Saturday, 20 July 2013

Nature of Light

Light is a form of electromagnetic radiations. They also contain particles called photons which carry energy. Photons are mass-less energy carriers. This modern model of Light is called quantum model of light.

This model represents light. The spring is a wave and the object at the center  is photon.

Light Spectrum

Visible light (or white light) can be split up into constituents of different wavelengths giving a band of colors called spectrum. A star's spectrum usually contains dark lines called absorption lines, caused by photons being absorbed at certain wavelengths by atoms in the star's atmosphere. These effects can be used to determine the chemical elements present in the star's atmosphere. It must be noted that every element absorb light of certain wavelength and release the rest. Since each element have different spectrum forming capacity, it is used as finger print of an element. Thus it is easier to analyze new elements when discovered. This phenomenon also explains different color detection capability of eyes. A stone looks red because the elements present in them absorb all lights except for red which enters our eye.

 Red Shift and Blue Shift

The spectrum of radiation received by an observer shifts if the source of the radiation is moving is moving relative to the observer - and celestial objects are always moving. Astronomers can detect the shift by measuring the position of spectral lines, which occur at characteristics places. Observers watching an object moving away see its spectral lines shifted toward longer wavelengths (area shift). For an approaching object, the lines are shifted to the shorter wavelengths (a blue shift).The grater the relative velocity between the source and observer the greater the shifts. Distant galaxies show large red shifts, indicating they are receding at enormous speeds; these are called cosmological red shifts.


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