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 Post subject: ENB No. 200 July 9 2006
PostPosted: Sun Jul 09, 2006 4:41 pm 
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***********************************
The SOCIETY for POPULAR ASTRONOMY
***********************************
====================================================
Electronic News Bulletin No. 200 2006 July 9
====================================================


Here is the latest round-up of news from the Society for Popular
Astronomy. It ought to be seen as an occasion for a celebration,
marking as it does the 200th issue of this excellent Bulletin!
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/maaeXVbabrPbMcixLLVb/


200 UP!
By Alastair McBeath, SPA Meteor Section Director

Fulsome congratulations go to the ENB team on achieving the 200th
scheduled issue (apart from the many additional "Specials" which have
been issued in that time too), from all at the Meteor Section. The
sterling
efforts of Editor Clive Down have carried us right through the
Bulletins'
second century since 2002, as well as most of the first hundred prior to
that, and Clive deserves our grateful thanks for his tireless efforts
and
enthusiasm in their compilation and production. We are also indebted to
the often unseen guidance from Professor Roger Griffin of the
Cambridge Observatories, whose generous assistance in checking the
material published here throughout has avoided numerous errors, not
simply in what has been published in the ENBs, but sometimes also for
the people originating the information. Very well done to both, and also
to those others working further behind the scenes who have supported
the ENBs in general. Here's to the next hundred and beyond!


LATE JULY SHOWER PROSPECTS
By Alastair McBeath, SPA Meteor Section Director

Though the late July meteor prospects are fairly rosy for helping to
celebrate the ENB's anniversary, this comes at the price of a moonlit
Perseid maximum in August, more of which anon. This time, we can look
forward to late July's new Moon on the 25th giving plenty of dark skies
for covering the two main southern-sky shower peaks of the Southern
Delta Aquarids (SDA) around July 28 and the Alpha Capricornids
(CAP) on July 30 or so. "Main" is a relative term here however, since
while the SDA peak Zenithal Hourly Rate (ZHR) of about 15-20 sounds
promising, the deep southerly declination of the radiant reduces the
observed rate considerably for British observers. The CAP ZHR at best
is far lower at about 5, but its rather more northerly radiant can help
in its
visibility from our latitudes. CAP meteors have a reputation for often
being bright, and because they are slow-moving too (a little slower than
the autumnal Taurids), they can be among the most impressive sights a
meteor watcher could hope for - albeit not nearly as plentiful as we
might
like! The effect of both these showers, coupled with a weak drizzle from
other very minor sources with radiants around Aquarius and Capricornus
in late month, usually helps raise observed hourly meteor numbers to
their
highest point since at least the Lyrids in April, to maybe 10-15 or more
an hour, under clear, darker skies, including the sporadics and a few
early
Perseids. Remember that any swift Perseids in late July will actually be
radiating from below the "W" of Cassiopeia, rather than the radiant's
near
-maximum position east of the Double Cluster in mid-August.

More information on July's showers, with southern-sky and Perseid
radiant charts, plus notes on how to make and submit meteor results,
can be found via the Section's homepage at:
http://popastro.c.topica.com/maaeXVbabrPbNcixLLVb/ .

Good luck and clear skies!


GRAVITY-WAVE DETECTOR TO BE TESTED
The Register

Einstein's famous Theory of General Relativity predicts that two stars
in orbit around one another must gradually lose energy from their
orbits in the form of gravitational radiation. In that and other
normal situations, however, such an effect is much too small to
detect. Violent events such as supernova explosions are expected to
produce gravitational radiation at possibly detectable levels. Now a
German/UK research group at the International Centre for Gravitational
Physics in Hanover has completed the construction of a gravitational-
wave detector and is about to start an 18-month campaign to make an
initial detection of such radiation.


MOON PROBE BOOSTS ORBIT
New Scientist

The European spacecraft SMART-1 travelled to the Moon very gradually
by the use of a novel propulsion system. It used solar energy to
ionize a small amount of xenon gas. The heavy xenon ions were
discharged into space to provide energy-efficient propulsion for the
journey, which lasted 14 months. Since its arrival 16 months ago the
craft has been in orbit round the Moon. Now all of the xenon has been
used up, and the probe is due to crash onto the lunar surface shortly.
If matters had taken their course it would crash into the back side of
the Moon, but on June 19 mission managers began a 17-day series of
manoeuvres to raise its orbit by 90 kilometres, postponing the crash
for a few weeks and causing it to occur on the near side of the Moon
so that it can be watched from the Earth; the event is now expected
to occur on September 3. In the absence of the propulsion gas, the
manoeuvres have relied on periodically braking a set of spinning
reaction wheels, whose normal purpose is to stabilise the spacecraft.
The braking transfers angular momentum from the wheels to the
spacecraft, and with suitable cunning can be made to change its orbit
slightly.


