From: LARRY KLAES (ljk4_at_msn.com)
Date: Fri Sep 19 2003 - 18:41:21 PDT
----- Original Message -----
From: bulletins_at_SkyandTelescope.com
Sent: Friday, September 19, 2003 7:53 PM
To: ljk4_at_msn.com
Subject: S&T's Weekly News Bulletin for September 19
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* * * SKY & TELESCOPE's WEEKLY NEWS BULLETIN - September 19, 2003 * * *
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Welcome to S&T's Weekly News Bulletin. Images, the full text of stories
abridged here, and other enhancements are available on our Web site,
SkyandTelescope.com, at the URLs provided below. (If the links don't work,
just manually type the URLs into your Web browser.) Clear skies!
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X-RAY FLASHES FIND A HOME
When is a gamma-ray burst not a gamma-ray burst? Easy -- when it doesn't
give off gamma rays! That answer may sound simplistic, but it could hold
the key to a scientific mystery.
Most aficionados agree that the brief, apparently random flashes of highly
energetic photons known as gamma-ray bursts (or GRBs) are born when a
massive, rapidly rotating star dies, exhausting its internal nuclear fuel
and collapsing abruptly. The collapse forms a spinning black hole in the
dying star's core. The black hole then gobbles up nearby star-stuff, only
to spit some of it back out, spewing jets of particles that slam into the
star's outer layers at near-light speeds.
Among the many signatures of this cosmic train wreck: a burst of gamma
rays visible to anyone who happens to be looking at one of the jets
head-on -- even if they live on the other side of the observable universe.
But what if the jet doesn't quite point directly at our solar system or
the dying star is so distant that its gamma rays have been redshifted into
the X-ray portion of the electromagnetic spectrum?...
> http://SkyandTelescope.com/news/article_1054_1.asp
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WHERE ARE THE FAINTEST KUIPER BELT OBJECTS?
At face value this month's announcement of the dimmest object ever
observed in the solar system seemed like yet another "farthest and
faintest" record for the Hubble Space Telescope (HST). But the story
behind the press release reveals much about the nature of the Kuiper
Belt -- the enigmatic outer debris left over from the formation of our
solar system -- and how it acts as a source for short-period comets....
> http://SkyandTelescope.com/news/article_1051_1.asp
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SATURN'S VARIED COLORS
Catching Saturn during its extreme axial tilt last March, astronomers
using the Hubble Space Telescope obtained some of the best multicolor
images ever taken of the ringed planet. Like Earth, Saturn is tilted with
respect to the Sun over its 29.5 year orbit. This allows observers to
watch as the planet experiences fluctuating atmospheric conditions
thoughout the Saturnian year.
Planetary scientist Erich Karkoschka (University of Arizona) captured
Saturn's south side during maximum tilt, 27 degrees, using Hubble's Wide
Field and Planetary Camera 2. The instrument used 30 separate filters to
obtain spectral data ranging throughout the infrared, visual, and
ultraviolet wavelengths. When combined, these data become a valuable tool
for understanding the chemical compositions of different layers of
Saturn's upper atmosphere....
> http://SkyandTelescope.com/news/article_1050_1.asp
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SPOTTING EXTRASOLAR SATURNS
Astronomers have the technology to detect Saturn-like rings around a
planet orbiting a faraway star, and they might even learn much about the
structure of a distant ring system. It is just a matter of finding one.
That was the take-home message in a presentation given at an international
planetary-science meeting in California earlier this month....
> http://SkyandTelescope.com/news/article_1048_1.asp
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ASTRO NEWS BRIEFS
Swift Satellite Setback
The launch of the $160 million Swift satellite won't come quite as swiftly
as might be desired by aficionados of gamma-ray bursts, or GRBs -- the
hyperenergetic explosions that the satellite should discover and document
with unprecedented ease. According to principal investigator Neil Gehrels
(NASA/Goddard Space Flight Center), the two instruments that will study
the X-ray and ultraviolet/visible-light afterglows of GRBs already have
been tested and installed in the spacecraft. However, two rounds of
electronics problems have plagued Swift's Burst Alert Telescope -- the
wide-angle camera that will detect and pinpoint GRBs in the first place,
hopefully several times each week. The workhorse instrument might not be
installed until November.
"At the moment things are going very well," says Gehrels, who is "pretty
confident" that Swift will be ready next May for launch, riding a Delta
rocket from Kennedy Space Center and assuming a gently inclined, low-Earth
orbit. Swift should be beaming real-time GRB data down to astronomers
worldwide within a month of its launch, which originally had been
scheduled for this October. In the meantime, some GRB researchers are
lobbying NASA to extend the mission of the $25 million High Energy
Transient Explorer, or HETE-2, which currently provides them with fairly
rapid coordinates for one or two GRBs monthly. Currently HETE-2 is funded
only through next January.
Dark Energy Detailed
Another study has just found that "dark energy" is real. The Supernova
Cosmology Project, an international consortium of 48 astronomers, has
published its newest findings about the changing expansion rate of the
universe. Observations of 11 new Type 1a supernovae at large distances
(redshifts 0.36 to 0.86) confirm that the expansion of the universe has
been speeding up, and at a rate that means that dark energy amounts to
about 75 percent of all the matter and energy in the cosmos. Also, a lack
of interstellar reddening in the supernovae shows, to a new degree of
accuracy, that the results are not being thrown off by interstellar
absorption within the supernovae's galaxies.
Perhaps most interesting to cosmologists, the team got a rough
confirmation of the dark energy's equation of state (the pressure it
exerts per unit density), a crucial step toward figuring out what dark
energy actually is. The value, "w = -1" to an accuracy of about 25
percent, supports Albert Einstein's decades-old idea of a "cosmological
constant" built into space-time itself, and argues against newer ideas of
dark energy being some kind of actual substance ("quintessence") that
exerts negative gravity.
> http://SkyandTelescope.com/news/article_1053_1.asp
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HIGHLIGHTS OF THIS WEEK'S SKY
* Saturn shines to the right of the waning Moon from about 1 a.m. until
dawn on September 20th.
* New Moon on Thursday, September 25th.
* On September 23rd, the equinox occurs at 6:47 a.m. Eastern Daylight
Time, marking the start of fall in the Northern Hemisphere and spring in
the Southern Hemisphere.
For details, see This Week's Sky at a Glance and Planet Roundup:
> http://SkyandTelescope.com/observing/ataglance/
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describing some simple things everyone can do to bring the stars back.
There Once Was a Sky Full of Stars
by Bob Crelin
> http://SkyandTelescope.com/campaigns.asp?id=369
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Copyright 2003 Sky Publishing Corp. S&T's Weekly News Bulletin is provided
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