From: Larry Klaes (email@example.com)
Date: Mon Jun 11 2001 - 13:18:04 PDT
From: firstname.lastname@example.org [mailto:email@example.com]On
Behalf Of John Wagoner
Sent: Saturday, June 09, 2001 6:59 AM
Subject: [skyline] S&T's News Bulletin for June 8, 2001
SKY & TELESCOPE'S NEWS BULLETIN - JUNE 8, 2001
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ASTRONOMERS MASS IN PASADENA
This past week many of the world's research astronomers turned their
attention to Pasadena, California, for the 198th meeting of the
American Astronomical Society. This twice-yearly convention drew some
1,300 professional astronomers, educators, and astronomy hobbyists to
the Pasadena Civic Auditorium to hear front-line research reports on
topics ranging from signs of asteroids in other planetary systems to
developments in galactic black holes to the frontiers of cosmic
evolution. Over 800 papers were presented, according to AAS press
officer Stephen P. Maran. Sky & Telescope editors were there and filed
the following reports.
BROWN DWARFS WITH CIRCUM"STELLAR" DISKS
Are brown dwarfs more like stars or planets? They can't shine by
nuclear fusion as stars do, because they have less than 7 percent of
the Sun's mass (less than 75 Jupiters' worth). But they're usually
found drifting alone in interstellar space, unlike what's usually
called a planet. A key distinction is how they form. A star condenses
directly from an interstellar gas cloud, from the "top down." A planet
begins by accretion of small rocky bodies inside another star's
protoplanetary disk, from the "bottom up."
A team of astronomers led by Charles Lada (Harvard-Smithsonian Center
for Astrophysics) and August Muench (University of Florida) have added
another piece to the puzzle. They have discovered that like young
stars, young brown dwarfs are often surrounded by dust disks -- and
may end up with planets of their own.
Using an infrared camera on the European Southern Observatory's
3.5-meter New Technology Telescope in Chile, Lada's team looked at the
rich cluster of more than 1,000 newborn stars in the Great Orion
Nebula. Brown dwarfs are easiest to find when they're young (they cool
off with age), and those in the Orion Nebula are only about a million
years old. The astronomers identified more than 100 candidates. Of
these, 63 percent show the telltale infrared sign of having a warm
Disks are a near-universal byproduct of star formation. The team
expects that with further investigation, the percentage of brown
dwarfs showing disks will rise to the proportion of young stars having
them: around 80 percent.
But classifying things isn't so simple. Merely possessing a disk in
its youth clearly can't distinguish a star from a planet. Jupiter,
Saturn, and Uranus are surrounded by rich "planetary" systems of their
own that must have condensed out of orbiting disks. We call a planet's
planets moons, but the distinction is probably otherwise meaningless.
Ever since 1918 astronomers have known that Mira, the brightest of the
red long-period variable stars, has a hot, faint companion. The
companion was long called a peculiar intermediate object somewhere
between a white dwarf and a blue main-sequence star.
Now two astronomers say they have got the companion all figured out.
By matching its ultraviolet spectrum to model systems, Edward M. Sion
and John J. Bochanski (Villanova University) determined that it is a
relatively cool white dwarf (10,000 deg. K) surrounded by a hotter
accretion disk of gas that is being collected from Mira's outflowing
stellar wind at a rate of a billionth of a solar mass per year.
This result establishes that an accretion disk can form merely by
stellar-wind capture. It was not previously clear that a stellar wind
could carry enough angular momentum to allow this to happen. The
process may be an important source of disks around other white dwarfs,
neutron stars, and black holes.
A TRUE BINARY QUASAR
The Sloan Digital Sky Survey (see three stories below) isn't the only
gigantic sky-mapping project showing off its stuff at this week's AAS
meeting in Pasadena. Astronomers from 2MASS, the recently completed
Two Micron All Sky Survey (featured in the July Sky & Telescope)
unveiled many new infrared findings, from the Sun's interstellar
backyard to the far reaches of the cosmos.
One unexpected discovery came from a search of the 2MASS data for
active galactic nuclei. In the course of identifying 200 new ones, a
team headed by Brant Nelsen and Roc Cutri (Infrared Processing and
Analysis Center) turned up a pair of quasars only 4 arcseconds apart.
