Arthur Covington

Arthur Edwin Covington (born September 21, 1913 in Regina , † March 17, 2001 in Kingston , Ontario ) was a Canadian physicist who carried out the first radio astronomical measurements in Canada. Through this he made the valuable discovery that sunspots emit large amounts of microwaves at 10.7 cm wavelength ( solar radioflux ), which offers a simple, ground-based and weather-independent method for measuring and predicting sunspot activity and radio wave propagation . The corresponding measured value is also referred to as the Covington index after him . The sunspot discovery program continues to this day.

Youth and training

Covington was born in Regina and grew up in Vancouver . He showed an early interest in astronomy and built a 5-inch refractor telescope (about 13 cm) after meeting members of the local branch of the Royal Astronomical Society of Canada . He was also interested in amateur radio and was active for a while at the VE3CC station. He began his career as a radio operator on Canadian National Railway ships . He graduated from school and finally earned his bachelor's degree from the University of British Columbia in 1938 . In 1940 he received his master’s degree in the same post for building an electron microscope . He then moved to the University of California at Berkeley, where he did his doctorate in nuclear physics in 1942 . He was still at Berkeley when he was invited in 1942 to join the National Research Council (NRC) in Ottawa as a radar technician to work on the NRC's Radio Field Station .

Solar observations

Immediately after the war Covington, began to be interested in radio astronomy, and built a small telescope from electronic parts of a scrapped SCR-268 radar, which he combined with parts of another receiver that originally tests of a silicon - detector receiver should serve for radar applications . These electronics were attached to a 1.2 m parabolic dish on a Type III target radar. The system operated at a frequency of 2800 MHz or a wavelength of 10.7 cm. Initially, the measuring device was aimed in the direction of various celestial objects, including Jupiter , the Milky Way , aurora borealis and the sun , but the device proved to be too insensitive to observe any source other than the sun. For this reason a solar research program was started. Over time, Covington and his co-workers noticed that the sun's radiation varied at four inches, which was unexpected. The common belief at the time was that solar radiation behaves at centimeter wavelengths like a black body made of hot gas.

Covington concluded that the effect was related to the sunspots, as the flux seemed to vary with the number of visible spots. The device's 7-degree resolution made it impossible to isolate a single spot on the sun's surface, making the claim difficult to demonstrate. An opportunity to measure this directly arose on November 23, 1946, when a partial solar eclipse swept over the Ottawa area. Covington was able to conclusively show that the microwave rays fell very steeply when the moon covered a certain very large sunspot. This also showed that magnetic fields are instrumental in sunspot activities.

It was an absolute coincidence that the original device operated in a frequency range suitable for detecting the four-inch signals, and it was never intended for productive use. As the importance of the sunspot measurements became apparent, plans were made to continue these observations over a longer period of time. Since the Radio Field Station was still actively used for radar research, which caused severe interference, a new location about 8 km away on Goth Hill was selected. Here the total flux was measured and the measured values ​​were combined into three mean values ​​per day.

The exact location of "Goth Hill" is not known, as this expression does not appear in today's maps. According to the City of Ottawa City Archives, it is probably an area of ​​0.75 km² south of downtown Ottawa, an area that formerly belonged to Robert Goth and appears in the 1878 Beldon Atlas. The terms "hill" and "ridge" were commonly used for otherwise unknown stretches of land across the Gloucester Township area. The Goth Area is located at the eastern end of Runway 25 of Ottawa Macdonald-Cartier International Airport , west of the Canadian Forces Station Leitrim. This location fulfills all known descriptions.

Covington then began designing a device that could directly resolve individual parts of the sun. The new telescope consisted of a 46 m long section of 3 1½-inch metal waveguide cuts with gaps in places to make a simple interferometer that had a fan-shaped measurement range. The amount of incident flux was improved by placing the waveguide in a metal trough, which also allowed the aiming direction to be changed somewhat by moving the waveguide within the trough. In general, however, it was operated in such a way that measurements were taken by the sun passing through the "beam", i. H. wandered the reception section. The new telescope began operating in 1951, which enabled direct measurements of the solar corona flux and the temperature of the regions above the sunspots (around 1,500,000 ° C). The Goth Hill Observatory also contained a number of other instruments for a variety of measurements.

