Sky & Telescope - March 2021 - 7

Observing Accessories
I really enjoyed Tom Dobbins's " Tips
for Planetary Observers " (S&T: Nov.
2020, p. 52). His idea to place the
diagonal mirror between the polarizing
ﬁ lters in a variable ﬁ lter is brilliant!
Rotating the eyepiece to adjust the
brightness and reduce glare is a huge
improvement for observing ﬁne detail.
But dielectric mirror diagonals have
an added beneﬁt. While a diagonal
with a metallic-ﬁ lm mirror preserves
the polarization from the polarizing
ﬁ lter, a dielectric-ﬁ lm mirror does not.
For a certain orientation of the ﬁ rst
polarizing ﬁ lter, rotating the eyepiece,
and the second ﬁ lter, results not in
variable extinction of the brightness
but instead variable color ﬁ ltration.
On October 2nd, I was observing
Mars, and with this hack, I could tune
the color ﬁ ltration of the planet from
cyan through to magenta. So, one can
adjust the color to improve the visibility of whatever feature they're inter-

ested in and still enjoy the beneﬁts of
glare reduction. Finding this speciﬁc
orientation of the ﬁrst polarizer is easy.
It simply requires rotating the front
polarizer incrementally and turning
the eyepiece at that point. I found a
position where I mostly get brightness
extinction rather than color change.
Then, to get the color variation feature,
rotate this ﬁ rst polarizer 45° from that
spot in either direction.
I've never seen such a dramatically
clear view of Mars with any of my prior
telescopes before using this setup. Thank
you again for your wonderful column!
John Guerra
Concord, Massachusetts

The Goldilocks Zone
Monica Young's article " To Touch The
Sun " (S&T: Nov. 2020, p. 20) captures
my imagination and scaffolds my

1971

1996

Michael Robertson
Princeton, Minnesota

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75, 50 & 25 YEARS AGO by Roger W. Sinnott
1946

thinking and understanding, leaving
me curious and on the edge of my seat
for the next act! Thank you so much
for adding another S&T article that is
somehow both engaging and leaves me
wanting more.
And thank you, Sky & Telescope, for
consistently providing such a large
variety and range of information,
from tables regarding Jupiter's activities and moons to articles on pairing
star diagonals to reorient stargazing
and the many other wonderful topics
over the years. It's difﬁcult to imagine the editorial process that assures
these articles are both receptive to
the diverse interests of subscribers
and provide high-caliber information
without overwhelming.
That's the Goldilocks Zone for me!

March 1946
Blue Moon " In his quiz column . . . Dr. L. J. Lafleur quotes
an explanation found in the Maine
Farmers' Almanac for 1937. In
effect, this is that at one time the
various full moons of the year were
given names according to the order
in which they occurred . . . But
seven times in 19 years there were
- and still are - 13 full moons in
a year. This gives 11 months with
one full moon each and one with
two. This second in a month, so I
interpret it, was called Blue Moon,
and was considered unlucky and
a real nuisance as it occurred at
various times of the year and upset
scheduling of church festivals. "
This was the most consequential blunder ever to appear in the
pages of S&T. The key phrase is
" so I interpret it. " As Donald W.
Olson discovered in 1999, writer
J. Hugh Pruett had not seen the
Maine Farmers' Almanac ﬁrsthand
and guessed wrong, thereby plant-

ing the seed for today's most widespread meaning of Blue Moon.
March 1971
Touchdown " [The] Soviet spaceship Venus 7 arrived at that planet
on December 15, 1970, after a
120-day flight. But the report that
it apparently did not reach the
planet's surface needs modification.
. . . It now appears that an actual
soft landing took place. On January 26th, the Moscow newspaper
Isvestya published an announcement that computer analysis of the
radio transmissions revealed weak
signals continuing 23 minutes more,
although at only one percent of the
previous intensity. . . . Telemetry
data after the landing revealed a
temperature of 475° ± 20° centigrade, and a barometric pressure of
90 ± 15 atmospheres. . . .
" This is the first occasion on
which scientific observations have
been made from the surface of
another planet. "
The mission is better known
today by its Russian name: Venera 7.

March 1996
Quasar Homes " Extragalactic
astronomers were astounded
last year when the Hubble Space
Telescope apparently failed to
find some of the galaxies in which
every quasar is thought to reside.
Now two recent studies indicate
that most, if not all, 'naked quasars' are indeed clothed - though
scantily at times. . . .
" Kim K. McLeod (HarvardSmithsonian Center for Astrophysics) and George H. Rieke (University of Arizona) . . . reanalyzed
the Hubble images for a few of
the nominally naked quasars by
calculating a one-dimensional
profile for the images that the
orbiting telescope obtains of point
sources. They then used these
profiles to subtract the quasars'
overwhelming glare from their far
dimmer surroundings. . . .
" [They could also] detect the
disputed quasars' hosts in nearinfrared images taken with the
2.2-meter Steward Observatory
reflector atop Kitt Peak. "
sk yandtelescope.org * MARCH 2 021

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Sky & Telescope - March 2021

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