Sky & Telescope - August 2022 - 6

RUSSELL E. MILTON / WIKIMEDIA COMMONS / CC BY-SA 3.0
FROM OUR READERS
 In 1983, Comet IRAS-Araki-Alcock (C/1983
H1) passed just 0.03 astronomical units from
Earth, the closest confirmed cometary approach
in 200 years.
cago newspaper. The next day, more
than 200 people called to ask how to
see the comet.
Answering those calls was part of
Comet IRAS-ArakiAlcock
" Saving
Apollo 16, " the Focal Point
by Mark Gingrich (S&T: Apr. 2022, p.
84), reminded me of something that
happened in May 1983, shortly after I'd
started working at the Adler Planetarium
in Chicago.
Comet IRAS-Araki-Alcock (C/1983
H1) made the front page of the Chimy
job, but the comet was only 2ndmagnitude,
not much brighter than the
limiting magnitude in the city. Worse,
the comet had no tail obvious to the
unaided eye. To see the comet reliably,
one needed to know where in the sky
to look. It would also have helped to
drive an hour outside the city.
Almost no one who called knew
how to find the Big Dipper. By midafternoon,
I was getting tired of disappointing
people.
At the time, Venus was bright in the
evening sky. The temptation was strong
to say, " Yep, that bright one, just after
sunset. Can't miss it! " But I resisted.
Fred Ringwald * Fresno, California
Red Galaxies
In the article " An Unusual Home "
by Shannon Hall (S&T: Apr. 2022, p.
34), she notes that one way to identify
small galaxies apparently near a larger
one as being more distant in the line
of sight rather than genuine satellites
is to see if they are redder than the
other galaxy. However, dead galaxies
will naturally be redder than ones still
actively forming stars. Could this lead
to astronomers overlooking genuine
dead satellite galaxies, biasing the
conclusions from the Satellites Around
Galactic Analogs (SAGA) Survey?
Michael Baxter
London, England
"
Monica Young replies: You make
a good point that older galaxies
Sirius and the Sun
Thanks to Bob King's " A Sirius NakedEye
Challenge " (S&T: Mar. 2022, p. 48),
I saw Sirius with the naked eye at 7:12
p.m. CDT on March 27th - the very
minute the Sun's westernmost limb
touched the horizon at my location in
Ottawa, Illinois. I was surprised at how
easy it was to see it in binoculars just 10
minutes before and just as surprised at
how easy it was to lose. The naked-eye
view came and went for a few minutes.
Since some of the planets are occasionally
brighter than Sirius, my next challenge
will be to see them while the Sun
is still up - when they're not at dangerously
small elongations, of course. I've
already seen Venus in the daylight.
Rick Wiegmann Koshko
Ottawa, Illinois
Spotting Mercury
The blurb at the end of Sun, Moon &
Planets on page 46 of the April 2022
issue of Sky & Telescope notes, " . . . Gary
Seronik never misses a chance to catch
a mercurial Mercury appearance. " I
6
AUGUST 2022 * SKY & TELESCOPE
have the same outlook. Since January
2011, I've spotted Mercury at least once
at every elongation. I usually start with
binoculars or unaided eyes and occasionally
try for the crescent with a scope.
On April 11, 2022, I glimpsed Mercury
through a gap in the clouds with
my 15×56 binoculars. On April 12th,
I saw it again in clear skies three minutes
after sunset with the same binoculars,
then caught it with unaided eyes
25 minutes after sunset. Three minutes
later, I was able to hold it steadily in
view with unaided eyes. Sometimes it's
easy to see Mercury with the naked
eye; however, oftentimes it's difficult
or impossible without optical aid.
This one makes 72 elongations in a
row for me. Sort of like an old golfer,
that score matches my age. I started in
January 2011 with the hope of spotting
Mercury at each of its seven elongations
that year and just kept going.
I'm glad to see that someone else
appreciates spotting Mercury.
Joe Stieber
Maple Shade, New Jersey
will also look redder, so the SAGA team
members had to be careful with their color
cuts in order to not bias the survey. What
they did was make two color cuts by galaxies'
g-r and r-i colors. (The g-r color, for
example, is the difference in an object's
magnitude as measured in the g and the
r bands.) Having two color measurements
gave the team a crude photometric redshift
for any given galaxy.
Photometric redshifts are common in
larger surveys with thousands of objects,
but the key here was that the team was
looking at such low redshifts that those
formulae wouldn't apply, so they had to
make their own.
Across Philly for S&T
As an 80-year-old retired university
professor and a serious, lifelong amateur
astronomer, I very much enjoyed
both William Sheehan and Klaus
Brasch's " A Golden Age for Amateur
Astronomy " (S&T: Nov. 2021, p. 14)
and the letters it provoked (S&T: Mar.
2022, p. 6). In several cases, these letters
were virtually pieces taken out of
my own biography.
I particularly remember how I'd
eagerly anticipated the monthly
appearance of Sky & Telescope for sale
at the Franklin Institute bookstore.
This would provide an excuse for me
to take a break from pursuing my PhD
at the University of Pennsylvania and
Sky & Telescope - August 2022

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