Follow-up spectra taken at the Keck Observatory revealed that both
have the same high redshift of 1.8. These are not, however, two
gravitationally lensed images of the same object. They seem to be a
genuine couplet, says Nelson, as indicated by their undistorted,
pointlike shapes as well as their distinct radio and optical
They join a select club. "There are only about 20 true quasar pairs,"
says Nelson. Their apparent separation of 4 arcseconds implies that
they are at least 130,000 light-years apart -- too far apart to be
interacting but close enough to be gravitationally bound together.
A STAR CLUSTER OVERFLOWING WITH X-RAYS
Deep in the rich inner region of our Milky Way, only about 100
light-years from the galaxy's central black hole, lies a compact
cluster of infant stars whose combined outflow of stellar winds rival
the winds seen in distant starburst galaxies. This is the first
discovery of such energetic X-ray gas in a young star cluster in the
Milky Way. Astronomers may be able to use it to better understand the
dynamics of the richest star-forming regions elsewhere -- and in our
own galaxy's earliest history.
Using the Chandra X-ray Observatory, Farhad Yusef-Zadeh (Northwestern
University) and his colleagues took a 14-hour exposure the Arches
Cluster, a tight group of 150 O-type stars just 1 light-year across
near the Milky Way's core some 25,000 light-years from the Sun. The
cluster is very young, less than 2 million years old. It is unique in
that despite containing so many short-lived massive stars, it shows no
evidence that a supernova has yet occurred within it. The cluster's
high-energy gas seems to consist of pristine stellar winds.
According to Yusef-Zadeh, the Chandra observations indicate hot winds
flowing from cluster stars at speeds of 1,000 kilometers per second.
Where the winds collide, they heat to 60 million degrees K and produce
brilliant X-ray emission. Collaborator Casey Law (Harvard-Smithsonian
Center for Astrophysics) goes a step further and says the gas is so
hot that it is likely to leave the cluster and heat up much larger
surrounding environs. If so, this effect would help to explain the
heated gas regions long observed in the center of the Milky Way.
Because of its remarkable energy, astronomers hope to use the cluster
as a relatively nearby laboratory to study processes that happen in
X-ray-bright starburst galaxies. Future research will include looking
for more such hot, compact clusters in the inner Milky Way.
STUFF OF LIFE FROM IRRADIATED ICE
Deep inside dark, cold interstellar clouds where starlight never
penetrates, a surprising amount of chemistry is going on. Astronomers
using millimeter-wave and submillimeter spectroscopy have identified
about 120 compounds in such clouds, including many of the building
blocks of life. At the AAS meeting in Pasadena, a large group
astronomers from NASA's Ames Research Center and elsewhere described
their efforts to study the chemistry of organic (carbon-based)
compounds under the weird conditions inside these clouds -- the places
where stars and planets are born.
The interior of a dense molecular cloud can chill to as cold as 10
deg. K (-263 deg. C). At such temperatures many atoms and molecules
that are normally gases condense to form icy coatings on dust grains.
Molecules this cold shouldn't react much with each other, especially
when embedded in ice. So how do they perform so much organic
The key ingredient seems to be high-energy cosmic radiation.
Ultraviolet light can also do the job where starlight manages to
penetrate. Any ionizing radiation can break apart molecules inside the
ice, creating highly reactive ions that recombine to form larger, more
Several researchers from NASA/Ames described using supercold vacuum
chambers and ultraviolet lamps to simulate the molecular-cloud
environment. "Basically, we freeze mixed gases onto an extremely cold
window and then give the ices the equivalent of a good suntanning,"
says Louis Allamandola. The resulting residues contain hundreds of
complex compounds, some of which play roles in the metabolism of life
on Earth. Comments Scott Sandford, "It appears that the universe is,
in some sense, hard-wired to produce relatively complex organics."
Perhaps, then, we're being too self-centered when we say interstellar
clouds created the special substances needed for life on Earth. A
truer perspective might be that when life processes got started, they
simply took advantage of whatever compounds happened to be lying
SLOAN SURVEY SHOWS ITS STUFF
The most ambitious astronomical survey program ever undertaken, the
Sloan Digital Sky Survey (SDSS), yesterday released to the public its
first year's worth of observations. Although the data spans only 5
percent of the sky area the project will eventually cover, Sloan
astronomers have already been mining it to produce a wealth of studies
about everything from brown dwarfs to dark-matter clumps to quasars.