Algonquin Radio Observatory

The increasing use of radar and radio applications in the Ottawa area caused interference problems, which led Covington to look for a more suitable, electromagnetically quieter location for the program. This led to the establishment of the Algonquin Radio Observatory (ARO) in Algonquin Provincial Park , about 150 km northwest of Ottawa, but relatively easily accessible via the major highways. A new telescope for solar flux with a 1.8 m parabolic dish was built in 1960, which was operated in parallel with the Goth Hill instrument before it fully took over its role in 1962. In 1964, an identical instrument was installed at the Dominion Astrophysical Observatory (DAO) in British Columbia . This was followed by a more powerful version of the waveguide instrument, this time focused by a series of thirty-two 3m bowls mounted over a 215m waveguide that opened in 1966.

The ARO was greatly expanded in 1966 with the commissioning of the 46 m deep space telescope. It was a major research facility in the 1960s and 1970s, although limitations in design made it less usable in the 1980s. For a while, this instrument was joined by a smaller 18-meter telescope, which was originally located at the David Dunlap Observatory outside Toronto and operated by the University of Toronto . The original solar observatories remained in operation until 1990 when funding cuts at the NRC forced the closure of the entire Algonquin site. In 1991, the 1.8 m bowl was implemented for use as a backup device to the DAO.

Covington's work led to other sun-related discoveries. In 1969, observations led to the finding that certain types of larger sunspot outbreaks were preceded by a certain type of radio signal, which allowed for improved predictions of approaching solar storms. When other teams also began studying solar flux, they noticed that the different teams all came to different conclusions about total flux due to differences between the meters and other effects. Covington endeavored to compare these measurements and calculate a single flux value, which was published in 1972. He also played a role in the establishment of the Indian River Observatory , an amateur-built 200-meter interferometer.

retirement

Covington remained the director of the ARO until he retired in 1978. One of the buildings of the Dominion Astrophysical Observatory was posthumously named after him in 2003 . He had many hobbies, including a penchant for rare books, many of which were donated to Queen's University's Riche Covington Collection .

Individual evidence

1. ^ ^{A b c d} The Development of Solar Microwave Radio Astronomy in Canada, bibcode : 1967JRASC..61..314C
2. ^ ^{A b} Arthur Edwin Covington (1913-2001). In: astro-canada.ca. Canadian Museum of History, accessed February 5, 2018 . 
3. ^ ^{A b} Arthur Edwin Covington (1914-2001). Queen's University Libraries, August 28, 2003, archived from the original on February 6, 2012 . 
4. ↑ ^{a b} Ken Tapping: The History of the 10.7cm Solar Flux. Archived from the original on August 14, 2003 . 
5. ↑ Algonquin Radio Observatory, Lake Traverse, Ont., Canada, bibcode : 1969SoPh .... 9..241C .
6. ^ Ken Tapping: Introducing the Solar Radio Monitoring Program. Archived from the original on June 28, 2003 . 
7. ↑ Decrease of 2800 MHz solar radio emission associated with a moving dark filament before the flare of May 19, 1969 . In: Sol Phys . tape 33 , 1973, pp. 439 , doi : 10.1007 / BF00152431 .
8. ^ A. Covington: Observations and comments for the solar event of October 24, 1969 . In: Sol Phys . tape 24 , 1972, p. 405 , doi : 10.1007 / BF00153382 .
9. ^ H. Tanaka, JP Castelli, AE Covington, A. Krüger, TL Landecker, A. Tlamicha: Absolute calibration of solar radio flux density in the microwave region . In: Solar Physics . tape 29 , no. 1 , March 1973, p. 243-262 , doi : 10.1007 / BF00153452 .
10. ^ Frank Roy, Ken Tapping: A Brief History of the Indian River Observatory Radio Interferometer . In: J. Royal Astronomer. Soc. Can. tape 84 , no. 4 , August 1990, p. 260–274 ( org.uk [PDF; 704 kB ]).
11. ^ New NRC Building Named After Father of Canadian Radio Astronomy. National Research Council Canada, September 27, 2003, archived from the original on October 31, 2006 . 
12. ^ The Riche-Covington Collection. Queen's University Libraries, accessed February 5, 2018 .