Chapter 15
Radio Astronomy
Abstract Radio astronomy is becoming increasingly important in astrophysics, with
increasingly complex, sensitive, and large instruments coming online. In the chapter,
we introduce some of the concepts in radio telescope design. As teaching radio
telescopes are still rare, we introduce radio astronomy with three practicals. Mapping
the Milky Way, detecting meteors, and observing Jupiter, the last two of which can
be undertaken with low-cost radio setups.
15.1 Introduction
In the early 1930s, Karl Jansky (after whom the jansky is named) was working on
improving shortwave radio reception. Using a directional antenna, he noticed a signal
that appeared and disappeared over a 24 h cycle. Using his equipment as a primitive
radio telescope, he was able to determine that the source of the signal was not the
Sun (although the Sun is a bright radio source), as he had previously suspected, but
something in Sagittarius. We now know that this source is the supermassive black
hole and radio source, located at the centre of the Milky Way, known as Sgr A*.
So began the age of radio astronomy, and the number of known astronomical radio
sources rapidly increased.
In the early 1960s, two physicists, Arno Penzias and Robert Wilson, were working
on the Bell Lab’s horn antenna in New Jersey (interestingly, Jansky was also working
at Bell Labs when he discovered Sgr A). Penzias and Wilson were working on cryogenically cooled microwave receivers and were troubled by a continuous background
signal being received. The signal was coming from all parts of the sky and was uniform in intensity. After a complete examination of the entire instrument, including
removing a white dielectric deposit from within the horn (i.e., bird droppings), they
concluded that the signal was not an artifact, but something real.
The physicists contacted astrophysicist Robert Dicke, thinking he might be able
to help with the source of the mysterious signal. Dicke was, as it turns out, an inspired
choice. He was working on the theory of the evolution of the universe, the Big Bang,
and the prediction that there should be a remnant signal from the age of deionisation,
© Springer Nature Switzerland AG 2020
M. Gallaway, An Introduction to Observational Astrophysics,
Undergraduate Lecture Notes in Physics,
https://doi.org/10.1007/978-3-030-43551-6_15
205
Radio Astronomy
Abstract Radio astronomy is becoming increasingly important in astrophysics, with
increasingly complex, sensitive, and large instruments coming online. In the chapter,
we introduce some of the concepts in radio telescope design. As teaching radio
telescopes are still rare, we introduce radio astronomy with three practicals. Mapping
the Milky Way, detecting meteors, and observing Jupiter, the last two of which can
be undertaken with low-cost radio setups.
15.1 Introduction
In the early 1930s, Karl Jansky (after whom the jansky is named) was working on
improving shortwave radio reception. Using a directional antenna, he noticed a signal
that appeared and disappeared over a 24 h cycle. Using his equipment as a primitive
radio telescope, he was able to determine that the source of the signal was not the
Sun (although the Sun is a bright radio source), as he had previously suspected, but
something in Sagittarius. We now know that this source is the supermassive black
hole and radio source, located at the centre of the Milky Way, known as Sgr A*.
So began the age of radio astronomy, and the number of known astronomical radio
sources rapidly increased.
In the early 1960s, two physicists, Arno Penzias and Robert Wilson, were working
on the Bell Lab’s horn antenna in New Jersey (interestingly, Jansky was also working
at Bell Labs when he discovered Sgr A). Penzias and Wilson were working on cryogenically cooled microwave receivers and were troubled by a continuous background
signal being received. The signal was coming from all parts of the sky and was uniform in intensity. After a complete examination of the entire instrument, including
removing a white dielectric deposit from within the horn (i.e., bird droppings), they
concluded that the signal was not an artifact, but something real.
The physicists contacted astrophysicist Robert Dicke, thinking he might be able
to help with the source of the mysterious signal. Dicke was, as it turns out, an inspired
choice. He was working on the theory of the evolution of the universe, the Big Bang,
and the prediction that there should be a remnant signal from the age of deionisation,
© Springer Nature Switzerland AG 2020
M. Gallaway, An Introduction to Observational Astrophysics,
Undergraduate Lecture Notes in Physics,
https://doi.org/10.1007/978-3-030-43551-6_15
205