In a press conference at the AAS meeting in Pasadena, they proudly
showcased a few of their flashier results.
* Sloan astronomers announced that they have turned up the two
farthest quasars yet detected, with redshifts of 6.0 and 6.2. The
farther of these dates back to when the universe was just 800 million
years old. The discoveries were nothing new for SDSS; according to
Penn State astronomer Donald Schneider, the Sloan team has uncovered
26 of the 30 farthest known quasars and more than half of all known
quasars beyond a redshift of 4.
* One interesting finding involved something SDSS hasn't seen.
Gravitational lensing of extremely distant quasars ought to be fairly
common; mass concentrations along our line of sight should sometimes
distort and split the most distant images. The amount of lensing can
be a good diagnostic of mass distribution in the universe. But lensed
double images are lacking among Sloan's quasars. Gordon Richards (Penn
State) suspects that the reason is merely inadequate resolution. Dual
quasar images should typically appear 0.6 to 0.8 arcsecond apart, says
Richards, "but most of the Sloan data is at 1.5 arcseconds
[resolution]." The database does contain suspiciously elongated
quasars; many of these are scheduled to be observed more closely with
the higher-resolution Gemini and Magellan telescopes.
* Measurements of ever more galaxies and farther quasars are putting
tighter constraints on events in the early universe. Large scale
galaxy-distribution results support the current model of the cosmos in
which there is much more dark matter than visible matter (and an even
larger amount of "dark energy"). Michael Turner (University of
Chicago) says we are also closer to dating a key cosmic turning point
that's presently just beyond reach: when the intergalactic gas
throughout the universe first became ionized by radiation from the
* The origins of different galaxy types should also become clearer.
"Our data show that different types of galaxies cluster differently,
indicating that galaxies are influenced by their environment," says
David Weinberg (Ohio State University).
* Closer to home, Sloan has been recording vast numbers of asteroids
almost by accident. The survey's five-color photometry confirms the
chemical segregation of the asteroid belt; rocky bodies tend to be in
the inner part of the belt and carbonaceous bodies in the outer parts.
Sloan has also found fewer than expected main-belt asteroids smaller
than 4 kilometers.
The Sloan survey is imaging one fourth of the celestial sphere to
magnitude 23 using a specialized 2.5-meter telescope at Apache Point,
New Mexico. Precise brightnesses will be measured in five colors for
100 million celestial objects. The survey will also measure the
redshifts of more than 1 million galaxies and 100,000 quasars.
Observations began in 1998 and should last for five years; astronomers
will surely mine the SDSS data for decades thereafter. Says Turner,
"We have broken new ground in the way we are doing astronomy."
SWARMS OF MIDDLEWEIGHT BLACK HOLES
They're so new that astronomers still have trouble deciding what to
call them. But there's a growing belief that a puzzling new class of
X-ray sources represents "middleweight" black holes -- holes seemingly
too heavy to originate from a collapsing star, but too light to
represent the core of a galaxy.
These "Intermediate-luminosity X-ray Objects," or IXOs for short, were
first identified two years ago in data from the German Rosat
satellite. According to codiscoverer Edward Colbert (Johns Hopkins
University), they are too luminous to be normal X-ray binary stars,
which would blow apart if they produced so much energy. But they're
offset by hundreds of light-years from the centers of their host
galaxies, so they can't be supermassive black holes either. (If they
were, they would pull the galaxy's core right onto them.) The best
explanation so far is that they are middleweight black holes, with
tens to thousands of times the mass of our Sun. But how such objects
form is a mystery.
Using the Chandra X-ray Observatory, various groups of astronomers
have found that the middleweights usually show up in starburst
galaxies where vigorous star formation is under way. Andrew Zezas and
Giuseppina Fabbiano (Harvard-Smithsonian Center for Astrophysics) and
colleagues found dozens of them in the Antennae (NGC 4038/4039), the
famous merging pair of galaxies in Corvus. Others have shown up in
other starburst galaxies such as M82 and NGC 253. "There is a strong
correlation between IXOs and starburst activity," says Fabbiano, "so
we're probably talking about a young population of black holes."
