Sky & Telescope - September 2016 - 6

Letters

Shout-out for Sketching

Recently, I used Craigslist to give away my
6-inch Meade reﬂector and mount. It was
a ﬁne telescope when I bought it 30 years
ago while in graduate school for $350,
but it had become too heavy for me to
haul around, especially to dark-sky areas.
Besides, the primary mirror needed to be
cleaned, and there was no clock drive.
I was astounded by the response.
Within minutes of posting the ad, I
received a ﬂood of responses - 119 in
all - from all sorts of people: young,
old, men, women, husbands, daughters,
uncles, a Boy Scout leader, and a young
man wanting it for his grandfather. I'd
say only 10% of them had any experience
with telescopes; those who did valued this
one because it had been made in the U.S.,
and they wanted to restore it.
I ended up giving it to the ﬁrst person
who had sent me a request, and he immediately drove through Bay Area traﬃc to
my house in Silicon Valley. He'd never
used a telescope before - but he was
ready to start.
Helen Gjerde
Saratoga, California

I want to thank the editors of Sky &
Telescope for publishing a section dedicated to sketches of astronomical objects
(S&T: June 2016, p. 73). It was refreshing
to see some space given to another form
of recording observations, one using the
age-old tradition of pencil and paper. As
noted in the introduction there, sketching
is a way to keep a record of observations
while providing that personal connection
with objects in the night sky. Sketching is
not just for artists; it's a useful tool for all
observers to enhance their ability to see
deeper details. In a sense, sketches represent what is truly observed at the eyepiece.
I urge you to make this a more regular
part of S&T's content. Having a gallery for
sketches or including them with astrophotography submissions would add to the
magazine's appeal and educational value.
Cindy L. Krach
Maui, Hawai'i

KEVIN KILBURN

Free Telescope Draws a Crowd

Grubb's "Twin Equatorials"
In Thomas Dobbins's article on anomalous appearances of the transits of
Mercury (S&T: May 2016, p. 38), the
photograph of William Huggins seated
with a refracting telescope caught my
eye. Huggins did indeed use a small
Clark refractor for his early spectroscopic
work, but the photograph actually shows
him seated in front of a 15-inch Grubb
refractor that was counterbalanced by an
18-inch reﬂector (not in view).
This refractor-reﬂector combination,
the ﬁrst of only four so-called "twin equatorials" manufactured by Howard Grubb
between 1871 and 1902 to maximize the
use of a small observatory, was made
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September 2016 sky & telescope

These paired telescopes, one of only four "twin
equatorials" produced by Howard Grubb more
than a century ago, remain in use at Godlee
Observatory in Manchester, England.

speciﬁcally for Huggins's visual and photographic spectroscopic investigations,
respectively. Later "twins" included a
7-inch refractor and 20-inch photographic
reﬂector made for British astronomer
Isaac Roberts, and an 8- and 16-inch
pairing put on display in Manchester,
England, in 1887. This latter combo was
dismantled after the exhibition, its telescopes sent separately to observatories in
South America and India.
The fourth and ﬁnal "twin," which
combined an 8-inch refractor and 12-inch
reﬂector, is the only one still in regular
use. It's been housed since 1946 at the
University of Manchester's Godlee Observatory and maintained by the Manchester
Astronomical Society.
One ﬁnal point: the refractor illustrated
in Dobbins' article ended up at Cambridge
Observatory early in the 1900s but eventually fell into disuse and was dismantled. In
2006, however, Mark Hurn, the librarian
at the University of Cambridge's Institute
of Astronomy, discovered its 15-inch objective lens in a little-used cupboard!
Kevin Kilburn
Manchester, England

Editor's note: Krach coordinates the Astronomical League's recently instituted Sketching Award.

Our Same-Faced Moon
Planetary scientist Paul Spudis favors the
small oﬀset between the Moon's centers
of ﬁgure and mass to explain why its
rotation has synchronized with its orbital
period (S&T: Apr. 2016, p. 16). Yet any
large moon that's close to its planet will
become elongated by tidal interaction.
Won't this elongation become frozen in
as the body solidiﬁes and then hasten
tidal locking - even if its shape would
have been perfectly symmetrical without
tidal distortion?
Keith Brescia
Falls Church, Virginia
Researcher Mark Wieczorek replies: It's true
that the Moon would despin even if it were
initially perfectly spherical. Nevertheless,
it's almost inevitable that the Moon initially
had an asymmetric shape as a result of
large impact craters, with a portion of this
global shape being of the "American football" variety. So, after despinning, the Moon

Sky & Telescope - September 2016

Table of Contents for the Digital Edition of Sky & Telescope - September 2016