42
2 Observations of Radio and X-ray Pulsars
fields and their interaction relations was presented and later referred to as Maxwell’s
equations. The equations for electromagnetism have always been called the second
great unification in physics after the first one realized by Isaac Newton (1643–
1727). Maxwell’s equations brought first together electricity, magnetism and light
as different manifestations of the same phenomenon and predicted that the electromagnetic waves from stars radiate at any wavelength. As a result, many astronomers
started to investigate the electromagnetic radiations from celestial bodies with the
ways similar to optical observations. However, the radio waves from celestial bodies
have never been received in the low-frequency bands because of the limit of the
technical conditions at that time. Moreover, according to the theory of blackbody
radiation, the radiations from ordinary celestial bodies are not obvious in the radiofrequency bands. So, it had been believed for a long time that it was vain to investigate
the universe in the radio-frequency bands.
In the early 1930s, an engineer at Bell Telephone Laboratories, Karl Guthe Jansky
(1905–1950), built a directional antenna with a diameter of about 30 m and a height
of 6 m, mounted on a turntable that slowed it to be rotated in any direction, in order to
investigate the static interference of short wave transatlantic voice transmissions. The
antenna was designed to receive radio waves at a frequency of 20.5 MHz (wavelength
about 14.6 m). Jansky noticed that his analog pen-and-paper recording system kept
recording a repeating signal of unknown origin. Since the signal peaked about every
24 h, Jansky initially suspected that the interference might come from the Sun. And
then, it was shown by further analyzing that the signal peaks repeated exactly with a
period of 23 h and 56 min. That is to say, the time interval between the signal peaks was
the exact length of a sidereal day, and the source of the interference should be certain
celestial object outside the solar system. By comparing his observations with optical
astronomical maps, Jansky eventually concluded that the source of the interference
came from the center of the Milky Way, and the radiation source was strongest when
the antenna was pointed to the constellation of Sagittarius. In 1933, his discovery
was widely publicized by the New York Times and his paper “Electrical Disturbances
Apparently of Extraterrestrial Origin” was also published, but he found little support
from astronomers. On the one hand, two kinds of different technical approaches
are applied, respectively, to the optical and radio telescopes while few astronomers
were familiar with radio observation technology at that time. On the other hand,
the resolution of Jansky’s radio antenna was so low that the radio radiations from
celestial bodies were unable to be really observed. Jansky wanted to investigate the
radio waves from the Milky Way in further detail, but he could not be supported by
Bell Telephone Laboratories or astronomers, and thus did no further work in the field
of astronomy after 1935. Nevertheless, his classic paper has been regarded as a mark
of the birth of radio astronomy. To commemorate his historical merits in the field of
radio astronomy, the fundamental unit of radio flux density was named after Karl G.
Jansky (Jy) in 1966.
In 1937, an American radio amateur, Grote Reber (1911–2002), was inspired by
Jansky’s work and built a parabolic radio telescope with a diameter of 9 m in his
backyard. After experiencing two detection failures when his receiver was operated,
respectively, at the frequencies of 3300 MHz and 900 MHz, Reber successfully
2 Observations of Radio and X-ray Pulsars
fields and their interaction relations was presented and later referred to as Maxwell’s
equations. The equations for electromagnetism have always been called the second
great unification in physics after the first one realized by Isaac Newton (1643–
1727). Maxwell’s equations brought first together electricity, magnetism and light
as different manifestations of the same phenomenon and predicted that the electromagnetic waves from stars radiate at any wavelength. As a result, many astronomers
started to investigate the electromagnetic radiations from celestial bodies with the
ways similar to optical observations. However, the radio waves from celestial bodies
have never been received in the low-frequency bands because of the limit of the
technical conditions at that time. Moreover, according to the theory of blackbody
radiation, the radiations from ordinary celestial bodies are not obvious in the radiofrequency bands. So, it had been believed for a long time that it was vain to investigate
the universe in the radio-frequency bands.
In the early 1930s, an engineer at Bell Telephone Laboratories, Karl Guthe Jansky
(1905–1950), built a directional antenna with a diameter of about 30 m and a height
of 6 m, mounted on a turntable that slowed it to be rotated in any direction, in order to
investigate the static interference of short wave transatlantic voice transmissions. The
antenna was designed to receive radio waves at a frequency of 20.5 MHz (wavelength
about 14.6 m). Jansky noticed that his analog pen-and-paper recording system kept
recording a repeating signal of unknown origin. Since the signal peaked about every
24 h, Jansky initially suspected that the interference might come from the Sun. And
then, it was shown by further analyzing that the signal peaks repeated exactly with a
period of 23 h and 56 min. That is to say, the time interval between the signal peaks was
the exact length of a sidereal day, and the source of the interference should be certain
celestial object outside the solar system. By comparing his observations with optical
astronomical maps, Jansky eventually concluded that the source of the interference
came from the center of the Milky Way, and the radiation source was strongest when
the antenna was pointed to the constellation of Sagittarius. In 1933, his discovery
was widely publicized by the New York Times and his paper “Electrical Disturbances
Apparently of Extraterrestrial Origin” was also published, but he found little support
from astronomers. On the one hand, two kinds of different technical approaches
are applied, respectively, to the optical and radio telescopes while few astronomers
were familiar with radio observation technology at that time. On the other hand,
the resolution of Jansky’s radio antenna was so low that the radio radiations from
celestial bodies were unable to be really observed. Jansky wanted to investigate the
radio waves from the Milky Way in further detail, but he could not be supported by
Bell Telephone Laboratories or astronomers, and thus did no further work in the field
of astronomy after 1935. Nevertheless, his classic paper has been regarded as a mark
of the birth of radio astronomy. To commemorate his historical merits in the field of
radio astronomy, the fundamental unit of radio flux density was named after Karl G.
Jansky (Jy) in 1966.
In 1937, an American radio amateur, Grote Reber (1911–2002), was inspired by
Jansky’s work and built a parabolic radio telescope with a diameter of 9 m in his
backyard. After experiencing two detection failures when his receiver was operated,
respectively, at the frequencies of 3300 MHz and 900 MHz, Reber successfully