Sky and Telescope - December 2015 - 9

ATTENTION, SKETCHERS! Send your best astronomical renderings to gallery@SkyandTelescope.com (put "sketch" in the subject line),
and if we get enough good-quality submissions we'll showcase them in a future issue.

Concerns About Green Lasers

Check out our online guide to using laser
pointers safely: http://is.gd/green_lasers.

With all the recent press about airplanes
being targeted with green laser pointers,
is there anything we honest astronomers
should do to avoid encounters with the
law when using ours for harmless star
sighting or aligning? I use mine only
brieﬂy and turn it oﬀ every time I see a
plane approaching. But it can be hard to
tell when a plane happens upon the same
path as where the laser is pointing.
Dennis Fisher
Upper St. Clair, Pennsylvania

Seeing Pluto by Eye
From my rural location, I was able to
glimpse Pluto for the ﬁrst time ever on
the night of July 11-12 using 132× on my
10-inch Schmidt-Cassegrain telescope. It
would have been utterly impossible without the superb ﬁnder chart on S&T's website (http://is.gd/Pluto_2015). Pluto was
barely visible under the sky conditions I
had, though the next night I was able to
spot it a little more easily. On July 13-14,
with stars in Ursa Minor visible down to
magnitude 6.3, Pluto was distinctly visible with averted vision and some direct

Kelly Beatty replies: You're wise to be cautious, especially since the beams of these
handy devices are becoming more intense.

December 1940
Star Power "The sun
continuously pours out
enormous quantities of
radiation into space. . . .
We know, however, from
radioactive measurements that the age of
the earth is at least 1,500
million years. The sun
must be at least as old, and there is no reason
to assume that its radiation 1,500 million years
ago was much less than it is now. . . .
"The way [to understand a star's energy]
was opened when [Ernest] Rutherford discovered, in 1919, the transmutation of atomic
nuclei. . . . But it took until 1938 before the
particular transmutations responsible were discovered and the agreement of the theory with
the observational facts established. . . .
"It has been shown that the carbon cycle
accounts successfully for the radiation of the
most important class of stars, the so-called
main sequence. . . . [Red giants and white
dwarfs] have diﬀerent mechanisms of energy
production [which] are not yet known. . . ."
Physicist Hans A. Bethe (Cornell University)
was modestly describing the discovery that would
earn him a Nobel Prize in 1967.
December 1965
Comet Ikeya-Seki "Favorably placed observers
on October 20-21 viewed a comet so brilliant
that it could be seen with the naked eye in broad

For the Record
✹In the caption for the galaxies NGC 5905
and 5908 (S&T: July 2015, p. 59), the identiﬁcations were inadvertently switched. They
are labeled properly in the chart on page 60.
Write to Letters to the Editor, Sky & Telescope,
90 Sherman St., Cambridge, MA 02140-3264,
or send e-mail to letters@SkyandTelescope.com.
Please limit your comments to 250 words.

Roger W. Sinnott
daylight, if the sun was
hidden behind the side
of a house or even an
outstretched hand. This
beautiful phenomenon is
rare: the most recent daylight comets had been
1927 IX, 1910 I, 1901 I, and
the great comets of 1882,
1843, and 1811. . . .
"And after perihelion passage on October
21st, the comet's tail became three-quarters of
the earth-sun distance in length. It was seen
curving upward from the southeastern horizon
during morning twilight."
Ikeya-Seki belonged to the Kreutz family of

Comet Ikeya-Seki (C/1965 S1) looms over
the lights of Los Angeles in the predawn
sky of October 29, 1965.

S&T ARCHIVES / WILLIAM LILLER

75, 50 & 25 Years Ago

vision. I really enjoyed knowing that New
Horizons was just hours from its closest
approach as I watched.
Scott Harrington
Evening Shade, Arkansas

sungrazing comets. To be
visible by day, so near the
Sun, it had to shine many
times brighter than the
full Moon.
December 1990
Surface of Venus
"NASA's Magellan
spacecraft . . . is now
performing so well that by this time next year
geologists should have a better global map of
Venus than they do for most of the Earth. . . .
The heart and soul of Magellan is an imaging system known as synthetic-aperture radar.
. . . The beam's 12.6-centimeter wavelength
enables it to pass unimpeded through the
planet's thick mantle of clouds. . . .
"Magellan's scientiﬁc potential hinges on its
ability to resolve surface features as small as 120
meters across - about 10 times better than that
achieved in previous radar studies by the Soviet
Union's Venera orbiters and by the huge Arecibo
radio antenna in Puerto Rico. While extremely
useful, these earlier eﬀorts simply didn't provide
the ﬁne-scale knowledge necessary to decipher
the planet's geologic history. Comments [Brown
University investigator James] Head, 'Magellan
is a microscope on Venus.'"
In the years since J. Kelly Beatty's report,
other spacecraft have explored Venus's atmosphere and climate, but for wholesale surface
mapping the Magellan mission of 1990-94
remains the last word.

Sk yandTelescope.com December 2015

http://www.is.gd/green_lasers http://www.is.gd/Pluto_2015 http://www.SkyandTelescope.com

Sky and Telescope - December 2015

Table of Contents for the Digital Edition of Sky and Telescope - December 2015