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--- un:ra [2024/05/29 00:57] – created asad
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 ====== Radio astronomy ======
-Human eye can detect [[electromagnetic radiation]] within a narrow range from 400 nm to 700 nm, but astronomical objects emit light of all wavelengths from picometer-length gamma rays to a meter-length radio waves. Radio astronomy deals with celestial electromagnetic radiation at radio wavelengths, from 0.3 mm ($\nu=c/\lambda=1$ THz) to 30 m (10 MHz).
+Radio astronomy is a branch of astronomy where radio emission from astronomical objects are studied. The boundaries of the radio window of the [[em|electromagnetic spectrum]] is defined by the [[opacity]] of Earth's atmosphere and the [[quantum noise]] in coherent amplifiers.
-{{https://www.cv.nrao.edu/~sransom/web/x374.jpg?nolink&800}}
+{{https://smd-cms.nasa.gov/wp-content/uploads/2023/08/ems-introduction.jpeg}}
-Atmospheric opacity and quantum noise determine the boundary between far-infrared and radio astronomy at 1 THz and the ionosphere reflect back all waves longer than 30 m. Below 2 MHz even our Galaxy becomes an absorber, its ionized gas prevents radio radiation from propagating.
-If we had radio eyes and looked at the sky, the [[Sun]] would still be very bright, but different. Its non-thermal emissions would dominate over the thermal [[blackbody]] radiation, the corona would be visible as a hazy envelope. The [[planets]] would be seen not in reflected light, but in their own invisible light. The [[Milky Way]] would shine not because of its [[stars]], but mainly because of the innumerable high-speed electrons in its interstellar medium. Instead of stars, the night-sky would be filled with compact active galaxies.
-Only radio and optical astronomy can be done from the ground efficiently.