Sky & Telescope - April 2023 - 7

fields west from Lambda Ori until the
milky background turned to blacker sky, "
according to what I wrote at the time.
Alan Whitman
Okanagan Falls, British Columbia
Back to Astronomy
I found John Wolfram's Focal Point " A
Telescope for the Times " (S&T: Nov.
2022, p. 84) to be a lovely and very relatable
telling of a rekindling of the love of
amateur astronomy. I too started this
hobby as a youngster and have the same
telescope I bought myself as a teenager
20 years ago. Like Wolfram, in recent
years I dove back into the hobby, buying
a new scope and getting into astrophotography
on top of visual astronomy. It
really was like picking back up an old
childhood friendship. I'm also thankful I
took the leap to get a new telescope, and
I agree that this is an incredible time to
be an amateur astronomer.
Katelyn Beecroft
London, Ontario
Legacy Cameras
I appreciated seeing a picture of the
Legacy Camera CCD chip and the brief
description of how the data were collected
in Karen Masters' " The Neverending
Survey " (S&T: Jan. 2023, p. 20).
I would love to see a survey article in
S&T on newer camera designs such as
those on Pan-STARRS, the Vera C. Rubin
Observatory, and the James Webb Space
Telescope, and the data science associated
with them. Who knows, some
inventive amateurs may come up with
interesting projects that complement
what the professionals are doing.
I appreciate what the Alfred P. Sloan
and W. M. Keck Foundations have
done for astronomy. I hope some newer
wealthy individuals can see the importance
of astronomy to humanity.
Vinai Varanyananda
Bangkok, Thailand
Cosmic Appreciation
I'm writing to express my appreciation
for David Grinspoon's Cosmic
Relief column. At first, I was intrigued
but skeptical. Soon, however, I was
completely won over.
His columns are engaging, imaginative,
and informative and have become
a favorite of mine.
Thanks, David.
Stuart White
Albuquerque, New Mexico
FOR THE RECORD
* In " What Makes a Good Planetary Telescope "
(S&T: Jan. 2023, p. 58), the amount
of light in the Airy disk of a telescope with
a 33% central obstruction is not 68%, with
32% going into the diffraction rings. The
correct percentage is 65% of light concentrated
in the Airy disk, with the remaining
35% going into the diffraction rings.
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
1948
1973
º April 1948
Gauging the Earth " The annular
eclipse of May 8th-9th is getting
almost as much attention as total
eclipses of the sun usually do. It
is going to help measure the size
and shape of the earth with great
accuracy. The National Geographic
Society, the Army's Map Service
[and other agencies are] sending
expeditions to seven observing
points in Burma, Siam, China,
Japan, Korea, and the Aleutians.
" By timing exactly the instants
1998
when the moon first contacts the
sun, when the ring of light around
the moon first appears and first
disappears, and when the eclipse
is just over, as seen from the various
stations, the scientists will be
able to compute how far apart their
observing positions are with errors
not exceeding 150 feet. "
In those days, star sights with a
sextant yielded positions accurate
to about a mile. LORAN radio navigation
was not even that good.
º April 1973
Gegenschein " Pioneer 10,
launched on March 3, 1972, on a
620-million-mile journey to Jupiter,
is the first space probe to explore
the outer solar system beyond the
orbit of Mars. [One instrument is
making] periodic maps of the diffuse
skyglow . . .
" A puzzling, often-studied
feature of the skyglow is the
gegenschein or counterglow, which
is seen as a gradual brightening
opposite the sun from the observer.
The gegenschein has been attributed
to backscattering by dust particles
in interplanetary space or to
various Earth-associated phenomena
such as gas or dust tails. . . .
" [Measurements] taken when
Pioneer 10 was 5.8 million miles
from Earth and 1.011 astronomical
units from the sun, showed . . . that
the gegenschein was still there . . .
Since the antisolar direction from
the spacecraft was not the same as
the antisolar direction from Earth,
it is evident that the gegenschein is
not associated with the earth. "
º April 1998
More Runaway Stars " Our
mental image of the Virgo Cluster
underwent a shakeup last year
when the Hubble Space Telescope
discovered that trillions of stars lie
between, rather than merely within,
the grouping's individual galaxies
. . . Further signs of Virgo's intergalactic
stars are now reported by
Roberto H. Méndez (Munich University
Observatory) and his colleagues
in Astrophysical Journal Letters for
December 10, 1997.
" The astronomers used the 4.2meter
William Herschel Telescope
to seek planetary nebulae within a
blank, 50-square-arcminute patch
of the Virgo Cluster's core. A planetary
nebula can be seen only for
a few thousand years of a star's
multibillion-year life, and only
the brightest planetaries can be
detected at the cluster's distance
(50 million light-years). Consequently,
the 11 planetaries found
by Méndez's team may indicate
that as many as half of the Virgo
Cluster's stars are intergalactic. "
sk yand tele scope .o r g * APRIL 2023
7

https://skyandtelescope.org/

Sky & Telescope - April 2023

Table of Contents for the Digital Edition of Sky & Telescope - April 2023