Sky and Telescope - August 2017 - 53
p Seen as imaged during the Apollo 15 mission, the 2.4-km-wide crater Linné sits near the
TOP: N ASA; BOT TO M: N ASA / LUN A R RECONN AISSA NCE ORBITER
western edge of Mare Serenitatis. Its extensive apron of highly reflective ejecta is obvious near full
Moon - but spotting the crater itself can be challenging.
indeed other observers perceived that the
tiny new crater, presumed to be volcanic,
was enlarging, suggesting that the eruption had continued.
More than a decade later, another
reported lunar change again excited
European astronomers. The British Selenographic Journal of February 21, 1879,
reported that Hermann Klein, an experienced German observer, had discovered a deep and conspicuous new crater
near the Hyginus Rille (known today as
Rima Hyginus). For the next year many
observers searched for "Hyginus N" (for
nova or new), finding instead a shallow
depression that appeared dramatic only
under very oblique sunlight.
And for many decades, from the 1870s
onward, amateur astronomers debated
the appearance and disappearance of tiny
craterlets on the floor of Plato. When
they weren't seen, proponents invoked a
mist or other obscuration.
Reality Check
Change does occur on the Moon,
because craters form all the time. Last
year a team led by Emerson Speyerer
(Arizona State University) published a
compilation of 222 new craters spotted in before-after pairings of Lunar
Reconnaissance Orbiter images. None
of these, including two seen as bright
flashes from Earth as they formed, are
more than a few tens of meters across -
far too small to be seen telescopically.
But there's no convincing evidence
for the kinds of lunar surface changes
reported by Gruithuisen, Schmidt, and
Klein. These ephemeral sightings weren't
the result of geologic or atmospheric
phenomena - the real causes were poor
seeing, poor illumination, inferior optics,
or bad eyesight. In Epic Moon, authors
William Sheehan and Thomas Dobbins
explain that observers of that era expected
changes to occur on the Moon, so this
became the default explanation for
unusual sightings. Although a handful
of 19th-century astronomers did express
misgivings about the veracity of earlier
maps, the desire for a dynamic Moon
overwhelmed caution.
The search for lunar changes continues, now gentrified under the catchall
term transient lunar phenomena. Remarkably, some past reported changes do
involve accurately documented observa-
tions of topographic appearances that
only reoccur under specific illumination
and libration conditions. Our astronomical predecessors were often careful
observers but not critical thinkers.
You can see for yourself how difficult
it can be to make reliable observations
by looking at some famous examples.
For example, Herschel's "volcanic
eruptions" occurred when earthshine
flooded Aristarchus - a very bright
crater whose visibility varies according
to seeing and illumination conditions.
Check on Aristarchus each time you
observe the Moon before first quarter to
see if you detect any "eruptions."
Gruithuisen's walled city is hard to
find unless the illumination is just so;
otherwise its ramparts become scraggly
ridges. The "wall" pattern is within the
dark pyroclastic deposits between Sinus
Aestuum and the crater Schröter.
The bright apron of pulverized ejecta
that surrounds Linné is easy to spot
whenever the Sun is positioned high
over western Mare Serenitatis. Conversely, glimpsing its small crater pit
requires decent seeing, a low Sun angle,
a telescope with an aperture of at least
4 or 6 inches, and high magnification.
As you look at these and other
regions you might notice small features
that don't appear on previous maps. If
so, please don't tell me.
