Gertrude Is Largest Known Crater on Largest Uranian Moon Titania

Summary: Gertrude is the largest known crater on largest Uranian moon Titania, which was discovered by Uranus discoverer William Herschel on Jan. 11, 1787.

Gertrude (center left, between 270 and 300 degrees east), the largest known crater on largest Uranian moon Titania, lies in the Titania’s Uranus-facing southern hemisphere; U.S. Geological Survey, The Southern Hemispheres of Umbriel, Titania, and Oberon; prepared for the Voyager Imaging Science Team in Cooperation With the Jet Propulsion Laboratory, California Institute of Technology and The National Aeronautics and Space Administration, 1988; mosaic made with Voyager 2 images 1523U2-001 and 1137U2-001: U.S. Geological Survey, via IAU Gazetteer of Planetary Nomenclature

Gertrude is the largest known crater on largest Uranian moon Titania, which was discovered by German-British astronomer William Herschel (Nov. 15, 1738-Aug. 25, 1822) on Jan. 11, 1787, five years nine months 29 days after his discovery of Titania’s primary body, Uranus.

Gertrude is centered at minus 15.8 degrees south latitude and 287.1 degrees east longitude, according to the International Astronomical Union’s Gazetteer of Planetary Nomenclature. Gertrude’s northernmost and southernmost latitudes extend to minus 14.1 degrees south and minus 17.6 degrees south, respectively. The impact crater’s easternmost and westernmost longitudes reach 297.1 degrees east and 277.1 degrees east, respectively. Gertrude’s diameter spans 326 kilometers.

Gertrude’s diameter approximates one-fifth of Titania’s diameter. As the largest Uranian satellite, Titania has an approximate diameter of 1,578 kilometers, according to planetary geologist Jeffrey M. Moore and his four planetary scientist co-authors, Paul M. Schenk, Lindsey S. Bruesch, Erik Asphaug and William B. McKinnon, in their article, “Large Impact Features on Middle-Sized Icy Satellites,” in the October 2004 issue of Icarus. Titania’s radius is calculated at 788.9 kilometers, according to “Uranian Satellite Fact Sheet” by Goddard Space Flight Center (GSFC) planetary scientist David Richard Williams on the NASA Space Science Data Coordinated Archive (NSSDCA) website.

Moore and his four co-authors describe Gertrude as a “raised rim, circular feature” (page 436). The authors’ colorized digital elevation models (DEMs) of map-projected Voyager 2 image (Flight Data Subsystem FDS 26843.13) reveal Gertrude’s typical impact rim, which rises approximately 2 kilometers above the crater’s floor. In their July 4, 1986, article in Science, astronomer Bradford A. Smith and 39 co-authors (including astrophysicist and cosmologist Carl Sagan and astrogeology pioneer Eugene Shoemaker) proposed the formation of Titania’s few large impacts from bombardment by impactors or orbital debris or both.

An annular (ring-shaped) dome is centrally located on the crater’s floor. The dome has a diameter of approximately 150 kilometers and reaches an elevation of 2 to 3 kilometers. The authors note that the dome is superimposed by only a few craters.

The compatible elevations of Gertrude’s rim and central dome are also comparable with the elevations of the crater’s environs. Moore’s team finds that Gertrude’s low topographic relief and paucity of impact ejecta-created landforms suggest the crater’s post-impact modification, for example, through coverage by emplaced materials.

Gertrude lies in Titania’s Uranus-facing southern hemisphere. Two smaller craters, Lucetta and Mopsa flank Gertrude.

Lying to Gertrude’s west, Lucetta is centered at minus 14.7 degrees south latitude, 277.1 degrees east longitude. The small crater obtains northernmost and southernmost latitudes at minus 14.4 degrees south and minus 15 degrees south, respectively. It marks its easternmost and westernmost longitudes at 279.6 degrees east and 274.6 degrees east, respectively. Lucetta’s diameter measures 58 kilometers.

