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Sci Tech
Why an infra-red telescope?
The universe is expanding and all the stars, planets and galaxies are moving away from each other. A good analogy is a balloon that is being inflated. Because of this expansion the wavelengths of electromagnetic radiation from distant stars and galaxies are getting stretched as the radiation approaches Earth. This is known as the Doppler Effect.
The wavelengths shift from the short ultraviolet to the longer near-infrared, mid-infrared and in the case of extremely far away galaxies, to the far infra-red. To understand this, consider the following analogy: Imagine a person at the receiving end of a long conveyor belt.
Some way further up the conveyor belt is another person who places packets at equal time intervals so that the packets are conveyed to the receiver at equal time intervals by the belt moving at a uniform speed. Now, if the person sending the packets starts moving away, increasing the distance between himself and the receiver, but still continues to place the packets on the conveyor belt at the same time intervals, the time interval between successive packets received starts increasing or ‘stretching’.
This is analogous to wavelengths of electromagnetic radiation being stretched as they approach Earth from galaxies which are moving away. The packets in the analogy could be likened to the crests of an electromagnetic waveform. As the universe expands, the sources of radiation move further and further away. This results in greater intervals or stretching of the wavelength as measured by the distance between crests.
This stretching moves the wavelength into the infrared (long) region of the electromagnetic spectrum; it is called ‘red shift.’ Hence an infra-red optimised telescope is required to study far away galaxies. — K.S.R.
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