Sky & Telescope - July 2020 - 52

A Mystery in
Saturn's C Ring
Have observers witnessed upheavals in the Crepe ring?

n 1890, the philosopher and educator
William James wrote: "Round about
the accredited and orderly facts of every
science there ever ﬂoats a sort of dustcloud of exceptional observations, of
occurrences minute and irregular and
seldom met with, which it always proves
more easy to ignore than to attend to."
The history of visual planetary
observing provides no better example of
James's maxim than a series of controversial observations of Saturn's C ring
that were unfolding about the time he
penned those words.
The March 1887 issue of the British journal The Observatory contained
breaking news from the Belgian astronomer François Terby of the University of

During a 1992 observing run at the Pic
du Midi Observatory Stephen O'Meara
glimpsed delicate blotches in the C ring
that were not as narrow as the ephemeral
spokes in the adjacent B ring.

J U LY 2 0 2 0 * S K Y & T E L E S C O P E

Louvain. During the previous month he
had detected "dark masses" in Ring C
through his 8-inch refractor.
Anomalies in the C ring had also
caught the attention of one of Britain's
leading lunar and planetary observers,
Thomas Gwyn Elger. Using an 8.5-inch
Newtonian reﬂector on February 16,
Elger noticed a pronounced difference
in the brightness of the ansae of Ring
C. In the April issue of The Observatory
he also reported:
On February 25, though the f
[following] ansa of the dark ring
was very dusky, it was perfectly
distinguishable, while the p
[preceding] ansa was noted as
unequally dark, certain parts of its
surface appearing quite black. On
the following night, with excellent
deﬁnition, the p ansa exhibited on
its inner margin three or four large
re-entering angles, like the teeth of
a saw, the space between this jagged
outline and the ball being perfectly
black. . . On March 18, between 9h
and 10h (with a superb image of the
planet, showing Encke's division as a
hair-line on the ansa of ring A) the f
ansa of the obscure ring was a sombre
but easy object, while the p ansa again
exhibited a serrated border. . .

Elger noted that this strange aspect
was not without precedent. William
Stephen Jacob, the director of the Madras
Observatory in India, had seen the inner
edge of the C ring appear irregular "like
the fold of a curtain" on one occasion in
1852 through a 6.2-inch refractor.

The Monthly Notices of the Royal
Astronomical Society published two
lengthy reports by Elger of his Saturn
observations during 1887 and 1888.
These accounts contain detailed descriptions of extraordinary appearances
in the C ring - the frequent unequal
brightness of the ansae, the presence
of amorphous dusky patches, and the
occasional scalloped appearance of its
inner edge.
There was no shortage of corroboration from experienced observers. The
Reverend Phillip Kempthorne of Wellington College and Major Harry Watson, observing from Newbridge, Ireland,
both noted similar phenomena.
The Belgian astronomer Paul Henri
Stroobant saw a pair of prominent
dark notches in the western ansa of
the C ring on April 30, 1890, using the
15-inch refractor at Royal Observatory
in Brussels.
Observing with a 10-inch reﬂector
from Malta, the Reverend T. H. Foulkes
reported than on May 20, 1896, the
C ring ". . . did not possess its usual
uniform appearance, but was decidedly
'lumpy.' I counted six or seven of these
darker shadings, which seemed to have
a tendency to circular formation. . .
Though this planet has been observed
by me for the last 25 years, I have never
before seen this curious formation." Six
nights later he claimed that ". . . the
crape [sic] ring presented a strange and
beautiful appearance in the ansæ
. . . which seemed to be all mottled with
swarming tiny spots, granulated."
These reports were greeted with
widespread skepticism and became the
subject of acrimonious debate. One of
the leading lights of the British Astronomical Association, William Frederick
Denning, noted that the anomalies
". . . were not seen at many observatories where such features, if real, could
hardly have escaped detection."
Many critics attributed the peculiar
appearances in the C ring to the effects
of atmospheric turbulence. Elger countered that they ". . . were invariably seen
to greater advantage in proportion to
the goodness of the night for observing
purposes. . ."

STEPHEN JA MES O'ME A R A

JULY 2020 OBSERVING
Exploring the Solar System by Thomas A. Dobbins

Sky & Telescope - July 2020

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