(Axel Boer) #1

75, 50 & 25 Years Ago Roger W. Sinnott

September 1964
Why the X-rays? “Can
neutron stars be the
sources of the intense
X-rays discovered last year
in Scorpius and Taurus?

... The hypothesis
seemed attractive for the
Taurus source... for it is
centered on the Crab nebula, the remnant of a
supernova explosion in A.D. 1054. It had been
suggested that such outbursts produce neutron
“To test the neutron star conjecture for the
Taurus source, Naval Research Laboratory sci-
entists sent a rocket-borne X-ray detector aloft
from White Sands, New Mexico, on July 5th.
It attained an altitude of 144 miles at the right
time and place to observe an occultation of the
Crab nebula by the moon.
“A point source such as a neutron star would
have disappeared abruptly when the moon’s
edge reached it. Instead, the X-ray intensity
diminished gradually during the fi ve minutes of

September 1939
Lost Meteorite “In
1859, Dr. John Evans,
government geologist
for Washington and Or-
egon, was exploring the
southern coastal region
of the latter state.... He
said [of the meteorite he
found], that ‘the mass, about three feet of which
is above ground, is in the mountains , about 40
miles from Port Orford on the Pacifi c and easily
accessible by mules.... ’
“Many eastern scientists have in recent
years searched for this valuable object. In 1932,
Dr. H. H. Nininger, president of the Society for
Research on Meteorites, looked over the terri-
tory without success. But he remarks, ‘I think
there is no doubt that the meteorite is some-
where around there.’”
Samples of the chunk that Evans harvested
were sent to the Vienna Academy of Science and
the Smithsonian Institution. But Evans died in
1860 and the Port Orford meteorite has never
been found. Some now suspect it was a hoax.

The X-rays actually arise in the hot gas of the
nebula surrounding the Crab pulsar, a rapidly spin-
ning neutron star detected in 1968. As the pulsar
gradually spins down, it dumps the lost rotational
energy into the gas and powers the X-rays.

September 1989
Outspoken Astronomer
“The Chinese astrophysi-
cist Fang Lizhi has become
China’s best-known dis-
sident. Fang is a theoreti-
cal cosmologist who has
recently been working on
the topology of the uni-
verse.... Fang was not directly involved in the
Chinese student uprising last spring. But after
the government cracked down on the movement
[at Tiananmen Square], it singled out Fang as a
prime instigator. He took refuge in the American
embassy... with his wife Li Shuxian, who is
herself a physicist, and their son.”
Allowed to leave China a year later, Fang
settled at the University of Arizona and studied
the early universe, galaxy clusters, and the
interstellar medium. He passed away in 2012.

and a lawn chair.
Some years ago Walter Scott Houston
wrote in his Deep-Sky Wonders column
that some of his most enjoyable observing
was naked-eye: “I always feel good when
I look at the stars,” he wrote. I agree: an
hour or so of plain stargazing helps put
your life in proportion.
Greg Thorup
Cumberland, Maine

Thank you for publishing Jim Mullaney’s
article! Probably half the members of
my astronomy club pursue the hobby as
Mullaney describes it. One of our club
offi cers even prefers to describe herself
as “a stargazer” instead of an “amateur
astronomer,” because even though she
has enormous high-tech ability, she often
chooses binoculars or the simplest tele-
scope to view, appreciate, and contemplate
the beauty and mystery of the night sky.
Mullaney’s article is courageous in a world
of gadget-driven amateur astronomy.
Donald Weitzman
Los Angeles, California

Moving Mars?
The news article “Mixed Message for Rock
Makeup” by Emily Poore (S&T: May 2014,
p. 12) suggests that the mixed composi-
tion of the asteroid belt resulted from the
orbital movement of Jupiter and that the
planet at one point came perhaps as close
to the Sun as the present orbit of Mars. So
where did Mars go?
Orbital shifts of the outer planets have
been also implicated in the origin of the
Late Heavy Bombardment, for example,
but similar orbit changes of the inner
planets are rarely, if ever, discussed. If the
Earth were slightly closer to a less lumi-
nous early Sun, wouldn’t this help ease the
constraints in explaining the faint young
Sun paradox?
Greg Konesky
Via e-mail

Editor’s Note: In the Grand Tack model,
Mars hadn’t fully formed when Jupiter and
Saturn forayed inward. During this time
there was only a rocky planetesimal disk.
The inward movement of Jupiter and Saturn

truncated this rocky disk (causing it to shrink
from 1.5 astronomical units to 1 a.u.). It’s
possible that Mars began forming around
1 a.u. and then moved out due to the gravita-
tional perturbations before it could beef up to
the size of Venus and Earth. A moving Mars
might also have helped scatter iron-rich plan-
etesimals into the inner asteroid belt, where
they’re commonly found today.
As to the faint young Sun paradox, that
arises about 3½ to 4 billion years ago, after
the period on which the Grand Tack and
related models focus. We have not heard of
expectations that the planets were migrating
substantially at this point. One recent expla-
nation for the paradox is that the composi-
tion of early Earth’s atmosphere would have
allowed life to arise, even with the faint Sun
(S&T: Oct. 2013, p. 11).

For the Record
✹ June 2014, p. 47: The caption for Alpha
Librae should identify the F4 star as the
secondary, not primary.
You can fi nd all errata for our 2014 issues

10 September 2014 sky & telescope

Ltte_layout.indd 10 6/23/14 12:18 PM

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