Giovanni Donati Discovered Great Comet of 1858 Wednesday, June 2, 1858

Summary: Italian 19th-century astronomer and comet discoverer Giovanni Donati discovered the Great Comet of 1858 Wednesday, June 2, 1858, from Florence, Italy.

Comet Donati (C/1858 L1; 1858 VI) on Wednesday, Sep. 29, 1858, the day on which the long-period comet's discover, 19th-century Italian astronomer Giovanni Battista Donati, was promoted from assistant (aide-astronome) to assistant astronomer (astronome-adjoint) at La Specula in Florence, Italy; steel engraving of Comet of Donati of 1858 as it appeared Sep. 29, 1858, 7:00 p.m. MST, from Observatory of Harvard College, in G.P. Bond, Account of the Great Comet of 1858 (1862), Plate VII, between pages 26 and 27: Not in copyright, via Internet Archive

Italian 19th-century astronomer and comet discoverer Giovanni Battista Donati discovered the Great Comet of 1838, popularly namesaked Comet Donati or Donati's Comet, on Wednesday, June 2, 1858, from La Specola in Florence, Italy.

La Specola (Italian; "astronomical observatory") was constructed between 1780 and 1789 at the initiative of Leopold II (May 5, 1747-March 1, 1792), who reigned Sep. 30, 1790, until his death as the second-to-last Holy Roman Emperor (Latin: Romanorum Imperator; German: Römisch-Deutscher Kaiser) and the second of three from the House of Habsburg-Lorraine. The observatory was built as an annex to the Imperial Regio Museo di Fisica e Storia Naturale (The Imperial-Royal Museum for Physics and Natural History), which had opened in 1785. The scientific complex was located in the former Palazzo Torrigiani, at 17, via Romana, in the Oltrarno quarter on the Arno River's left, south bank.

Giovanni Donati (Dec. 16, 1826-Sep. 20, 1873) made his discovery at 10:00 p.m. He telescopically discerned the new comet as a "faint nebulosity" in Leo the Lion constellation, according to co-authors Antonella Gasperini and Daniele Galli of Arcetri Observatory (Osservatorio Astrofisico di Arcetri) and Laura Nenzi of the University of Tennessee's Department of History in "The worldwide impact of Donati’s comet on art and society in the mid-19th century" (page 340), published in Symposia Proceedings of the International Astronomical Union in January 2009.

Donati sighted the cometary solar system traveler near Leo's head, as described (page 126) by Ronald Stoyan in Atlas of Great Comets, published as first English edition, translated by Storm Dunlop, in 2015. The Sickle asterism, configured as a backward question mark, represents the head and shoulders of the starry lion.

At the time of his cometary discovery, Donati was employed at La Specola as an assistant (aide-astronome) to the observatory's director, Italian astronomer, engineer and optical instrument maker Giovanni Battista Amici (March 25, 1786-April 10, 1863). He had been appointed to La Specola on Sunday, Aug. 1, 1852, and had been promoted to the assistantship in October 1854. His great discovery in June led to his promotion, less than four months later, to assistant astronomer (astronome-adjoint) on Wednesday, Sep. 29, 1858. On Thursday, Dec. 22, 1859, approximately nine and one-half months after Comet Donati's last visibility, Donati was appointed to La Specula's directorship, according to Royal Greenwich Observatory astronomer Edwin Dunkin (Aug. 19, 1821-Nov. 26, 1898) in his obituary (page 153) on Donati, published in the February 1974 issue of Monthly Notices of the Royal Astronomical Society (pages 153-155).

Donati's June discovery initially was designated as 1858 VI. Its official designation is C/1858 L1. Comet Donati and Donati's Comet are its popular designations.

