SKY_September2014.pdf

Letters

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
stars.
“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
measurement.”

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

at skypub.com/errata.

10 September 2014 sky & telescope

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