¢ Contributing Editor CHUCK WOOD
has been taking S&T readers on telescopic lunar explorations since July 1999.
p Of the hundreds of new craters identified by
NASA's Lunar Reconnaissance Orbiter, this one
- 43 meters across - is the largest. Colors
represent elevation, with dark blues the lowest.
s k y a n d t e l e s c o p e .c o m
* AUGUST 2017
53
http://www.skyandtelescope.com
Sky and Telescope - August 2017
Table of Contents for the Digital Edition of Sky and Telescope - August 2017
Contents
Sky and Telescope - August 2017 - Cover1
Sky and Telescope - August 2017 - Cover2
Sky and Telescope - August 2017 - 1
Sky and Telescope - August 2017 - Contents
Sky and Telescope - August 2017 - 3
Sky and Telescope - August 2017 - 4
Sky and Telescope - August 2017 - 5
Sky and Telescope - August 2017 - 6
Sky and Telescope - August 2017 - 7
Sky and Telescope - August 2017 - 8
Sky and Telescope - August 2017 - 9
Sky and Telescope - August 2017 - 10
Sky and Telescope - August 2017 - 11
Sky and Telescope - August 2017 - 12
Sky and Telescope - August 2017 - 13
Sky and Telescope - August 2017 - 14
Sky and Telescope - August 2017 - 15
Sky and Telescope - August 2017 - 16
Sky and Telescope - August 2017 - 17
Sky and Telescope - August 2017 - 18
Sky and Telescope - August 2017 - 19
Sky and Telescope - August 2017 - 20
Sky and Telescope - August 2017 - 21
Sky and Telescope - August 2017 - 22
Sky and Telescope - August 2017 - 23
Sky and Telescope - August 2017 - 24
Sky and Telescope - August 2017 - 25
Sky and Telescope - August 2017 - 26
Sky and Telescope - August 2017 - 27
Sky and Telescope - August 2017 - 28
Sky and Telescope - August 2017 - 29
Sky and Telescope - August 2017 - 30
Sky and Telescope - August 2017 - 31
Sky and Telescope - August 2017 - 32
Sky and Telescope - August 2017 - 33
Sky and Telescope - August 2017 - 34
Sky and Telescope - August 2017 - 35
Sky and Telescope - August 2017 - 36
Sky and Telescope - August 2017 - 37
Sky and Telescope - August 2017 - 38
Sky and Telescope - August 2017 - 39
Sky and Telescope - August 2017 - 40
Sky and Telescope - August 2017 - 41
Sky and Telescope - August 2017 - 42
Sky and Telescope - August 2017 - 43
Sky and Telescope - August 2017 - 44
Sky and Telescope - August 2017 - 45
Sky and Telescope - August 2017 - 46
Sky and Telescope - August 2017 - 47
Sky and Telescope - August 2017 - 48
Sky and Telescope - August 2017 - 49
Sky and Telescope - August 2017 - 50
Sky and Telescope - August 2017 - 51
Sky and Telescope - August 2017 - 52
Sky and Telescope - August 2017 - 53
Sky and Telescope - August 2017 - 54
Sky and Telescope - August 2017 - 55
Sky and Telescope - August 2017 - 56
Sky and Telescope - August 2017 - 57
Sky and Telescope - August 2017 - 58
Sky and Telescope - August 2017 - 59
Sky and Telescope - August 2017 - 60
Sky and Telescope - August 2017 - 61
Sky and Telescope - August 2017 - 62
Sky and Telescope - August 2017 - 63
Sky and Telescope - August 2017 - 64
Sky and Telescope - August 2017 - 65
Sky and Telescope - August 2017 - 66
Sky and Telescope - August 2017 - 67
Sky and Telescope - August 2017 - 68
Sky and Telescope - August 2017 - 69
Sky and Telescope - August 2017 - 70
Sky and Telescope - August 2017 - 71
Sky and Telescope - August 2017 - 72
Sky and Telescope - August 2017 - 73
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Sky and Telescope - August 2017 - 76
Sky and Telescope - August 2017 - 77
Sky and Telescope - August 2017 - 78
Sky and Telescope - August 2017 - 79
Sky and Telescope - August 2017 - 80
Sky and Telescope - August 2017 - 81
Sky and Telescope - August 2017 - 82
Sky and Telescope - August 2017 - 83
Sky and Telescope - August 2017 - 84
Sky and Telescope - August 2017 - Cover3
Sky and Telescope - August 2017 - Cover4
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