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 Post subject: ENB No. 192 March 5 2006
PostPosted: Sun Mar 05, 2006 3:11 pm 
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The SOCIETY for POPULAR ASTRONOMY
***********************************
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Electronic News Bulletin No. 192 2006 March 5
====================================================


Here is the latest round-up of news from the Society for Popular
Astronomy. The SPA is Britain's liveliest astronomical society, with
members all over the world. We accept subscription payments online
using our secure site and can take credit and debit cards. You can
join or renew via a secure server or just see how much we have to
offer by visiting http://popastro.c.topica.com/maaeytzaboLgncixLLVb/

Philip's, a publisher of astronomy books and planispheres for the
amateur astronomer, is sponsoring this bulletin. For information on
Philip's title see the end of this bulletin.


MID FEBRUARY'S FIREBALLS
By Alastair McBeath, SPA Meteor Section Director

Mid February produced a run of fireballs to brighten up the month
meteorically, including the following.

February 15-16: ~17:30 UT (Glasgow); and ~00:25 UT, two sightings of
a magnitude -6/-10 object, seen from Cheshire and Lancashire. Some
details on the 00:25 UT event are available on the SPA Observing Forum,
at: http://popastro.c.topica.com/maaeytzaboLgocixLLVb/ .

February 16-17: ~19:30 UT, a brilliant fireball producing a probable
sonic boom soon after, seen from Perth & Kinross.

February 20-21: ~19:40 UT, very bright event seen to the west from
Dartmoor, Devon.

February 21-22: Around 19:40 +/- 10 mins, a magnitude -8/-10 or
brighter fireball was seen from three sites in County Durham, Cumbria
and Merseyside.

Anyone else who saw any of these, or any other bright meteors (a
fireball
is a meteor of at least magnitude -3 with respect to the stars and
planets),
should send a report to the SPA as soon as possible, please. Details of
what to submit and where to can be found at:
http://popastro.c.topica.com/maaeytzaboLgpcixLLVb/ .


RAPID GALAXY MERGING DOMINATES UNIVERSE'S EARLY HISTORY
RAS

A group at the University of Nottingham has used deep images taken by
the Hubble Space Telescope to study galaxies when they were only two
billion years old. The majority of the most massive galaxies in the
early Universe appear to have been undergoing multiple mergers which
led to the creation of new stars from colliding gas clouds. The
results indicate that a typical massive galaxy in today's Universe has
formed by the merging of four or five smaller galaxies. Mergers are
rare today, involving only about one per cent of galaxies, whereas 10
billion years ago nearly all massive galaxies were undergoing mergers.
The research may have some relevance to our own Galaxy. The spiral
arms are not thought to have formed through any merger process, but
the bulge at the centre of the Galaxy, a spherical high-density region
featuring many old stars and probably a black hole, may have resulted
from mergers.


GALAXIES SHROUDED IN SILICATES
NASA

Astronomers using the Spitzer Space Telescope have observed 77 bright
and dusty galaxies that they have called 'ultraluminous infrared
galaxies', most of which seem to consist of two spiral-shaped galaxies
in the process of merging into one. In 21 of them, evidence is seen
of a lot of silicate crystals -- somewhat akin to sand. Such crystals
have not been observed previously outside our own Galaxy, where they
exist around certain types of stars, such as our Sun. Silicates
require heat to transform into crystals. The crystals are delicate
and easily destroyed; the astronomers suppose that supernovae in the
centres of the galaxies that were observed in the infrared are
maintaining the supply, probably shedding the crystals both before
and as they blow apart, but that particles from the supernova blasts
then bombard the crystals and return them to an amorphous form. The
whole process is thought to be relatively short-lived.


