Elger Crater Honors British Astronomer Thomas Gwyn Elger

Summary: Elger Crater honors British astronomer Thomas Gwyn Elger, whose selenographic contributions include his lunar guide, The Moon, published in 1895.

Detail shows Elger Crater (lower left center), with nearby neighbor Capuanus P (right) and Ramsden G (left), in Palus Epidemiarum; R.S. Saunders and D.E. Wilhelms, Geologic Map of the Wilhelm Quadrangle of the Moon (1974): U.S. Geological Survey, via USGS Publications Warehouse

Elger Crater honors British astronomer Thomas Gwyn Elger, whose comprehensive lunar guide, The Moon, published in 1895, included his carefully drawn quadrants of the lunar near side.

Elger Crater is a lunar impact crater in the lunar near side’s southwestern quadrant. The crater’s eroded, rough rim features a southern break and a northern outward bulge. Lava has resurfaced the crater’s interior floor.

Elger Crater is centered at minus 35.4 degrees south latitude, minus 29.81 degrees west longitude, according to the International Astronomical Union’s (IAU) Gazetteer of Planetary Nomenclature. The southern hemisphere crater confines northernmost and southernmost latitudes to minus 35.05 degrees south and minus 35.76 degrees south, respectively. The western hemisphere crater limits easternmost and westernmost longitudes to minus 29.38 degrees west and minus 30.23 degrees west, respectively. Elger Crater has a diameter of 21.51 kilometers.

The middle-latitude primary crater parents two satellites. Elger A and Elger B lie in isolation from their parent as the Elger Crater system’s southwestern components.

Elger Crater resides along the southern edge of Palus Epidemiarum. The Marsh of Epidemics is a small lunar mare (Latin: mare, “sea”) that lies in the terrain that wedges between southeastern Mare Humorum (Sea of Moisture) and southwestern Mare Nubium (Sea of Clouds).

Palus Epidemiarum is centered at minus 32 degrees south latitude, minus 27.54 degrees west longitude. The dark, basaltic plain’s northernmost and southernmost latitudes reach minus 28.88 degrees south and minus 36.47 degrees south, respectively. Its easternmost and westernmost longitudes extend to minus 21.72 degrees west and minus 33.43 degrees west, respectively. Palus Epidemiarum’s length spans 300.38 kilometers.

Capuanus P and Ramsden G reside as Elger Crater’s nearest named neighbors. Capuanus P is Elger’s eastern neighbor. Ramsden G claims western neighborship.

Eastern neighbor Capuanus P numbers among the Capuanus Crater system’s 11 satellites. Capuanus P is sited between its parent, to the east-northeast, and Elger Crater.

Capuanus P is centered at minus 35.44 degrees south latitude, minus 28.59 degrees west longitude. The elongated satellite marks northernmost and southernmost latitudes at minus 34.45 degrees south and minus 36.4 degrees south, respectively. The Capuanus Crater system’s most easterly satellite posts easternmost and westernmost longitudes of minus 27.55 degrees west and minus 29.5 degrees west, respectively. Capuanus P’s elongated diameter measures 68.52 kilometers.

Western neighbor Ramsden G numbers among the Ramsden Crater system’s two satellites. Ramsden G’s location along southern Palus Epidemiarum places it closer to neighborly Elger Crater than to its parent.

Ramsden G is centered at minus 35.35 degrees south latitude, minus 31.67 degrees west longitude. It records northernmost and southernmost latitudes of minus 35.17 degrees south and minus 35.53 degrees south, respectively. The Ramsden Crater system’s most southerly component registers easternmost and westernmost longitudes of minus 31.45 degrees west and minus 31.89 degrees west, respectively. Ramsden G has a diameter of 11.02 kilometers.

Elger Crater honors British astronomer Thomas Gwyn Empy Elger (Oct. 27, 1836-Jan. 9, 1897). The International Astronomical Union (IAU) approved Elger as the crater’s official name in 1935, during the organization’s Vth (5th) General Assembly, which was held in Paris, France, from Wednesday, July 10, to Wednesday, July 17. The letter designations of the Elger Crater system’s two satellites were approved in 2006.

Elger’s obituary in the Feb. 12, 1897, issue of the Monthly Notices of the Royal Astronomical Society notes his election as a Fellow of the Royal Astronomical Society (FRAS) on Feb. 10, 1871. His first communication to the society concerned the colors of the components of binary star system Gamma Delphini (γ Delphini; Gamma Del, γ Del). He reported his 33 observations of the pair in the Dec. 13, 1872, issue of the Monthly Notices of the Royal Astronomical Society.

The obituary observes that Elger’s qualities as “. . . a careful and indefatigable selenographer . . .” (page 211) particularly established his reputation in astronomy. Elger’s comprehensive lunar guide, The Moon: A Full Description and Map of Its Principal Physical Features, published in 1895, included his carefully drawn maps of the lunar near side’s four quadrants.

The takeaways for Elger Crater, which honors British astronomer Thomas Gwyn Elger, are that the lunar crater resides in southern Palus Epidemiarum (Marsh of Epidemics) in the near side’s southwestern quadrant; that the primary crater parents two satellites; and that the crater’s namesake particularly is remembered for his detailed, illustrated lunar guide, The Moon, published in 1895.

Detail of Shaded Relief and Color-Coded Topography Map shows Elger Crater’s (bottom center) neighborhood in the near side’s southwestern quadrant: U.S. Geological Survey, Public Domain, via USGS Astrogeology Science Center / 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 shows Elger Crater (lower left center), with nearby neighbor Capuanus P (right) and Ramsden G (left), in Palus Epidemiarum; R.S. Saunders and D.E. Wilhelms, Geologic Map of the Wilhelm Quadrangle of the Moon (1974): U.S. Geological Survey, via USGS Publications Warehouse @ https://pubs.usgs.gov/imap/0824/plate-1.pdf

Detail of Shaded Relief and Color-Coded Topography Map shows Elger Crater’s (bottom center) neighborhood in the near side’s southwestern 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

For further information:

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