Sky and Telescope - June 2016 - 8

Letters

The Inconstant (Carbon) Stars
Alan MacRobert refers to visual estimates
of carbon-star brightness as "notoriously
unreliable" (S&T: Feb. 2016, p. 44). I'd be
very interested in any studies that have
investigated this claim and, if possible,
quantiﬁed it. It certainly makes sense,
and one could speculate on possible
causes. However, a few years ago I found
that the color of comparison stars makes
no diﬀerence to the overall accuracy of
visual estimates of Mira-type variables
(see arxiv.org/abs/1203.6394).
Alan Whiting
Alexandria, Virginia

The "Draw" of Saturn
Thank you, Dean Regas (S&T: Feb. 2016,
p. 76), for the reminder of my ﬁrst view of
Saturn through my very own "telescope."
I had put together a set of lenses and
tubing and leaned it over a fence while
pointing in the planet's direction. There
it was, a round blob with ears, and it was
the thrill of my young lifetime. (I later

75, 50 & 25 Years Ago
June 1941
Coronium "A theory
that explains the origin
of the mysterious green
lines detected in the
spectrum of the sun's
corona [during total
solar eclipses] has been
recently oﬀered by Dr.
Bengt Edlen, of Sweden. According to this
theory these lines, once believed caused by an
unknown element, called coronium, are due
to the extreme ionization of iron atoms in the
sun's corona. Some as yet unknown and powerful excitation from the sun strips them of
their normal quota of electrons. In this case,
13 of these electrons are removed."
The true nature of coronium had puzzled
solar physicists ever since the total solar eclipse
of August 7, 1869, a widely witnessed event that
was visible from Alaska to North Carolina. Like
helium, it seemed to be a new element unknown
on Earth. Edlen's theory ﬁnally accounted for
the mysterious spectral lines, and later work
established extreme coronal temperatures as the
excitation cause.

June 2016 sky & telescope

received a Skyscope 3.5-inch Newtonian
that resolved the blob to my satisfaction.)
Having been introduced to astronomy
by my father at a very young age, I started
reading about it as soon as I discovered
my local library. So, when my sixth-grade
class went to Lick Observatory in June
1946, I was well prepared and dazzled the
class and the astronomer with my knowledge. I "showed" them Albireo, the wellknown double star in Cygnus, through
the 12-inch refractor there. But the trip's
high point, without question, was seeing
Saturn through Lick's amazing 36-inch
refractor.
Bill Pitsker
Petaluma, California

[Cassiopeiae]." NGC 663 ﬁts that description slightly better.
In his own copy of the catalog, Messier
hand-wrote a position, 1 h 20m +61°°, which
(corrected for precession) is about equidistant from both of those clusters. But it
might not be an observed position - perhaps he chose the 1 h 20m line in his star
atlas and followed it up to a declination
"between Epsilon and Delta," similar to
what I contend he did for his handwritten
position of M102.
Many early identiﬁcations of Messier
objects situated in rich star ﬁelds are, I
fear, doomed to remain uncertain.
Michael A. Covington
Athens, Georgia

The Case for M103

For the Record

I second Tom Reiland's suggestion (S&T:
Feb. 2016, p. 8) that M103 might be NGC
663 and not NGC 581. In Messier's published catalog, this was among the unconﬁrmed objects for which no position was
given except "between Epsilon and Delta

✹The stars labeled Beta and Zeta Tauri
(S&T: Jan. 2016, p. 45) are actually Iota
Aurigae and Beta Tauri, respectively.
✹In the table of galaxies within the Beehive
Cluster (S&T: March 2016, p. 59), NGC
2624 is also called MCG +3-22-19.

Roger W. Sinnott
June 1966
Ex-Variable Star? "[An]
astonishing report by
two Canadian astronomers, Serge Demers
and J. D. Fernie of David
Dunlap Observatory,
[states] that a very wellknown Cepheid variable
star, RU Camelopardalis, has recently ceased
to pulsate and now appears to be practically
constant in brightness! . . .
"These observations were carefully made,
and no explanation in terms of a misidentiﬁed star or instrumental fault is possible. . . .
According to the two Canadian astronomers,
. . . 'the pulsation has indeed died away. [For
the star] to accomplish this in only four years is
most remarkable, since simple theory (Eddington, 1926) would indicate a required time-scale
of the order of 103 to 10 4 years.'"
Soon, however, RU Cam was again pulsating.
The star is now classiﬁed as a Cepheid of the W
Virginis type, with light curves prone to unexpected changes in amplitude or period. These
stars are much less luminous than the better-

behaved Cepheids that
astronomers use as intergalactic distance gauges.
June 1991
Space Junk "Unless
spacefaring nations
stem the exponential
increase in small bits of
junk orbiting our planet, some low-Earth orbits
(lower than 2,000 kilometers) may become too
risky to use in just 10 or 20 years. This is the
dire conclusion of a report issued recently by
the congressional Oﬃce of Technology Assessment (OTA). . . .
"'Cleaning up' space is possible with
today's technology but wouldn't be worth
the expense. Instead, the best plan is to keep
future spacecraft from fragmenting or shedding bits of debris. Shielding spacecraft is also
important, but methods need further study."
Today, NASA and the U.S. Department of
Defense actively track more than 21,000 objects
in orbit. Maneuvering active spacecraft to avoid
collisions is a top concern, especially for crewed
craft like the International Space Station.

http://www.arxiv.org/abs/1203.6394

Sky and Telescope - June 2016

Table of Contents for the Digital Edition of Sky and Telescope - June 2016