FAINT STARS MAY SUPPLY COSMIC X-RAY FOG
New Scientist

New studies suggest that millions of stars too faint to be seen
individually are collectively responsible for the haze of X-rays that
suffuses the Milky Way galaxy. The sky is covered with a diffuse fog
of X-rays from a variety of sources, some of them outside our own
Galaxy, but much of it originates within the Milky Way. Previous
observations with the Chandra X-ray Observatory identified individual
sources for only 30% of the Milky Way's X-ray glow, and the proposed
explanations of the unidentified remainder have proved unsatisfactory.
Now, researchers at the Max-Planck-Institute for Astrophysics in
Germany say that the X-ray glow is due to individual stars that are
simply too faint to be seen in previous surveys. They compared
infrared observations made with the Cosmic Background Explorer (COBE)
satellite in the 1990s with the most detailed map of the Galaxy in
X-rays -- one produced from 10 years' observations with the Rossi
X-ray Timing Explorer (RXTE) satellite, which has been in orbit since
1995. They found that both satellites saw peaks of radiation in the
same places. That is significant, because old stars produce much of
the infrared light detected by COBE, so whatever is causing the
diffuse glow of X-rays must be caused by middle-aged and old stars in
the Galaxy. The researchers think that the relevant stars are mostly
white dwarfs in 'cataclysmic binary' systems, that produce X-rays by
pulling material from stellar companions; some X-rays might also be
produced by 'active' stars whose outer atmospheres are producing
flares. The team estimates there may be more than a million
cataclysmic variables and about one billion active stars in the
Galaxy.


POSSIBLE MARS AURORAE
ESA

Evidence is accumulating that aurorae occur over the night side of
Mars, especially over areas of the surface where variations in the
magnetic properties of the crust have been detected. Observations
from Mars Express show structures (inverted-V features) of accelerated
electrons and ions above the night side of Mars, almost identical to
those that occur in connection with aurorae on Earth. On our planet,
as well as on Jupiter, Saturn, Uranus and Neptune, aurorae occur at
the feet of the planetary magnetic field lines near the poles, and are
produced by charged particles -- electrons, protons or ions -- moving
along those lines.

A few years ago it was suggested that auroral phenomena could exist on
Mars too. That hypothesis was reinforced by the Mars Global
Surveyor's discovery of crustal magnetic anomalies, most likely the
remnants of a one-time planetary magnetic field. Scientists have now
found that the structures of accelerated particles are indeed
associated with the crustal magnetic anomalies at Mars, but that
strong acceleration mainly occurs in a region close to local midnight.
No identification of the auroral emission lines is possible at
present, since even the composition of the upper atmosphere on the
night side is unknown. Since we see Mars as always sunlit, the night
side of Mars cannot be observed from the Earth.


AMATEURS OBSERVE XENA DIRECTLY
McDonald Observatory

A group of amateur astronomers has used the 82-inch telescope at
McDonald Observatory to make the first 'through-the-eyepiece'
sighting of the so-called tenth planet, an object (officially
designated 2003UB313 but nicknamed Xena) orbiting the Sun in the
Kuiper Belt beyond Neptune. The object is 19th magnitude, which is
just at the limit of what can be seen with the human eye through the
82-inch. These days, it is unusual for large telescopes at
professional observatories even to possess eyepieces. The astronomers
at McDonald don't use eyepieces for their observations -- images are
recorded onto computers. But the eyepiece capability makes three of
McDonald's research telescopes accessible to the public on a few
nights each month. The 82-inch and 107-inch telescopes may be the
largest in the world available for public observing sessions.


PLUTO'S NEW MOONS PROBABLY BORN WITH CHARON
SwRI

A team of U.S. scientists concludes that two newly discovered small
moons of Pluto were very probably born in the same giant impact that
gave birth to Pluto's much larger moon, Charon. The team also argues
that many other large binary Kuiper Belt Objects (KBOs) may also
possess small moons, and that the small moons orbiting Pluto may
generate debris rings around Pluto. The evidence for the small
satellites being born in the Charon-forming collision is strong; it is
based on the supposed facts (not yet conclusively established) that
the small moons are in circular orbits in the same orbital plane as
Charon, and that they are also in, or very near, orbital resonances
with Charon.

There is a growing realization that binary 'ice dwarf' pairs like
Pluto + Charon are common in the Kuiper Belt, so it is natural to
suppose that numerous multiple systems may be discovered there in
years to come. Finding small satellites around KBOs is difficult
because their large distances from the Sun make them appear very
faint. One way to see how common it is for KBOs to have multiple
satellites might be to search around objects that are thought to have
been ejected from the Kuiper Belt into orbits that bring them much
closer to the Sun. So far, about 160 such objects, called Centaurs,
have been discovered. Astronomers hope to use Hubble to search for
faint moons around some of them.


