Sky & Telescope - March 2023 - 6

FROM OUR READERS
An Edge-On
Masterpiece
I just got done reading Howard
Banich's article " The Great Edge-On
Galaxy of Autumn " (S&T: Nov. 2022,
p. 28), which was very interesting. It
reminded me that I had imaged NGC
891 from Chiefland, Florida, back in
the fall of 2018. It made me interested
to review what my image had
looked like. I was able to detect the
two smaller galaxies on either side of
NGC 891 that Banich mentions in his
article. Again, great article! Thanks!
Sandy Goodstein
Lebanon, Pennsylvania
Sandy Goodstein captured this image
of NGC 891 through a Celestron 11-inch
EdgeHD Schmidt-Cassegrain with an SBIG ST4000XCM
camera.
star catalog, so I undertook a project to
recreate his database of angular measurements.
I wanted to construct my
own catalog using his algorithms and
techniques. This required building a
four-axis telescope, with arcminute absolute
pointing, to serve as Tycho's " trigonal
sextant. " I spent about 18 months
making observations.
After reducing the thousands of data
points to form the catalog, I was able to
recreate Tycho's catalog to good accuracy,
as well as extract other astronomical
parameters like length of the year and
the diameter of the Sun.
For those interested in such a project,
and the telescope required, please visit
https://is.gd/BraheRecreation.
Dave Skillman
Greenbelt, Maryland
A Fine Southern Beacon
I enjoyed Fred Schaaf's Evenings with
the Stars column about Fomalhaut (S&T:
Oct. 2022, p. 45) and felt compelled to
add a couple of additional observations
related to my favorite bright star. From
my latitude of 42.5°N and thereabouts,
as Fomalhaut (and Altair) set, Sirius
rises. This celestial concurrence presents
a brief window between August and
January during which most people in the
continental United States may observe
11 first-magnitude stars at once.
Fomalhaut also helps point the way
to the horizon-skimming Alnair (Alpha
Gruis) and Beta Gruis. The latter, a
variable, 2nd-magnitude, red M-class
star, lies to the right of the fish's mouth,
Fomalhaut. The somewhat brighter
B-class Alnair is a study in contrast that
culminates a bit earlier, soon after Enif
(Epsilon Pegasi), the nose of Pegasus,
crosses the meridian. Both stars in the
Crane are roughly -46.5° declination, so
binoculars are required from the IllinoisWisconsin
border where I live, though
an eagle-eyed observer with a dark, clear
horizon may be able to make out Alnair
or even Beta Gruis on a perfectly clear,
post-cold front evening from as far
north as Springfield, Illinois.
6 MARCH 2023 * SKY & TELESCOPE
I hope Schaaf continues writing
articles that emphasize learning the sky
with one's eyes.
Ed Furlong
Walworth, Wisconsin
Speak the Plain Truth . . .
In " Cut Out the Undercuts " (S&T: Nov.
2022, p. 70), Jerry Oltion is dead on-target
regarding eyepiece barrel undercuts
and " backward " finder mount saddles.
Every time I see either, I wonder how
long we must wait. Both are aggravating
at the least, often worse.
Never say never (again), but in 35
years of observing I've only had an eyepiece
fall out once. And that was because
I simply didn't tighten the set screw. The
ironic part? The eyepiece had an undercut
barrel! It's too bad manufacturers
don't offer optional smooth barrels.
Len Philpot
Pineville, Louisiana
In Tycho Brahe's Footsteps
I enjoyed Jerry Oltion's " Replicating the
Great Quadrant " (S&T: June 2021, p.
72), about building a replica of Tycho
Brahe's impressive instrument. A few
years ago, I became interested in finding
out exactly how Tycho constructed his
Going the Distance
Govert Schilling's article " Keep Your
Distance " (S&T: Oct. 2022, p. 12) nicely
covers the history of astronomical distance
measurements, which started with
terrestrial measurements. The circumference
of Earth would have been necessary
for determining the baseline during
the triangulation to Mars, from which
the astronomical unit was derived.
In 200 BCE, Eratosthenes measured
Earth's circumference by noting that on
the longest day of the year, the Sun was
at an angle of about 7° in Alexandria,
while in Aswan in southern Egypt it was
directly overhead. Someone likely paced
the distance from the north to the south
end of Egypt to complete the triangle.
But from these measurements, he was
able to determine the circumference to
within a reasonable approximation of
modern measurements. One could say
that Edwin Hubble's measurement of the
distance to Andromeda could be traced
back to an Egyptian 2,200 years ago pacing
the length of Egypt.
Kenneth A. Devine
Aurora, Ontario
I enjoyed the article by Govert Schilling.
I was very fortunate to have a gifted
astronomy teacher and friend, William
Gutsch, an accomplished educational
expert in astronomy and past chairman
https://www.is.gd/BraheRecreation
Sky & Telescope - March 2023

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