Sky and Telescope - October 2015 - 8

Letters
cal considerations played hardly any role
at all in the naming of three craters along
Mare Nectaris for Christian ﬁgures is
mistaken. It was almost inevitable that
Riccioli, a 17th-century Jesuit, would
name a crater "Catharina." Saint Catherine is one of the traditional patron saints
of scientists in general and astronomers
in particular. In Orthodox icons, she is
frequently depicted with an armillary
sphere, a quadrant, or some other piece of
astronomical equipment.
Bishop Theophilus, contrary to the
article, is not a Catholic saint, and indeed
he's remembered as the persecutor of
the much-loved Saint John Chrysostom.
So it is unlikely that naming a crater for
him would earn many "points with the
Church." Instead, Theophilus and his
canonized nephew, Saint Cyrillus, are on
the Moon for an impeccably astronomi-

75, 50 & 25 Years Ago
September-October 1940
Dark Matter "[A very interesting star] is Harvard Variable 10302, located in one of the dark
patches of nebulosity that abound in Sagittarius. [It is] a Cepheid-type variable [with] an
absolute magnitude of -1.5. Since the observed
median apparent magnitude is 14.2, the star
should be 45,000 light years from the sun. . . .
"When measured, however, H. V. 10302 was
found to have the unusually large color index of
about +3m.0, which is comparable to the colors
of the very red N-type stars. . . . The extreme
redness of the star indicates that it lies in a
region of the Milky Way that is heavily obscured
by ﬁne dust particles. . . . When the obscuration is allowed for, the star is found to be only
2800 light years away.
"This investigation is but one phase of a
larger program to determine the distribution of
dark matter in space, and thus to aid in solving
the problem of the size and structure of the
Milky Way system."
What gives Henrietta
Swope's report such a
modern ring is her reference to "dark matter."
Today this term has a
far grander meaning in
cosmology. So much
dark matter is needed
to explain, gravitation-

October 2015 sky & telescope

cal reason. In the late 300s, Theophilus
published a century-long list of accurate
Easter dates based on the 19-year-long
Metonic cycle; in the early 400s, Cyrillus
published a 110-year-long list. This Easter
computus remained an active topic of
astronomical research into the 1800s, and
consequently the revered "giants" of this
ﬁeld - Theophilus, Cyrillus, Dionysius
Exiguus, and Beda - were all assigned
craters by Riccioli.
Norman Hugh Redington
Cambridge, Massashusetts
Andrew Livingston replies: I'm very grateful
to Mr. Redington for pointing out the Easter
connection, and I'd be delighted if he or
anyone else can identify the man with the
many eyes on the left of page 31. But there's
no denying the "S." in Riccioli's label "S.
Theophil." The Coptic Church considers him

a saint, and he still appears in some lists of
current Roman Catholic saints, even though
historian Edward Gibbon described him as
far from saintly: "a bold, bad man, whose
hands were alternately polluted with gold
and with blood." And Riccioli couldn't have
been too impressed either with Theophilus
and Cyrillus's wholesale destruction of classical learning - but, as elsewhere, he prudently left things open to interpretation. As
for Saint Catherine, usually shown with the
wheel of her martyrdom, she is the patron
saint of a long list of professions from lawyers
to wheelwrights. But astronomy? Here the
oﬃcial patron is Saint Dominic, for whom
there's no crater on the Moon.

For the Record
✹ July issue, p. 38: The biblical citation in
Nick Kanas's article on celestial frontispieces
should be Isaiah 40:26.

Roger W. Sinnott
ally, the observed structure and distribution of
galaxies in the universe that theorists believe it
must consist of exotic subatomic particles that
permeate everything.

when warping harnesses were used in ﬁguring
the mirror segments for the Keck telescopes, its
scientists credited Leonard with pioneering the
warping technique.

October 1965
Warping Harness "Arthur S. Leonard . . .
well-known satellite observer and optical
designer from Davis, California, [exhibited his
unobstructed] 'Yolo' reﬂector (named after
the county in which he lives). What a strangelooking telescope! . . .
"At the eyepiece end of the main body is
an 8-inch spherical mirror of 192 inches focal
length. Tilted 3° 04´ from being perpendicular
to the incoming starlight, this primary reﬂects
the image to a 6-inch mirror of the same focal
length. Mounted in a harness to warp its ﬁgure,
the secondary reﬂects light back through the
main body and out of the adapter tube. . . ."
Art Leonard's novelty at the 1965 convention
of the Western Amateur
Astronomers had farreaching consequences.
A mechanical engineer,
he'd worked out the
math for how a mirror
deforms under stress -
and then designed a harness to do so precisely.
Twenty-ﬁve years later,

October 1990
Close Encounter "The Whirlpool galaxy,
M51, and its unusual companion, NGC 5195,
apparently brushed each other only 70 million
years ago. Computer simulations by Sethanne
Howard (Georgia State University) and Gene
G. Byrd (University of Alabama) show that the
companion actually skimmed the edge of the
larger system's disk. . . .
"The companion currently orbits M51 with a
period of about 500 million years and an inclination to the plane of the disk of 50° or so. The
smaller galaxy is spiraling in toward the larger
one; the two should merge in less than three
more orbits. . . ."
Recent modeling eﬀorts do favor this scenario
(that is, several encounters with the smaller
galaxy in an eccentric
orbit). These also show
that a single close pass
of two stray galaxies,
under the right conditions, can create most of
the features seen in the
M51 system.

Sky and Telescope - October 2015

Table of Contents for the Digital Edition of Sky and Telescope - October 2015