Lying to Gertrude’s east, Mopsa is centered at minus 11.9 degrees south latitude, 302.2 degrees east longitude. Mopsa registers northernmost and southernmost latitudes at minus 11.4 degrees south and minus 12.4 degrees south, respectively. Its easternmost and westernmost longitudes occur at 305.9 degrees east and 298.5 degress east, respectively. Mopsa has a diameter of 101 kilometers.

Characters in plays by Elizabeth playwright William Shakespeare (bapt. April 26, 1564-April 23, 1616) inspired the names of Titanian craters Gertrude, Lucetta and Mopsa. Gertrude recalls the protagonist’s mother in “The Tragedy of Hamlet, Prince of Denmark.” Lucetta’s namesake is a waiting woman in “Two Gentlemen of Verona.” Mopsa is named after a shepherdess in “The Winter’s Tale.” The IAU approved the craters’ name in 1988, during the organization’s XXth (20) General Assembly, held Tuesday, Aug. 2, to Thursday, Aug. 11, in Baltimore, Maryland.

The takeaways for Gertrude as the largest known crater on largest Uranian moon Titania are that Gertrude's diameter of 326 kilometers equates to approximately one-fifth of Titania's diameter and that the large Titanian impact crater's namesake is the protagonist's mother in Elizabethan playwright William Shakespeare's The Tragedy of Hamlet, Prince of Denmark.

Uranus’ south pole (bright area on left) in NASA Hubble Space Telescope image obtained in 2006; NASA’s Voyager 2 spacecraft’s images of Uranus, its rings and its satellites, obtained during January 1986 flyby, covered only the Uranian system’s southern hemisphere because of the current closeness of the planet and satellites’ subsolar points to their south poles; NASA, ESA (European Space Agency, L. Sromovsky and P. Fry (University of Wisconsin), H. Hammel (Space Science Institute) and K. Rages (SETI Institute): NASA Hubble Space Telescope (NASA Hubble), CC BY 2.0 Generic, via Flickr

Acknowledgment

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

Image credits:

Gertrude (center left, between 270 and 300 degrees east), the largest known crater on largest Uranian moon Titania, lies in the Titania’s Uranus-facing southern hemisphere; U.S. Geological Survey, “Pictorial Map of Titania Ut 10M -90/0 AN,” The Southern Hemispheres of Umbriel, Titania, and Oberon; prepared for the Voyager Imaging Science Team in Cooperation With the Jet Propulsion Laboratory, California Institute of Technology and The National Aeronautics and Space Administration, 1988; mosaic made with Voyager 2 images 1523U2-001 and 1137U2-001: U.S. Geological Survey, via IAU Gazetteer of Planetary Nomenclature @ https://planetarynames.wr.usgs.gov/images/umbriel_titania_oberon_I-1920_300dpi.pdf

Uranus’ south pole (bright area on left) in NASA Hubble Space Telescope image obtained in 2006; NASA’s Voyager 2 spacecraft’s images of Uranus, its rings and its satellites, obtained during January 1986 flyby, covered only the Uranian system’s southern hemisphere because of the current closeness of the planet and satellites’ subsolar points to their south poles; NASA, ESA (European Space Agency, L. Sromovsky and P. Fry (University of Wisconsin), H. Hammel (Space Science Institute) and K. Rages (SETI Institute): NASA Hubble Space Telescope (NASA Hubble), CC BY 2.0 Generic, via Flickr @ https://www.flickr.com/photos/nasahubble/46455057294/;
Public Domain, via Windows to the Universe @ https://www.windows2universe.org/uranus/uranus_polar_regions.html

For further information:

Buratti, Bonnie J.; and Joel A. Mosher. “Comparative Global Albedo and Color Maps of the Uranian Satellites.” Icarus, vol. 90, no. 1 (March 1991): 1-13.
Available via ScienceDirect @ https://www.sciencedirect.com/science/article/abs/pii/001910359190064Z?via%3Dihub

