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PostPosted: Thu Dec 27, 2007 11:12 am 
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The SOCIETY for POPULAR ASTRONOMY
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Electronic News Bulletin No. 234 2007 December 23
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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
at 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/maajc7zabDIKzcixLLVb/


GEMINIDS - FIRST IMPRESSIONS
By Alastair McBeath, SPA Meteor Section Director

Initial details coming through from the Geminid maximum, predicted to
happen within 2h20m of 16:45 UT on December 14-15 (see ENB 232,
http://popastro.c.topica.com/maajc7zabDIKAcixLLVb/ suggest it may have been rather stronger than
normal. The "live" International Meteor Organization (IMO) results,
accessible via the http://popastro.c.topica.com/maajc7zabDIKBcixLLVb/ homepage, have shown peak
Zenithal Hourly Rates (ZHRs) around 135-160 from ~14:30-18:40
UT then, with activity dropping back below 100 by 21h or so. Typical
peak rates in the last decade have been nearer ~120. With data still
coming through, and the IMO "live" data not computed as reliably as
for a proper analysis, these values are liable to change, and will need
to be confirmed later. However, UK visual results reaching the SPA
already have indicated relatively excellent Geminid numbers were being
seen even when the radiant was still very low, from the end of evening
twilight through to ~22h UT, but showing a declining curve during that
interval, which may infer the pattern of activity, if not the actual
numbers, in the IMO data was correct. Assistant Meteor Director
David Entwistle has carried out a review of his own radio data
throughout the Geminids, and found a most probable main peak at
18:07 UT on December 14-15, with two other peaks through to 22h
that evening. As the radiant was still a short way below the horizon
from Britain till after 15:00, other results will need to be checked to
see if the radio reports can further confirm the IMO findings. Visually,
there were some pleasing shower fireballs about on December 14-15
especially, with a couple of Geminids up to magnitude -6 recorded
during full meteor watches as submitted till now, though few who
attempted meteor imaging had much success. With other information,
this may imply a normal, or perhaps slightly fainter than normal,
magnitude distribution. More results will be needed to confirm this
aspect too.

Weather conditions across the British Isles were rather patchy for the
shower peak. There were quite good conditions at times in the week
leading up to the maximum, allowing helpful information on the rising
Geminid activity to be collected by some observers, but these
deteriorated to produce mist, fog and low clouds by December 13-14
and 14-15 for a disappointing number of places. Even those with better
skies often managed less watching than they had hoped then. Ireland
and Northern Ireland seem to have done best on one or both of these
nights, along with people at places to report from overseas so far.
Grateful thanks go to the following, who all provided positive results
from the shower visually, using imaging or radio methods directly, or
via the SPA Forums (see: http://popastro.c.topica.com/maajc7zabDIKCcixLLVb/ ), or the UK
Weather World's Space Weather Forum (at: http://popastro.c.topica.com/maajc7zabDIKDcixLLVb/ )
: Karl Antier (Provence, France), "astroeddie" (Hartlepool), Walter
Bradford (Co. Durham), Sarthak Dasadia (Gujarat, India), Paul
Domaille (Guernsey), David Entwistle (Lancashire), "gregger"
(Derbyshire), Tony Markham (Staffordshire), Conor McDonald (Co.
Derry), Martin McKenna (Co. Derry), Frank Ryan (Co. Clare,
Ireland), Jeff Stevens (Staffordshire), Richard Taibi (Maryland, USA),
and the Director (Northumberland). All further observations from the
Geminids would be most welcome. Details of what to send and where
to can be found via the Section's http://popastro.c.topica.com/maajc7zabDIKEcixLLVb/


LATEST FIREBALL SIGHTINGS
By Alastair McBeath, SPA Meteor Section Director

Following the flurry of fresh fireballs from the UK that appeared during
early December (see the SPA's Recent Fireball Sightings page at:
http://popastro.c.topica.com/maajc7zabDIKFcixLLVb/ and those seen during the best from the
Geminids, there have been a couple more in recent days. Of those, one
was seen from four places from the details available now, in Cheshire,
Lincolnshire and Worcestershire, around 19:40 UT on December
15-16. This may have passed over eastern England or the North Sea
nearby, on a generally south to north track, but details are still very
sketchy regarding it. Two of the initial sighting reports can be traced
from the web address above. Anyone else who saw any of the recent
fireballs, or any others (a fireball is a meteor that reaches at least
magnitude -3, so 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/maajc7zabDIKGcixLLVb/ .


