Sky and Telescope - October 2016 - 8

Letters
Given this truth, his ﬁrst graph (p. 23)
contains all the information a stargazer
needs to decide what color light to use. It
shows that, with yellow or blue rays, the
rod cells are activated by much fainter
light than the cone cells are. So the rods
become washed out - and sensitive night
vision is lost - if one uses a light bright
enough to activate the cones.
However, with red rays, the rods and
cones are activated about equally, so the
rods are not washed out much by light
that activates the cones. This is why
observers should use dim red lights.
I can say that my experience is not
like Dick's, for I suﬀer essentially no loss
of night vision after reading a star chart
by dim red light. I hope that the amber
lights that he recommends do not become
acceptable at the star parties I attend.
Roger Venable
Chester, Georgia
Thank you for this very interesting
article. Perhaps red light became conven-

75, 50 & 25 Years Ago
October 1941
A Magazine Is Born "The editors note and
announce the closing with this issue of another
period for The Sky, and its combination with
another journal of ﬁne standing - The Telescope, at present published bi-monthly by the
Bond Astronomical Club, Harvard Observatory, Cambridge, Mass.
"Sky and Telescope will be the name of these
combined publications, beginning with the
issue of November, 1941. The present Sky editors will continue in the same capacity with the
new magazine, but Sky Publishing Corporation
will be located at Harvard Observatory.
"Of the same size and format as The Sky,
the new magazine will have four additional
pages each month [beyond the present 24],
thereby making it possible to retain all the best
features of both original
periodicals . . ."
Thus editors Charles
and Helen Federer
marked their move from
New York City's Hayden
Planetarium to a broader
publishing arena. They

October 2016 sky & telescope

tional wisdom purely by adoption long
ago from photographic darkroom practice, in which dim red was used because
black-and-white emulsions were not
sensitive to it, rather than its suitability
for low-light human vision.
Ken Wood
Newport, Wales
My variable-intensity red light is always
used at the brightest setting because,
at age 77, my old eyes need maximum
brightness to really see anything. At star
parties I always use a red light because
that's the norm, but I'd read that green
light works well at low levels. So on my
own I gave green light a try and found
that my night vision didn't suﬀer. I just
use it at a lower intensity.
The jury might still be out, but I
think most observers will ﬁnd any color
other than red to be intrusive in a group
setting. However, when observing by ourselves, it might be worth experimenting
with other colors. Eyes diﬀer from person

to person, and you might just ﬁnd - as I
did - that red isn't your "sweet spot."
Jack Kramer
Lily Lake, Illinois

For the Record
✹In Richard Wilds's article on dark nebulae
(S&T: July 2016, p. 30), Altair's brightness
is 1st (not 2nd) magnitude. Also, the star
labeled 12 Scuti in the ﬁnder chart is actually Eta (η) Scuti; the 4th-magnitude star to
its immediate east (left) is 12 Aquilae. Also,
the second and third sentences of the second
paragraph on p. 33 should read: "Using 27
Aql as your starting point, slide 34′ to the
southwest, in search of B139. A small planetary nebula, NGC 6778, shines 5′ below
this southeast-northwest dark smudge."
✹The 99%-reﬂ ective mirror coatings mentioned in our Test Report of the Astro-Tech
14-inch Ritchey-Chrétien telescope (S&T:
July 2016, p. 62) are a manufacturer's
speciﬁcation, not a value measured by Sky
& Telescope.

Roger W. Sinnott
would also drop The Sky's quaint but lovable
subtitle, "Magazine of Cosmic News."
October 1966
Polarized Variables "Not a few readers of
this magazine have spent long hours at the
telescope following the brightness changes
of the Mira-type or long-period variable stars.
Now K. Serkowski . . . reports the unexpected
discovery that the light of many long-period
variables is partially polarized. Moreover, this
polarization is intrinsic - arising in the stars
themselves rather than the interstellar medium
- and its amount can vary considerably.
"Dr. Serkowski's observations were made at
Lowell Observatory in Arizona, with two singlechannel polarimeters attached to the 21-inch
reﬂector. . . . Previously,
the highest known
polarization for any star
in high galactic latitudes
was 0.6 percent. [But] the
light of V Canum Venaticorum has a polarization
of six percent."
Polish astronomer
Krzysztof M. Serkowski

(1930-81) is also remembered for the Serkowski
law, an empirical formula for the wavelength
dependence of interstellar polarization.
October 1991
Stellar Flare-up "In this year of major ﬂares on
the Sun, we can rest assured that our star is
very well behaved compared to some others.
A ﬂare that released 100 million times more
energy than typical white-light solar events has
been recorded on the 6th-magnitude star V711
Tauri, report Gregory W. Henry (Tennessee
State University) and Douglas S. Hall (Vanderbilt University). It may have been the most
intense stellar ﬂare ever observed.
"V711 Tauri is an RS Canum Venaticorum
star, a pair of closely orbiting yellow subgiants (types G5 and K1).
. . . The big ﬂare lasted
6 to 7 hours. Covering
about 8 percent of the
K star's visible disk, it
blazed with 10 times the
total light of the Sun and
brightened the entire
system by 0.7 magnitude
in blue light. . . ."

Sky and Telescope - October 2016

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