Davies, Merton E.; Tim R. Colvin; Frank Y. Katayama; and Peter C. Thomas. “The Control Networks of the Satellites of Uranus.” Icarus, vol. 71, issue 1 (July 1987): 137-147.
Available via ScienceDirect @ https://www.sciencedirect.com/science/article/abs/pii/0019103587901680

International Astronomical Union (IAU) / U.S. Geological Survey (USGS) Gazetteer of Planetary Nomenclature. “Gertrude.” USGS Astrogeology Science Center > Gazetteer of Planetary Nomenclature > Nomenclature > Uranus.
Available @ https://planetarynames.wr.usgs.gov/Feature/2150

International Astronomical Union (IAU) / U.S. Geological Survey (USGS) Gazetteer of Planetary Nomenclature. “Lucetta.” USGS Astrogeology Science Center > Gazetteer of Planetary Nomenclature > Nomenclature > Uranus.
Available @ https://planetarynames.wr.usgs.gov/Feature/3501

International Astronomical Union (IAU) / U.S. Geological Survey (USGS) Gazetteer of Planetary Nomenclature. “Mopsa.” USGS Astrogeology Science Center > Gazetteer of Planetary Nomenclature > Nomenclature > Uranus.
Available @ https://planetarynames.wr.usgs.gov/Feature/4028

International Astronomical Union (IAU) / U.S. Geological Survey (USGS) Gazetteer of Planetary Nomenclature. “Target: Titania.” USGS Astrogeology Science Center > Gazetteer of Planetary Nomenclature > Nomenclature > Uranus.
Available @ https://planetarynames.wr.usgs.gov/Page/TITANIA/target

Johnson, Torrence V.; Robert H. Brown; and James B. Pollack. “Uranus Satellites: Densities and Composition.” JGR (Journal of Geophysical Research) Space Physics, vol. 92, issue A13 (Dec. 30, 1987): 14884-14894.
Available via Wiley Online @ https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/JA092iA13p14884

Johnson, Torrence V.; Robert Hamilton Brown; and Laurence A. Soderblom. “The Moons of Uranus.” Scientific American, vol. 256, no. 4 (April 1987): 48-61.
Available via JSTOR @ https://www.jstor.org/stable/24979362

Lavoie, Sue; Lisa Gaddis; and Rafael Alanis, webmaster. “c2684313.ibg.” NASA Jet Propulsion Laboratory PDS Imaging Node > Data.
Available @ https://pds-imaging.jpl.nasa.gov/data/vg2-u-iss-2-edr-v1.0/vg_0003/browse/titania/c2684313.ibg

Levy, David H. Skywatching. Revised and updated. San Francisco CA: Fog City Press, 1994.

Marriner, Derdriu. “William Herschel Discovered First Two Uranian Moons on Jan. 11, 1787.” Earth and Space News. Wednesday, Jan. 12, 2011.
Available @ https://earth-and-space-news.blogspot.com/2011/01/william-herschel-discovered-first-two.html

McNally, D. (Derek), ed. XXth General Assembly Transactions of the IAU Vol. XX B Proceedings of the 20th General Assembly Baltimore, MD, August 2-11, 1988. Alphen aan den Rijn, Netherlands: Kluwer Academic Publishers, Jan. 1, 1990.
Available @ https://www.iau.org/publications/iau/transactions_b/

Moore, Jeffrey M.; Paul M. Schenk; Lindsey S. Bruesch; Erick Asphaug; and William B. McKinnon. “Large Impact Features on Middle-Sized Icy Satellites.” Icarus, vol. 171, no. 2 (October 2004): 421-443.
Available @ http://planets.oma.be/ISY/pdf/article_Icy.pdf

Moore, Patrick, Sir. Philip’s Atlas of the Universe. Revised edition. London UK: Philip’s, 2005.

