Sky and Telescope - March 2018 - 6

FROM OUR READERS

Perfecting Your Nightscapes

Tom Mason
Azusa, California

When Will the Sun Die?
Peter Tyson's article on the fate of our
solar system (S&T: Oct. 2017, p. 22)
was very interesting and informative.
One other factor possibly affecting the
future of Earth is intelligent intervention. If human civilization can avoid
extinction catastrophes, including
self-inflicted annihilation, a billion
years is a long time to implement effective strategies to compensate for a 10%
increase in solar luminosity.
Some possibilities include increasing
the overall reflectivity of Earth, putting
reflectors in orbit to block a fraction
of the Sun's light, and increasing the
radius of Earth's orbit.
Obviously, implementing any of
these strategies on the required scale
would be no small task, but the incentive for coordinated action eventually
would become compelling.
Tom Wik
Livermore, California

6

M A RCH 2 018 * SK Y & TELESCOPE

I think it is a bad mistake to publish
over-processed photographs (S&T: Jan.
2018, p. 36). The night sky is such a
subtle thing to see, and to lose that
subtlety by over-processing is a terrible
mistake. When our club shows celestial
objects to beginners, a number of them
are so disappointed because of their

"Written in the Star" seems to add about
a billion years to the Sun's expected
lifespan. I've seen one reference that has
the Sun leaving the main sequence in
about 5.4 billion years, whereas your figure is 6.5 billion years. Do we really have
enough computing accuracy to know
which figure is better - or whether we
need a different one entirely?
Larry Gerstman
Long Beach, New York

"

Greg Laughlin (Yale) replies: Our
understanding of the future evolution of the Sun (or at least its evolution up to
the tip of the red-giant branch when mass
loss makes things slightly uncertain) hasn't
changed much during the past 30 years. The
classic 1993 Astrophysical Journal paper by
J. Sackmann, A. Boothroyd, and K. Kraemer
("SBK"; see https://is.gd/gOzgfN) remains
authoritative and, additionally, continues to
make for good reading.
The discrepancies stem from exactly

Ken Spencer
Sea Cliff, New York

what one adopts for the main sequence's
endpoint. One reasonable definition is the
moment at which the hydrogen at the very
center of the Sun's core is exhausted. SBK's
calculations have this occurring 9.37 billion years after the Sun's earliest formation
phases, or "only" 4.83 billion years from now.
But there will still be hydrogen in the
layers just above the center, which will allow
the Sun to continue more or less normal
operations for well over a billion additional
years. In that sense, SBK's definition of the
main sequence's end is about 6.5 billion
years from now, after the Sun is left with a
significantly hydrogen-depleted core and
has begun to move fairly rapidly to lower
temperatures, becoming a "subgiant" star.

A Fond Memory of NGC 253
Like Matt Wedel, I also vividly remember my first sight of NGC 253, the Silver
Coin Galaxy in Sculptor (S&T: Nov.
2017, p. 43). It was August 9, 1977, at
Nairne in the dark hills east of Ade-

TOM & D ONN A M ASON

As soon as I retrieved my January issue
from the mailbox, I recognized the cover
picture by Rogelio Bernal Andreo. My
wife, Donna, and I took this daytime
version of the same waterfall on August
30, 2014, while in Big Sur, California.

experience seeing Hubble photographs.
We do a disservice by not representing
the night sky faithfully.
I have been a professional photographer all my life, both as a newspaper staffer and as a freelancer for
magazines. With the advent of digital
photography back in 2000, my newspaper realized that there needed to be
rules to limit what photographers could
do in manipulating their photographs.
That pretty much allowed us only the
options of burning, dodging, and minor
corrections to exposure and color. If
photographs were over-processed, or
faked outright by combining two or
more photographs into a single image,
the newspaper would suffer reduced
credibility with its readers.
With this in mind, I hope that you'll
consider changing your guidelines for
what is acceptable in terms of image
processing for the magazine.


https://www.is.gd/gOzgfN

Sky and Telescope - March 2018

Table of Contents for the Digital Edition of Sky and Telescope - March 2018

Contents
Sky and Telescope - March 2018 - Cover1
Sky and Telescope - March 2018 - Cover2
Sky and Telescope - March 2018 - 1
Sky and Telescope - March 2018 - Contents
Sky and Telescope - March 2018 - 3
Sky and Telescope - March 2018 - 4
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