TUNGUSKA ANNIVERSARY YEAR
By Alastair McBeath, SPA Meteor Section Director

June 30, 2008 will see the one-hundredth anniversary of the detonation
of an object in the air high above the Siberian taiga, around the Stony
Tunguska river area of northern central Russia. Numerous events are
planned to mark the anniversary, and the event is liable to be in the
astronomical news throughout the year as a result (assuming a similar,
or larger, event does not happen first, of course). In the last week,
two announcements have been made in this regard. One is a major
international conference "100 Years Since Tunguska", primarily for
professionals scientists, to be held in Moscow from June 26-28. The
programme announced so far intends to present detailed reviews on
many aspects of the event and its aftermath, including the possibilities
for averting a repeat of such an event in future. Official languages will
be Russian and English. Anyone seriously interested in participating
should see the http://popastro.c.topica.com/maajc7zabDIKHcixLLVb/ website.

The second item concerns a review of the detonation fireball, to be
published shortly in the International Journal of Impact Engineering, by
a team of researchers from the Sandia National Laboratory in the USA
led by Mark Boslough, who was part of the team who correctly
predicted fireballs from the impacts of Comet Shoemaker-Levy 9 with
Jupiter in 1994 would be visible from Earth. Using three-dimensional
computer models based on the amount of destruction caused to the
taiga, and the fact the forest was probably not in the best of health
before the event anyway (so making the trees more susceptible to blast-
felling), the team found the observed effects could have been caused
by a much smaller object than previously thought. Its size and mass
would depend on too many variables to estimate (such as its velocity
and physical composition), so the team only suggested that instead of
the commonly-quoted values of 10 to 20 megatonnes of TNT (unhelpful
figures in themselves, since they do not equate simply with a specific
energy output in Joules), the energy released by the airburst may have
been as little as 3 to 5 megatonnes of TNT. Given the limited
information available for such theoretical work to be based on, it seems
unlikely this will be the last word on the matter.


QUADRANTIDS 2008
By Alastair McBeath, SPA Meteor Section Director

Last quarter on December 31, means the Moon will be a waning
crescent for the Quadrantid maximum, due on January 4, around
06:40 UT. The Moon then will be rising only around or after 05h UT
for most of Britain. The shower's peak is typically short and sharp, so
this maximum timing may be a little too late for the UK if it proves
accurate, with morning astronomical twilight beginning between roughly
06:00-06:20 UT for sites here. However, rates should still be worth
seeing as they rise towards the maximum overnight on January 3-4.
Although the shower's radiant is circumpolar, set in a fairly starless
void of northern Bootes, it is very low during the first half of the night,
and is only properly observable after midnight UT. The maximum ZHR
for the Quadrantids has been around 120 in recent times, though it
does vary somewhat from year to year, sometimes as low as 60, at
others up to 200, and has occasionally persisted for a couple of hours.
The peak time may alter slightly too, and some years since 2000 seem
to have brought an additional, primarily radio meteor, maximum about
9-12 hours after the visual one. Fainter radio and telescopic
Quadrantids have been observed to peak up to 14 hours before the
main visual event in the past as well. Quadrantids are of medium-speed,
often reasonably bright near the maximum. For more information on
these and others of January's showers, see: http://popastro.c.topica.com/maajc7zabDIKIcixLLVb/ .
Good luck!


LONG INTERGALACTIC PARTICLE BEAM
New Scientist

Jets are seen emanating from various types of object, but the most
powerful ones come from the cores of active galaxies, where gas
thought to be falling towards a giant black hole generates heat,
high-energy particles and magnetic fields, which in some cases combine
to eject narrow columns of hot gas laced with high-energy particles.
Recently discovered is a jet emerging from a large elliptical galaxy
called CGCG 049-033, about 600 million light-years away. Indian
astronomers noticed emission from that galaxy during a broad search
for radio sources, and then observed it with their 'Giant Metre-wave
Radio Telescope' near Pune and the 100-metre Effelsberg radio dish in
Germany. The jet they saw is nearly 1.5 million light-years long: if
it sprang instead from the centre of the Milky Way, it would stretch
halfway to the Andromeda galaxy.