Donati's June discovery numbered as his fourth cometary find. His first cometary discovery happened Sunday, June 4, 1854. He sighted his second discovered comet, C/1855 L1 Donati, on Sunday, June 3, 1855, and his third, C/1857 V1 Donati-van Arsdale, on Tuesday, Nov. 10, 1857. After his Great Comet of 1858, Donati brought his career total of discovered comets to six. He sighted his fifth comet, C/1864 O1 Donati-Toussaint, on Saturday, July 23, 1864, and sixth comet, C/1864 R1 Donati, on Friday, Sep. 9, 1864 (Obituary, page 154).

Donati's Comet became a naked-eye apparition as of Thursday, Aug. 19, 1858. Its lengthy naked-eye visibility lasted through Saturday, Dec. 4, 1858 (page 131), according to "The Earliest Comet Photographs: Usherwood, Bond, and Donati 1858," published in the May 1996 issue of Journal for the History of Astronomy by Jay Myron Pasachoff (July 1, 1943-Nov. 20, 2022), Williams College's Astronomy Department and Hopkins Observatory; Roberta J. M. (Jeanne Marie) Olson, Wheaton College's Art History Department; and Martha L. (Locke) Hazen (July 15, 1931-Dec. 23, 2006), Harvard-Smithsonian Center for Astrophysics.

Comet Donati's telescopically visual passage continued through March 1859. Her Majesty's Astronomer at the Cape of Good Hope, Irish-born South African astronomer Sir Thomas Maclear (March 17, 1794-July 14, 1879), reported the great comet's last telescopic sighting in "Observations of Donati's Comet, made at the Royal Observatory, Cape of Good Hope, between October 11th, 1858, and March 4th, 1859," published in volume 29 of Memoirs of the Royal Astronomical Society.

Orbital observations were recorded by Sir Thomas, his son, George William Herschel "G.W.H." Maclear (July 25, 1836-June 26, 1892) and his assistant, British astronomer William Mann (Oct. 25, 1817-April 30, 1873). Mann's observations via an 8 1/2-inch equatoreal, "which comprehended the whole interval of visibility, commencing on the 11th of October and ending on the 4th of March following." Sir Thomas and his son shared a 46-inch equatoreal, which was usable from Saturday, Oct. 16, to Monday, Nov. 15, "when the comet became too faint to be observed with that instrument armed with a spider-line micrometer" (pages 59-60).

The comet's faintness in February 1859 troubled Mann's observations. On Sunday, Feb. 27, he stated: "Difficult; the comet repeatedly obliterated by cloud." In his last note, Monday, Feb. 28, Mann reported: "Compelled to wait until the comet was separated sufficiently from a star of 12th magnitude. It was then too law and faint to allow of satisfactory measurement" (page 73).

Last observation of Donati's Comet occurred Friday, March 4, 1859, at 08:39:59.4 Cape Mean Time as the cosmic snowball's faintness and distance from Southern Hemisphere telescopic visibility increased. Mann recorded Comet Donati's last-known position at right ascension (RA) 22 hours 32 minutes 5.27 seconds, North Polar Distance (N.P.D.) 152 degrees 5 minutes 1.33 seconds (page 72).

portrait of 19th-century Italian astronomer and comet discoverer Giovanni Battista Donati by Italian artist Adolfo Matarelli (1832-1887): Public Domain, via Wikimedia Commons

Acknowledgment

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

Image credits:

Comet Donati (C/1858 L1; 1858 VI) on Wednesday, Sep. 29, 1858, the day on which the long-period comet's discover, 19th-century Italian astronomer Giovanni Battista Donati, was promoted from assistant (aide-astronome) to assistant astronomer (astronome-adjoint) at La Specula in Florence, Italy; steel engraving of Comet of Donati of 1858 as it appeared Sep. 29, 1858, 7:00 p.m. MST, from Observatory of Harvard College, in G.P. Bond, Account of the Great Comet of 1858 (1862), Plate VII, between pages 26 and 27: Not in copyright, via Internet Archive @ https://archive.org/details/accountofgreatco00bonduoft/page/41/mode/1up

portrait of 19th-century Italian astronomer and comet discoverer Giovanni Battista Donati by Italian artist Adolfo Matarelli (1832-1887): Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:GB_Donati.jpg

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