Sky & Telescope - February 2019 - 6

FROM OUR READERS

Right-Sizing
Aperture

Cosmic Mystery

Klaus Brasch * Flagstaff, Arizona

I found that Tom Dobbins's article hit the nail on the head. It highlights the term
"empty magniﬁcation."
This has hit home many times with me. One night, my 10-inch f/4.5 Newtonian
apparently outperformed instruments even as large as 60-inch aperture, on the same
target, under terrible seeing conditions, taking videos. Computer stacking works well
for shifting objects, but not if the seeing prevents details from coming through.
Dave Nakamoto * Azusa, California

Back to Venus?
Shannon Hall's article "Destination:
Venus?" (S&T: Sept. 2018, p. 14) is a
real eye-opener, and I sincerely hope
that it helps to turn things around for
further exploration of our sister planet
by NASA.
An item that was mentioned only in
passing intrigues me. The article mainly
concerns volcanism, but it also notes
"a giant impact crater." It is certainly
fascinating that the Venusian surface
is otherwise largely smooth or volcanic, indicating relatively recent activity
6

FE B RUA RY 2 019 * SK Y & TELESCOPE

over the entire planet that would erase
evidence of other impacts.
But the fact that there is this one big
crater seems to me to merit attention.
Wouldn't further investigation help us
determine how recently the inner solar
system has been subjected to signiﬁcant
bombardment? I think that has major
implications for planetary defense of
our home planet . . . and thus offers yet
another practical urgency in favor of
returning to Venus.
Joel Marks
Milford, Connecticut

Shawn Dilles
Vienna, Virginia

Old-School Astronomy
Jerry Oltion's Big, Bold, Bright, and
Beautiful articles (S&T: Oct. 2018, p. 28
and May 2018, p. 22) have been much
more than nostalgic for me. I purchased
my 8-inch Coulter Dobsonian in 1990
and have spent many hours sketching
bright and beautiful wonders in the
sky. As I've watched observing decrease
and astrophotography increase, I've felt
like a relic of old-school astronomy. But
Oltion's articles have heartily afﬁrmed
my love and desire for observational
sketching without holding it in opposition to photography. I appreciate all
aspects of our hobby and am glad to be
fully afﬁrmed in my little corner of it.
Pastor Mark Chapman
Upsala, Minnesota

Guided Tour
Jerry Oltion's "A Tourist's Guide to
the Autumn Highlights" (S&T: Oct.
2018, p. 28) made me want to set up
my telescope and wait for nightfall like
nothing else I have read in more than
40 years as an amateur astronomer.
Jaime Tomé
San Juan, Puerto Rico

Diverse Interests
Antonio Peña's article on David Malin's
work in color astronomy (S&T: Nov.
2018, p. 30) reminded me of my ﬁrst
and only encounter with this ultimate
expert in imagery.
While doing a lecture tour in Europe
in the 1990s, David visited our local
planetarium in Aarhus, Denmark, and
I was a bit surprised and also annoyed
to learn that he insisted on using his

LIT TLEFIELDEMERY (CC BY-SA 4.0)

Having used a variety of telescopes
at various Northern and Southern
Hemisphere sites, I really enjoyed Tom
Dobbins's analysis of the optimal telescope aperture for lunar and planetary
observing (S&T: Nov. 2018, p. 52) and
concur with his overall conclusions.
However, a number of other factors
also come into play. As with real estate,
location really makes a difference. For
p It's hard to beat the views with the 24-inch
Clark refractor at Lowell Observatory.
instance, that elite group of amateur
solar system imagers (Christopher Go,
Damian Peach, and Leo Aerts, among others) works mainly at low elevation near seas
and oceans, far removed from major mountains. Hence, they frequently enjoy atmospheric inversions or smooth laminar ﬂow air currents. Often as well, haze and high
humidity prevail at such sites, with diminished transparency but very steady seeing.
The best seeing conditions I've experienced over the years were at Mt. Wilson
Observatory, the Atacama Desert, and Mount Pinos in California. While these are
arid mountain locations, they border the Paciﬁc Ocean and hence enjoy frequent
westerly laminar air ﬂow. In contrast, at my current location east of Flagstaff,
where dark, crystal-clear skies and superb transparency dominate, seeing is often
rather poor. That's ideal for deep-sky but rarely for lunar and planetary observing.
Still, while 12- to 16-inch-aperture telescopes may be best all-around as Dobbins attests, size still matters. Under comparatively rare superb seeing conditions
at Lowell Observatory, the venerable 24-inch Clark telescope outperforms smalleraperture instruments hands down every time.

I've been reading your magazine for over
40 years and have always appreciated
the clear, crisp, and accurate science
writing. But my appreciation hit a new
high with David Nakamoto's article on
BL Lacertae objects (S&T: Sept. 2018,
p. 30). This is one of the best articles I
have ever read, combining clarity, accuracy, and good organization with an
underlying mystery tale to solve.

Sky & Telescope - February 2019

Table of Contents for the Digital Edition of Sky & Telescope - February 2019