Radio waves, x-rays and infra red light are all examples of this invisible light, that man cannot perceive without the use of appropriate instruments. With respect to all the existing wavelengths the interval of visible light is extremely short.

Let’s reconsider the three drawings: the objects within the galaxy that produce energy, emit radiation to the various wavelengths at varying intensities, according to the physical phenomena that produce the emission. The first drawing on the left represents the galaxy NGC300 as it is seen by the human eye. The eye is a receiver capable of only perceiving objects with wavelengths within the interval of visible light. The second drawing represents the galaxy as it is seen by an instrument capable of perceiving infra red light. The third drawing represents how it appears when an instrument capable of revealing only x-rays is used: in this case the galaxy appears as a whole lot of bubbles, in which each bubble corresponds to an area or an object that emits x-rays intensely.

Therefore, the Universe can be observed in quite different ways: it all depends upon the receivers used, their degree of sensitivity in perceiving the various wavelengths of the electromagnetic waves, and on the intensity of the light, emitted by the object at those wavelengths, that is then received by the instruments.

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