Kimberly Weaver (NASA/Goddard Space Flight Center) says it might be
possible to form 100-solar-mass stars in a very dense young star
cluster. "If they collapse, they would form very massive black holes,
which could subsequently merge into a black hole of a few hundred
solar masses," she explains. However, she admits there's hardly any
clue to the middleweights' origin. And Colbert says there are other
cases, such as in NGC 1313 and IC 342, where IXOs occur outside of
star-forming regions. "There are probably a couple of different types
of these objects," he says.
Or maybe IXOs aren't middleweight black holes at all. Andrew King
(University of Leicester, England) points out that if an object
happens to be beaming X-rays narrowly in our direction, we will
overestimate its energy output based on the false assumption that it
is sending the same energy in all other directions too. "This is
definitely a possibility," admits Fabbiano. "To find out, we need
larger and more sensitive surveys."
"Beaming solves the problem," agrees Richard Mushotzky (NASA/Goddard),
one of the original discoverers of IXOs. "But right now, I don't know
if it's really probable. This is very much new ground."
A PRE-SUPERNOVA TAKES SHAPE
Why is the Crab Nebula shaped like a crab? What prevented it from
expanding as a uniform, spherical shell? Astronomers have long debated
why supernova remnants take the shapes they do. Irregularities in the
surrounding gas and asymmetry in the explosion itself have been the
prime contenders. Now Michael Jura (University of California, Los
Angeles) and his colleagues at the Jet Propulsion Laboratory have
identified what they believe is a pre-supernova star, and its gassy
outpourings may provide a firmer understanding of what caused the
nonuniform shapes of the Crab and other supernova remnants.
The ticking time bomb is HD 179281, a massive G-type star in Lyra.
Until about 1,600 years ago it was a red hypergiant -- a highly
evolved star that shed its outer layers at the fantastic rate of one
solar mass per 3,000 years. Jura and colleagues used one of the
10-meter Keck telescopes and the Owens Valley Submillimeter Array to
map its surrounding gas and dust. They found that much of the material
has piled up in a semicircular arc to one side of the star. The group
predicts that when the star explodes sometime in the next 100,000
years, it will form a "clumpy" remnant like the one from Kepler's
supernova, which appeared in Ophiuchus in 1604.
TWO TYPES OF SPIRALS
Spiral galaxies have not just one but two entirely different kinds of
spiral arms, and they form by entirely different means. This
surprising announcement comes from three astronomers presenting their
work this week at the AAS meeting in Pasadena.
The big, main arms that shape a spiral galaxy's disk have been
familiar for more than a century. Astronomers long ago concluded that
they are "density waves" of stars and gas piling up under the
influence of their own gravity as they orbit around a galaxy. These
arms tend to fade away as they approach a galaxy's center.
When the Hubble Space Telescope began providing very sharp galaxy
pictures, they often showed many intricate spiral lanes of dust and
gas continuing right down into a galaxy's bright, innermost core.
Debra Elmegreen and Kate Eberwein (Vassar College) and Bruce Elmegreen
(IBM Watson Research Center) say these delicate structures are shaped
not by gravity but by acoustic pressure waves -- in other words, by
Theorists have predicted that "acoustic spirals" indeed ought to form
in a galaxy's nuclear regions if the speed of sound in the
interstellar medium approaches the orbital speed. Under these
conditions, the tightly curving orbits of gas masses should amplify
random pressure waves and herd them toward the center in a jumble of
spiral swirls. The three astronomers found that the detailed
predictions for acoustic waves closely match the characteristics of
the delicate traceries seen by Hubble in the centers of two galaxies,
NGC 4736 and NGC 4450.
This realization may help solve an old puzzle. Astronomers have long
wondered how the black hole powering an active galactic nucleus
collects gas from the rest of the galaxy. Somehow, the orbiting gas
has to get rid of angular momentum and orbital energy and fall to the
center. This often happens where two galaxies collide or suffer a
close flyby; the resulting turmoil sends gas everywhere. But what
about normal spiral galaxies? The two that the astronomers studied are
cases in point. Both are LINERs, so called because their centers show
strong emission lines from gas possibly heated by a supermassive black
The acoustic-wave model may fill the bill. As Bruce Elmegreen
explains, "Random sonic turbulence, starting like common noise, grows
into long spiral arms that are most easily seen as dust features. The
strongest of these arms probably contain shock fronts -- sonic booms.
As a result, large pressure forces and energy dissipation in the gas
[and loss of angular momentum] lead to its steady accretion to the
center, where it can feed a black hole."
AN ASTEROID BELT LIKE OUR OWN?