Nelson, Jon; and Anil Natha and Luis Espinoza, webmasters. “Uranus Approach.” NASA JPL Caltech Voyager > Mission > Science > Uranus.
Available @ https://voyager.jpl.nasa.gov/mission/science/uranus/

Nemiroff, Robert; and Jerry Bonnell. “Titania’s Trenches.” NASA (National Aeronautics and Space Administration) APOD (Astronomy Picture of the Day). Jan. 11, 1997.
Available @ https://apod.nasa.gov/apod/ap970111.html

Nemiroff, Robert; and Jerry Bonnell. “Uranus’ Largest Moon: Titania.” NASA (National Aeronautics and Space Administration) APOD (Astronomy Picture of the Day). March 4, 1996.
Available @ https://apod.nasa.gov/apod/ap960304.html

Plescia, J.B. “Cratering History of the Uranian Satellites: Umbriel, Titania and Oberon.” Journal of Geophysical Research, vol. 92, issue A13 (Dec. 30, 1987): 14918-14932.
Available via Wiley Online @ https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/JA092iA13p14918

Russell, Randy. “The Poles of Uranus.” Windows to the Universe > Solar System > Planets > Uranus. Last modified May 5, 2009.
Available @ https://www.windows2universe.org/uranus/uranus_polar_regions.html

Shehktman, Lonnie; and Jay Thompson. “Titania: In Depth.” NASA Science Solar System Exploration > Moons > Uranus.
Available @ https://solarsystem.nasa.gov/moons/uranus-moons/titania/in-depth/

Shehktman, Lonnie; and Jay Thompson. “Titania: By the Numbers.” NASA Science Solar System Exploration > Moons > Uranus.
Available @ https://solarsystem.nasa.gov/moons/uranus-moons/titania/by-the-numbers/

Smith, B.A.; L.A. Soderblom; R. Beebe; D. Bliss; J.M. Boyce; A. Brahic; G.A. Briggs; R.H. Brown; S.A. Collins; A.F. Cook; S.K. Croft; J.N. Cuzzi; G.E. Danielson; M.E. Davies; T.E. Dowling; D. Godfrey; C.J. Hansen; C. Harris; G.E. Hunt; A.P. Ingersoll; T.V. Johnson; R.J. Krauss; H. Masursky; D. Morrison; T. Owen; J.B. Plescia; J.B. Pollack; C.C. Porco; K. Rages; C. Sagan; E.M. Shoemaker; L.A. Sromovsky; C. Stoker; R.G. Strom; V.E. Suomi; S.P. Synnott; R.J. Terrile; P. Thomas; W.R. Thompson; and J. Veverka. “Voyager 2 in the Uranian System: Imaging Science Results.” Science, new series, vol. 233, no. 4759 (July 4, 1986): 43-64.
Available via JSTOR @ https://www.jstor.org/stable/1697495
Available via Zenodo @ https://zenodo.org/record/1230972#.XcxDzFdKiUk

U.S. Geological Survey. “Pictorial Map of Titania Ut 10M -90/0 AN.” The Southern Hemispheres of Umbriel, Titania, and Oberon. Prepared for the Voyager Imaging Science Team in Cooperation With the Jet Propulsion Laboratory, California Institute of Technology and The National Aeronautics and Space Administration. Reston VA: U.S. Department of the Interior, 1988.
Available @ https://planetarynames.wr.usgs.gov/images/umbriel_titania_oberon_I-1920_300dpi.pdf

U.S. Geological Survey. Plate 3. “Pictorial Map of Titania Ut 10M -90/0 AN.” The Southern Hemispheres of Umbriel, Titania, and Oberon. Prepared for the Voyager Imaging Science Team in Cooperation With the Jet Propulsion Laboratory, California Institute of Technology and The National Aeronautics and Space Administration. Reston VA: U.S. Department of the Interior, 1988.
Available @ https://pubs.usgs.gov/imap/1920/plate-3.pdf

