Is it Day or Night?

Why sky appears blue even in night? What are those two stars above that water tank?   Irrespective of day or night, our atmosphere scatters blue colour. This was found by Sir. Chandrasekhara Venkata Raman, FRS or Sir. C.V. Raman! He was the recipient of the Nobel Prize for Physics in 1930 for the discovery that when light traverses a transparent material, some of the light that is deflected changes in wavelength. This phenomenon is now called Raman scattering and is the result of the Raman effect.  Raman scattering or the Raman effect is the inelastic scattering of a photon. It was discovered by C. V. Raman and K. S. Krishnan in liquids, and by G. Landsberg and L. I. Mandelstam in crystals. The effect had been predicted theoretically by A. Smekal in 1923.  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. However, 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 . Chemists are concerned primarily with such transitional Raman

 effect.  Those two stars are: binary star system Alpha Centauri AB / Rigil Kent ( 4.39 light years from sun) and Hader / Beta Centauri 525.21 Ly away) to its right is Southern Cross or Crux . above is Libra and to left is Scorpios and Lupus constellations.  If we draw a cross line from between these two stars and draw a line from Acrux or Alpha 1 Crux, both will point to south pole point! There is no specific star pointer for Earth's Southern pole as in North pole where we have Polaris!

Image Settings: F2.8, ISO 100. 30 sec exposure. Taken in 2013.  Camera: Fujifilm Hybrid DSLR.