21-02-2010, 09:24 AM
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RADIO ASTRONOMY
Introduction:
¢ Study of celestial objects in radio frequency.
¢ Require large radio telescope to observe longer wavelengths.
¢ Study of elements in universe using radio telescope.
Electromagnetic Spectrum:
The electromagnetic spectrum includes radio frequency (RF), infrared (IR), visible light, ultraviolet (UV), X-rays, and gamma rays.
Radiation with shorter wave length-blue light.
Radiation with longer wave length-red light.
Radio waves (EM waves) have 1mm-100km wave length.
EM radiation is emitted by two methods:
Thermal emission : depend on temperature of emitting objects.
Non-thermal emission : does not depend on temperature of emitting objects
THERMAL EMISSION:
Object with temperature above absolute zero emits thermal radiation.
It causes atom to move and bump one other-change the direction-emits radiations.
Blackbody radiation.
Blackbody:-absorb all radiation and reflects nothing.
At equilibrium temperature it re-radiates energy- Blackbody radiation.
Free-Free emission.
Occurs when gas is ionized.
when gas is ionized charged particles moves around ionized gas.
Electrons accelerated by charged particles and gas emits radiation..
Spectral Line Emission:
Involve transition of electron from higher energy level to lower energy level
Protons emits energy equal to energy difference between two levels.
NON-THERMAL EMISSION:
Synchrotron Emission:
Does not have characteristic signature curve of blackbody radiation.
Due to the acceleration of charged particles with in the magnetic field.
Gyrosynchrotron Emission:
Emitted from pulsars (results from death of massive stars).
It posses magnetic field “accelerate electrons-emit radiations.
Appear as flash of light .
Masers:
Stands for Ëœmicrowave amplification by stimulated emission of radiationâ„¢.
It occurs in molecular clouds and envelop of old stars.
It amplifies or faints emission lines at specific frequency.
Principle of operation:
The radiations on the parabolic surface is reflected to focus.
It induces an electric current to receiver.
Signal is amplified to get the image.
Two components :
1.Large radio antenna
2.sensitive radio receiver.
Sensitivity of radio telescope depend on area and efficiency of antenna.
Sensitivity of radio receiver is used to amplify the signals.
Telescope has two characteristics:
It should have large collecting area.
Resolution should be good.
Diameter should be many times greater than wave length of radiation.
Types of telescopes:
The Very Large Array (VLA):27 antennas separated by 36km.
The Australia Telescope Compact Array (ATCA):6antenna separated by 6km.
The Giant Metrewave Radio Telescope (GMRT):30 dishes of 45meter separated by 25km.
Arecibo (biggest single dish telescope,300m).
Advantage and Disadvantage:
Not affected by the weather.
Radio telescope observe day and night.
To get good quality of images with all details is more complicated.
To produce images complicated procedure is required (observer does not see straight away the images).
Technical Innovation From Radio Astronomy:
Radio location of cell phone calls :it utilizes the difference in arrival time of calls at different towers to find locations.
Transistors and Cryogenic coolers :HEMT amplifiers are installed in antenna to improve the sensitivity.
Low noise amplifiers operates at cryogenic temperature.
Medical and scientific imaging :Used for non-invasive measurement of temperature of subcutaneous human tissue.
Emerging Technologies:
Communications Disruptive Warning and Prevention of Damage from Solar Flares.
Grid Computing Applications.
Laser Metrology and Precision Rangefinders.
Conclusion:
Requires collaborative effort and greater funding.
Only a few endeavors lead to useful and marketable technologies-radio astronomy is one among them.
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