Radio Astronomy - Blog Posts
When I was in Ireland in 2013, I kept seeing signs for ‘quasar.’ I finally learned that it’s the European way of saying laser tag. It has nothing to do with quasars, which are a specific type of a specific type of galaxy. Listen to this week’s (pretty short) podcast on two types of active galaxies: quasars and blazars.
Below the cut, I have the transcript, sources, music credits, and timeline of people I talked about! If you have suggestions for topics I could cover, please send me a Tumblr message or tweet at me on Twitter at @HDandtheVoid, or you can ask me to my face if you know me. Please subscribe on iTunes, rate my podcast and maybe review it, and tell friends if you think they’d like to hear it!
(My thoughts on the next episode are the SOFIA observatory, Chuck Yaeger, or the great Stephen Hawking. The next episode will go up April 2nd.)
Glossary
active galaxy or active galactic nucleus- a galaxy with a small core of emission embedded at the center. This core is typically very variable and very bright compared to the rest of the galaxy. These galaxies emit much more energy than they should; this excess energy is found in the infrared, radio, UV, and X-ray regions of the electromagnetic spectrum.
blazar - a subcategory of active galaxy, it is an extremely bright, distant object, powered by a black hole, which emits massive amounts of energy. It is distinct from a quasar because it is even brighter.
extragalactic objects - objects outside our Milky Way galaxy.
interferometry - a group of techniques to extract information from superimposing electromagnetic waves to create interference. In radio astronomy, this is done by using a wide spread of receivers to look at the same distant object, then bringing that data together with a correlator that can create a larger, clearer picture than an individual radio telescope alone could.
lunar occultations - when stars pass behind the Moon. This is the basis for a method of determining and mapping star positions.
quasar - a subcategory of active galaxy, it is an extremely bright, distant object, powered by a black hole, which emits massive amounts of energy. It is distinct from a blazar because it is less-bright. The name is a contraction of “quasi-stellar radio source” (which is not necessarily true of all quasars—90% are radio-quiet).
torus - a donut shape.
Script/Transcript
Timeline
Walter Baade, German (1893-1960)
Rudolph Minkowski, German-American (1895-1976)
Fritz Zwicky, Swiss (1898-1974)
Gordon Stanley, New Zealander (1921-2001)
John Bolton, English-Australian (1922-1993)
Owen Bruce Slee, Australian (1924-2016)
Allan Rex Sandage, American (1926-2010)
Cyril Hazard, English (1928- )
Maartin Schmidt, Dutch (1929- )
Hong-Yee Chiu, American (1932- )
Stephen Hawking, English (1942 -2018)
Jedidah Isler
Sources
Active Galaxies via NASA (Dec 2016)
Galaxy shapes via Cornell University (April 2000)
Galaxies and Black Holes by David Merritt, published on NED by Caltech and NASA
Cyril Hazard via University of Pittsburgh
The Discovery of Quasars and its Aftermath via Journal of Astronomical History and Heritage (2014)
“Characteristically, Fritz Zwicky (1898–1974; Figure 11) immediately pointed out that ‘All of the five quasi-stellar galaxies described individually by Sandage (1965) evidently belong to the subclass of compact galaxies with pure emission spectra previously discovered and described by the present writer. (Zwicky, 1965: 1293).’ A few years later, Zwicky was less circumspect and wrote: ‘In spite of all these facts being known to him in 1964, Sandage attempted one of the most astounding feats of plagiarism by announcing the existence of a major new component of the Universe: the quasi-stellar galaxies ... Sandage‘s earthshaking discovery consisted in nothing more than renaming compact galaxies, calling them ‘interlopers‘ and quasistellar galaxies, thus playing the interloper himself. (Zwicky and Zwicky, 1971: xix)’”
Lunar occultations via Sky and Telescope
Quasars and Blazars by Matthew Whiting (a chapter in his thesis, What made the quasar blush? Emission mechanisms in optically-red quasars) via the Australia Telescope National Facility (2000)
Jedidah Isler on quasars and blazars via TED Talks (March 2015)
Quasar definition via Space.com (Feb 2018)
Intro Music: ‘Better Times Will Come’ by No Luck Club off their album Prosperity
Filler Music: ‘Into The White’ by Pixies off their album Wave of Mutilation.
Outro Music: ‘Fields of Russia’ by Mutefish off their album On Draught
I’ve gotten some feedback that episodes can be too technical. Unfortunately, that feedback came too late to save you from this week’s episode, which requires me to summarize the electromagnetic spectrum, radio astronomy, a concept called interferometry, and government regulations to talk about the topic that originally started me on this path: radio quiet zones. Please, bear with me! Pardon my mess! It was all very interesting stuff, I couldn’t resist digging into it.
Below the cut are my sources, music credits, a vocab list, a timeline of the astronomers I mention, and the transcript of this episode. I’ve bolded those sources I mention in the podcast, including the podcast that started me on this topic: The Adventure Zone! Please let me know what you think I should research next by messaging me here, tweeting at me at @HDandtheVoid, or asking me to my face if you know me. I’d love it if you would subscribe on iTunes, rate my humble little podcast and maybe review it, and tell friends if you think they’d like to hear it!
(My thoughts on the next episode are SOFIA, which you need to listen to find out what it stands for, or the pilot Chuck Yaeger. The next episode will go up February 26th.)
