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The SOCIETY for POPULAR ASTRONOMY
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Electronic News Bulletin No. 233 2007 December 9
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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/maai1MsabDmrccixLLVb/



RECENT FIREBALLS
By Alastair McBeath, SPA Meteor Section Director

After a relatively quiet late autumn for UK fireball sightings, there has
been a clutch of fresh reports, mostly by lone witnesses, from the
closing days of November and the opening ones of December, as the
SPA's Fireball Sightings webpage demonstrates, at:
http://popastro.c.topica.com/maai1MsabDmrdcixLLVb/ .
Of these, the better-seen was a very bright
event reported so far by two observers, one near Brussels in Belgium,
the other at Grave in the Netherlands, at 18:08 UT on November
25-26. These sightings suggest the object probably moved generally
south to north from a point high above the Belgium-Holland border area
north of Antwerp, over or near Rotterdam, ending around the Dutch
coast further north. This probable trail might have been seen from SE
England or East Anglia too, though no reports have come through from
Britain as yet. Grateful thanks go to the observers, and Chris Steyaert
of the Belgian VVS meteor group for forwarding details on the Dutch
observation. Anyone else who saw one of the recent fireballs, or any
others (a fireball is a meteor that reaches at least magnitude -3, as
bright as the planet Jupiter at its very best), and who has not yet done
so, is invited to send me a full report as soon as possible. The details
I need, and where to send them, are outlined on the "Fireball Observing"
page of the SPA website, at: http://popastro.c.topica.com/maai1MsabDmrecixLLVb/
.


ALPHA AURIGID OUTBURST - UPDATE
By Alastair McBeath, SPA Meteor Section Director

The strong, bright meteor, Alpha Aurigid outburst, seen despite the
near-full Moon from parts of North America, and detected by radio
there and elsewhere in the world, on September 1 this year was last
discussed in ENB 228 ( http://popastro.c.topica.com/maai1MsabDmrfcixLLVb/ ).
Now, the October issue of the International Meteor Organization's journal "WGN" (35:5,
pp. 108-112) has featured a fresh, detailed review of what happened,
by Jürgen Rendtel. This largely confirmed the preliminary findings, with
a peak at 11:20 +/- 3 mins UT on September 1, when Zenithal Hourly
Rates (ZHRs) were 132 +/- 26. Rates were above half this maximum
value for a total of 45 minutes, but the maximum itself was not quite
central to the interval, as a faster decline followed the highest counts,
which dropped back below 66 by 11:38 UT, though they had first
risen above this level at 10:53 UT. The highest rates were sustained for
only a few minutes, while the shower meteors during the outburst were
confirmed as being unusually bright, and not simply because of the
moonlight hiding the fainter events.


POSSIBLE NEW FIREBALL STREAM AND ITS PARENT?
By Alastair McBeath, SPA Meteor Section Director

In late November, the discovery of a possible new meteoroid stream
associated with a Near Earth Object (NEO) 2002NY40 was announced
by a team of researchers led by Spanish astronomer Josep Trigo in the
Royal Astronomical Society's "Monthly Notices" (available online at:
http://popastro.c.topica.com/maai1MsabDmrgcixLLVb/
It has long been supposed that because the
few meteorites which have had accurate orbits calculated for them have
aphelia in or near the main asteroid belt, and orbital characters similar
to many of the NEOs, such asteroids are likely to form a reservoir for
some of the meteorites reaching Earth. Evidence to identify specific
streams, or even to associate some meteorites with more than a couple
of possible main belt minor planets, has so far been lacking, although
the Geminid shower, due to reach maximum next weekend, with their
parent asteroid of 3200 Phaethon (as discussed in the previous ENB)
are an interesting potential exception. Evidence for this latest proposed
"stream" is also a little scant, based on just two fireballs recorded in
2006, one over Finland, the other over Spain. Unfortunately, unlike the
visual association of meteors with particular showers, this possible
fireball stream needs its meteors to be imaged from multiple stations, to
allow their orbital characteristics to be determined before they can be
confirmed as possibly associated with the same minor planet. Even so,
this is an interesting development in the field of NEO meteoroid stream
studies.