Jets usually come in fairly well-matched pairs, pointing in opposite
directions. The new jet's counterpart, however, appears much shorter,
possibly because it is pointing away from us, so light from its far
end might not have had time to reach us yet. Interestingly, the radio
waves emitted by the newly discovered jet are strongly polarised,
indicating a powerful magnetic field wrapped around the jet. The
magnetic field acts as a containing sheath, preventing the gas in the
jet from dispersing.


THE SUN IS BRISTLING WITH X-RAY JETS

Japan's Hinode spacecraft has discovered that the Sun is bristling
with X-ray jets, consisting of blobs of hot gas thousands of miles
across emitted at speeds up to 1000 km/s. They evidently
constitute a significant part of the mass of the solar wind, and may
help explain the superheating of the Sun's corona. X-ray jets have
been seen before, but never in such abundance. Now Hinode's X-ray
telescope can take pictures rapidly enough to see that jets happen all
the time, as often as 240 times a day. They appear at all latitudes,
within coronal holes, inside sunspot groups, everywhere. They are a
major form of solar activity. Each jet is triggered by a magnetic
eruption or 'reconnection event' -- the same process that powers solar
flares albeit on a much smaller scale. The energy in a typical jet is
about a thousand times less than the energy of a medium-sized solar
flare, so individually the jets are comparatively weak but
collectively they are very significant.


LARGEST DIGITAL SURVEY OF MILKY WAY
Science Daily

A collaboration of over 50 astronomers, the IPHAS consortium, led from
the UK, with partners in Europe, USA and Australia, has used the Isaac
Newton telescope on La Palma to make a survey of our galaxy. The
survey is only partly completed; the recently published piece is of a
part of the northern Milky Way. It is in two broad-band colours, and
a narrow-band filter that isolates the emission from hydrogen in the
red part of the spectrum (H-alpha emission). The new catalogue
includes some 200 million nebulae and stars, and can be expected to
foster studies of the stellar demographics of the Milky Way and of its
three-dimensional structure. It is claimed that the distinctive
H-alpha marker emphasises some of the least-understood stars in the
Galaxy -- those at the early and very late stages of their evolution,
fewer than one in a thousand stars -- so the IPHAS data should help to
improve the picture of stellar evolution. IPHAS is also embracing a
recent change in the way astronomers share data. As well as being
available on the web it is also being published through a 'Virtual
Observatory' interface, where it can be cross-referenced with other
catalogues. The interface is intended to be an effective way of
exploiting the IPHAS survey, which aims eventually to include 700-800
million objects.


WHERE DO GAS-GIANT PLANETARY ATMOSPHERES BECOME UNSTABLE?
University College London

Planetary scientists have been trying to discover how near a gas-giant
planet can be to its star and still retain a stable atmosphere. We
know that Jupiter, 5 AU from the Sun, has a thin, stable atmosphere;
we also know that closely orbiting extra-solar planets like HD 209458b
-- which is about 100 times closer to its star -- has a very expanded
atmosphere which is boiling off into space. The astronomers have now
found that the limiting distance for a stable atmosphere is 0.15 AU.
where a change takes place because the cooling mechanism breaks down.
Closer than that, the atmosphere around the planet heats up
uncontrollably. Three-dimensional models have been computed that
incorporate the cooling effect of winds blowing around the planet,
and make proper allowance for the effects of H3+ in the atmosphere.
H3+ is an electrically-charged form of hydrogen which re-radiates
sunlight strongly back into space and which is created in larger
quantities in hotter planets. Closer than 0.15 AU to a Sun-like
star, however, molecular hydrogen becomes unstable and no more
H3+ is produced. The self-regulating, 'thermostatic' effect then
disintegrates and the atmosphere begins to heat up uncontrollably
and evaporates off into space.


MARS ROBOT FINDS POSSIBLE FORMER HOT SPRING
BBC News

NASA says that some of its scientists believe that a patch of ground
disturbed by the Mars rover 'Spirit' shows evidence of deposits that
may have been produced when hot-spring water or steam from a fumarole
came into contact with volcanic rocks. Spirit has been driving with a
seized wheel that constantly digs a trough as the vehicle trundles
across the Martian landscape. In May this year, it was noticed that
the churned-up soil had a much brighter appearance than usual.
Further investigation revealed it to be extremely rich in silica. The
researchers think that the bright material must have been produced in
one of two ways -- either as hot-spring deposits, or else Spirit has
stumbled across a fumarole, where acidic steam rises through cracks in
rocks and strips them of all of their mineral components apart from
silica. Inevitably NASA has felt obliged to point out that such
hot-spring environments on the Earth play host to microbes; but of
course it does not follow that the possible existence of analogous
environments elsewhere implies the existence of analogous (or any)
forms of life.