RELATIVISTIC JET FROM NEUTRON STAR
RAS

Certain objects which seem to have a lot of energy to spare emit
'relativistic jets' -- beams of particles shot into space at nearly
the speed of light. Some scientists have supposed that the only
objects capable of producing such jets must be black holes, but now a
team using the Spitzer Space Telescope has detected the faint jet of a
certain neutron star called 4U 0614+091, located about 10,000
light-years away in the constellation Orion. The discovery is
interesting, but elucidation of the real nature of relativistic jets
remains a matter for future studies.


MASSIVE NEUTRON STAR RULES OUT EXOTIC MATTER
New Scientist

Among the people who consider themselves to be in the scientific field
there are some who, confronted with a novel problem, prefer to 'solve'
it in an ad-hoc fashion by speculating about 'new physics' rather than
to work patiently at it and show how it fits into the established
scheme of things. One such problem has concerned neutron stars, which
as their name suggests consist of neutrons and are very small and
incredibly dense. The avant-garde have speculated that in the
interiors of especially massive neutron stars, matter might be
transformed into exotic states never seen elsewhere. One group
believes that the enormous pressure could cause the neutrons to break
down, freeing the individual quarks of which they are said to be made;
some of them even went so far in 2002 as to claim tentative evidence
of the actual existence of such a quark star. Others think that the
pressure might lead to a form of matter called a Bose-Einstein
condensate, a weird quantum state in which the neutrons do not
dissociate into quarks, but their individual identities blur and they
behave jointly as a single particle. In principle, it is possible to
distinguish between the accepted state of matter and the proposed
exotic states, because both free quarks and Bose-Einstein condensates
would be more easily compressed than neutrons. So a star of a
particular mass would have a smaller radius if it were made of
exotic matter.

Now the exotic-matter theories have received a blow from a new study
by the University of Arizona which has used measurements made by the
XMM-Newton and Rossi X-ray Timing Explorer space telescopes to
determine the radius and mass of a neutron star called EXO 0748-676.
The radius came out at 13.8 km, while the mass was surprisingly
large, at 2.1 solar masses. That mass strongly suggests that the star
is made of normal neutrons. That is because as the mass of a neutron
star increases, it must become more and more rigid to avoid collapsing
into a black hole under the force of its own gravity. The exotic
models of neutron stars predict that they would collapse into black
holes before reaching a mass as high as 2.1 solar masses.


VENUS EXPRESS REVEALS STORM
The Register

The first scientific results are already beaming back from the
European Space Agency's Venus Express mission. After spending nine
days in an elongated orbit around the planet in April, the spacecraft
has confirmed the existence of a double-vortex atmospheric system at
the south pole. Venus Express made its observations shortly after
arriving at the planet, when it was initially captured into the
elongated orbit that took it between 400 km and 350,000 km from the
surface. It has been known for quite a long time that winds blow
westwards around the planet at very high speeds -- they take only four
or five days to complete a circuit of the entire globe. Coupled with
the recycling of the very hot atmosphere, that super-rotation is
expected to produce a vortex over each pole. Although previous
missions had seen the expected atmospheric disturbances at both poles,
only the north pole has been studied in any detail, and the recently
observed double-eye structure had not been seen before.


TWO DUST DISCS AROUND NEARBY STAR
STScI

Beta Pictoris is a star located 63 light-years away in the southern
constellation Pictor. It is much younger than the Sun, twice as
massive, and nine times more luminous. It entered the limelight over
20 years ago when the IRAS satellite detected excess infrared
radiation from the star. Astronomers attributed the excess to the
presence of warm circumstellar dust. A dust disc was actually imaged
by ground-based telescopes in 1984; the disc is seen nearly edge-on.
Hubble observations in 1995 suggested that the disc is warped. Now
more detailed Hubble images show a distinct secondary disc that is
tilted by about 4 degrees to the main one. The secondary disc is
visible out to roughly 24 billion miles from the star. The best
explanation, according to certain astronomers who are keen on finding
planets, is that an unseen planet of up to 20 times the mass of
Jupiter is in an orbit within the secondary disc, and its gravity is
sweeping up material from the primary disc.


SATURN'S RINGS
The Register

The explanations of certain enigmatic features in Saturn's rings are
are getting nearer, according to scientists analysing the data sent
back by the Cassini spacecraft. They observed a bright arc of
material looping round the edge of the G-ring, one of the most tenuous
of all the rings. The researchers now believe that it is a long-lived
feature of the ring, held in place by resonant interactions with the
moon Mimas. If so, that would be a point of similarity to the rings
that encircle Neptune.

Initially it was thought that the bright arc must have been formed
through a series of collisions between small icy bodies orbiting in
the plane of the G-ring. However, the suspicion now is that the arc
is actually the source of the G-ring, as particles break away from the
arc and drift outwards. In addition, the research team has learned
more about the origins of the E-ring. It is now almost certain that
that double-banded ring is formed from ice erupting from geysers at
the south pole of the moon Enceladus. To form two bands of material,
the particles in the ring must orbit Saturn on inclined orbits, but
with a very small range of inclinations. More research is needed to
discover how the double structure comes about.



Bulletin compiled by Clive Down

(c) 2006 the Society for Popular Astronomy


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