STAR CLUSTER'S HIGH SPEED PUZZLES ASTRONOMERS
New Scientist

The Arches cluster is a group of young stars only about 100 light-
years from the centre of our Galaxy, a region where strong gravitation
might be expected to disrupt a cluster. Astronomers who took an image
of the cluster in 2002 with the VLT and another in 2006 with the Keck
telescope found that in the intervening four years the cluster had
moved an amount that corresponded to a speed through space of more
than 200 km/s -- faster than can easily be explained. In fact most of
the presently believed `facts' about the innermost part of the Galaxy
are difficult to explain. Many of the stars there appear to be young,
only about 6 million years old, and astronomers wonder how they were
able to form, because gas clouds ought to have been shredded by the
gravity of the supposed central black hole before they could condense
into stars. An idea that the young stars could be carried into the
central cluster by other clusters that had formed farther out seems
not to hold water, because calculations indicate that most clusters
would be destroyed before they could get so close. Anyway the new
measurements show that the Arches cluster, at least, cannot perform
such stellar deliveries, because its orbit does not take it close
enough to the centre.


GALAXIES PROVIDE HINTS OF EARLY MILKY WAY
ESO

It is believed by some astronomers that galaxies build up by the
merging of smaller units which they call proto-galaxies, which
themselves arise from the clumping together of gas which initially
filled the Universe almost uniformly. After stacking images totalling
92 hours' integrations of the same patch of sky with large telescopes
(not always with the same one) an international team claims to have
seen 27 proto-galaxies that date from a time when the Universe was
about 2 billion years old. The observation is said to represent
further evidence that galaxies like the Milky Way were created by the
clumping of smaller clouds of gas and dust, although the logical
connection between the observation and that assertion is not easily
appreciated.


VOYAGER 2 TO REACH MAJOR MILESTONE
University of California

The interplanetary spacecraft Voyager 2 was launched on 1977 August 20
and visited four planets in the course of its journey into space. It
is expected soon to cross the 'termination shock', the quasi-spherical
boundary around the Solar System that marks where the solar wind slows
down to subsonic speed. Because the crossing of the shock is expected
to be an abrupt and relatively brief event, scientists are working to
ensure that the most is made of the opportunity. This news item has
been put out by the University of California as a window-dressing
exercise to draw attention to the fact that one of its scientists has
been busy with a model that has predicted the location of the shock,
which is approximately 90 times farther from the Sun than we are. The
solar wind -- a stream of charged particles ejected by the Sun in all
directions -- travels at supersonic speeds when it leaves the Sun,
until it eventually encounters the interstellar medium made up of
plasma, neutral gas and dust. At the termination shock, located at
7--8.5 billion miles from the Sun, the wind is decelerated to less
than the speed of sound. The boundary of the termination shock is not
fixed, however, but wobbly, fluctuating in both time and distance from
the Sun, depending on solar activity.


NASA OUTLINES MANNED MARS MISSION
BBC News

NASA has given details of its strategy for sending a human crew to
Mars within the next few decades. It envisages despatching a
'minimal' crew on a 30-month round trip in a 400-ton spacecraft. In
2004, the US President announced a programme to send manned flights to
the Moon by 2020 and -- at an unspecified date -- to Mars. The 'Mars
ship' would be assembled in low Earth-orbit from three or four Ares V
rockets -- the new heavy-lift launch vehicle that NASA is developing.
Notionally started in 2031, the journey from Earth to Mars would take
six or seven months in a spacecraft powered by a cryogenic-fuel
system. The cargo lander and surface habitat would be sent to Mars
separately, launched before the crew in 2028/9. Once there, the
astronauts could spend up to 16 months on the Martian surface, and
would use nuclear energy to power their habitat. But the document
points out that options for aborting the mission or for any sort of
rescue or re-supply would be extremely limited. The difficulties
mean that the astronauts would have to be self-sufficient. They
would need to be confident and capable people, well versed in the
maintenance and repair of equipment and perhaps even able to
manufacture new parts. Estimates of the cost of mounting such a
mission vary enormously, from $20bn to $450bn.


