ASTROPHYSICS · bit about physics

Age of universe


Age of universe

cosmology is the science of universe and large scale structure of begin in studies extensively by the begining of the 20th centuary by Albert einstien.

the general theory of relativity which had sufficient ideology to construct mathematical models of the universe.

and it given strong base by Edwin hubble’s own measurements of hus constant.

The age ofuniverse is approximatly about 13 billion years.

it was in  the midst of  this chaos that the hubble space telescope was launched 1990.the hubble’s space telescope was on the high side implying a rather young universe,also depending on what theoretical mode is accepted.Scientists say the universe could be just 8 billion years old if the hubble constant is precisely 80.

modern physics · theoretical physics


Physical optics is a branch of optics which deals with nature of light, mechanism of its production, emission and propagation through space. It deals with the phenomenon of Interference, Diffraction and Polarization of light. From the experimental observations, it is evident that light is form of energy.

There are two methods of transfer of energy.

(i) by stream of particle movement

(ii) by means of wave motion Based on these modes of transfer of energy

(i) Corpuscular theory was proposed by Newton

(ii) Wave theory was proposed by Huygen,

(iii) Electromagnetic theory was proposed by Maxwell and

(iv) Quantum theory was proposed by Max planck

Physics – Newton’s corpuscular theory of light – Science

I Newton Corpuscular Theory (1675):

  • The Corpuscular theory of light was proposed by Newton in 1675. According
  • to him, light being a form of energy can be transported in the form of particles called
  • Corpuscles which are shot by a luminous object giving out light.
  1. Luminous body continuously emit tiny, spherical, small, massless, elastic particles
  • and he called them corpuscles, in all directions, with a high speed.(Object whether matchstick
  • or burning sun).
  1. These corpuscles travel in straight lines.
  • III. They readily pass through interspaces of matter.
  1. Different colours of light rectilinear propagation, reflection of light. But failed to
  • explain interference, diffraction, polarization, colours of thin films etc.

II Huygen’s Wave Theory:

  • According to this theory, light is a form of energy which advances in the form
  • of wave motion. The source of light is a sort of disturbance.(Consisting of simple Harmonic
  • disturbance like sound). Huygen assumed that light waves are longitudinal in nature. Now
  • just as sound needs a material medium for its propagation, light was also given a medium
  • through which it travels. This medium was called “ETHER”. Since light travels in vacuum,
  • ether was supposed to fill all space including vacuum. This ether was supposed to be
  • massless, colourless, invisible medium having high elasticity and practically no density.
  • This theory could explain reflection, refraction, total internal reflection, double
  • refraction etc. But failed to explain diffraction, polarization etc. Also, experimentally proved
  • the non-existence of ether.

III. Electro-magnetic Theory:

  • Maxwell proved that light gets propagated in the form of electromagnetic
  • waves. It consists of electric and magnetic fields which are at right angles to each other and
  • transverse to the direction of propagation of light. The alternately expanding and collapsing
  • 2
  • magnetic and electric fields propagate in space with a velocity of 8 1 3 10 ms- ´ . Thus the
  • difficulties of „ether‟ were removed.
  • This theory satisfactorily explained reflection, refraction, interference, diffraction,
  • polarization etc. But it could not explain photoelectric effect, Raman effect, emission of light,
  • x-rays, Compton effect etc.
  1. Quantum Theory:
  • According to this theory, light exhibits particle nature. Planck proposed this
  • theory to explain the black body radiation. According to him, light is made up of energy
  • packets called photons. Each photon carries an energy E = hg where h is called planck‟s
  • constant 34 6.625 10 JS – ´ and g is the frequency of radiation. A photon has no rest mass, it has
  • momentum, hence we say that they exhibit particle nature.
  • This theory could explain photoelectric effect, Raman effect, Compton effect etc. But
  • it could not explain interference, diffraction etc.

Dual Nature of Light:

  • Certain observed phenomena such as reflection, refraction, interference, diffraction,
  • polarization etc can be explained only if we assume light to be of wave nature. In other
  • words, light exhibits wave nature in these experiments.
  • Phenomena like emission, photoelectric effect etc can be explained only by assuming
  • light to be a particle.
  • Hence we conclude that light exhibits both wave nature and particle nature, it exhibits
  • dual nature in other words.
NASA - National Aeronautics and Space Administration


Thanks to cosmology club who published this in their twitter news letter.
Author: @akshayphysics
Acceptance Date: 28 Dec 2015
Article ID: T2015122801


A branch of astronomy that deals with the origin, structure and space-time relationships of the universe the cosmology as a study manifests visible universe and the non-visible part also.

We humans always thrilled and fascinated by the play of star light which is spectacular to see through eyes to look and feel the cosmic acts which are present in this universe. So my article here presents the stellar spectral importance (SSI). 

If history of spectral analysis is checked, we come across on experimenter William Wollaston who was Great physicist. Once passed a beam of sun light through a thin slit and then through a prism. 

The slit provided familiar rainbow spectrum with no color overlapping each other. When seen, Wollaston noticed, our star sun’s spectrum was having some black lines in it. This was fundamental idea. The early spectral studies actually began with discovery of so many secrets of lines absorbed by elements in the spectrum of sun.

It was absorbed by elements present in the star or sun, an intensive idea was got foundation further by German physicist Joseph Frauhofer in 1814. Bright and continuous spectrum is results of superposition of these lines have been named in honor of the discovery as Fraunhofer lines. To explain in simple Words for above sentences when metals heated beyond certain temperature, emits white light. The Early stellar spectra showing the Distinctive absorption lines these astronomers used to determine stars composition and temperature. This above method is still in use. This set of spectra comes from the original Henry Draper Catalogue.

But elements can only absorb light that can excite their electrons from one valence bond to another. This is not same for all metals. The frequency and wavelength corresponds to the energy, as the way the missing wavelength will give away the Ionization level or state of energy and the elements is identified. 

Thus the composition of the star is determined. But stellar spectroscopy is the study of specter of star light. it is very powerful tool that enables Astrophysicist to infer many Physicical and chemical properties of stars and to divide them in an order which is easier for further analysis. I personally think that SSI stellar spectral importance is the best discovery in cosmology. This is key to the mysteries present in stars and galaxies.

Contact Author:
Akshay Kumar