William Herschel First Glimpsed Uranian Ring System on March 4, 1787

Summary: German-British astronomer William Herschel first glimpsed the Uranian ring system on March 4, 1787, less than six years after discovering Uranus.

William Herschel’s sketches of Uranian ring system on March 4 and March 5, 1787 (figure 7) and on March 16, 1787 (figures 8-10); engraving by James Basire I (Oct. 6, 1730-Sept. 6, 1802) and/or James Basire II (Nov. 12, 1769-May 13, 1822); W. Herschel, “On the Discovery of Four Additional Satellites” (1797), Tab. III, between pages 78 and 79: Public Domain, via Biodiversity Heritage Library

German-British astronomer William Herschel first glimpsed the Uranian ring system on March 4, 1787, less than six years after his discovery of the ring system’s parent body, ice giant planet Uranus.

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

The conscientious observational astronomer continued to scrutinize the Uranian system. He evaluated the planet’s shape and considered the possibility of a ring or rings as shaping the planet’s outline. He detailed his ring search in an article read at the Royal Society’s Dec. 14, 1797, meeting.

Seven of the entries from Herschel's observational journals for 1787 and 1789 noted his detection of a ring system for the planet. He included four sketches of his sightings in his report to the Royal Society.

On Feb. 4, 1787, Herschel viewed Uranus with his 20-foot reflector telescope, power 300. In his observational journal entry, he noted: “Well defined; no appearance of any ring; much daylight” (page 67).

Yet, one month later, on March 4, he pondered: “I begin to entertain a suspicion that the planet is not round. When I see it most distinctly, it appears to have double, opposite points. See figure 7. Perhaps a double ring; that is, two rings, at rectangles to each other.”

He reported for the following day, March 5: “The Georgian Sidus not being round, the telescope was turned to Jupiter. I viewed that planet with 157, 300, and 480, which shewed it perfectly well defined. Returning to the Georgian planet, it was again seen affected with projecting points. Two opposite ones, that were large and blunt, from preceding to following; and two others, that were small and less blunt, from north to south. See figure 7.”

He reported that two days later, on March 7: “Position of the great ring R, from 70° S.P. to 70° N.F. Small ring r, from 20° N.P. to 20° N.F. 600 shewed R and r. 800 R and r. 1200 R and r.”

The next annular sighting reported by Herschel occurred a little over one year 11 and one-half months later, on Feb. 22, 1789. He summarized his findings as: “A ring was suspected.”

His entry for March 16, 1789, extensively described his ring findings: “7h 37’. I have turned my speculum 90° round. A certain appearance, owing to a defect which it has contracted by exposure to the air since it was made, is gone with it; (see fig. 9 and 10;) but the suspected ring remains in the place where I saw it last.

“7h 50’. Power 471 shews the same appearance rather stronger. Power 589 still shews the same.

“Memorandum. The ring is short, not like that of Saturn. It seems to be as in figure 8; and this may account for the great difficulty of verifying it. It is remarkable that the two ansæ seem of a colour a little inclined to red. The blur occasioned by the fault of the speculum is, to-night, as represented in figure 9. The other evening it was as in figure 10; and the ring is likewise as it was the same evening” (page 68).

Four evenings later, on March 20, Herschel observed: “7h 53’. When the satellites are best in focus, the suspicion of a ring is the strongest.”

Herschel’s entry for Dec. 15, almost nine months later, announced: “The planet is not round, and I have not much doubt but that it has a ring.”

The takeaways for William Herschel’s first glimpse of the Uranian ring system on March 4, 1787, are that he reported his annular search at the Dec. 14, 1787, meeting of The Royal Society of London; that only one of the entries (for Feb. 4, 1787) in his observational journals for 1787 and 1789 noted the absence of a ring system; and that the German-British astronomer included four sketches of his ringed sightings in his report.

The National Aeronautics and Space Administration’s (NASA) Hubble Space Telescope captured ever more oblique (shallower) tilts of Uranus, as viewed from Earth; the Uranian ring system culminated in fully edge-on view (right), obtained Aug. 14, 2007, by Hubble’s Wide Field Planetary Camera 2 (WFPC-2): courtesy NASA / ESA (European Space Agency / M. (Mark Robert) Showalter (SETI Institute), via NASA Hubblesite / Space Telescope Science Institute (STScI)

Acknowledgment

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

Image credits:

William Herschel’s sketches of Uranian ring system on March 4 and March 5, 1787 (figure 7) and on March 16, 1787 (figures 8-10); engraving by James Basire I (Oct. 6, 1730-Sept. 6, 1802) and/or James Basire II (Nov. 12, 1769-May 13, 1822); W. Herschel, “On the Discovery of Four Additional Satellites” (1797), Tab. III, between pages 78 and 79: Public Domain, via Biodiversity Heritage Library @ https://biodiversitylibrary.org/page/49110012

The National Aeronautics and Space Administration’s (NASA) Hubble Space Telescope captured ever more oblique (shallower) tilts of Uranus, as viewed from Earth; the Uranian ring system culminated in fully edge-on view (right), obtained Aug. 14, 2007, by Hubble’s Wide Field Planetary Camera 2 (WFPC-2): courtesy NASA / ESA (European Space Agency / M. (Mark Robert) Showalter (SETI Institute), via NASA Hubblesite / Space Telescope Science Institute (STScI) @ https://hubblesite.org/contents/media/images/2007/32/2175-Image.html?news=true

For further information:

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Available via Biodiversity Heritage Library @ https://biodiversitylibrary.org/page/49109920
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