Sky & Telescope - August 2022 - 30

Visual Astronomy
ings extending across them. Nevertheless, observers noted
such features from time to time. In February 1887, Charles
Émile Stuyvaert worked with the 15-inch Cooke refractor
of the Royal Observatory of Belgium to record radial markings
in both the A and B rings. In 1896, legendary observer
Eugène Michel Antoniadi used the 9-inch refractor at Camille
Flammarion's observatory at Juvisy-sur-Orge, in France, and
reported similar markings in the A ring. He had the impression
that the ring might be " breaking into fragments. "
Into the Unexpected
These observations became widely known thanks to Arthur
Francis O'Donel Alexander's magisterial 1962 book, The
Planet Saturn: A History of Observation, Theory and Discovery.
However, they were generally dismissed as quaint artifacts
from a bygone era of visual planetary observing - much like
the famously discredited canals of Mars.
In general, scientists regarded using telescopes to observe
planetary detail as passé in an era in which professional
astronomers increasingly relied on photography and, ultimately,
spacecraft reconnaissance to advance their research.
Nevertheless, in the 1970s a few amateurs continued to
champion visual planetary observing. The most successful
was Stephen James O'Meara.
Inspired by the efforts of the Bonds, Tuttle, and Philip Sidney
Coolidge, O'Meara was studying Saturn with the Harvard
Observatory's 9-inch refractor (the stuck dome of the more
famous 15-inch rendered that instrument inaccessible at
the time), when Harvard astronomer Fred Franklin asked if
O'Meara would assist in an observing project.
Among the many conundrums of planetary astronomy
at the time was the so-called quadrupole brightness asymmetry
in Saturn's A ring - an azimuthal variation of about
10% in the surface brightness of the ring (S&T: July 2021,
p. 52). French astronomer Henri Camichel discovered the
anomaly in photographs captured at France's Pic du Midi
Observatory in 1958.
SUBTLE SHADINGS One of the most intriguing renderings of
Saturn is this one by Émile Stuyvaert, recorded on February 8, 1887,
while using the 15-inch refractor of the Royal Observatory of Belgium.
It's one of few drawings made in the visual era that shows spokelike
markings in the inner part of the B ring - though it also shows them
on the inside of the A ring and even in the crepe ring, indicating the
features were likely illusory.
Franklin, a ring specialist, attributed the brightness variations
to gravitational interactions (clumping) among the
ring particles. In the mid-1970s, while Franklin was overseeing
photometric measurements with the 16-inch Boller and
Chivens reflector at Harvard's Oak Ridge Observatory, he suggested
that O'Meara embark on a simultaneous visual campaign
with the 9-inch. Within a month, just before Saturn
was lost in conjunction with the Sun, O'Meara succeeded in
recording 0.1-magnitude brightness variations in the A ring
that agreed with the Oak Ridge photometric studies.
When the project ended, O'Meara began to wonder
whether, despite the negative findings of professional astronomers,
similar brightness variations might be detected in the B
ring as well. So, he returned to the telescope, and on November
13, 1976 - just a few days before his 20th birthday - he
spotted faint radial markings that he called " spikes " (now
known as " spokes " ) on the eastern (morning) ansa of the B
ring. He detected no such features on the western (evening)
DETAILS REAL AND IMAGINED Saturn is a tantalizing
and frustrating object for the observer.
In addition to real features, various illusory and
optical effects complicate the picture, as shown
in these sketches by Belgian astronomer Émile
Stuyvaert. His depiction of the B ring spokes
might seem credible had he not also included
them in the A and C rings.
30 AUGUST 2022 * SKY & TELESCOPE
STUYVAERT SKETCH SERIES: WILLIAM SHEEHAN / PUBLIC DOMAIN;
STUYVAERT FULL DISK SATURN: THOMAS A. DOBBINS / PUBLIC DOMAIN
Sky & Telescope - August 2022

Table of Contents for the Digital Edition of Sky & Telescope - August 2022
