Sky & Telescope - January 2022 - 7

were the result of an antipodal reaction to
an impactor was popular when astronomers
first proposed the asteroid theory in the
1980s, but it fell out of favor after they
discovered the Chicxulub crater in 1991.
The paper by Mark Richards, Renne, Sprain,
and colleagues (https://is.gd/Chicxulub_
Deccan) details why, but the primary
reason, they argue, is that 65 million years
ago, the Chicxulub impact site's antipode
was too far east of the Deccan Traps to
cause that kind of reaction. Instead, they
suggest that the asteroid shook the planet
enough to ramp up the ongoing volcanism.
I enjoyed reading Shannon Hall's article
" The Case of the Dead Dinosaurs " but
found myself wishing she had provided
some more information. Among my
questions were: What are the relative
abundances of iridium and mercury in
both Earth's mantle and different asteroid
types, and what are the error bars in
dating both the Chicxulub impact and
the Deccan Traps events? (A graphic
image superimposing these events
would have been a nice inclusion.)
Douglas Warshow
Ann Arbor, Michigan
Camille M. Carlisle replies:
The recent paper " The Chicxulub
impactor: comet or asteroid? " (https://
is.gd/Chicxulub_Impactor) gathers
together useful research on the evidence in
favor of a carbonaceous chondrite asteroid
being the impactor. According to that paper,
scientists estimate that the total mass of
iridium in the geologic clay layer is 2.0-2.8
× 1011 g, and a 10-km-wide carbonaceous
chondrite-like asteroid would deliver about
2.3 × 1011 g - a very nice agreement. In
contrast, a 7-km-wide comet (which would
make the same size hole in Earth's crust
since it would hit it at a faster velocity) would
deliver less than a tenth as much iridium. To
your second question: My original intention
"
was to design a graphic timeline combining
the Chicxulub and Deccan timeframes and
lines of evidence. But I discovered that
there is so much debate over the times and
uncertainty ranges that it would have been
a disaster of contradictions. Alas, I had to
give up the idea.
FOR THE RECORD
* The Chicxulub impactor was 10 km
wide, not 200 km as stated in the graphic
on page 20 of the October issue.
* In the info box on page 31 of the October
issue, SagDIG is a member of the Local
Group but isn't a satellite of the Milky Way.
* On page 23 of the August 2021 issue,
all instances of NGC 7133 should
read IC 5132/33.
* In " Mars Bumbles Through the Beehive "
(S&T: June 2021, p. 50), the Beehive
Cluster is almost 16 million times more
remote than Mars.
SUBMISSIONS: Write to Sky & Telescope, One Alewife Center, Suite 300B, Cambridge, MA 02140, 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
1947
1972
º January 1947
Far UV " [At] White Sands Proving
Ground on October 10th, . . . the
ultraviolet spectrum of the sun at
wave lengths shorter than 3400
angstroms was obtained from
a V-2 rocket at a height of 88
kilometers. The limit of the spectrograph
was 1100 angstroms, [a
region] normally absorbed by the
ozone in the upper atmosphere.
The new spectra clearly show the
elimination of this absorption and
the appearance of the spectrum
in the ultraviolet as the rocket
ascended above the ozone layer. "
Captured German V-2 rockets
continued to open new frontiers.
1997
º January 1972
Dwarf Unveiled " Sirius B is
among the most important of the
several thousand white dwarfs
now known, since it forms a visual
binary with Sirius A, the brightest
star in the [night] sky. . . . But it is
10 magnitudes fainter than Sirius
A, so its spectrum is exceedingly
difficult to photograph without
serious contamination from the
brilliant primary. . . .
" During the past decade, the
angular separation between the two
components has been nearly the
maximum possible, [letting astronomers]
obtain the first 'clean' spectra
of Sirius B at the coudé focus of the
200-inch telescope. . . .
" J. L. Greenstein, J. B. Oke, and
H. L. Shipman [report] that Sirius
B has an effective temperature
of 32,000° Kelvin, radius 5,400
kilometers [, and is] a white dwarf
consisting primarily of helium. "
º January 1997
CCD Charm " Unless you are very
new to astronomy, you know about
the astroimaging revolution. Amateurs
are converting wholesale
from conventional emulsion-based
photography to digital imaging . . .
" During the 1980s backyard
observers chalked up about 20
extragalactic supernovae. That
number has more than doubled in
the first six years of this decade,
and most of the new finds were
captured by CCDs. . . .
" Closer to home are countless
asteroids waiting to be discovered.
With rare exceptions, the sky has
been swept clean of minor planets
brighter than 16th magnitude (and
thus within easy reach of conventional
amateur astrophotography).
But a CCD on even an 8-inch
telescope can easily reach 18th
magnitude in a few minutes. That
opens a remarkably wide door
to discovery. The experience of
veteran observer Paul Comba in
Arizona is a case in point. In the
six months after connecting a CCD
camera to his 18-inch reflector he
discovered 39 asteroids between
18th and 20th magnitude. "
As Dennis di Cicco anticipated,
a new " golden age " of amateur
asteroid discovery began. Today,
however, large professional surveys
are gobbling up asteroids
at an astounding rate, and the
sky has now been " swept clean "
almost to magnitude 21.
sk yand tele scope .o r g * JANUARY 2022
7
https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/127/11-12/1507/126064/Triggering-of-the-largest-Deccan-eruptions-by-the?redirectedFrom=fulltext https://academic.oup.com/astrogeo/article/62/3/3.34/6275176 https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/127/11-12/1507/126064/Triggering-of-the-largest-Deccan-eruptions-by-the?redirectedFrom=fulltext https://academic.oup.com/astrogeo/article/62/3/3.34/6275176 http://skyandtelescope.org

Sky & Telescope - January 2022

Table of Contents for the Digital Edition of Sky & Telescope - January 2022

Contents
Sky & Telescope - January 2022 - Cover1
Sky & Telescope - January 2022 - Cover2
Sky & Telescope - January 2022 - 1
Sky & Telescope - January 2022 - Contents
Sky & Telescope - January 2022 - 3
Sky & Telescope - January 2022 - 4
Sky & Telescope - January 2022 - 5
Sky & Telescope - January 2022 - 6
Sky & Telescope - January 2022 - 7
Sky & Telescope - January 2022 - 8
Sky & Telescope - January 2022 - 9
Sky & Telescope - January 2022 - 10
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Sky & Telescope - January 2022 - 84
Sky & Telescope - January 2022 - Cover3
Sky & Telescope - January 2022 - Cover4
Sky & Telescope - January 2022 - SA1
Sky & Telescope - January 2022 - SA2
Sky & Telescope - January 2022 - SA3
Sky & Telescope - January 2022 - SA4
Sky & Telescope - January 2022 - SA5
Sky & Telescope - January 2022 - SA6
Sky & Telescope - January 2022 - SA7
Sky & Telescope - January 2022 - SA8
Sky & Telescope - January 2022 - SA9
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