Sky & Telescope - January 2024 - 7

"
Monica Young replies: Regarding
the spin-up: The author did not want
to go into an attempted explanation of the
past spin-up of the Milky Way because
there are a few competing scenarios, with
no good evidence for any of them as of
yet. In fact, it could be as simple as several
blobs coming together with a net angular
momentum in one direction or the other,
but it's difficult to find the " archaeological "
evidence to back this up. However, the
author did want to mention that the Milky
Way sped up, because it's spinning fast
today and so must have spun up at some
point in its past.
Regarding the plots, I agree that we
should have given a better description for
the populations of stars being plotted. The
second graph is showing a selection of
stars from the first one. The plot on page
39 shows stars from across the Milky Way,
including some in the thin disk and some in
the thick disk. The red line separates points
that are " high-alpha " (thick disk) from those
that are " low-alpha " (thin disk). The color
represents the density of stars. The plot on
page 40 shows a selection of those stars
with high alpha-to-iron ratios, signifying
that they are in the thick disk.
Carving Pillars in Space
I have been wondering about something
for quite some time. Photos of dust and
gas pillars appear to be spreading from a
point source, similar to the way smoke
rises from a fire. While I know there is
no " up " in space, it still appears to me
that the gas and dust is rising from some
point to form the columns. What drives
this phenomenon? Why is it forming the
columns and not just spreading evenly?
Dennis Dibala
Wallis, Texas
"
75, 50 & 25 YEARS AGO by Roger W. Sinnott
1949
1974
1999
º January 1949
Big Eye " Dr. Ira S. Bowen, director
of Mount Wilson and Palomar
Observatories, has announced that
the 200-inch telescope might not
be in working order until next fall. In
figuring the mirror, a zone 18 inches
wide at the edge was allowed to
remain 20 millionths of an inch
too high, and the support system
has not been able to introduce the
desired correction of the figure. In
addition, the edge of the mirror has
been found to respond to temperature
changes more quickly than the
center. It is expected to install a set
of small fans and to insulate the mirror's
outer edge with aluminum foil.
Thereafter, if the supports are still
unable to correct the raised zone,
the mirror will have to be taken out
of the telescope for refiguring . . .
Dr. Bowen pointed out that the 100inch
telescope on Mount Wilson did
not work acceptably for a year and
a half, and he is undiscouraged by
this recent turn of events. "
Monica Young replies: These
photos of pillars in space are
interestingly misleading. In reality, these
dust and gas clouds started out roughly
spherical (or ovoid) in shape and were
then eroded away by the intense ultraviolet
radiation and stellar winds that come from
newborn stars. The denser middles take
longer to dissipate, hence the pillar-like
shapes. So rather than thinking of the
pillars as rising from somewhere, you might
instead think of them as forms that are
being sculpted out of what was initially a
much larger cloud.
FOR THE RECORD
* " A Planetary Imaging Primer " (S&T: Nov.
2023, p. 28) erroneously implies that water
vapor produces atmospheric dispersion. In
fact, all the elements within our atmosphere
contribute to atmospheric dispersion.
* " Raising the Bar " (S&T: July 2023, p.
74) and " Howdy, Neighbor " (S&T: Sep.
2023, p. 79) were created using data from
Telescope Live.
SUBMISSIONS: Write to Sky & Telescope, 1374 Massachusetts Ave., 4th Floor, Cambridge, MA 02138, USA, or email:
letters@skyandtelescope.org. Please limit your comments to 250 words; letters may be edited for brevity and clarity.
Aluminum foil, plus mild refiguring
by optician Don Hendrix, did the
trick. Regular observations with the
200-inch began in November 1949.
º January 1974
Redshifts " Are the quasistellar
radio sources really at the immense
distances implied by their optically
observed redshifts? Yes, say most
astronomers, [but] the assumption
would be unsafe if there existed a
physically connected close pair of
quasars whose components had
very different redshifts. . . .
" The radio source 4C-11.50 in
the constellation Serpens [is one
such pair] separated by only five
seconds of arc. At Lick Observatory,
both components were studied
with the 120-inch reflector by E. J.
Wampler and his collaborators. . . .
The redshifts for the brighter and
fainter members of the pair are
very unequal: z = 0.4359 and 1.901,
respectively. [They write,] 'We
believe that these observations add
support to noncosmological theories
of redshifts.' "
Back then, some astronomers
still wondered if quasars' extreme
redshifts were artifacts of antimatter,
gravitational wells, or even
wormholes - but not anymore.
º January 1999
Andromeda Galaxy " The census
of our galactic neighborhood has
just grown a bit more complete
with the discovery of another
satellite galaxy to M31. Designated
Andromeda V, this very dim, dwarf
spheroidal galaxy is 8° northeast
of M31 at roughly the same
distance from Earth (2.6 million
light-years). . . . Taft E. Armandroff,
James E. Davies, and George H.
Jacoby (Kitt Peak National Observatory)
found the object in September
1997 by digitally enhancing the
Second Palomar Observatory Sky
Survey plates [and confirmed it]
with Kitt Peak's 4-meter reflector in
Arizona, which resolved the galaxy
into individual stars . . . "
The list of M31's satellites, mostly
dwarf spheroidal galaxies, has now
reached Andromeda XXXIII.
sk yand tele scope .o r g * JANUARY 2024
7

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