U.S. Geological Survey. The Southern Hemispheres of Umbriel, Titania, and Oberon. Prepared for the Voyager Imaging Science Team in Cooperation With the Jet Propulsion Laboratory, California Institute of Technology and The National Aeronautics and Space Administration. Reston VA: U.S. Department of the Interior, 1988.
Available @ https://planetarynames.wr.usgs.gov/images/umbriel_titania_oberon_I-1920_300dpi.pdf

Williams, David R. (Richard), Dr. “Uranus Fact Sheet.” NASA GSFC (Goddard Space Flight Center) NSSDC (NASA Space Science Data Coordinated Archive) > Solar System Exploration > Planetary Science > Uranus.
Available @ https://nssdc.gsfc.nasa.gov/planetary/factsheet/uranusfact.html

Williams David R. (Richard), Dr. “Uranian Satellite Fact Sheet.” NASA GSFC (Goddard Space Flight Center) NSSDC (NASA Space Science Data Coordinated Archive) > Solar System Exploration > Planetary Science > Uranus.
Available @ https://nssdc.gsfc.nasa.gov/planetary/factsheet/uraniansatfact.html

William Herschel Discovered First Two Uranian Moons on Jan. 11, 1787

Summary: William Herschel discovered the first two Uranian moons on Jan. 11, 1787, almost five years 10 months after discovering their primary body, Uranus.

“The Georgian Planet attended by two satellites,” William Herschel’s sketch accurately predicting placements of his two satellite discoveries on Feb. 11, 1787, at about two o’clock in the morning; S south, N north, P preceding, F following, with the Georgian Planet (Uranus) (center), first satellite (now Titania) (below) and second satellite (Oberon) (above); W. Herschel, An Account of the Discovery of Two Satellites (1787), Tab. VII, opposite page 128: Public Domain, via Biodiversity Heritage Library

German-British astronomer William Herschel discovered the first two Uranian moons on Jan. 11, 1787, five years nine months 29 days after his discovery of the satellites’ primary body, Uranus.

William Herschel (Nov. 15, 1738-Aug. 25, 1822) discovered the seventh planet from the sun on March 13, 1781. He referred to the planet as Georgium Sidus (George’s Star) or the Georgian planet, in honor of his royal patron, George III (June 4, 1738-Jan. 29, 1820).

Herschel’s observations of the Georgian system continued after his discovery. Ascertaining whether satellites circled the planet numbered among his searches. On Jan. 11, 1787, Herschel succeeded in detecting two satellites. A little over one month later, the report of Herschel’s satellite discoveries was read at The Royal Society of London’s Feb. 15, 1787. He also shared his specific observational journal entries about his satellite discoveries 28 years four months 28 days after those discoveries in a report read at the June 8, 1815, meeting of The Royal Society of London.

Herschel reported at the Feb. 15, 1787, meeting that he had “. . . ſelected a ſweep which led to the Georgian planet; and, while it paſſed the meridian, I perceived near its diſk, and within a few of its diameters, ſome very faint ſtars whoſe places I noted down with great care” (page 126).

In his report at the June 8, 1815, meeting, Herschel shared his entry describing his discoveries. “1787, January 11d 12h 13m. There is a supposed first satellite about 42 or 43 degrees south following the planet; and a second about 45 degrees north preceding” (page 304).

Herschel reported at the Feb. 15, 1787, meeting that he had wanted to have “no doubts” about his Jan. 11, 1787, discoveries. He stated: “The leaſt hazineſs, otherwiſe imperceptible, may often obſcure ſmall ſtars; and I judged, therefore, that nothing leſs than a ſeries of obſervations ought to ſatisy me, in a caſe of this importance” (page 126).

Herschel then detailed his efforts to assure the accuracy of his suspected satellite discoveries. “To this end I noticed all the ſmall ſtars that were near the planet the 14th, 17th, 18th, and 24th of January, and the 4th and 5th of February . . .”

Herschel’s strategy proved effective for one suspected satellite and convinced him to scrutinize the second suspect. “. . . and though, at the end of this time, I had no longer any doubt of the exiſtence of at leaſt one ſatellite, I thought it right to defer this communication till I could have an opportunity of ſeeing it actually in motion.”