Astronomers have known for nearly two decades that some youngish
stars, such as Vega, Fomalhaut, and Beta Pictoris, are surrounded by
large disks of gas-free dust. The dust particles are warmed by the
star's light and reradiate this telltale energy in the far infrared.
Most such disks found so far are much larger than our solar system.
Yesterday, however, at the American Astronomical Society meeting in
Pasadena, researchers announced finding a dust disk circling within a
mere 6 astronomical units (900 million km) of its star.
The disk orbits Zeta Leporis, a hot, white A3 star with about twice
the Sun's mass and 15 times the Sun's brilliance. The star has an
estimated age of between 50 and 400 million years, roughly how old the
Sun was when our asteroid belt took shape. UCLA graduate student
Christine Chen and her advisor Michael Jura measured the temperature
of the dust belt (first discovered in 1991) by observing at two
infrared wavelengths with one of the 10-meter Keck telescopes. They
found that the tiny particles are heated on average to a toasty 350
deg. K (150 deg. F), which in turn reveals their distance from the
star. Chen and Jura estimate that the disk contains about 1,000 times
more material than our asteroid belt -- a mass comparable to Earth's.
The exciting aspect of this discovery is that the dust really
shouldn't be there. Micron-size particles orbiting so close to the
star would take a mere 20,000 years to spiral into the star due to
interaction with its brilliant flood of light. (In our own solar
system, collisions between asteroids continually replenish the
zodiacal dust band, which is dimly visible to Earthly skywatchers as
the zodiacal light.) The fact that the dust is seen at all means it
must be continuously resupplied. "There must be objects larger than
dust around Zeta Leporis," says Jura, "which may resemble asteroids in
our own solar system, that are creating the infrared-emitting dust by
violently colliding with each other."
Given the star's age, "maybe planets have already formed, or maybe
they are forming," Chen says. If they are still forming, the dust
might be a byproduct of planetary accretion, with rocks spewing fine
rubble as they collide and stick together to begin growing into
planets. Alternatively, if planet formation is over, the dust may be
coming from colliding bodies that are breaking up rather than
coalescing. Mark Sykes (University of Arizona) proposes that if a
Jupiter-mass body orbits the star not far from the disk, it would pump
up the orbital eccentricities of the rocks, randomizing their orbits
and increasing collisions. "This system may be quite analogous to what
things were like in the first 100 million years of our solar system,"
A LOOK AT GLOBULAR CLUSTER FORMATION
Globular clusters are among the oldest structures found in any galaxy.
Most of them date from as far back as 9 to 13 billion years ago, when
galaxies and the universe itself were young. But at the AAS meeting in
Pasadena, astronomers described their ongoing research into one
globular that's in its earliest stage of life. A team led by Jean
Turner (UCLA) has been studying a small but very bright infrared and
radio source in the nearby dwarf galaxy NGC 5253 in Centaurus. The
object is a massive "super nebula" that has given birth to an
enormously rich star cluster.
Only 6 to 10 light-years across, the nebula is estimated to contain a
million young stars that together emit a billion times the energy of
the Sun. This object dominates NGC 5253, says Turner; "It's one-fourth
the total energy output of the galaxy."
So many hot stars gathered in such a small space are bound to reshape
their surroundings. "This thing is beginning to blast its way out,"
Turner says; the combined radiation pressure from the young stars is
blowing the remaining nebula away. The expanding gas has created a
shock wave -- a wind bubble clearing out the region around the cluster
and thus preventing future star formation.
At the current outflow rate, this stage of the globular cluster's life
would only last some 15,000 years. The astronomers say, however, that
the gravity of the massive cluster should hold the gas and dust back
to some extent, slowing the shock wave and extending its existence. A
few other infant globulars have been found in other galaxies, but the
one in NGC 5253 is near enough that it offers the best opportunity for
studying them in action.
COMET LINEAR MOVING NORTH
Comet LINEAR (C/2001 A2) is gradually moving north, but it remains
only visible from the Southern Hemisphere. Observers report that it is
a naked-eye 5th magnitude and can be found moving from Eridanus into
Fornax over the coming week. The comet will be 20 to 30 deg. above the
eastern horizon before dawn. LINEAR will not be visible from the
Northern Hemisphere until late June. Here are coordinates for Comet
LINEAR for 0 hours Universal Time for the coming week:
Jun 9 4h 14m -27.3 deg.
