Jansky Crater Honors American Physicist and Radio Engineer Karl Jansky

Summary: Northeastern lunar near side Jansky Crater honors American physicist and radio engineer Karl Jansky, who is credited as a radio astronomy pioneer.

Detail of Near Side Shaded Relief and Color-Coded Topography shows Jansky Crater and nearest named western neighbor Neper Crater along southern edge of Mare Marginis (Sea of the Edge), north of Mare Smythii (Smyth's Sea) in the lunar near side's northeast quadrant: U.S. Geological Survey, Public Domain, via USGS Astrogeology Science Center / Gazetteer of Planetary Nomenclature

Northeastern lunar near side Jansky Crater honors American physicist and radio engineer Karl Jansky, who is credited with pioneering the development of radio astronomy through his discovery of detectable extrasolar radio waves.

Jansky Crater's location in the lunar near side's northeastern quadrant places the lunar impact crater along the moon's eastern limb. The worn crater's undesirable placement guarantees detail-less, foreshortened, side-on views for Earth-based moongazers. Also, an Earth-based observer's slightly differently angled views of the moon's month-long orbit, known as lunar libration, sometimes completely conceals Jansky Crater.

The eroded crater presents an outline that combines rough circularity with disturbed irregularity. Occasional craterlets dot the interior floor and rim of the relatively featureless crater.

Jansky Crater is centered at 8.63 degrees north latitude, 89.5 degrees east longitude, according to the International Astronomical Union’s (IAU) Gazetteer of Planetary Nomenclature. The parental crater's northernmost and southernmost latitudes span 9.84 degrees north to 7.41 degrees north, respectively. Its easternmost and westernmost longitudes stretch from 90.74 degrees east to 88.27 degrees east, respectively. Jansky Crater's diameter spans 73.77 kilometers.

Jansky Crater parents three satellites along the southern edge of Mare Marginis (Sea of the Edge). Jansky D, F and H all reside to the east of their parent.

In his lunar guide, Patrick Moore on the Moon (2001), English amateur astronomer Sir Patrick Moore (March 4, 1923-Dec. 9, 2012) described Mare Marginis as a "limb-sea" that never affords good views to Earth-based observers. Images obtained by NASA's (National Aeronautics and Space Administration) Lunar Orbiter and Apollo programs have confirmed the feature's status as a genuine lunar mare (page 167).

Mare Marginis is centered at 12.7 degrees north latitude, 86.52 degrees east longitude. The lunar mare's northernmost and southernmost latitudes reach 18.59 degrees north and 9.81 degrees north, respectively. The dark basaltic plain's easternmost and westernmost longitudes extend from 93.35 degrees east to 81.15 degrees east, respectively. Mare Marginis spans 357.63 kilometers.

Jansky Crater's nearest named neighbor is Neper Crater. Jansky Crater's western, dark-floored neighbor is centered at 8.76 degrees north latitude, 84.58 degrees east longitude. It obtains northernmost and southernmost latitudes of 11.15 degrees north and 6.39 degrees north, respectively. The worn, inner-terraced impact crater finds easternmost and westernmost longitudes at 86.99 degrees east and 82.18 degrees east, respectively. With a diameter of 144.32 kilometers, Neper Crater is almost twice Jansky Crater's size.

Jansky Crater lies to the north of the eastern portion of Mare Smythii (Smyth's Sea). The limb-sea is centered at minus 1.71 degrees south latitude, 87.05 degrees east longitude. The equatorial lunar mare’s northernmost and southernmost latitudes touch 4.5 degrees north and minus 7.46 degrees south, respectively. Its easternmost and westernmost longitudes reach 92.72 degrees east and 80.94 degrees east, respectively. Mare Smythii spans 373.97 kilometers.

Jansky Crater eponymizes American physicist and radio engineer Karl Guthe Jansky (Oct. 22, 1905-Feb. 14, 1950). The International Astronomical Union (IAU) approved Jansky Crater's name in 1964, during the organization’s XIIth (12th) General Assembly, held in Hamburg, Germany, from Tuesday, Aug. 25, to Thursday, Sept. 3. The designations of the crater system's three satellites as D, F and H were approved in 2006.

Bell Telephone Laboratories (Nokia Bell Labs since 2016) employee Karl Jansky pioneered the development of radio astronomy through his discovery of detectable extrasolar radio waves. In Astronomy Encyclopedia (2002: page 209), Sir Patrick Moore noted that the total solar eclipse of Wednesday, Aug. 31, 1932, convinced Jansky that the sun was not the source of static interference with ship-to-shore and other types of telecommunications. The decrease in wave intensity associated with solar-sourced radio emissions during the eclipse did not take place.

Jansky determined maximum intensity as matching the sidereal period of every 23 hours 56 minutes. He tracked the strongest static to the Milky Way's galactic plane, or center line, specifically in Sagittarius the Archer constellation, at right ascension of approximately 18 hours. Jansky identified the Milky Way galaxy's huge ionized clouds of interstellar matter as static sources.

Jansky detailed his studies in four publications, beginning with the December 1932 issue of the Proceedings of the I.R.E. (Institute of Radio Engineeers; Proceedings of the IEEE Institution of Electrical Engineers since 1963). He specified the extrasolar origins of the waves in three publications in 1933 (July's Nature, October's Proceedings of the I.R.E., December's Popular Astronomy).

In The Biographical Dictionary of Scientists: Astronomers (1984), science textbook author David Abbott noted the International Astronomical Union's naming jansky (symbol Jy) in 1973 as the unit of flux density, or strength, of a radiowave emission (page 83). Historical metrology expert Jan Gyllenbok (born Nov. 12, 1963) noted in Encyclopaedia of Historical Metrology, Weights, and Measures (2018: pages 127-128) that the unit had been proposed in 1951 and that adoption of jansky as the unit's name occurred in August 1973 during the IAU's XVth (15th) General Assembly.

The takeaways for Jansky Crater's honoring American physicist and radio engineer Karl Jansky are that the near side limb crater foils Earth-based moongazers with its location along the moon's eastern limb; that Jansky and its three satellites reside along the southern edge of limb sea Mare Marginis (Sea of the Edge); and that the crater eponymizes Karl Guthe Jansky, radio astronomy pioneer, who discovered extrasolar radio waves, which he traced to Sagittarius the Archer constellation, and who published his studies in 1932 and 1933.

Detail of Lunar Aeronautical Chart (LAC) 64 shows Jansky Crater with nearest named western neighbor Neper Crater in lunar near side's Mare Marginis (Sea of the Edge); scale 1:1,000,000; Mercator Projection: United States Air Force (USAF) Aeronautical Chart and Information Center (ACIC) via USGS/Gazetteer of Planetary Nomenclature

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

Detail of Near Side Shaded Relief and Color-Coded Topography shows Jansky Crater and nearest named western neighbor Neper Crater along southern edge of Mare Marginis (Sea of the Edge), north of Mare Smythii (Smyth's Sea) in the lunar near side's northeast quadrant: U.S. Geological Survey, Public Domain, via USGS Astrogeology Science Center / Gazetteer of Planetary Nomenclature @ https://planetarynames.wr.usgs.gov/images/moon_nearside.pdf

Detail of Lunar Aeronautical Chart (LAC) 64 shows Jansky Crater with nearest named western neighbor Neper Crater in lunar near side's Mare Marginis (Sea of the Edge); scale 1:1,000,000; Mercator Projection: United States Air Force (USAF) Aeronautical Chart and Information Center (ACIC) via USGS/Gazetteer of Planetary Nomenclature @ https://planetarynames.wr.usgs.gov/images/Lunar/lac_63_wac.pdf

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