Sky and Telescope - August 2017 - 8

From Our Readers

Jesse Hobbs
Murfreesboro, Tennessee

Monica Young replies: Multiple, in-

dependent lines of evidence point to
the existence of dark matter, and these have
led scientists to take it very seriously since

the 1970s - seriously enough to spend
millions (if not billions) of funding dollars on
researching its nature. That said, science
doesn't prove ideas true - it can only
prove ideas false. And any cosmologist
worth his or her salt would agree that dark
matter might yet be proven false. In these
pages, we attempt to present research
in such terms, noting when particular
searches have failed and therefore to what
extent they have narrowed the parameter
space for dark matter's existence.

Eclipse-Day Finderscope Fix
Looking forward to August's eclipse, I
purchased a solar ﬁlter for my 90-mm
refractor but wanted one for my ﬁnderscope as well. So I made one very
cheaply, and it works great. All you need
is a small length of PVC pipe (available
at any hardware store) slightly wider
than the diameter of the ﬁnderscope. I
cut the length so that it barely extends
past my mounted ﬁnderscope. I made a
shim out of electrical tape and glued it
to the inside of the pipe so that it could

p With a short length of PVC pipe and some
"eclipse glasses," you can quickly make a solar
filter (seen finished at left) for your finderscope.

sit ﬂush on the ﬁnderscope's front end.
Then I taped on a solar ﬁlter cut from a
pair of eclipse glasses. Now my ﬁnderscope solar ﬁlter is ready to go!
Curt Boudreau
Huntsville, Alabama

FOR THE RECORD

* The front page of the New York Times
(S&T: Jan. 2017, p. 70) is from January 25,
1925 (not October 25th).

75, 50 & 25 YEARS AGO by Roger W. Sinnott
1942

1967

1992

º August 1942
Shadow Bands "[A] peculiar
phenomenon seen at an eclipse
are shadow bands. These are wavy
rippling lines that flit across the
landscape at the beginning and
end of totality. No doubt they are
atmospheric, but the matter is still
one under a great deal of discussion. They were noticed as early as
1820 by [Hermann] Goldschmidt.
So far they have defied photography [since there] is no emulsion of
sufficiently high speed and high
contrast to catch them. . . ."
Apart from a poor 1925 image,
by the 1970s better ﬁlm emulsions
did on occasion record shadow
bands. Today's digital cameras are
much better than ﬁlm at discriminating low-contrast bands on a smooth
white screen - a project worth
considering on August 21st, when
the ﬁrst total-solar-eclipse track in
99 years sweeps the contiguous
U.S. coast to coast.

A U G U S T 2 0 1 7 * SK Y & TELESCOPE

º August 1967
Southern Telescopes "The dream
of many astronomers for really large
optical telescopes in the Southern
Hemisphere moved much closer to
reality this spring with the nearsimultaneous announcements that
150-inch reflectors will be erected in
Chile and New South Wales.
"On April 13th, while he was in
South America, President Lyndon
B. Johnson announced jointly with
President Eduardo Frei of Chile that
a 150-inch reflector will be built
at the Cerro Tololo Inter-american
Observatory near La Serena. . . .
"The second 150-inch reflector [will] be built by the Australian
and British governments for an
estimated $11,760,000 . . . at Siding
Spring Observatory near Coonabarabran in New South Wales."
Back then, the largest telescopes
south of the equator were 74-inch
(1.9-meter) reﬂectors at Radcliffe
Observatory in South Africa and at
Mount Stromlo in Australia. Today

no fewer than eight southern instruments probe the sky with apertures
from 6.5 to 9.2 meters.
º August 1992
Mystery Solved "Jules P. Halpern
(Columbia University) and Stephen
S. Holt (NASA-Goddard Space
Flight Center) have detected pulsed
X-ray emissions from Geminga, a
point source of high-energy gamma
rays that has defied explanation
for 20 years. . . . The discovery of a
0.237-second periodicity . . . suggests that Geminga is a pulsar, or
rapidly rotating neutron star. . . .
"David L. Bertsch and his colleagues looked for the same periodicity in data from the Compton
Gamma Ray Observatory. They
found it, clinching the source's
identification as a pulsar similar
to the ones in the Crab and Vela
supernova remnants."
With Geminga's basic nature
settled, astronomers still puzzle over
its unusual lack of radio emission.

CURT BOUDRE AU

"deduced" what goes on inside peculiar
stars, black holes, Martian history, and
so on, whereas in fact they have come
up with explanations that are consistent with most of the observed facts and
appear superior to competing explanations. But who's to say that a better
explanation might not come along, or
that further observations might support
conﬂicting theories?
Astronomers rarely deduce or produce anything incontrovertible. Dark
matter and dark energy are not incontrovertible truths. They are ad hoc
explanations designed to cover up holes
in modern cosmology big enough to
drive a galaxy through. Yet for some
reason your pages have never pointed
that out. You can do better.

Sky and Telescope - August 2017

Table of Contents for the Digital Edition of Sky and Telescope - August 2017