Light speed is constant irrespective of framespeeds.then how red shift occur? what it appears to be for...?

Question

...two neutrinos (if they see!) travelling near light speeds one along the direction of light beam and other opposite light beam? we can identify objects which travels only less than lightspeed through experiments-so there is possibility for particles with more speed than light? no problem with mass as neutrinos have no mass!

Answer 1

Neutrinos have a mass, it's just extremely small.

Red shift occurs by the doppler effect.  Since light travels the same speed and all physics must remain the same in all frames, an observer moving away from you will have their light red shifted because the light will make the same number of oscillations reaching you.  Since the light "has further to travel"  the oscillations are spread further apart and have a larger wavelength making them read shifted.  However that may be an over simplified version as the true reason has more to do with time-dialation and length contraction between the two frames.