Accordingly, Herschel tracked the strong candidate on Feb. 7 from “. . . about ſix o’clock in the evening, and kept it in view till three in the morning on Feb. the 8th . . .” He noted that “. . . during thoſe nine hours I ſaw this ſatellite faithfully attend its primary planet, and at the ſame time keep on, in its own courſe, by deſcribing a conſiderable arch of its proper orbit.”

Although he was “. . . chiefly attending to the motion of this ſatellite . . . ,” Herschel also sought to observe his other candidate. He attributed his lack of assurance concerning its motion “ . . . to my great attention to the ſormer ſatellite, or to the cloſeneſs of this latter, which was nearly hidden in the rays of the planet . . . Indeed, towards morning, when a change of place, in ſo conſiderable an interval as nine hours, would have been moſt conſpicuous, the moon interfered with the faint light of this ſatellite, ſo that I could no longer perceive it” (pages 126-127).

Feb. 9 brought closure on his two candidates. “. . . I ſaw my firſt diſcovered ſatellite nearly in the place where I expected to find it. I perceived alſo, that the next ſuppoſed ſatellite was not in the ſituation where I had left it on the 7th, and could now diſtinguiſh very plainly that it had advanced in its orbit, ſince that day, in the ſame direction with the other ſatellite, but at a quicker rate.”

Herschel decided that, because this ſatellite’s “more contracted orbit” placed it closer to the Georgian planet, he would “. . . call it in future the firſt ſatellite, though laſt diſcovered, or rather laſt aſcertained . . .” (page 127). Based upon his observations between Jan. 11 and Feb. 11, he provisionally placed the first satellite’s orbital period at “. . . about eight days and three-quarters, and the ſecond in nearly thirteen days and an half” (page 128).

Herschel’s approximations of the orbital periods of his two Uranian satellite discoveries were close to accurate. The first satellite revolves around Uranus in 8.705867 days, according to the Uranian Satellite Fact Sheet on the NASA (National Aeronautics and Space Administration) Space Science Data Coordinated Archive (NSSDCA) website. The second satellite completes its orbit of its primary body in 13.463234 days.

The two Uranian satellites with which William Herschel is credited received names in 1852 from their discoverer’s son, English polymath Sir John Herschel (March 7, 1792-May 11, 1871). Titania, the first satellite, and Oberson, the second satellite, were named after the queen and king of the fairies, respectively, in A Midsummer Night’s Dream by Elizabeth playwright William Shakespeare (bapt. April 26, 1564-April 23, 1616).

The takeaways for William Herschel’s discovery of the first two Uranian moons on Jan. 11, 1787, are that the German-British astronomer made his satellite discoveries approximately five years 10 months after his March 13, 1781, discovery of their primary body, the planet Uranus; that his son, English polymath Sir John Herschel, named them Titania and Oberson, after the queen and king of the fairies in Elizabethan playwright William Shakespeare’s A Midsummer Night’s Dream; and that William Herschel discovered Oberon first but designated Titania as the “firſt ſatellite” because of its closeness to “the Georgian planet.”

The Uranian system includes five major moons, two of which (Titania and Oberon) are credited, for discovery, to Uranus discoverer William Herschel; Atlas Image of Uranus obtained June 7, 1998, by 2MASS Southern Facility; Atlas Image courtesy of 2MASS (Two Micron All Sky Survey), a joint project of the University of Massachusetts (UMass) and the Infrared Processing and Analysis Center / California Institute of Technology (IPAC-Caltech), funded by the National Aeronautics and Space Administration (NASA) and the National Science Foundation (NSF): 2MASS Atlas Image Gallery, Public Domain, via Caltech IPAC / 2MASS (2 Micron All Sky Survey)

Acknowledgment

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

Image credits:

“The Georgian Planet attended by two satellites,” William Herschel’s sketch accurately predicting placements of his two satellite discoveries on Feb. 11, 1787, at about two o’clock in the morning; S south, N north, P preceding, F following, with the Georgian Planet (Uranus) (center), first satellite (now Titania) (below) and second satellite (Oberon) (above); W. Herschel, An Account of the Discovery of Two Satellites (1787), Tab. VII, opposite page 128: Public Domain, via Biodiversity Heritage Library @ https://biodiversitylibrary.org/page/51827593

The Uranian system includes five major moons, two of which (Titania and Oberon) are credited, for discovery, to Uranus discoverer William Herschel; Atlas Image of Uranus obtained June 7, 1998, by 2MASS Southern Facility; Atlas Image courtesy of 2MASS (Two Micron All Sky Survey), a joint project of the University of Massachusetts (UMass) and the Infrared Processing and Analysis Center / California Institute of Technology (IPAC-Caltech), funded by the National Aeronautics and Space Administration (NASA) and the National Science Foundation (NSF): 2MASS Atlas Image Gallery, Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Uranus,_Neptune,_and_their_moons_(2MASS).jpg; via Caltech IPAC / 2MASS (2 Micron All Sky Survey) @ https://old.ipac.caltech.edu/2mass/gallery/images_ss.html

For further information:

Dreyer, J.L.E. (John Louis Emil), comp. The Scientific Papers of Sir William Herschel Including Early Papers Hitherto Unpublished. Vol. I; Vol. II. London, England: The Royal Society and The Royal Astronomical Society, 1912.
Vol. I: Available via HathiTrust @ https://babel.hathitrust.org/cgi/pt?id=mdp.39015010954678
Vol. II: Available via HathiTrust @ https://babel.hathitrust.org/cgi/pt?id=mdp.39015010954744
Vol. I: Available via Internet Archive @ https://archive.org/details/scientificpapers032804mbp/
Vol. II: Available via Internet Archive @ https://archive.org/details/scientificpapers02hersuoft/

Herschel, J. (John), Sir. “I. On the Satellites of Uranus.” Monthly Notices of the Royal Astronomical Society, vol. III, no. 5 (March 14, 1834): 35-36.
Available via Oxford Academic Journals @ https://academic.oup.com/mnras/article/3/5/35/1043585

Herschel, J. (John), Sir. “III. On the Satellites of Uranus – An Abstract of This Paper, the Reading of Which Is Not Yet Concluded, Will Be Given in the Monthly Notice for March.” Monthly Notices of the Royal Astronomical Society, vol. III, no. 3 (Jan. 1834): 19.
Available via Oxford Academic Journals @ https://academic.oup.com/mnras/article/3/3/19/1018015

Herschel, Mr. (William). “XXXII. Account of a Comet. Communicated by Dr. Watſon. Read April 26, 1781.” Philosophical Transactions of the Royal Society of London. Vol. LXXI. For the Year 1781. Part II: 492-501. London, England: Lockyer Davis and Peter Elmsly, Printers to The Royal Society, MDCCLXXXII (1782).
Available via Biodiversity Heritage Library @ https://biodiversitylibrary.org/page/51826184

Herschel, William. “XVI. An Account of the Discovery of Two Satellites Revolving Round the Georgian Planet. Read Feb. 15, 1787.” Philosophical Transactions of the Royal Society of London, vol. LXXVII for the Year 1787, Part I: 125-129. London, England: Lockyer, Davis, and Peter Elmsly, Printers to The Royal Society, MDCCLXXXVII (1787).
Available via Biodiversity Heritage Library @ https://biodiversitylibrary.org/page/51827589
Available via Internet Archive @ https://archive.org/details/philtrans05978816

Herschel, William. “V. The Front-view is a method of uſing the reflecting teleſcope different from the Newtonian, Gregorian, and Caſſagrain forms.” Page 499. “XXVII. Catalogue of One Thouſand new Nebulae and Cluſters of Stars. Read April 27, 1786.” Philosophical Transactions of the Royal Society of London, vol. LXXVI for the Year 1786, Part II: 457-499. London, England: Lockyer Davis and Peter Elmsly, Printers to The Royal Society, MDCCLXXXVI (1786).
Available via Biodiversity Heritage Library @ https://biodiversitylibrary.org/page/51826827

