Title: Seeing the Universe in a Whole New Light
Podcaster: Nicole Gugliucci
Karl Jansky and the Discovery of Cosmic Radio Waves from NRAO, along with a picture of his Bruce array antenna – http://www.nrao.edu/whatisra/hist_jansky.shtml
Nicole’s Podcast Page – http://astronoise.wordpress.com/365‐days‐of‐astronomy/
Nicole Gugliucci (UVa/NRAO) –
Description: May 5th is the anniversary of the announcement of the discovery of radio waves from the cosmos in 1933. This opened up the field of astronomy to non-visible light and allowed us to see he universe in a whole new way. Today, I’ll be talking about Karl Jansky, the father of radio astronomy, and what about his job and his life led him to this startling discovery, with Rich Bradley of the National Radio Astronomy Observatory.
Bio: Nicole Gugliucci is a graduate student at the University of Virginia, working at the National Radio Astronomy Observatory. When not helping with the construction and data analysis for PAPER, she enjoys public outreach activities, especially those that allow her to talk about the fascinating discoveries to come out of radio astronomy.
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Rossiter & Associates (www.rossiters.org/associates), a process improvement consulting firm specializing in energy efficiency for oil refining, petrochemicals and chemical operations. Rossiter & Associates – Energy Efficiency by Design.
Welcome to the May 5th edition of the 365 Days of Astronomy Podcast. My name is Nicole Gugliucci and I am a graduate student in astronomy at the University of Virginia and the National Radio Astronomy Observatory. Today is a special anniversary for those of us in radio astronomy. On May 5th in 1933, the New York Times published an article with the title “New Radio Waves Traced to Centre of the Milky Way.” This reports on a low intensity radio static detected from the sky by radio engineer Karl Jansky. Today, I’ll be talking to Rich Bradley at the NRAO about the “father of radio astronomy” and his amazing discovery.
NG: Okay, Rich. Who was Karl Jansky, and what was his job?
RB: Well, Karl Jansky is a very interesting figure. He was working at Bell Labs, at the time, when he made this discovery, and he was really looking for sources of static in radio signals. So you could say he became an astronomer by chance. His background, actually, he was born in Oklahoma, but his family moved to Wisconsin. His father was a professor of electrical engineering at the University of Wisconsin, Madison. He grew up there and ended up attending the University of Wisconsin and got a bachelor in physics. He then stayed there for his masters but he didn’t finish it. He did the coursework, but he elected not to do the masters thesis, but later on he submitted his work on radio signals and got his degree.
NG: So how did he get the particular assignment that he was working on when he made this discovery?
RB: Well, when Jansky reported to work at Bell Labs, the first thing they did was give him a physical. What they realized is that he was suffering from a kidney disease, Bright’s disease. They basically turned him down at first, and it was his brother, his brother was about ten years older than Karl, and he had connections at Bell Labs. He basically talked them into hiring Karl, but they didn’t want to have him work in the New York City office and so they sent him out to, at the time it was Holmdel, [New Jersey,] is where he ended up going.
He worked for Harald Friis, and Harald was really a pioneer in the work of precision measurements of both radio signals and noise at low frequency. And so at the time, he and a fellow named Al Beck were hired to really look into this new frontier which was shortwave signals. These are signals above about 1.5 MHz up to about 30 MHz. This was the new frontier. Friis assigned Al Beck to study the signals and Karl to study the noise.
So during that time, Karl was looking for various types of noise. To do that, he had to develop an instrument. Radio tubes were used at the time, and he developed a state-of-the-art receiver. For his antenna, he built this rather elaborate Bruce array, which was basically a director and a reflector that was on a moveable platform. They used Model T Ford tires and a little concrete foundation to wheel this thing around. He could study the direction of these radio signals. So he began studying things that he thought would be present. In fact, he delayed the start of his study until the spring because that’s when the thunderstorms roll around. He identified those quickly and noticed the effect of the ionosphere where distance thunderstorms were providing this sort of intermittent static.
It was about 1931 or so when he noticed that there was something a little peculiar. It was this sort of steady background hiss that was also present, and he couldn’t identify it. He didn’t stop there. He continued to study this on almost a daily basis. At first it appeared that it was collocated with the Sun. He explored that avenue for a while until he realized that it was moving in the sky about 4 minutes a day relative to the sun. He then became really obsessed with learning a bit about astronomy. His background was physics and not astronomy. He was talking to George Southworth, who suggested that maybe he should explore if there was a correlation between this and what he called electric currents in the atmosphere of the Earth. That got him looking and actually tracing the signal in the sky. He also didn’t know anything about the coordinate systems used. So he met with an interesting fellow M. S.. M was a physics student. He was actually taking astronomy courses at Princeton at the time and working as a radio engineer at Bell Labs. He was able to describe right ascension and declination to Karl, and he began plotting the position of this. Now, his antenna was only able to rotate in azimuth, so he had to kind of infer when he would see these things rising and kind of indirectly give a right ascension and declination coordinates to these things. But, he was still thinking that it was related somehow to the sun. It was in 1932, I believe, there was a partial solar eclipse at Holmdel. He was observing the day before, the day of, and the day after, and realized there was no change to the signal. From that point on, he ruled out the sun.
He was able to identify the position in early 1933 as being located at the Galactic Center. Once he made that connection, he realized that it was of extraterrestrial origin. If you read the papers, you realize that he was very careful. It was not just him but Harald Friis that was obsessed with no overstating the results. He ended up very carefully wording the title and such so that if there was something else identified that they could back out of it.
NG: It sounds a little crazy saying that you’re getting radio signals from outer space, especially in the 1930s.
RB: That’s right. So he continued on. He published his first result and presenting his work at the URSI [International Union of Radio Science] meeting in Washington, DC. He continued to study and he realized that the radio source was not just a localized source but was also this band. So he identified signals coming from, essentially, the Milky Way, as well as the Galactic Center.
NG: Great! Thanks, Rich.
Optical astronomers were originally skeptical of this finding, since stars did not have an obvious mechanism for producing radio light. However, after World War II, engineers and scientists used what they learned from radar to systematically study the sky in radio wavelengths. Even today, we recognize and remember Jansky’s contribution, as the unit of flux commonly used in radio astronomy is called a Jansky, or 10 to the negative 26 watts per meters squared per Hertz. That’s a tiny amount of energy, but we’ve learned a lot about the universe from radio emissions, and we have Karl Jansky to thank for getting us all started.
End of podcast:
365 Days of Astronomy
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