Sky and Telescope - November 2015 - 6

Letters

20.40′

Venus - Jupiter Separation
June 30, 2015

20.30′

7 p.m.

Equatorial diameter (arcseconds)

Leonov's Near-Fatal Spacewalk

8 p.m.

9 p.m.

10 p.m.

11 p.m.

32.44″
32.42″

Jupiter's
Diameter
Venus's
Diameter

32.40″
32.38″
7 p.m.

8 p.m.

9 p.m.

10 p.m.

11 p.m.

Paciﬁc Daylight Time
Left: The dramatic convergence of Venus and Jupiter in the late-June sky (upper graph) coincided
almost exactly with the two planets having the same apparent diameter (lower graph). Right: When
closest on June 30th, Jupiter (at top) and a crescent Venus appeared in the same ﬁeld of an 80-mm
f/6 refractor. This is a composite of a 1/ 160 -second image of the planets' disks and a 0.8-second
exposure to bring out Jupiter's moons.

Coincidental Conjunction
I enjoy coincidences and unusual numeric
combinations, such as 3/14/15 at 9:26:54
a.m. or celebrating with my wife, Carol,
at our "1/3 century" wedding anniversary.
While I knew the recent close conjunction of Venus and Jupiter (S&T: June 2015,
p. 48) might generate some pretty photos,
it did not otherwise attract my attention
- until I looked a little closer.
It turned out that, as seen from my
home in San Diego, Jupiter and Venus
would appear closest to each other only
70 minutes before the two planets had the
same apparent diameter. That was a rare
coincidence worth watching! I don't know
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November 2015 sky & telescope

if many other amateurs noted this rare
occasion, but I was happy for clear skies
so that I could enjoy it.
Don Bruns
San Diego, California

From Fiction to Fact
At the end of his excellent article on the
novels De la Terre à la Lune (From the Earth
to the Moon) and Autour de la Lune (Around
the Moon) by Jules Verne (S&T: June 2015,
p. 32), Dean Regas states, "It's diﬃcult to
measure what impact the ﬁctional writings of Jules Verne had on the real NASA
missions that would follow." I note that
rocket pioneers Hermann Oberth, Robert
H. Goddard, and Wernher von Braun all
referred to these novels as sources of inspiration in their youth. Verne's impact on
space travel was real and widespread!
Ken Rumstay
Valdosta, Georgia

CHART SOURCE: DON BRUNS; IMAGE: RICHARD TRESCH FIENBERG

Separation (arcminutes)

20.50′

Your comment regarding the ﬁrst-ever
spacewalk in 1965 (S&T: May 2015, p. 10)
- "Only decades later did the world learn
that the spacewalk nearly killed Leonov."
- is not quite correct. This episode is well
documented in The Russian Space Bluﬀ by
Leonid Vladimirov, published in 1971. This
book was only available to me after I emigrated from communist Czechoslovakia,
but it conﬁrmed rumors that circulated
soon after the ﬂight among those who
were following the space race closely and
were not blinded by propaganda.
Pavel (Paul) Otavsky
Woodstock, Vermont

Size of Earth's Umbra
I was intrigued by Roger Sinnott's article
about crater timings made during lunar
eclipses (S&T: June 2015, p. 28), especially the variations in the size and shape
of Earth's umbra due to our atmosphere.
He details how an "occulting layer" of
mesosphere, about 87 kilometers thick,
can account for the apparent added
"oblateness" of the shadow when averaged over thousands of measurements
and many eclipses. Yet certain eclipses
yield larger values: 91 km for the one on
July 6, 1982, and 92 km for the eclipse of
September 27, 1996.
Has anyone studied whether Earth's
topography, at the leading or receding
edge of the umbra, has any eﬀect? In
the case of the July 1982 eclipse, the
Earth-Moon geometry put Africa's Atlas
Mountains (which crest at 13,700 feet or
4.2 km) near one of the umbral edges. At
the start of the September 1996 eclipse,
the edge of Earth's shadow contained the
Rocky Mountains. I can't imagine that
a giant mountain range would have no
eﬀect if it happened to be in the right
place at the right time.
Tom Sales
Somerset, New Jersey
Roger Sinnott replies: You've raised an
intriguing question. Any theory of the
umbra's size needs to consider everything
that happens to the sunlight as it grazes the

Sky and Telescope - November 2015

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