Somnath Bharadwaj and Pratik Khastgir, Department of Physics and Meteorology, IIT Kharagpur, 721 302 Indiahttp://www.cts.iitkgp.ernet.in/~phy1/ Somnath Bharadwaj and Pratik Khastgir, Department of Physics and Meteorology, IIT Kharagpur, 721 302 Indiahttp://www.cts.iitkgp.ernet.in/~phy1/
The Electromagnetic Spectrum
Somnath Bharadwaj and Pratik Khastgir, Department of Physics and Meteorology, IIT Kharagpur, 721 302 Indiahttp://www.cts.iitkgp.ernet.in/~phy1/
Radio wave
Less than 1 GHz
Somnath Bharadwaj and Pratik Khastgir, Department of Physics and Meteorology, IIT Kharagpur, 721 302 Indiahttp://www.cts.iitkgp.ernet.in/~phy1/
Microwave
1 GHz to 3 1011 Hz
30 cm to 1 mm
Somnath Bharadwaj and Pratik Khastgir, Department of Physics and Meteorology, IIT Kharagpur, 721 302 Indiahttp://www.cts.iitkgp.ernet.in/~phy1/
Space communication
Atmosphere is transparent from less than 1 cm to 30 m
Also suitable for radio astronomy
Somnath Bharadwaj and Pratik Khastgir, Department of Physics and Meteorology, IIT Kharagpur, 721 302 Indiahttp://www.cts.iitkgp.ernet.in/~phy1/
HI --- Neutral Hydrogen Ground state has two different energy levels
The 21 cm HI radiation
Somnath Bharadwaj and Pratik Khastgir, Department of Physics and Meteorology, IIT Kharagpur, 721 302 Indiahttp://www.cts.iitkgp.ernet.in/~phy1/
Star and Gas Distribution
Radio Interferometric Arrays
The GMRT 30 antennas 45 m diameter each
Frequency MHz 153 235 325 610 1420
z 8.3 5.0 3.4 1.3 0
32 MHz bands with 128 separate channels
Somnath Bharadwaj and Pratik Khastgir, Department of Physics and Meteorology, IIT Kharagpur, 721 302 Indiahttp://www.cts.iitkgp.ernet.in/~phy1/
HI in Galaxies
DDO 210 Source: Begum and Chengalur Dwarf Irregular Galaxy
Somnath Bharadwaj and Pratik Khastgir, Department of Physics and Meteorology, IIT Kharagpur, 721 302 Indiahttp://www.cts.iitkgp.ernet.in/~phy1/
Cosmic Microwave Background Radiation
T=2.73 K
CMBR
Somnath Bharadwaj and Pratik Khastgir, Department of Physics and Meteorology, IIT Kharagpur, 721 302 Indiahttp://www.cts.iitkgp.ernet.in/~phy1/
Blackbody Radiation
Somnath Bharadwaj and Pratik Khastgir, Department of Physics and Meteorology, IIT Kharagpur, 721 302 Indiahttp://www.cts.iitkgp.ernet.in/~phy1/
Molecular Rotations
Water 2.45 GHz used in microwave ovensExcites Rotations of water molecules
50 GHz to 10 THz T-rays
Somnath Bharadwaj and Pratik Khastgir, Department of Physics and Meteorology, IIT Kharagpur, 721 302 Indiahttp://www.cts.iitkgp.ernet.in/~phy1/
Infrared
3 1011 Hz to 4 1014 Hz
Near IR 760 - 3000 nmIntermediate IR 3000 - 6000 nm Far IR 6000 - 15000 nmExtreme IR 15000nm – 1 mm
Human body peaks at 10000 nm
Somnath Bharadwaj and Pratik Khastgir, Department of Physics and Meteorology, IIT Kharagpur, 721 302 Indiahttp://www.cts.iitkgp.ernet.in/~phy1/
Visible Light
3.84 1014 Hz to 7.69 1014 Hz
Mainly atomic transitions – outer levelsHot bodies ~5000K
Somnath Bharadwaj and Pratik Khastgir, Department of Physics and Meteorology, IIT Kharagpur, 721 302 Indiahttp://www.cts.iitkgp.ernet.in/~phy1/
Ultraviolet
8 1014 Hz to 3 1016 Hz
Enough energy to ionize atoms in upper atmosphere
Is harmful – absorbed by O3 in upper atmosphere
Produced in energetic atomic transitions
Somnath Bharadwaj and Pratik Khastgir, Department of Physics and Meteorology, IIT Kharagpur, 721 302 Indiahttp://www.cts.iitkgp.ernet.in/~phy1/
X-ray
2.4 1016 Hz to 5 1019 Hz
Energetic electrons incident on a metal
Hot astrophysical sources – Black Holes
Inner shell transitions in atoms
Somnath Bharadwaj and Pratik Khastgir, Department of Physics and Meteorology, IIT Kharagpur, 721 302 Indiahttp://www.cts.iitkgp.ernet.in/~phy1/
Centaurus Cluster
Credit: J. Sanders, A. Fabian,
Somnath Bharadwaj and Pratik Khastgir, Department of Physics and Meteorology, IIT Kharagpur, 721 302 Indiahttp://www.cts.iitkgp.ernet.in/~phy1/
Gamma Rays
Frequency greater than 5 1019 Hz
Produced in nuclear transitions
Electron-positron annihilation
Easy to detect – ionizes gas
