Sky and Telescope - April 2018 - 7

to write to Whitaker to ask a technical
question about the lunar craters created
when the S-IVB stages of Saturn rockets
slammed into the Moon - but I mailed
the letter anyway.
Whitaker sent me back a thoughtful,
non-condescending reply, along with a
Polaroid print of an Apollo 16 orbital
image showing one of those craters to
illustrate his point.
Besides his extensive, wonderfully
original research, Whitaker's 1999 book
Mapping and Naming the Moon: A History
of Lunar Cartography and Nomenclature
is a classic.
Perhaps the IAU's ofﬁcials will ﬁnd
a suitable crater near the one named
for Whitaker's longtime collaborator Gerard Kuiper. They should also
consider naming a crater after David
William Glyn Arthur, a colleague of
Whitaker, whose contributions to selenography are likewise fundamental.

Seeing Things in Orion

Bill Pohnan, Jr.
Streamwood, Illinois

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They say "familiarity breeds contempt,"
and that probably captures my perception of the Orion Nebula (S&T: Dec.
2017, p. 32) - which I've been observing and showing to guests for more
than 50 years, starting with a 2-inch
refractor. Yet, absent guests, it hasn't
featured in my observing routine for
years - despite now having a 55-cm
Dobsonian reﬂector and mercifully dark
skies. This article brought home to me,
in such wonderful detail, that I can (and
should) take a completely new look at it.
Paul Dawson
Olancha, California

In February 2016 I took my best-ever
image of the Orion Nebula. The combination of the camera's mounting angle
and my scope's orientation caused the
image to be rotated by 180° from the

75, 50 & 25 YEARS AGO by Roger W. Sinnott
1943

1968

WES ATCHISON

1993

º April 1943
Thorium in the Sun "A search for
the rare radioactive element, thorium, in the sun - begun in 1938
but delayed by insufficient experimental laboratory work - has now
proved fruitful. According to a Science Service report, Dr. Charlotte
E. Moore, of Princeton Observatory, and Dr. Arthur S. King, of the
spectroscopic laboratory at Mt.
Wilson, find that the strongest laboratory lines of the ionized element
coincide with hitherto unidentified
lines in the solar spectrum."
Since then observers have
found thorium in other stars and,
a decade ago, in the Ursa Minor
dwarf galaxy (a member of the
Local Group that's 225,000 lightyears away). Thorium's importance
lies in its unusually long half-life:
14.05 billion years. Comparing its
abundance to that of other heavy
elements, such as uranium, could
yield an independent estimate of a
galaxy's age.

p The iconic Orion Nebula, seen here with
south up, appears to harbor a ghost among the
tangle of red filaments near its left edge.

usual north-up view. I discovered that if
you look at M42 this way, there's a vague
human form - or what I tell my friends
is "Wes's Ghost" - on the nebula's left
side. I thought this was some artifact of
my imaging setup until I saw the M42
article. If you turn those images upside
down, the "ghost" is there in all of
them. Has anyone else ever noticed this?
Charles "Wes" Atchison
Sanger, Texas

º April 1968
First Pulsar "An extraordinary
object in the constellation Vulpecula has been reported by A. Hewish
and his coworkers at Cambridge
University's Mullard Radio Astronomy Observatory in England. Last
July they began operating a large
new antenna array . . .
"Soon they noticed that signals
which seemed at first to be weak
sporadic interference were being
detected [4 minutes earlier each
day, implying that] an extraterrestrial source was passing through
the antenna's fixed reception
pattern. The signals, when present, consisted of a series of pulses
each lasting about 0.3 second and
repeated every 1.337 seconds. . . .
"Whatever the physical nature
of this strange emitter is, it must be
very compact. . . . The source can
be no larger than the planet Mercury, and may be much smaller!"
The second author of Antony
Hewish's paper was graduate
student Jocelyn Bell, who had ﬁrst
noticed the odd signal and recog-

nized its importance. Yet the 1974
Nobel Prize for work related to the
discovery of pulsars went to Hewish and Martin Ryle instead - a
source of controversy ever since.
º April 1993
Big Bang "[In 1990] NASA's Cosmic Background Explorer (COBE)
satellite established that the spectrum of the microwave background
radiation is nearly that of a pure
blackbody, as the Big Bang theory
says it should be. Now the qualification 'nearly' can be dropped. . . .
"At the January AAS meeting,
John C. Mather (NASA-Goddard
Space Flight Center) presented a
new spectrum derived from hundreds of millions of COBE measurements [that is] indistinguishable from the theoretical curve for
a 2.726° Kelvin blackbody. . . . 'The
universe has passed its toughest
test yet, as far as the Big Bang
theory is concerned,' says Mather."
COBE's results were the death
knell of the steady-state theory, the
Big Bang's main contender.
sk yandtelescope.com * A PR I L 2 018

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Sky and Telescope - April 2018

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