Jethalal S. Zaveri
Prof. Muni Mahendra Kumar
Colour, one of the four inherent qualities of matter has been a boon to inquisitive mankind in general and scientists in particular. More than that, it has been the cause of many spectacular advances in some of the sciences (and even arts). Astronomers in their quest of knowledge of the universe are able to probe and pry into the macrocosmos and see millions of distant stars and galaxies, which are thousands of millions light years away. With the growth of knowledge from their insights, astronomy developed a whole new kind of study called Astrophysics. The science of spectroscopy became an indispensable branch of astronomy. On its findings are based all the modern theories about the universe.
| [1] The prism is now replaced by a more efficient light splitting instrument viz. diffraction gratings of lines closely ruled on glass. |
The secrets of the universe are written largely in code language of light and can be known by deciphering light itself. Everybody knows that white sunlight bent apart by a prism [1] becomes a rainbow of all the colours. This is called a spectrum. It was found many years ago that the sun's spectrum was not a perfect rainbow but slashed by many dark lines, but nobody knew what they meant at that time. Later studies showed that light emitted by elements at very high temperatures showed bright slashes in their spectrum. Today the knowledge of atomic theory and the true nature of light has established that each element or kind of atom can emit and absorb energy only at the specific wave-length determined by its atomic structure. Its pattern may have many lines or a few but its position on the spectrum is always the same and unlike that of any other. Thus every element can reveal its identity by its spectral line signature written by the ink of its own unique colour or the fingerprint of its individual personality.
The discovery of Helium, christened as the sun element by its discoverer, Sir Joseph Norman Lockyer, more than a hundred years ago, was the result of the accurate interpretation of the sun's spectral lines with elements in its atmosphere. Indeed, the white radiance of the cosmos shattered into its component colours can reveal the identity of atoms pulsating thousands of millions of miles away. Over the years, the spectral lines from a star proved to hold amazing quantities of information: the composition of the star, the speed of the star moving towards or away from us, the speed of its rotation, temperature of its surface, the strength of its magnetic field, etc. Stars are no longer pin-points of inscrutable light but objects with individual personalities.
All this is possible because colour is an inherent quality of matter. Stars emit coloured light and each star can be pictured as a colourful spectrum, which is its fingerprint. Its composition is found by identifying the patterns of lines that its chemical elements cast across its spectrum. The speed of a star moving towards or away from us is indicated by the so-called 'Doppler effect’ or shift of its spectral lines. The shift is towards the blue (or left) end of the spectrum if the star is advancing, towards the red (or right) if receding. The greater the star's speed, the more its lines shift. The amount of shift is calculated by comparing the lines with those of a laboratory specimen