Jun 11 4 01 -26.8
Jun 13 3 46 -26.1
Jun 15 3 30 -25.1
THIS WEEK'S "SKY AT A GLANCE"
Some daily events in the changing sky, by the editors of Sky &
JUNE 10 -- SUNDAY
* Brilliant Mars is certainly the main attraction in the
southeastern sky these evenings, but there's more going on here too.
Look for Antares, the orange "Rival of Mars," to the planet's upper
right during evening, and directly to its right after midnight.
They're separated by about 1 1/2 fist-width's held at arm's length.
Fainter stars of Scorpius are scattered around Antares.
JUNE 11 -- MONDAY
* One of those fainter stars near Antares (see yesterday) is
especially newsworthy. Delta Scorpii has been shining at about
magnitude 1.7 for months now, some 75 percent brighter than its normal
magnitude 2.3. It's the middle star of the nearly vertical line of
three twinkling less than a fist-width to the right of Antares. Delta
is now very clearly the brightest of these three. Keep an eye on it
for further changes likely in the coming months!
JUNE 12 -- TUESDAY
* The two brightest stars in the evening sky this month are pale
yellow-orange Arcturus, nearly overhead in the south during and after
dusk, and pale blue-white Vega, climbing high in the eastern sky.
Brilliant Mars, however, far outshines them both.
JUNE 13 -- WEDNESDAY
* Last-quarter Moon (exact at 11:28 p.m. Eastern Daylight Time).
* Mars is at opposition tonight (though it won't be quite at its
closest to Earth until the 21st).
JUNE 14 -- THURSDAY
* Earliest sunrise of the year, if you live near 40 degrees north
* Jupiter is in conjunction with the Sun.
JUNE 15 -- FRIDAY
* Venus should be at dichotomy sometime around now, appearing
exactly half-lit in a telescope. The best time to view Venus
telescopically will be in a blue sky around breakfast time, when it's
still much higher than the Sun. To find Venus in the daytime sky,
you'll probably need a polar-aligned telescope with setting circles to
measure its offset from the Sun. (Look 3h 06m west of the Sun and 11.4
degrees south. Be sure not to blind yourself by accidentally looking
at the Sun through the telescope!)
JUNE 16 -- SATURDAY
* The red long-period variable star R Aquilae should be nearing its
maximum brightness (6th magnitude) around now.
THIS WEEK'S PLANET ROUNDUP
MERCURY is lost in the glare of the Sun.
VENUS (magnitude -4.3) blazes in the east during dawn.
MARS (magnitude -2.3, between Scorpius and Sagittarius) is at
opposition this week! It rises in the southeast around sunset, and by
dark it dominates the low southeast, shining brilliant yellow-orange.
Mars is at its highest in the south shortly after midnight. Don't miss
any chance to observe Mars in a telescope! It's now 20 arcseconds in
diameter, larger than at any time since 1988, and practically at the
maximum apparent diameter of 21 arcseconds that it will reach on June
21st. See the observing guide and Mars maps in the May Sky &
Telescope, page 102, and the guide to finding Mars's two tiny moons in
the June issue, page 102.
Telescopic observers can download Mars Previewer (3 megs), which
displays observing data and a customized map of Mars's apparent disk
for any date and time. Go to
JUPITER is lost in the glare of the Sun.
SATURN is hidden low in the glow of dawn.
URANUS and NEPTUNE (6th and 8th magnitude, respectively) are in
Capricornus in the southeast in the early morning hours.
PLUTO (magnitude 14) is in Ophiuchus in the southeast during evening.
Finder charts for Uranus, Neptune, and Pluto are in the April Sky &
Telescope, page 104, and at
(All descriptions that relate to the horizon or zenith -- including
the words up, down, right, and left -- are written for the world's
midnorthern latitudes. Descriptions that also depend on longitude are
for North America. Eastern Daylight Time, EDT, equals Universal Time
[GMT] minus 4 hours.)
More celestial events, sky maps, observing projects, and news of the
world's astronomy research appear each month in SKY & TELESCOPE, the
essential magazine of astronomy. See our enormous Web site and
astronomy bookstore at http://www.skypub.com/ . Clear skies!
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This archive was generated by hypermail 2.1.2 : Mon Jun 11 2001 - 13:26:29 PDT