Glossary
aperture synthesis - the process of collecting electromagnetic radiation from a variety of separate, small telescopes and then combining this data to recreate the image at a higher resolution than would be possible with a single telescope.
frequency - the number of times a wave oscillates up and down per second.
hertz - the number of times an electromagnetic wave cycles per second. One cycle per second is 1 hertz.
interferometry - a group of techniques to extract information from superimposing electromagnetic waves to create interference. In radio astronomy, this is done by using a wide spread of receivers to look at the same distant object, then bringing that data together with a correlator that can create a larger, clearer picture than an individual radio telescope alone could.
radiation - energy that travels and spreads out as it goes.
Script/Transcript
Timeline
Joseph-Louis Lagrange, French (1736-1813)
Armand-Hippolyte-Louis Fizeau, French (1819-1896)
Edward W. Morley, American (1838-1923)
Albert A. Michelson, American (1852-1931)
Sir Martin Ryle, British (1918-1984)
Bernard Yarnton Mills, Australian (1920-2011)
Derek Vonberg, British (1922-2015)
Antony Hewish, British (1924- )
Sources
Electromagnetic spectrum via NASA
Observatories across the EM spectrum via NASA
Fermi satellite via NASA
The Neil Gehrels Swift Observatory via NASA
NuSTAR via Caltech
NuSTAR via NASA
Chandra X-Ray Observatory via Harvard
The Galaxy Evolution Explorer (GALEX) via Caltech
Kepler satellite via NASA
Hubble Space Telescope via NASA
Spitzer satellite via Caltech
Stratospheric Observatory for Infrared Astronomy (SOFIA)
Planck satellite via ESA
Spekt-R Radioastron from Russia
High Energy Stereoscopic System (HESS)
W. M. Keck Observatory on Mauna Kea
South Africa Large Telescope (SALT) in Namibia
The Combined Array for Research in Millimeter-Wave Astronomy (CARMA) via Caltech
CARMA public page (decommissioned)
Very Large Array (VLA) via NRAO
Space radio telescope (1997) via NRAO
Highly Advanced Laboratory for Communications and Astronomy (HALCA) via NASA
A timeline of the history of radio interferometry via University of Groningen (Netherlands)
Interferometers via the LIGO Laboratory
Michelson-Morley Experiment via University of Virginia
Astronomical Interferometry via Magdalena Ridge Observatory
Interferometry via XKCD
How Radio Works via How Stuff Works
Radio Spectrum Allocation via the Federal Communications Commission
Interferometry via the European Space Observatory
National Radio Quiet Zone via National Radio Astronomy Observatory
“minimize possible harmful interference to the National Radio Astronomy Observatory (NRAO) in Green Bank, WV and the radio receiving facilities for the United States Navy in Sugar Grove, WV.”
National Radio Quiet Zone via CNN
“Tucked in the Allegheny Mountains, researchers are listening to exploding galaxies at the edge of the universe – a signal that is so faint, it’s about a billionth of a billionth of a millionth of a watt.”
The Quiet Zone: Where mobile phones are banned via BBC News (May 2015)
Enter The Quiet Zone: Where Cell Service, Wi-Fi Are Banned via NPR (Oct 2013)
Green Bank Observatory in West Virginia, USA
Karen O’Neil: “The types of energies we look at are less than the energy of a single snowflake falling on the Earth.”
Characteristics of radio quiet zones via International Telecommunication Union (Sept 2012)
“transmissions below 15 GHz are restricted within a certain radius around the Arecibo Observatory, located in Puerto Rico. Since no observations are carried out, nor are any expected to be carried out above that frequency in the future, no restrictions are needed on higher frequency transmissions. The reverse is not necessarily true, however. For example, some restrictions may be imposed on transmissions below 30 GHz in the neighbourhood of the large international ALMA observatory even though it is not expected to ever observe below that frequency, due to its susceptibility to interference at these lower frequencies in the signal path.”
“It is important to emphasize that a RQZ does not imply a complete absence of radio transmissions. The existence of, and coexistence with, a range of man-made devices will always be necessary. A RQZ may include options for notification of other users and for negotiation in mitigating interference. On the other hand, a RQZ does not consist entirely of mitigating techniques implemented by the radio astronomy facility; some level of control on externally-generated interference is intrinsic to a RQZ.
A RQZ is therefore a buffer zone that allows for the implementation of mechanisms to protect radio astronomy observations at a facility within the zone from detrimental radio frequency interference, through effective mitigation strategies and regulation of radio frequency transmitters.”
ALMA Observatory website
The Scientific Committee on Frequency Allocations for Radio Astronomy (IUCAF) website
Google Map of worldwide radio quiet zones (Aug 2016)
ITU-R Recommendations of Particular Importance to Radio Astronomy by A. Richard Thompson
“the necessity of maintaining the shielded zone of the Moon as an area of great potential for observations by the radio astronomy service and by passive space research, and consequently of maintaining it as free as possible from transmissions.”
The Adventure Zone: Amnesty setup episode via Maximum Fun
Intro Music: ‘Better Times Will Come’ by No Luck Club off their album Prosperity
Filler Music: ‘Junkyard Chandelier’ by Radical Face aka Ben Cooper, who primarily releases music as Radical Face but also has at least three other bands or band names he’s working with/has released music as.
Outro Music: ‘Fields of Russia’ by Mutefish off their album On Draught
