William Herschel Saw Uranian Rings But Puzzling Views Created Doubt

Summary: Uranus discoverer William Herschel saw Uranian rings but puzzling views created doubt in the German-British astronomer about his annular discoveries.

Rare edge-on view of entire Uranian ring system, obtained Aug. 14, 2007, by NASA Hubble Space Telescope’s Wide Field Planetary Camera 2 (WFPC-2), shows edge-on rings spiking above and below Uranus; blocking out of the planet’s bright glare in the photo interferes with visibility of continuity of ring system across the planet’s face; fan-shaped image artifact represents residual glare, along with edge between inner and outer rings’ exposure: courtesy NASA / ESA (European Space Agency / M. (Mark Robert) Showalter (SETI Institute), via NASA Hubblesite / Space Telescope Science Institute (STScI)

Uranus discoverer William Herschel saw Uranian rings but puzzling views created doubt in the German-British observational astronomer about his annular discoveries.

After discovering Uranus on March 13, 1781, William Herschel (Nov. 15, 1738-Aug. 25, 1822) continued to study the seventh planet from the sun. In a report read at the Royal Society of London’s Dec. 14, 1797, Herschel summarized his 10-year search for definitive observational proof of a ring system on “the Georgian planet.”

He cited his journal entry for Feb. 4, 1787, as detecting “. . . no appearance of any ring . . .” (page 67). He specified that he had examined the planet with his 20-foot reflector telescope, power 300.

Three subsequent journal entries, for March 4 through March 7, noted annular views. The March 7 entry identified “the great ring R” and “Small ring r.”

But, without offering an explanation, Herschel quoted his March 8 entry as stating: “R and r are probably deceptions.”

He expressed doubt in his next journal entry: “Nov. 9. The suspicion of a ring returns often when I adjust the focus by one of the satellites, but yet I think it has no foundation.”

Four entries in 1789 offered positive notations concerning the existence of the Uranian ring system. In particular, Herschel discerned “. . . two annae . . . of a colour a little inclined to red” (page 68) on March 16.

In 1792, however, puzzling views created doubt in the keen-eyed astronomer. His entry for Feb. 26 extensively detailed his efforts to suss Uranus as ringed or ringless.

“6h 34’. My telescope is extremely distinct; and, when I adjust it upon a very minute double star, which is not far from the planet, I see a very faint ray, like a ring crossing the planet, over the centre. This appearance is of an equal length on both sides, so that I strongly suspect it to be a ring. There is, however, a possibility of its being an imperfection in the speculum, owing to some slight scratch: I shall take its position, and afterwards turn the speculum on its axis.

“8h 39’. Position of the supposed ring 55°, 6 from N.P. to S.F.

“9h 56’. I have turned the speculum one quadrant round; but the appearance of the very faint ray continues where it was before, so that the defect is not in the speculum, nor is it in the eye-glass. But still it is now also pretty evident that it arises from some external cause; for it is now in the same situation, with regard to the tube, in which it was 3 1/2 hours ago: whereas, the parallel is differently situated, and the ring, of course, ought to be so too” (pages 68-69).

In assessing his annular study, Herschel assigned great value to these findings. He stated: “. . . the observation of the 26th seems to be very decisive against the existence of a ring” (page 70).

Eight days later, on March 5, Herschel noted: “I viewed the Georgian planet with a newly polished speculum, of an excellent figure. It shewed the planet very well defined, and without any suspicion of a ring” (page 69).

Herschel evaluated the possibility of a ring system in the context of the hypothesis that established his observational guidelines. “When the surmises arose at first, I thought it proper to suppose, that a ring might be in such a situation as to render it almost invisible; and that, consequently, observations should not be given up, till a sufficient time had elapsed to obtain a better view of such a supposed ring, by a removal of the planet from its node. This has now sufficiently been obtained in the course of ten years; for, let the node of the ring have been in any situation whatsoever, provided it kept to the same, we must by this time have had a pretty good view of the ring itself,” he explained (page 70).

Herschel cited the last 1792 ring entry that he presented at the Royal Society’s Dec. 14, 1792, meeting as critical to the conclusion that he was drawing about the seventh planet’s ring system. “Placing therefore great confidence on the observation of March 5, 1792, supported by my late views of the planet, I venture to affirm, that it has no ring in the least resembling that, or rather those, of Saturn.”

Yet, despite his dismissal of a Saturn-styled ring system around his planetary discovery, Herschel included in his Dec. 14, 1792, report an entry for Dec. 4, 1793: “There is a suspicion of some apparatus about the planet” (page 69).

The takeaways for puzzling views creating doubt despite William Herschel’s sightings of the Uranian rings in 1787 and 1789 are that the German-British astronomer concluded his 10-year search for rings around the planet that he had discovered in 1781 by valuing ringless views obtained Feb. 26 and March 5, 1792, but that he included in his Dec. 14, 1797, report an entry for Dec. 4, 1793, that suspects “some apparatus around the planet.”

a ringed view of Uranus in a false color image assembled from exposures taken July 3, 1995, by Hubble Space Telescopes Wide Field Planetary Camera-2 (WFPC2); NASA ID: PIA01280; image addition date 1998-08-02; image credit NASA / JPL (Jet Propulsion Laboratory) / STScI (Space Telescope Science Institute): May be used for any purpose without prior permission, via NASA JPL Photojournal

Acknowledgment

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

Image credits:

Rare edge-on view of entire Uranian ring system, obtained Aug. 14, 2007, by NASA Hubble Space Telescope’s Wide Field Planetary Camera 2 (WFPC-2), shows edge-on rings spiking above and below Uranus; blocking out of the planet’s bright glare in the photo interferes with visibility of continuity of ring system across the planet’s face; fan-shaped image artifact represents residual glare, along with edge between inner and outer rings’ exposure: courtesy NASA / ESA (European Space Agency / M. (Mark Robert) Showalter (SETI Institute), via NASA Hubblesite / Space Telescope Science Institute (STScI) @ https://hubblesite.org/uploads/image_file/image_attachment/15853/print.jpg

a ringed view of Uranus in a false color image assembled from exposures taken July 3, 1995, by Hubble Space Telescopes Wide Field Planetary Camera-2 (WFPC2); NASA ID: PIA01280; image addition date 1998-08-02; image credit NASA / JPL (Jet Propulsion Laboratory) / STScI (Space Telescope Science Institute): May be used for any purpose without prior permission, via NASA JPL Photojournal @ https://photojournal.jpl.nasa.gov/catalog/PIA01280;
Generally not subject to copyright in the United States; may use this material for educational or informational purposes, including photo collections, textbooks, public exhibits, computer graphical simulations and Internet Web pages; general permission extends to personal Web pages, via NASA Image and Video Library @ https://images.nasa.gov/details-PIA01280

For further information:

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