Sky & Telescope - July 2022 - 6

SKY & TELESCOPE
FROM OUR READERS
Reading Through the Years
Recently, I completed
reading all issues of Sky &
Telescope back to the first
issue in November 1941. It
took me 42 years. It took
some time to locate all the
paper issues. Since I retired
in 2014, I've had more
time to read.
It was something I'd
wanted to do for quite a
long time. S&T published
a short note some years ago about how
I came to begin reading them in February
1966 during my 9th-grade math
class (S&T: June 2006, p. 12). It has
been quite an adventure reading back
through the years. It really helps one
gain a perspective of what was happenCharles
A. and Helen Spence
Federer published the first issue
of Sky & Telescope in November
1941 after merging its two
predecessor magazines, The
Sky and The Telescope.
ing at the time. I'm now
reading its predecessor
magazines, The Sky and
The Telescope. I've really
wanted to have all those
in paper also, but they are
exceedingly hard to find. I have some
paper issues of The Sky, but only one of
The Telescope. I'll have to read most of
both of these magazines off the DVD
disks on my computer.
Keep up the good work!
Larry Black * Cedar Rapids, Iowa
I always read with great interest the articles
on developments in cosmology, such
as the recent piece " The Hubble Constant:
Tension and Release. " This article
mentioned a concept that I feel could use
further explanation, the sound horizon.
The article defines it as " the maximum
distance that a sound wave could have
traveled [in the primordial universe]
before recombination occurred. "
Though it's been a while, if I recall
from freshman physics, a sound wave is
a longitudinal wave of varying pressure
fronts that assume air molecules as the
medium of transmission. I must admit
I'm at a loss as to how this translates to
plasma in the primordial universe. I'm
sure I'm missing something.
Marc Pfeiffer
Washington, D.C.
Camille Carlisle replies: The sound
horizon can indeed be a complex
concept. I asked Arwen Rimmer your question,
and here's what she said:
" The primordial plasma was not of
"
Friction is F = μN
Thanks for the interesting article " Derrick's
Mission to Mars " (S&T: Feb. 2022,
p. 26), about an astronomer's community
outreach program in Philadelphia.
In the article, the author Nicole Nazzaro
uses basic equations from physics
to explain how to encourage a " Wow! "
reaction from youngsters. She cites the
equation for force as an example.
That immediately brought back a
50-plus-year-old memory from my
9th-grade physics class at Cass Technical
High School in downtown Detroit,
Michigan. The teacher introduced the
unit on friction with the statement
" Friction is FUN! " and then wrote the
formula F = μN, which was also mentioned
(though in a slightly different
form) in the S&T article.
I can still picture that formula on the
chalkboard five decades later. I must have
said " Wow! " at the time. It certainly got
this kid involved in a lifetime of physics,
astronomy, and technology.
Thanks, Derrick Pitts and Nicole
Nazzaro!
Chuck Plachetzki
Suttons Bay, Michigan
6
JULY 2022 * SKY & TELESCOPE
Lunar Reconnaissance
In his article titled " Chang'e 5 and the
Age of Lunar Lavas " (S&T: Feb. 2022,
p. 52), Charles A. Wood says he " can't
wait for more dated samples from the
Moon to fill in the crater curve gaps. " I
believe that we need to obtain samples
from the entire Moon, especially the
farside. The farside of the Moon may differ
considerably from the nearside, and
its crater curve needs to be developed so
that we can more fully understand lunar
and solar system history.
James Scott
Vernon, New Jersey
Cosmologically Complex
I found the article " The Hubble Constant:
Tension and Release " by Arwen
Rimmer (S&T: Mar. 2022, p. 14) an
interesting, informative summary that
touches upon numerous important cosmological
concepts. I especially enjoyed
the intellectually open manner in which
Rimmer presents how various research
groups are attempting to clarify varied,
complex cosmological questions.
Philip Levine
Randolph, Massachusetts
uniform density. Gravity acted on these
variations, causing expansions and contractions
in the medium. These motions in turn
caused oscillations in the plasma that are
analogous to the way sound waves travel
through air. So the phrase " sound horizon "
is kind of a metaphor.
Here's an Astrobites article that has a
pretty good description of the sound horizon:
https://is.gd/the_early_universe. "
Blast from the Past
Peter Tyson's inaugural Spectrum article,
" High Standards " (S&T: Jan. 2015,
p. 6), solicited advice from the readership
on improving the magazine. I simply
could not resist the offer! My input
resulted in a follow-up inquiry from Mr.
Tyson, which I readily answered. In a
nutshell, I recommended the magazine
adopt an even more intense practitioner
orientation. I suggested that the core
readership wanted to learn how to better
participate in this hobby.
Since that interchange, I've been
wowed by S&T's content, both thematically
and application-wise. Each
issue seems to develop new perspectives
on how to aid and educate the
https://www.is.gd/the_early_universe.'
Sky & Telescope - July 2022

Table of Contents for the Digital Edition of Sky & Telescope - July 2022
