Earth and Space News: Gill Crater Honors British Astronomer Sir David Gill

Summary: Gill Crater honors British astronomer Sir David Gill, who was a pioneer in using astrophotography to determine star brightness and positions.

Detail of southwest-facing view, obtained in 1971 by Apollo 15 mission’s Hasselblad camera, shows lunar near side’s Gill Crater system; NASA ID AS15-96-13093: James Stuby (Jstuby), Public Domain (CC0 1.0), via Wikimedia Commons

Gill Crater honors British astronomer Sir David Gill, who explored his interest in astronomical distance and stellar brightness via mastery of the heliometer and pioneering use of astrophotography.

Gill Crater is a south polar-latitude impact crater that lies near the lunar near side’s southeastern limb. Impacts have pummeled the eroded crater’s rim. Craterlets gouge the old crater’s relatively level interior floor.

Gill Crater is centered at minus 63.77 degrees south latitude, 75.95 degrees east longitude, according to the International Astronomical Union’s (IAU) Gazetteer of Planetary Nomenclature. The southern hemisphere crater finds its northernmost and southernmost latitudes at minus 62.71 degrees south and minus 64.82 degrees south, respectively. The eastern hemisphere crater posts easternmost and westernmost longitudes of 78.33 degrees east and 73.56 degrees east, respectively. Gill Crater’s diameter measures 63.9 kilometers.

Gill Crater parents eight satellites in the south polar latitudes on the lunar near side. One satellite, Gill D, resides to the east of its parent. Seven of the Gill Crater system’s eight satellites associate with their parent’s western side.

Gill Crater lies to the southwest of Mare Australe (Southern Sea). The middle- to polar-latitude lunar mare (Latin: mare, “sea”) wraps around the lunar near side’s southeastern limb in its occupancy of far side and near side portions of the moon’s eastern and southern hemispheres.

Mare Australe is centered at minus 47.77 degrees south latitude, 91.99 degrees east longitude. The southern hemisphere lunar mare records northernmost and southernmost latitudes of minus 31.84 degrees south and minus 64.2 degrees south, respectively. The eastern hemisphere lunar mare registers easternmost and westernmost longitudes at 113.36 degrees east and 70.43 degrees east, respectively. Mare Australe has a length of 996.84 kilometers.

Gill Crater honors British astronomer Sir David Gill (June 12, 1843-Jan. 24, 1914). The International Astronomical Union (IAU) approved Gill as the crater’s official name in 1964, during the organization’s XIIth (12th) General Assembly, held in Hamburg, Germany, from Tuesday, Aug. 25, to Thursday, Sept. 3. The letter designations for the Gill Crater system’s eight satellites received approval in 2006.

Gill’s obituary in the Feb. 12, 1915, issue of the Monthly Notices of the Royal Astronomical Society acknowledged his “. . . incalculable influence . . .” on “. . . precision of observation” (page 237). In 1863, Gill’s collaboration with Scottish physicist David Thomson (Nov. 27, 1817-Jan. 31, 1880) in reviving King’s College’s Cromwell Tower Observatory inspired Gill’s interest in observational astronomy.

From 1872 to 1876, Gill directed the equipping of Dun Echt Observatory in northeastern Aberdeenshire, northeastern Scotland. The private observatory was founded by James Ludovic Lindsay, 26th Earl of Crawford and 9th Earl of Balcarres (July 28, 1847-Jan. 31, 1913).

A 4-inch (10-centimeter) heliometer numbered among the fine instruments designed under Gill’s supervision for Dun Echt Observatory. Gill acquired mastery of the heliometer in preparation for Lord Crawford’s private expedition to observe the Dec. 9, 1874, transit of Venus from the Indian Ocean island of Mauritius (French: République de Maurice). Heliometers originally were designed for measurements of seasonal variations in the sun’s diameter. The accuracy of heliometers expanded their usage to the measurement of angular distances between stars and other celestial bodies.

In 1879, Gill was appointed as successor to English astronomer Edward James Stone (Feb. 28, 1831-May 6, 1897) as Her Majesty’s Astronomer at the Cape of Good Hope. He began his duties at the Royal Observatory on South Africa’s Cape Peninsula on May 29, 1879. Gill sailed from the Cape on Oct. 3, 1906. His formal retirement, after 27 years eight-plus months of service, took place Feb. 20, 1907.

Gill’s scrutiny of his photographs of the Great Comet of 1882 (formally designated C/1882 R1, 1882 II, 1882b) revealed to him the value of astrophotography in determining the brightness and positions of stars. Between 1885 and 1890 the Royal Observatory at the Cape of Good Hope conducted an extensive photographic survey of Southern Hemisphere stars ranged between minus 18 degrees south declination and the south celestial pole (minus 90 degrees south declination). Dutch astronomer Jacobus Cornelius Kapteyn (Jan. 19, 1851-June 18, 1922) analyzed Gill’s glass plate photographs with a measuring instrument of his own design known as the parallactic instrument of Kapteyn. The Gill-Kapteyn collaboration yielded the Cape Photographic Durchmusterung (CPD), a star catalog of magnitudes and positions for 454,875 southern sky stars published in three volumes from 1895 to 1900.

The takeaways for Gill Crater, which honors British astronomer Sir David Gill, are that the eroded lunar impact crater lies southwest of Mare Australe (Southern Sea) near the near side’s southeastern limb; that the south polar region crater parents eight satellites; that the crater’s namesake is credited with pioneering astrophotography as an effective resource for measuring stellar brightness and positions; and that Sir David Gill’s photographs of the Great Comet of 1882 inspired his exploration of astrophotography.

Detail of Shaded Relief and Color-Coded Topography Map shows Gill Crater (upper left) as high-latitude occupant of the lunar near side’s south polar region: 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:

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Earth and Space News

Wednesday, June 5, 2013

Gill Crater Honors British Astronomer Sir David Gill

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