VENUS PROBE CONFIRMS LIGHTNING ON VENUS
NASA

ESA's Venus Express mission has confirmed that the Venus atmosphere
generates lightning. There are three other planets where there is
lightning -- the Earth, Jupiter and Saturn. Lightning on Venus -- or
any other planet -- is important because the electrical discharges can
alter the chemistry of an atmosphere by breaking molecules into
fragments that can then join up in unexpected ways. The lightning on
Venus differs from that on the Earth, Jupiter and Saturn in that it is
not associated with water clouds. Instead, on Venus the lightning is
associated with clouds of sulphuric acid. With its primary mission
completed, Venus Express now embarks upon its 'extended mission' which
will last initially for 7 months. Among other things, it will look
for infrared radiation from possible lava flows.


SPITZER OBSERVES PROTO-PLANETARY DISC
University of Illinois.

Astronomers using the Spitzer space telescope have observed a
flattened envelope of gas and dust surrounding a young proto-star.
Located about 800 light-years away in the constellation Cepheus, the
object is obscured by dust and can only been seen at infrared
wavelengths. The brightest structure consists of a bipolar jet -- an
almost linear flow of shocked molecular hydrogen gas ejected from the
protostar's magnetic poles; each jet is about 3/4 of a light-year in
length. In star-formation theory, a cloud of gas and dust collapses
to form a star and its planets. As it collapses, it has to rotate
faster as a consequence of the law of conservation of angular
momentum. If it were not for the force of the growing magnetic field
ejecting some of the gas and dust along the magnetic axis, forming the
bipolar jet seen by Spitzer, the proto-star would eventually spin so
fast as to break apart. The planet-forming region is perpendicular
to, and roughly centred on, the polar jets. There, seen in silhouette
against a bright background of galactic infrared emission, is the
flattened disc of a circumstellar envelope. Theoreticians have long
regarded circumstellar discs as the birthplace of planets, and many of
them are already well known.


HEAVY NEGATIVE IONS IN TITAN'S ATMOSPHERE
University College London

Scientists analysing data gathered by the Cassini spacecraft have
confirmed the presence of heavy negative ions in the upper regions of
Titan's atmosphere. Those particles may act as the basis for even
more complicated molecules, and their discovery was unexpected because
of the chemical composition of the atmosphere, which lacks oxygen and
mainly consists of nitrogen and methane. The observation has now been
verified on 16 different encounters. Cassini's electron spectrometer
has detected negative ions which have 10,000 times the mass of a
hydrogen atom. Additional rings of carbon can build up on these ions,
forming molecules called polycyclic aromatic hydrocarbons.

Their existence poses questions about the processes involved in
atmospheric chemistry and aerosol formation, and it is thought most
likely that the negative ions form in the upper atmosphere before
moving closer to the surface, where they probably form the mist which
shrouds the satellite and which has hidden its surface from us in the
past. It was that mist which stopped the Voyager mission from seeing
Titan more closely in 1980 and was one of the reasons that Cassini was
launched.


CHANDRA DISCOVERS FAST-MOVING STAR
NASA

Astronomers using the Chandra X-ray observatory have discovered one of
the fastest-moving stars ever noticed in our galaxy. The object,
called RX J0822-4300, is a neutron star created by the Puppis A
supernova explosion about 3700 years ago and is moving away from the
centre of Puppis A at more than 1200 km/s, fast enough to escape
completely from the Milky Way some millions of years from now.
Probably the explosion of the supernova was lop-sided, kicking the
neutron star in one direction and the debris from the explosion in the
other.




Bulletin compiled by Clive Down

(c) 2007 the Society for Popular Astronomy


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