“Alcohol has taught me one truth”,

the drunkard said aloud.

A young man, standing on the edge of a cliff, about to end his life, and thus far absorbed in his own world, suddenly wanted to hear the drunkard complete the statement. But nothing happened for a minute. With impatience boiling inside him he shot the question directly to him instead,

“What truth?”

“Happiness is opaque.” The drunkard replied promptly.

“Really?” The young man mocked.

“It never allows the light of our congenital talents to express themselves.”

“Then what does?”

Half a minute went by in silence.

“The prism of adversity allows us to express our true colours. Only after going through it does our V-I-B-G-Y-O-R, the one reflecting our core, is visible to the whole world.”

The young man – as the drunkard’s words made a nest in his conscience – found himself standing with his back at the cliff…already.

Rayleigh Scattering

This is an excellent piece of a short story by a very well renowned Indian English novelist Mr. Novoneel Chakraborty that I came across during my post-graduation days. Thought, I had to share it with my students.
Though on a lighter note;

‘Rayleigh scattering of sunlight in the atmosphere causes diffuse sky radiation, which is the reason for the blue colour of the sky and the yellow tone of the sun itself’. When photons are scattered from an atom or molecule, most photons are elastically scattered (Rayleigh scattering), such that the scattered photons have the same energy (frequency and wavelength) as the incident photons. A small fraction of the scattered photons (approximately 1 in 10 million) are scattered by an excitation, with the scattered photons having a frequency different from, and usually lower than, that of the incident photons. In a gas, Raman scattering can occur with a change in energy of a molecule due to a transition to another (usually higher) energy level.

Rayleigh scattering, named after the British physicist Lord Rayleigh (John William Strutt), is the (dominantly) elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the radiation. Rayleigh scattering does not change the state of material, hence it is a parametric process. The particles may be individual atoms or molecules. It can occur when light travels through transparent solids and liquids but is most prominently seen in gases. Rayleigh scattering results from the electric polarizability of the particles. The oscillating electric field of a light wave acts on the charges within a particle, causing them to move at the same frequency. The particle, therefore, becomes a small radiating dipole whose radiation we see as scattered light.

Rayleigh scattering of sunlight in the atmosphere causes diffuse sky radiation, which is the reason for the blue colour of the sky and the yellow tone of the sun itself.

Rayleigh scattering of molecular nitrogen and oxygen in the atmosphere includes elastic scattering as well as the inelastic contribution from rotational Raman scattering in air; since the changes in wavenumber of the scattered photon are typically smaller than 50 cm−1. This can lead to changes in the rotational state of the molecules. Furthermore, the inelastic contribution has the same wavelengths dependency as the elastic part.

File:Why is the sky blue.jpg

a piece of blue glass, through which the light shines orange, seeming to behave like the sky at sunset. There is a long commentary on why the sky is blue. Image Source:

In addition, the oxygen in the Earth’s atmosphere absorbs wavelengths at the edge of the ultra-violet region of the spectrum. The resulting colour, which appears like a pale blue, actually is a mixture of all the scattered colours, mainly blue and green. Conversely, glancing toward the sun, the colours that were not scattered away — the longer wavelengths such as red and yellow light — are directly visible, giving the sun itself a slightly yellowish hue. Viewed from space, however, the sky is black and the sun is white. The reddening of sunlight is intensified when the sun is near the horizon because the volume of air through which sunlight must pass is significantly greater than when the sun is high in the sky. The Rayleigh scattering effect is thus increased, removing virtually all blue light from the direct path to the observer. The remaining unscattered light is mostly of a longer wavelength, and therefore, appears to be orange.

Diagram of Raman scattering:  Incident light (yellow) that loses or gains no energy is scattered back at the same wavelength is called Rayleigh scattering.  If some of the energy is transferred to the ground state, the scattered light is scattered at a longer wavelength (red).  Fluorescence is another effect that causes light to be re-emitted at longer wavelengths.  It often masks Raman scattering.

Diagram of Raman instrumentation: Incident laser light (yellow) is scattered at the light surface. Most of the light is scattered at the same wavelength as the incident light.The lightt that is Raman shifted also is scattered in random directions. A lens is used to collect the light, and a filter is used to block the wavelength of the incident light. Longer wavelengths (Raman scattering) is transmitted to the monochromator and detection system. The frequency shift of the scattered light will determine the chemical structure of the sample material.