Sky & Telescope - January 2023 - 59

PAIR OF JUPITERS: LEFT IMAGE: DAMIAN PEACH; RIGHT IMAGE: NASA / ESA,
A. SIMON, M.H. WONG, OPAL TEAM; DISTANT TARGETS: SEAN WALKER / S&T
Unevenly heated from place to place, the atmosphere is
filled with currents and eddies. Seeing is caused by moving
cells of air at altitudes ranging from roughly 100 meters (328
feet) to more than 16 kilometers (10 miles). Because warm,
rarefied air refracts light less than cool, dense air, these cells
change the focal position of the image in a telescope by bending
incoming rays of light differently. They have two distinct
effects on a telescopic image. The image can be displaced
laterally, causing it to move randomly around a mean position
in the field of view. The image can also move inside and
outside the telescope's focal plane, giving it an undulating
appearance that's only intermittently unblurred. Both effects
invariably occur in combination to some degree.
By keeping a patient vigil at the eyepiece, an observer
can enjoy those magic moments that Percival Lowell called
" revelation peeps. " The human eye-brain combination is a
remarkably powerful differentiating sensor that can reject
poor images while retaining impressions of fleeting moments
of clarity. That's why as recently as the late 1970s and early
1980s the eagle-eyed visual observer Stephen O'Meara was
able to discover the ephemeral spokes in Saturn's B ring
(S&T: Aug. 2022, p. 28) and determine the rotation period of
Uranus (S&T: Sep. 2012, p. 54) using only a 9-inch refractor.
It wasn't long after the dawn of the 21st century that the
unrivalled supremacy of the eye ended abruptly. Planetary
observing was radically transformed in the span of only a
few years by inexpensive webcams equipped with efficient
sensors that took tens of frames every second, combined with
free software like Registax that could automatically select
and combine the sharpest ones. At the trifling expense of
little more than $100, it suddenly became possible to capture
planetary details beyond the grasp of even the most skilled
visual observer using the same instrument under the same
conditions. This paradigm shift gave backyard astronomers
unprecedented opportunities to contribute to planetary
science. Professionals soon began to increasingly rely on
dedicated amateurs to monitor the planets, often in support
of spacecraft missions.
DISTANT TARGETS The planets all appear smaller than large lunar craters. This composite shows the crater Copernicus and the major planets, all
recorded at the same image scale through a 12½-inch Newtonian reflector.
sk yand tele scope .o r g * JANUARY 2023 59

Sky & Telescope - January 2023

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

Contents
Sky & Telescope - January 2023 - Cover1
Sky & Telescope - January 2023 - Cover2
Sky & Telescope - January 2023 - 1
Sky & Telescope - January 2023 - Contents
Sky & Telescope - January 2023 - 3
Sky & Telescope - January 2023 - 4
Sky & Telescope - January 2023 - 5
Sky & Telescope - January 2023 - 6
Sky & Telescope - January 2023 - 7
Sky & Telescope - January 2023 - 8
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Sky & Telescope - January 2023 - 11
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Sky & Telescope - January 2023 - 28
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Sky & Telescope - January 2023 - 58
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Sky & Telescope - January 2023 - Cover3
Sky & Telescope - January 2023 - Cover4
Sky & Telescope - January 2023 - SA1
Sky & Telescope - January 2023 - SA2
Sky & Telescope - January 2023 - SA3
Sky & Telescope - January 2023 - SA4
Sky & Telescope - January 2023 - SA5
Sky & Telescope - January 2023 - SA6
Sky & Telescope - January 2023 - SA7
Sky & Telescope - January 2023 - SA8
Sky & Telescope - January 2023 - SA9
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