Astrophysics.pdf - The Wave Nature of Radiation The wave theory championed by Dutch astronomer Christiaan Huygens in 1670s viewed light as a wave

Astrophysics.pdf - The Wave Nature of Radiation The wave...

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- The Wave Nature of Radiation - The wave theory, championed by Dutch astronomer Christiaan Huygens in 1670s, viewed light as a wave phenomenon, in which color was determined by frequency or wavelength. Electromagnetic Radiation Radiation is any way in which energy carried in the form of rapidly fluctuating electric and magnetic fields is transmitted through space from one point to another without the need for any physical medium between the two locations. All types of electromagnetic radiation travel through space in the form of waves - energy is transmitted without any physical movement of material from place to place. The acceleration of electric charges caused by vibration or collision gives off the disturbance in the electric field traveling through space as a wave. Electric and magnetic fields, which are always oriented prependicular , are inextricably linked to one another - a change in either one necessarily creates the other. Electric and magnetic fields together form an electromagnetic wave that moves through space at the speed of light in the direction perpendicular to both fields comprising it. wave velocity(v) = wavelength(λ) ÷ period(T) = wavelength(λ) × frequency(f) The velocity of electromagnetic radiation equals to the speed of light( c ) - 2.998 × 10 8 m/s in a vacuum . Light travels at the same speed through the same medium. It can take light millions or even billions of years to transverse astronomical distance, thus we can never observe the universe as it is - only as it was. The visible spectrum covers the range of wavelengths from 400 nm to 700 nm. The part of visible light our eyes react most sensitively has a wavelength around 550
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nm (yellow-green part) at which the Sun emits most of its electromagnetic energy - our eyes have evolved to take greatest advantage of the available light. Atmospheric Opacity There are only a few spectral windows at well-defined locations in the electromagnetic spectrum - optical (soft, near infrared), part of the radio domain, and much of the infrared portion - where Earth’s atmosphere is transparent. Radio waves having wavelengths less than about a centimeter are absorbed by water vapor (H 2 O) and oxygen (O 2 ) Decameter or kilometer radio waves, such as AM broadcasting, and visible light can be reflected by the thin, electrically-conducting ionosphere at an altitude of roughly 100 km, which keeps out the extraterrestrial waves and keeps in the terrestrial waves. Water vapor (H 2 O) and carbon dioxide (CO 2 ) are strong absorbers of infrared radiation. Ultraviolet, X-ray, and gamma-ray radiation are almost completely blocked by the ozone layer (O 3 ) high in the Earth’s atmosphere. Atoms and molecules of oxygen and nitrogen absorb X-ray, and gamma-ray radiation.
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