Sky and Telescope - October 2018 - 7

1860s found that it appeared forked - thus
the feature is sometimes referred to as
Dawes' Forked Bay. Later mappers, including Richard A. Proctor (and Flammarion
and Schiaparelli) continued to follow Beer
and Mädler's convention in using this as the
Martian prime meridian. Since then, the IAU
has designated Airy, a 43-km-wide crater, as
the location of the "Martian Greenwich."

Funding SETI
David Grinspoon attributes the 1990s
cut in funding for the search for extraterrestrial intelligence to "anti-intellectual budget cutters" (S&T: July 2018,
p. 12). But there are other, more legitimate reasons why SETI funding was not
a high priority in the 1990s.
First, radio-based SETI is a huge
signal-processing problem, and it would
have been reasonable to expect that
hardware costs would decrease dramatically in the future (as they in fact have).
Second, high-power radio-frequency
transmissions (with effective radiated

power exceeding 1 megawatt) might be
an infrequent or short-lived aspect of
technologically advanced civilizations.
Note that much of the UHF band, a
frequency space once dedicated to TV
transmissions, has been switched to use
by mobile phones.
Third, there hasn't been any irrefutable evidence of extraterrestrial life,
though Mars provides some tantalizing
hints. We also might be on the verge
of detecting the signature of life in the
atmospheres of planets outside our solar
system. Finding that life of any kind
exists elsewhere would be a huge boost
in the incentives for SETI funding.
Erik Magnuson
Cardiff, California

A Wish for Wedel
We wish upon a star that somehow
Mathew Wedel can ﬁnd a way to con-

1968

1993

Frederick J. Summers
Ferndale, California

FOR THE RECORD

* "Hunting Phobos and Deimos" (S&T: July
2018, p. 53) should note that Phobos can
appear as much as 22 arcseconds (not 16)
from the limb of Mars.
* The Gallery caption for NGC 1514 (S&T:
July 2018, p. 75) should have stated that
new findings show the companion star's
orbital period to be 3,306 days, or a little
over 9 years.

SUBMISSIONS: Write to Sky & Telescope, 90 Sherman St., Cambridge, MA 02140-3264, U.S.A. or email: letters@
skyandtelescope.com. Please limit your comments to 250 words; letters may be edited for brevity and clarity.

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

tinue the amazing articles explaining
Earth's events when the light that we
now see departed the celestial objects
he names (S&T: June 2018, "Fifteen
Steps to Forever," p. 64; December 2016,
"Twelve Steps to Inﬁnity," p. 24). These
space-and-time journeys with light
underscore the fascinating, incomprehensible size of the universe.

º October 1943
Mira's Maximum "A recent publication from Stockholm reports on
the discovery of old record books
kept by the 18th-century Swedish
astronomer, Peter Wargentin. They
contain valuable observations of
Mira Ceti in the years 1751-1782. . . .
Happily they cover the brightest
maximum ever observed for that
much-examined variable star.
"Mira has a period of over
330 days. Individual cycles differ
considerably in amplitude. . . . The
newly discovered old observations
show that Mira attained magnitude
1.2 on November 11-12, 1799 -
about twice the brightness of its
more recent maxima."
º October 1968
Mascons "Mass concentrations
of dense material lie beneath the
surface of the moon, report Paul M.
Muller and William L. Sjogren of the
Jet Propulsion Laboratory. Their
evidence for . . . these 'mascons'

comes from small changes noted in
the motion of Lunar Orbiter 5, when
very precise radio Doppler tracking
was continued for 80 consecutive
circuits of the moon. . . .
"Five conspicuous mascons,
each about 50 to 200 kilometers in
extent and perhaps 50 kilometers
below the surface, were detected
under . . . Mare Imbrium, Mare
Serenitatis, Mare Crisium, Mare
Nectaris, and Mare Humorum. . . .
"The JPL investigators comment
in Science for August 16, 1968: . . .
'Does each of these mascons
represent an asteroidal-sized body
which caused its associated mare
by impact?' "
NASA's 2012 GRAIL mission
gave new insight into mascons. A
Purdue University study concluded
that large asteroid impacts carved
huge craters, liquiﬁed the interiors,
and drew in surrounding material
that melted and congealed there.
º October 1993
M31's Double Nucleus "Over the
last three years astronomers using

the Hubble Space Telescope have
become accustomed to finding
curious structures at the centers of
active galaxies or galaxies undergoing collisions. But now they've
found something odd in the core
of a seemingly normal, quiet spiral.
New Hubble images show that
neighboring M31 in Andromeda
has a double nucleus.
"Tod R. Lauer (National Optical
Astronomy Observatories), Sandra
M. Faber (University of California,
Santa Cruz), and their colleagues
made the announcement at the
Space Telescope Science Institute
on July 20th. Their observations
with Hubble's Planetary Camera
reveal that the bright spot identified
as the nucleus in ground-based
images is actually offset from
the true dynamical center of the
galaxy, marked by a fainter spot 5
light-years (½ arc second) to the
southwest."
Further study, using HST's corrected optics, showed the nucleus
to be a lopsided disk of stars orbiting M31's central black hole.

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Sky and Telescope - October 2018

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