Herschel, William. “Observations of the Satellites of the Georgian Planet, Accompanied by a Theoretical Determination of Their Situation, Whereby Their Identity May Be Ascertained.” Pages 304-343. “XIX. A Series of Observations of the Satellites of the Georgian Planet, Including a Passage Through the Node of Their Orbits; ii: 293-362. London, England: W. Bulmer and Co., MDCCCXV (1815).
Available via Biodiversity Heritage Library @ https://biodiversitylibrary.org/page/51981802
Available via Biodiversity Heritage Library @ https://biodiversitylibrary.org/page/51828400

Herschel, William. “XIX. A Series of Observations of the Satellites of the Georgian Planet, Including a Passage Through the Node of Their Orbits; ii: 293-362. London, England: W. Bulmer and Co., MDCCCXV (1815).
Available via Biodiversity Heritage Library @ https://biodiversitylibrary.org/page/51981791

Lassell, Mr. (William). “Bright Satellites of Uranus (Nos. II. And IV. Of Herschel I.). Observations by Mr. Lassell, with the 20-foot Equatoreal Reflector.” Monthly Notices of the Royal Astronomical Society, vol. 10, issue 6 (April 12, 1850): 135.
Available via Oxford Academic @ https://academic.oup.com/mnras/article/10/6/135/2601301

Lassell, Mr. (William). “Satellites of Uranus. Observations by Mr. Lassell.” Monthly Notices of the Royal Astronomical Society, vol. 8, issue 3 (Jan. 14, 1848): 43-47.
Available via Oxford Academic @ https://academic.oup.com/mnras/article/8/3/43/993946

Lassell, W. “Beobachtungen der Uranus-Satelliten.” Astronomische Nachrichten, vier und dreissigster band (vol. 34), no. 812 (May 26, 1852): 325-328. Altona, Germany: Hammerich & Lesser, 1852. Available via Harvard ADSABS (NASA Astrophysics Data System Abstracts) @ http://adsabs.harvard.edu//full/seri/AN.../0034//0000169.000.html

Lassell. “Entdeckung von 2 neuen Uranus Trabanten.” Astronomische Nachrichten, drei und dreissigster band (vol. 33), no. 783 (Nov. 4, 1851): 259-260. Altona, Germany: Hammerich & Lesser, 1852.
Available via Harvard ADSABS (NASA Astrophysics Data System Abstracts) @ http://articles.adsabs.harvard.edu/full/seri/AN.../0033//0000136.000.html

Levy, David H. Skywatching. Revised and updated. San Francisco CA: Fog City Press, 1994.

Moore, Patrick, Sir. Philip’s Atlas of the Universe. Revised edition. London UK: Philip’s, 2005.

Williams, David R. (Richard), Dr. “Uranus Fact Sheet.” NASA GSFC (Goddard Space Flight Center) NSSDC (NASA Space Science Data Coordinated Archive) > Solar System Exploration > Planetary Science > Uranus.
Available @ https://nssdc.gsfc.nasa.gov/planetary/factsheet/uranusfact.html

Williams David R. (Richard), Dr. “Uranian Satellite Fact Sheet. .” NASA GSFC (Goddard Space Flight Center) NSSDC (NASA Space Science Data Coordinated Archive) > Solar System Exploration > Planetary Science > Uranus.
Available @ https://nssdc.gsfc.nasa.gov/planetary/factsheet/uraniansatfact.html

Young, Kelly. “Uranus Moons Seen Overtaking Each Other for First Time.” NewScientist > Space. May 18, 2007.
Available @ https://www.newscientist.com/article/dn11891-uranus-moons-seen-overtaking-each-other-for-first-time/