2.1 A Brief History of Radio Astronomy
43
detected the radio signals from outer space in his third attempt at 160 MHz. He
began to repeat Jansky’s observations, and then plotted first a radio source map of
the Milky Way by conducting the sky survey. His observation data revealed the
existence of radio sources like Cygnus A and Cassiopeia A for the first time. In
1940, the radio source map was published in the Astrophysical Journal, and widely
attended by international astronomical community. For nearly a decade from 1937,
only Reber had been engaging dedicatedly in radio astronomy research all over the
world. So, Reber really became a pioneer of radio astronomy.
During the Second World War, the radar stations of the British Army had ever
received the interference signals from the Sun in the same day. During the daytime,
the direction of the interference signals moved with the Sun, and the interference
signals would disappear after sunset; the interference signals occurred repeatedly in
the second day, and until the third day gradually declined and eventually disappeared.
It was confirmed by astronomical observations later that a large sunspot and solar flare
was passing through central line of the solar disk at that time and thus the interference
signals detected by the radar stations were exactly the radio signals from the Sun.
After the end of the Second World War, some members from the radar team of the
British Army, such as Martin Ryle, Antony Hewish and Bernard Lovell, entered in
the research field of radio astronomy, and received the radio signals emitted from
celestial objects by sufficiently utilizing idle radars on the battleground. Soon after,
a series of amazing discoveries was gotten by radar astronomical observations and
thereby opened up an age of radio astronomical research.
1950s is a key age of rapidly developing the radio astronomy and almost every
carefully designed observation can get important findings. At the University of
Cambridge, Ryle, Hewish and their colleagues used the Cambridge interferometer
to map the radio sky, and published the Second Cambridge Catalogue of Radio
Sources (2C) and the Third Cambridge Catalogue of Radio Sources (3C). Meanwhile,
astronomers sufficiently utilized the extensive radio observation data to investigate
the Sun’s activity, search the supernova remnants, measure the velocity of meteors,
discover the anagalactic nebulae and plot the map of hydrogen distribution of the
Milky Way. The “four great discoveries” in the field of modern astronomy in 1960s,
including the quasar, pulsar, Cosmic Microwave Background (CMB) and interstellar
molecules, were closely related to the rapid development of radio astronomy. The
view of astronomical research is expanded by radio astronomical observations, and
furthermore a new field of astronomy also created.
2.2 Principles of Radio Telescopes
According to the radar detection principle, the radio telescopes receive the radio
signals at single wavelength and display a curve of denoting signal intensity changes
in the receiver. The electromagnetic radiations in the radio-frequency band can cross
through the interstellar gas and dust which the visible light is unable to penetrate,
and thus the radio telescopes can observe deeper into the universe than the optical
43
detected the radio signals from outer space in his third attempt at 160 MHz. He
began to repeat Jansky’s observations, and then plotted first a radio source map of
the Milky Way by conducting the sky survey. His observation data revealed the
existence of radio sources like Cygnus A and Cassiopeia A for the first time. In
1940, the radio source map was published in the Astrophysical Journal, and widely
attended by international astronomical community. For nearly a decade from 1937,
only Reber had been engaging dedicatedly in radio astronomy research all over the
world. So, Reber really became a pioneer of radio astronomy.
During the Second World War, the radar stations of the British Army had ever
received the interference signals from the Sun in the same day. During the daytime,
the direction of the interference signals moved with the Sun, and the interference
signals would disappear after sunset; the interference signals occurred repeatedly in
the second day, and until the third day gradually declined and eventually disappeared.
It was confirmed by astronomical observations later that a large sunspot and solar flare
was passing through central line of the solar disk at that time and thus the interference
signals detected by the radar stations were exactly the radio signals from the Sun.
After the end of the Second World War, some members from the radar team of the
British Army, such as Martin Ryle, Antony Hewish and Bernard Lovell, entered in
the research field of radio astronomy, and received the radio signals emitted from
celestial objects by sufficiently utilizing idle radars on the battleground. Soon after,
a series of amazing discoveries was gotten by radar astronomical observations and
thereby opened up an age of radio astronomical research.
1950s is a key age of rapidly developing the radio astronomy and almost every
carefully designed observation can get important findings. At the University of
Cambridge, Ryle, Hewish and their colleagues used the Cambridge interferometer
to map the radio sky, and published the Second Cambridge Catalogue of Radio
Sources (2C) and the Third Cambridge Catalogue of Radio Sources (3C). Meanwhile,
astronomers sufficiently utilized the extensive radio observation data to investigate
the Sun’s activity, search the supernova remnants, measure the velocity of meteors,
discover the anagalactic nebulae and plot the map of hydrogen distribution of the
Milky Way. The “four great discoveries” in the field of modern astronomy in 1960s,
including the quasar, pulsar, Cosmic Microwave Background (CMB) and interstellar
molecules, were closely related to the rapid development of radio astronomy. The
view of astronomical research is expanded by radio astronomical observations, and
furthermore a new field of astronomy also created.
2.2 Principles of Radio Telescopes
According to the radar detection principle, the radio telescopes receive the radio
signals at single wavelength and display a curve of denoting signal intensity changes
in the receiver. The electromagnetic radiations in the radio-frequency band can cross
through the interstellar gas and dust which the visible light is unable to penetrate,
and thus the radio telescopes can observe deeper into the universe than the optical