Styles of light 

The study of 'Light' as energy opened new vistas for human thought. The famous scientist who has shown with child's sense of wonder has shown the light as energy was Sir Isaac Newton. God said 'Let there be Light'. There was no light! Instead, there was Newton and then it was all Light.
Light Reflects: A ray of light incident on a polished surface like a mirror comes back into the same medium. We see our images in mirrors because of this style & exhibited by light called 'Reflection'.
Light bends: A tall man with long legs, when stands in a lake finds his legs have been shortened (an illusion). Place a coin at the bottom of a beaker and pour water in the beaker and look into it; The coin appears to be raised along with the bottom of the beaker (again illusion). These illusions are due to another style exhibited by light called 'refraction'. Which is due to the light rays travelling from one transparent medium to the other bend.

* Refraction of light requires minimum two transparent media.
* A light ray travelling from rarer medium (of lesser refractive index) to a denser medium (of greater refractive index) bends towards the normal.
* A light ray travelling from denser to rarer medium bends away from the normal.
When light 'misbehaves'....
   A refracting light ray suddenly reflects totally after overcoming critical condition which results in the form of illusions like 'mirages' and 'loomings'.
  A light ray OA from an object O (figure) in water incident normally travels without bending into air. A light ray OB incident at an angle i, bends away from the normal, when it enters into air with an angle of refraction r; Now as angle of incidence increases, angle of refraction also increase. For a particular angle of incidence C, the refracted ray grazes the surface of separation such that the angle of refraction is 90º.

       Now, the angle of incidence C is called 'Critical angle.' Critical because, now we cannot say whether the refracted ray belongs to denser (water) medium or rarer (air) medium. This ray is some what like a cat on a wall or patient in critical condition. At critical state, the refractive index of water with respect to air is     according to Snell's Law.
     (Greater the refractive index, lesser will be the critical angle)
     Now, if the angle of incidence is greater than the critical angle (even by few seconds), the refracted ray (earlier) reflects into the denser medium (water) as if the surface of separation is a perfect mirror. This phenomenon is called 'Total Internal Reflection' (TIR).
Optical fibre - a light pipe
     An optical fibre is a flexible transparent fibre device used for either image or information transmission in which light is propagated by Total Internal Reflection.
Newton and Prism
    On a fateful day, when Isaac Newton passed the Sun's rays (white light) through that wonder device called 'glass prism' (which was used as a paper weight in those days) the light ray was split into seven of its constituent colours (exhibited its another style) seen in the rainbow (VIBGYOR) the brilliant and beautiful colours of the rainbow formed in the blue SKY (SKY is blue due to scattering of light) is explained by the simple experiment with prism on earth. (Earlier Newton explained the motion of celestial bodies in heaven by observing the fell of apple on the earth.

Dispersion - Spectrum
     The white light when passed through a glass prism splits into seven of its constituent colours is called 'Dispersion' and the coloured pattern is called 'Spectrum'. The instrument which produces and measures the spectrum is called 'Spectrometer.' When different substances are heated to their incandescence and the light emitted is passed through the prism of the Spectrometer, each substance will give its characteristic spectrum.
Spectra - the 'finger prints' of matter
     Millions of human beings are born every second on earth. But, one characteristic that will not replicate even in case of 'twins' is 'finger prints.' Similarly, every substance in the Universe will have its characteristic spectrum.

Fraun hofer lines
      These are the dark lines observed in Sun's absorption spectrum. From these lines elements like H₂, O₂, Na etc and Helium in abundance was found in the Sun's atmosphere, the light gas which has already escaped earth's atmosphere (Gravity).
Present and Future of Stars
      Spectral analysis is used to study the chemical composition, state of motion and temperature of the planets, Sun and other stars. Days have gone when stars predict the fates and future of a human being. Instead, man is revealing the present and future (Jatakam) of stars.