NEW TYPE OF EXPLOSION?
Space.com

Astronomers using the Swift telescope have detected a new type of
cosmic outburst. They think it might portend an even brighter event
to come, a supernova. The event, detected on Feb. 18 in the
constellation Aries, looked something like a gamma-ray burst (GRB),
but it was relatively close --about 440 million light-years away --
and lasted about 33 minutes, whereas most GRBs are billions of
light-years away and last less than a second or just a few seconds.
Other aspects of the newfound eruption were inexplicable. It was
dimmer than most, but even so, it outshone the entire galaxy in which
it occurred. It has been catalogued as GRB 060218, and is the
second-closest GRB ever detected. Italian researchers using the Very
Large Telescope in Chile found signs in the event's optical afterglow
that it may become a supernova. They suggest that a very massive star
may have collapsed into a black hole and then exploded. If the event
is indeed a supernova in the making, scientists may get the first look
at one unfolding from start to finish.


HEAT FROM EXTRASOLAR PLANET DETECTED
NASA

Astronomers have used the Spitzer Space Telescope to detect a strong
flow of heat radiation from a planet orbiting a nearby star. This is
the closest extrasolar planet to Earth to have been detected directly.
The planet orbits a star, HD 189733, that is 63 light-years away in
the direction of Vulpecula. It was discovered last year and found to
be about 1.26 times Jupiter's diameter, 1.15 times Jupiter's mass, and
density about 0.75 grams per cubic centimetre which indicates that it
is a gas giant. The observations also gave the orbital period (2.219
days) and the distance from the parent star -- only about three per
cent of the distance between Earth and the Sun. Such close proximity
keeps the planet at about 844 Celsius according to the team's
measurement. To distinguish the planet's glow from that of its hot
parent star, the astronomers first measured the total infrared light
from both the star and its planet. Then, when the planet was eclipsed
by the star in the course of its orbit, they measured the infrared
light coming from just the star, and did a subtraction sum to see how
much light belonged to the planet. Under optimal circumstances the
method could be used to make a crude temperature map of the planet
itself. The heat signal from this planet is so strong that Spitzer
was able to resolve its disc, in the sense that the team could tell
they were seeing an extended object in the data, not a mere point of
light.


THREE CEPHEIDS WITH CIRCUMSTELLAR ENVELOPES
ESO

A team of astronomers has discovered envelopes around three Cepheids,
including the Pole star. This is the first time that matter has been
found surrounding members of that important class of rare and very
luminous stars whose luminosity varies in a very regular way.
Cepheids play a crucial role in cosmology, being one of the first
steps on the cosmic distance ladder. The envelopes around L Carinae,
Polaris and Delta Cephei were revealed by interferometers and were
found to be 2 to 3 times as large as the actual stars. The physical
processes that have created the envelopes are still uncertain, but, by
analogy with what happens around other classes of stars, it is most
probable that the environments were created by matter ejected by the
stars themselves. Cepheids pulsate with periods of a few days. As a
consequence, they go regularly through large-amplitude oscillations
that create very rapid motions of the apparent surface (the
photosphere) with velocities up to 30 km/s. It would not be
surprising if there were links between the pulsation, the mass loss
and the formation of the envelopes.


PHILIP'S RECENT TITLES:

Philip's The Sky at Night Volume 2 is the latest volume in Sir Patrick
Moore's series of essays written to accompany the BBC television
series of the same name. It tracks developments in astronomy,
astrophysics and space exploration in the period from 2001 November
to 2005 March -- £9.99
Philip's Stargazing 2006 by Heather Couper and Nigel Henbest - £6.99
Published last year:
Philip's Solar System Guide by Peter Grego contains an abundance of
information and images, and is a practical and colourful introduction to
our corner of the Universe. It describes how to observe not only the
planets but also the Moon, Sun, comets, meteors, asteroids and other
objects found within our Solar System -- £9.99

Philip's Solar System Observer -- a pack for the amateur Solar-System
observer. It contains three items for exploring and enjoying our
corner of the Universe: Philip's Solar Observer's Guide, Philip's Map
of the Solar System and Philip's Solar System Phenomena poster --
£12.99

For more information on those and other Philip's titles please visit
www.philips-maps.co.uk or call 020 7644 6935 for a catalogue.




Bulletin compiled by Clive Down

(c) 2006 the Society for Popular Astronomy


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