Sky & Telescope - June 2021 - 7

Articles like these are why I have been
reading S&T for more than 50 years!
Jim Hartley
Fair Oaks, California

Earth's debris, and created a big, centerﬁlled doughnut that then coalesced into
Earth and its Moon (S&T: Aug. 2018, p. 26).

Missing Arecibo

Camille M. Carlisle replies: That

is an interesting question you've
posed! I asked planetary scientist Sean
Raymond, who has worked on the asteroidbelt formation scenarios. He says, " The
Moon is thought to have formed from a
late giant impact from a big (Mars-sizedish) object that is often called Theia. Most
researchers think that Theia grew near Earth
and was made of basically the same stuff
(https://is.gd/EarthMoonGenetics).
But there is a crazy new idea that Theia
might have originated farther out, in the
primordial asteroid belt, and even delivered Earth's water when it collided
(https://is.gd/BroughtWatertoEarth). New
results are shooting down that idea, but it's
worth thinking about. "
Also, the impactor likely didn't bounce
off Earth but was obliterated, mixed with

Having spent a couple of wonderful
years at the Arecibo Observatory as a
graduate student in the 1970s, I share
David Grinspoon's dismay at its demise
in " Adiós, Arecibo " (S&T: Mar. 2021, p.
12). But Arecibo's dish is not a paraboloid - it's spherical. The antenna's
surface still reﬂects like a sphere when
the focal point is moved to observe a
different part of the sky.
This is the design magic that allows
the dish to be ﬁ xed in the ground and
still observe objects up to 20° from
the zenith. It was an ingenious design
concept and will be sorely missed.
Nathan Krumm
Pearblossom, California

1971

1996

* Joel Marks's observation of a geostationary satellite (S&T: Jan. 2021, p. 6) was
made with an unguided telescope, and
his impression was that the geosat appeared to move through the background
stars even though the satellite was itself
motionless in the eyepiece field.
* Saint Raphael is from the Book of Tobit.
Therefore, all of Julius Schiller's constellations in the Southern Hemisphere (S&T: Jan.
2021, p. 64) are from the Old Testament.
* Discounting political alterations, time
zones are centered on even 15° meridian
lines. They don't begin and end on those
lines as stated in " Finding North by Day "
(S&T: Feb. 2021, p. 72).
* An electron went missing from Branch 2
of the " Rare Reactions " diagram (S&T: Apr.
2021, p. 17). The electron combines with a
proton in Beryllium-7 to produce Lithium-7
and a neutrino.

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75, 50 & 25 YEARS AGO by Roger W. Sinnott
1946

FOR THE RECORD

June 1946
Vermont Gathering " The war is
over and many of us are finding
time to pursue our old hobby of
telescope making. Consequently,
there has been considerable
demand for the Springfield telescope makers to hold again their
annual Telescope Makers Convention at Stellafane. The date is set
for the weekend of August 3rd, during the first quarter of the moon.
" The banquet and program
will be that evening. We are glad
to report that Russell Porter will
be here from Caltech to give the
latest information on the 200-inch
at Palomar. . . . There should be a
new generation of telescopes both
wonderful and weird that are worthy of exhibit on Breezy Hill. "
John W. Lovely's announcement
followed a four-year wartime lapse
in Stellafane conventions, their ﬁrst
interruption since 1926. Hopefully,
the current lapse, due to COVID-19,
will end on August 5-8, 2021.

June 1971
Cygnus X-1 " Perhaps the most
spectacular discovery from Uhuru
data is the very rapid variation of
the X-ray emission from Cygnus
X-1, a source in our Milky Way
which has been known since 1966.
. . . Unlike other strong sources,
Cygnus X-1 shows a jagged rise
and fall [in counts] collected over
0.384-second intervals. . . .
" This [has] led to the suspicion
that the actual period might be
shorter than the sampling interval of the detector . . . On this
viewpoint, a reexamination of
the records indicated a period of
0.073 second. [Investigators] note
that the very short but persistent
pulse period can be reasonably
interpreted only by the rapid rotation of a collapsed star. This, they
suggest, might be a 'black hole'
instead of a neutron star. "
As the ﬁrst dedicated X-ray satellite, Uhuru was, in fact, looking at
a stellar-mass black hole orbiting
a 9th-magnitude star about 7,200
light-years away. According to a

2021 study, Cygnus X-1 spins 800
times a second and has the mass
of 21 Suns.
June 1996
Spring Comet " 'Something from a
fantasy world.' 'Absolutely beautiful!' 'The most unbelievable sight
I've ever seen in the sky.' These
are among the acclamations that
arrived in our offices as Comet
Hyakutake, C/1996 B2, sailed past
Earth in late March. . . .
" When Japanese amateur Yuji
Hyakutake stumbled upon an
11th-magnitude smudge with his
25×150 binoculars in the predawn
hours of January 30th, little did he
realize that it would soon become
a huge naked-eye spectacle
whose great tail spanned halfway
across the heavens. "
Edwin Aguirre went on to say
that some observers were calling
the comet " electric-arc blue " or
" aquamarine. " And on March 22nd
in Norway, Bjørn Granslo estimated that its head was nearly as
bright as Arcturus.
sk yandtelescope.org * JUNE 2 021

https://www.is.gd/EarthMoonGenetics https://www.is.gd/BroughtWatertoEarth http://www.skyandtelescope.org

Sky & Telescope - June 2021

Table of Contents for the Digital Edition of Sky & Telescope - June 2021