We experience polarity of light when we wear a pair of sun-glass or look at a computer through an anti-glare filter. Starlight can be polarized by dust, its magnetic fields, or irregular geometry of the source. Our eyes are not capable of detecting polarized light. Sunlight is unpolarised; the light therefore comes at random angles. Polaroid sunglasses let in polarized light.
Light is called a transverse wave. it means light oscillates in a diction perpendicular to the direction in which it travels. However, light is free to oscillate right or left, up or down or at any angle to the vertical or horizontal. Some crystals have a special property that forces light to oscillated in one direction in which the crystal and magnetic fields. In free space, the electric and magnetic fields are perpendicular to each other and perpendiculars to the direction of propagation
Groups of light waves are called polarized when the electric fields oscillate in just one direction, instead of in random pattern. The intensity and distribution of polarized light can provide information about the environment of its source. In recent applications, the electrons in coronal mass ejection from the sun scatter light waves that are polarized thereby providing three- dimensional information on solar masses. Light is polarized when it is scattered off molecules terms of its spectrum and polarity. a spectra – polarimetry measures light in this manner.
A spectro-polarimeter can help in the study of the physical conditions in stars and galactic nuclei as well as in the interstellar medium. The strength and structure of magnetic fields can be measured by the scattered light from the source obscured by high- density matter or lost in the glare of a nearby bright object. A polarimeter can give new insights into the earliest moments of the cosmos after its’ birth’ as well as the death throes of stars.
A meaningful interpretation of solar features (E.g. Sunspots, pores and active regions.) demands quantitative measurements. An advanced Stokes Polarimeter made by the National Center for Atmospheric Research is a typical device for the purpose. It can provide high spatial resolution with quantitative measurements of magnetic fields at multiple heights in the solar atmosphere . A wealth of information can be extracted from the four Stokes parameters known as I (for intensity of light ), Q and U (for linear polarization ) and V (for circular polarization).
Accurate measurement of polarization is a good supplement to spectral resolution . Spectro-polarizer continues to produce new discoveries in solar physics, its applications to other stars, the interstellar medium and galaxies still in the early stage of development. Plasma, the commonest state of matter in the universe, creates magnetic fields in stellar atmospheres and in the interstellar medium.
A spectrum – polar meter at the Kodaikanal Solar Tower Telescope, is used to determine the direction and brightness of solar magnetic fields. Such a device for stars would have a different design as the stars have concentrated light with hardly any surface features visible.