Sky & Telescope - November 2021 - 6

M56: NASA / ESA; THE PLANISPHERE: CLARENCE UNDERWOOD
FROM OUR READERS
Locating Messier 56
Mathew Wedel's tip for finding M56 in
" Lost in Space " (S&T: Aug. 2021, p. 43)
is outstanding! The asterisms are striking
in binoculars. It illustrates once
again how much the human brain
loves patterns.
Bob Wieting * Simi Valley, California
In his Binocular Highlight column for August,
Matt Wedel discussed his solution to locating
M56 in Lyra for anyone struggling to find this
spectacular globular cluster.
Binoculars for the Nearsighted
I
enjoyed Alan Dyer's article " Buying
Binoculars for Astronomy " (S&T: Aug.
2021, p. 60). While I am quite nearsighted,
I prefer to use my binoculars
without my eyeglasses. Thus, there's
one feature of binoculars that companies
almost never advertise but is quite
important to me, the diopter adjustment
range. Even the salespeople don't always
know this number, and Alan Dyer's
article did not mention it. So I usually
end up buying binoculars and hoping
for the best. My Vixen Optics 10×50
Porro-prism binoculars are excellent in
this regard and seem to compensate for
nearsightedness up to -8 diopters.
Stewart Novick
Bolton, Connecticut
Alan Dyer replies: You are correct
that most manufacturers don't state
the range of diopter adjustment. People
with eye prescriptions where one eye differs
widely from the other can find binoculars
difficult to use. Most diopter adjustments
vary by ± 3 or 4 diopters, which is enough
to accommodate a good number of people.
But for those who know their eyes are
very unequal and who do not wish to use
eyeglasses when observing, the best advice
I can give, in the face of no published specifications,
is to buy binoculars from a supplier
that allows easy returns should they prove
unsuitable. The same is true of interpupillary
distance (IPD), which is typically adjustable
over the range of around 55 to 70 mm (2 to
2.8 inches). Fortunately, the manufacturers
usually provide the IPD range.
"
6
NOVEMBER 2021 * SKY & TELESCOPE
Go To, Shoot, Enjoy, Repeat!
Hurrah for Greg Redfern's " Four Tips
for Better Astropics " (S&T: Aug. 2021,
p. 54)! I appreciate that it encourages
single-exposure amateurs like me. I'm
currently using somewhat older equipment
with a slightly different goal.
His third tip mentions covering your
setup for multi-night action. That has
been my mainstay for years. I use a white
drawstring kitchen bag to cover my
short 5-inch (127-mm) Orion refractor,
a modified Canon camera, and a
piggybacked, even-older Pentax camera
with a selection of Takumar lenses. I
also clothespin a larger clear bag to the
spreader under my Celestron mount. It
controls the temperature and keeps out
moisture (and bugs) indefinitely.
I take advantage of poor conditions
to perfect my mount's polar alignment
using the drift method, shooting
1-second guide-star tests at 10-minute
intervals. This technique provides excellent
tracking during the days, or weeks,
that I have the telescope out.
Then I use the camera as an eyepiece!
I choose objects from the Orion DeepMap
600 star chart that are relatively
large but quite dim. I rarely need more
than a 2-minute exposure to reveal
much greater detail and color than I can
see visually, even with my larger telescope.
Thanks to this modest setup, my
list of viewable objects has grown enormously,
far beyond the Messier catalog,
and now includes many dark nebulae
and supernova remnants.
Steven Marshall
Milwaukee, Wisconsin
pThis replica of a cuneiform tablet depicts the
ancient night sky. The original was found in the
buried ruins of an Assyrian library and currently
resides in the British Museum in London.
I read Douglas MacDougal's article
about ancient astronomers' treatment
of planetary positions with interest and
appreciation. In my last semester at
Brown University, I was the only student
enrolled in the History of Astronomy
course taught by Otto Neugebauer,
whom MacDougal calls " the pioneering
Archaeoastronomy
When I received notice of the August
digital issue in my email, Douglas MacDougal's
" Alas, Babylon! When Mars
Draws Near . . . " (S&T: Aug. 2021, p. 24)
caught my eye. It involved a look at
ancient cuneiform texts that Babylonian
stargazers used to record the movement
of celestial objects. Mesoamerica also
had an interesting heritage of ancient
skywatchers. I recently read Prehistoric
Astronomy in the Southwest by J. McKim
Malville and Claudia Putnam. There are
many books on the topics of archaeoastronomy
and ancient astronomy. A good
book about astronomy's past recorders
is essential to better understanding the
science today and tomorrow!
Most ancient peoples watched the sky.
Tens of thousands of years ago, they used
bones and cave walls to record lunar
cycles. And, of course, the ancient Chinese
provided many records of historic
celestial events. Knowledge of the sky
once was fundamental to many cultures.
I greatly enjoyed the article. I'm a fan
of the topic!
Clarence Underwood
Pittsburg, California
Sky & Telescope - November 2021

Table of Contents for the Digital Edition of Sky & Telescope - November 2021