SATURN'S RINGS 'MAY LIVE FOREVER'
BBC News

Saturn's iconic rings may be much older than has been thought. New
data from the Cassini probe show that the thin bands of orbiting
particles, which range in size from grains of sand to boulders, were
probably there billions years ago, and are likely to be very
long-lived, so we are not seeing Saturn at some special time.
Previously, researchers believed that the rings were created perhaps
100 million years ago, when a moon or comet shattered in Saturn's
vicinity. Cassini sees features that suggest the rings cannot have
formed in a comparatively recent one-off cataclysmic event because
they display a range of ages -- some of them very young; to explain
that, the researchers have put forward the idea that material is
constantly coming together to form small 'moonlets' and that such
aggregations are then breaking up again in a perpetual recycling
process. The scientists still hold to the idea that the rings
resulted from a collision event -- but it must have been a long time
in the past. There is enough mass in the rings to make a moon with a
diameter of 300 km. To break up an object that big is really
difficult -- the last obvious time was the so-called Late Heavy
Bombardment, when the Solar System experienced its last period of
concentrated impacts about four billion years ago.


GRAIL MAY REVEAL MOON'S INTERNAL STRUCTURE
Topix

NASA has announced the selection of a new lunar mission, called
Gravity Recovery and Interior Laboratory, or GRAIL, twin spacecraft
to be launched in 2011 at a cost of $375 million. The craft are
intended to be in orbit around the Moon for several months to measure
its gravity field in unprecedented detail. Scientists will use the
gravity-field information from the two satellites to infer the Moon's
sub-surface structures and, indirectly, its thermal history.


DEEP CUTS TO UK ASTRONOMY
RAS

Astronomers are dismayed at the level of cuts to UK astronomy research
announced by the Science and Technology Facilities Council (STFC).
The reductions amount to at least £80m over three years, with a
further £40m likely to be cut to create headroom for UK involvement in
new projects. Cuts announced include UK participation in the Gemini
South observatory in Chile, all UK research in ground-based solar-
terrestrial physics and high-energy gamma-ray astronomy, UK involve-
ment in the astronomical observatory on La Palma, and large cuts (~50%)
at the Astronomy Technology Centre in Edinburgh.

Astronomy projects likely to be cut in part, subject to the current
review being carried out by STFC, include the UK Infra-red Telescope
(UKIRT), UK research in ground-based gravitational-wave astronomy, UK
involvement in the Dark Energy Survey, the Zepplin3 underground search
for dark matter, the robotic Liverpool Telescope, the Merlin radio
telescope centred on Jodrell Bank and the Astrogrid project, which was
to form the UK contribution to a global virtual observatory. These
will all have to compete against new project proposals for a
contingency fund set aside by STFC. As a concession, the STFC will
seek to negotiate continuing access to the Gemini North observatory on
Hawaii. Without Gemini North, UK astronomers would have no access to
any of the largest telescopes in the northern hemisphere.

In an attempt to get the government to reverse the funding cuts to
Particle Physics and Astronomy there is an online petition which you
may wish to sign at http://popastro.c.topica.com/maajc7zabDIKJcixLLVb/


SPACECRAFT MISSION DIVERTED
NASA

NASA has approved the re-targeting of the EPOXI mission (the same
spacecraft as launched an impactor into comet Tempel 1 in 2005 and was
called Deep Impact at that time) for a fly-by of comet Hartley 2 on
2010 October 11. Hartley 2 was chosen as EPOXI's destination after
the initial target, comet Boethin, could not be found. Scientists
theorize that comet Boethin may have broken up into pieces too small
for detection. In addition to investigating comet Hartley 2, the
spacecraft will use the larger of its two telescopes to observe
several previously discovered planetary systems outside our solar
system; for comparison it will also observe the Earth as though it
were an extra-solar planet.




Bulletin compiled by Clive Down

(c) 2007 the Society for Popular Astronomy


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