Sky & Telescope - January 2025 - 7

so a naked-eye astronomer watching a
star blink out instantaneously during
a lunar occultation would have quickly
realized that stellar angular diameters
are considerably less than one arcsecond.
This simple test makes it much
more plausible that stars are suns.
Gerald Newsom
Columbus, Ohio
The Perseids Perform
I'm a huge fan of Sky & Telescope's
podcast (https://is.gd/SKYpodcast)!
I eagerly look forward to the first of
every month, when new episodes drop.
I'm 36, live in suburban New Jersey,
and have a 6-inch Dobsonian to
indulge in my hobby. But I had never
witnessed a meteor shower in all these
years. This year's Perseid shower was
my first, and holy moly, did I get my
mind blown!
My balcony faces north-northwest.
I had a full view from Ursa Minor to
Aquila, with Drago bang in the center.
I was craning my neck trying to
locate Perseus. Then I remembered
Kelly Beatty mentioning in the podcast
that the appearance of the meteors
radiating from Perseus is only a trick
of perspective, whereas, in reality, they
would be visible all over the sky.
There was a particularly bright red
streak that will be forever engraved in
my memory.
I have seen shooting stars before.
But this was different. It was an
incredible celestial event! I was
extremely bummed that I couldn't see
the aurora earlier this year, but this
more than compensated for it.
I wanted to drop a note and say
thanks to Kelly Beatty and everyone
at Sky & Telescope for all the incredible
work you do. The research that goes
into every episode and the succinct
narration is brilliant. It's like little
nuggets of gold for stargazers who are
just getting into the hobby - like me.
Keep up the good work! I wish you
all clear skies!
Tiru Raghavan
Union, New Jersey
FOR THE RECORD
* In " Intermediate-mass Black Hole in
Omega Centauri " (S&T: Nov. 2024, p. 9),
the fastest stars in the cluster's center are
moving at a projected velocity of 113 kilometers
per second (250,000 mph).
* In " Wil Tirion, 1943-2024 " (S&T: Nov.
2024, p. 10), the two volumes of Uranometria
2000.0 were coauthored with Barry
Rappaport and George Lovi.
* In " Portrait of a Supernova " (S&T: Nov.
2024, p. 12), in the light curve of SN
2023ixf, the visible filter is in blue and the
blue filter is in green. Also, the date June
14 should read June 4.
SUBMISSIONS: Write to Sky & Telescope, 1374 Massachusetts Ave., 4th Floor, Cambridge, MA 02138, USA, or email:
letters@skyandtelescope.org. Please limit your comments to 250 words; letters may be edited for brevity and clarity.
75, 50 & 25 YEARS AGO by Roger W. Sinnott
Astronomers' early studies
1950
1975
º January 1950
Seeing " Enrique Gaviola, of the
National Astronomical Observatory
at Cordoba, Argentina, has made
an excellent beginning in the evaluation
of photographic seeing [with
a 60-inch reflector. The sharpest
images] were several times larger
than the theoretically expected
values while the average diameters
were 15 to 23 times larger. . . .
" Many years ago America's
2000
'father of astrometry,' the late Frank
Schlesinger, [noted that] star images
wandered from their mean positions
even during good seeing . . .
Another aspect that Schlesinger
discussed was the refraction of our
atmosphere as a whole. He showed
that all stellar images should be
short spectra, vertical with the blue
end nearer the zenith. . . .
" What, then, does Gaviola add?
[He lists] three main characteristics
of seeing: dancing, change of
position; pulsation, change of size;
scintillation, change of intensity. "
of bad seeing paved the way for
today's adaptive optics.
º January 1975
Star Tracking " My telescope
is an Edmund 4¼-inch reflector,
equipped with a common 1/15r.p.m.
synchronous motor. The
polar axle turns at the solar tracking
rate, [but] I became interested
in astrophotography and decided
I needed a variable-speed control,
the kind that changes the frequency
of the alternating current
(a.c.) to the motor. I went to a friend
back in school, electrical engineering
graduate student Capt. James
R. Harris, and we designed one. . . .
" The three integrated circuits
(IC's), filament transformer, and
other components are all easily
obtained. By going mainly to
surplus electronics stores, I held
the overall cost of parts down to
about $10, a fantastic saving over
commercial speed controls. "
The advent of IC's and the ubiquity
of Radio Shack stores were a
godsend for hobbyists. The drivecontrol
circuit of Capt. Vernon P.
Saxon, Jr., rode that wave. I built
one while editing his article and in
a follow-up note told how to make
the scope track at solar, lunar, sidereal,
and guiding rates.
º January 2000
Water from Space " The 8,100
residents of Monahans, Texas, will
forever remember March 22, 1998
- the day two fist-size meteorites
plunked onto their town . . . One
landed not far from seven children
playing basketball. The stony
chondrites soon made their way to
the laboratories of NASA's Johnson
Space Center, whose scientists
found something amazing inside:
microscopic droplets of liquid
water. More remarkably, the droplets
are trapped in purplish crystals
of nearly pure salt (halite). . . .
[Each] 4.6-billion-year-old meteorite
has quite a story to tell. 'It takes
a large body of water to make large
halite crystals,' notes investigator
Michael E. Zolensky . . . "
sk yand tele scope .o r g * JANUARY 2025
7

https://www.is.gd/SKYpodcast http://skyandtelescope.org

Sky & Telescope - January 2025

Table of Contents for the Digital Edition of Sky & Telescope - January 2025