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The SOCIETY for POPULAR ASTRONOMY
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Electronic News Bulletin No. 227 2007 September 2
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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/maahHAjabAZEDcixLLVb/



PERSEIDS 2007 - PRELIMINARY RESULTS
By Alastair McBeath, SPA Meteor Section Director

Some fine weather coincided with the Perseid maximum weekend for
many parts of the British Isles this year, and observers were out in
droves as a result. Including those who contributed notes to the SPA
and UK Weatherworld Forums, 86 people have provided some
information from their efforts so far. Those who sent in details
directly
to the Meteor Section (sometimes as well as posting notes on the
Forums mentioned) included:

Tom Banks (Cheshire), Mary Bartley (Flintshire), Ian Brantingham
(Moray), Jeff Brower (British Columbia, Canada), Tony Buick (no
location given), Maybel Delglyn (no location given), David Entwistle
(Hants), Mike Feist (Sussex), Shelagh Godwin (Herefordshire), Alan
Heath (Notts), Marco Langbroek (Netherlands), Trevor Law (Hants),
James Martin (with Matt Chapman and Mike Kelly; Isle of Man),
Tony Markham (Staffs), Jane Mills (Northants), Laurence Roberts
(Essex), Clive Rogers (Warwicks), Robin Scagell (Bucks), Dave
Scanlan (Hants), Jonathan Shanklin (Cambs), Jeff Stevens (Argyll),
Richard Taibi (Virginia, USA), Danny Thomas (Surrey), David
Woodward (Shrops), Julie Yellowley (Northumberland), and the
Director (Northumberland).

The overall impression was that most observers with better skies were
somewhere between happy and satisfied with what they saw. A few,
who had perhaps taken some of the wilder media claims too literally
(SPA Comet Director Jonathan Shanklin spotted that The Times was
predicting 80 meteors a minute, for instance!), expressed
disappointment, but they were very much in the minority. Some who
attempted imaging mentioned the usual frustrations of such work -
meteors just missed, or which passed apparently through the frame
but went unrecorded - which the swift Perseids often create. Slow,
bright meteors typically record a little better that way, so it was no
surprise to find a few probable Kappa Cygnid trails had been caught
among the Perseids.

With most good-sky meteor watch data available from August 11-12
and 12-13, thanks partly to the moonlit mornings in the week
preceding the peak, there is as yet only a rough impression of the
usual slowly rising activity. Average Zenithal Hourly Rates (ZHRs)
around midnight UT on August 11-12 had reached 50-60 in SPA
data, but oddly seemed only a little better by the following night,
closest to the expected, possibly multiple, maximum, averaging a fairly
constant 60-70 between 23:30-03:00 UT. In the hour or so around
22:00 UT on August 12-13, ZHRs reached their highest level in our
results, at about 80 +/- 15. The radiant was still fairly low for part
of
this time, however. Several of those visual observers who have
covered numerous past Perseid returns commented that activity they
saw on August 12-13 was good, but not that good, from the shower
this time, which seems in-line with these findings.

The preliminary "live" International Meteor Organization (IMO) visual
results have suggested a protracted period with Perseid ZHRs around
80 or more from at least 16h UT on August 12 to 19h UT on August
13. Several possible submaxima were apparent within that interval.
Being "live" of course means the results change every time somebody
adds any fresh data, thus they are not definitive, nor are they so
rigorously controlled as would be needed for a proper analysis, but they
do give some ideas about what happened. Best ZHRs seem to have
been around 120 +/- 5 at 22:35 UT on August 12. This seems to
support the SPA's "early" peak, though the actual ZHR values were
rather different. Both datasets may change further as more results
come through however, but the overall patterns of fairly constant rates
for at least several hours after this first peak, seem present in both.

Magnitude and train details from the SPA results thus far suggested
fairly typical values. The Perseid mean magnitude, corrected to a
limiting magnitude - LM - +6.5 sky, was +2.3, while the same value
for the sporadics was +3.5 (August 11-12 and 12-13 only; skies
with LM +5.5 better and <20% cloud cover). Persistent trains were
left by 34% of Perseids and 6.5% of sporadics. The brightest
Perseids reported till now were around magnitude -6, with 51
individual fireballs detected from August 10-11 to 13-14 inclusive,
30 of those on August 12-13 alone.

Assistant Meteor Director David Entwistle's initial review of the early
international radio meteor results across the expected Perseid peak,
suggested a similarly broad and ill-defined maximum, from roughly
22h-06h UT on August 12-13. There were hints of somewhat
increased activity around 23h-00h and 01h-03h UT then, perhaps with
weaker enhancements around 10h-11h and 12h-13h UT on August
13. More data should be available by mid September, and a further
assessment may be possible after then.

One noteworthy event was the direct observation of the Perseids, as
far as we know for the very first time, in daylight, using thermal
imagers! Laurence Roberts and colleagues from the company he works
for set up a whole series of such equipment, and ran it from 03h-07h
UT on August 12-13, collecting a total of around 11 hours of data
from the various sensors and video cameras. This followed the
accidental recording of a meteor crossing the daylight sky using such
gear by Laurence and the same team on June 21, around 08h UT.
After Laurence first contacted the Section on June 23 this year about
it, we were able to establish that very little thermal imaging work has
yet been attempted on meteors, except for some overnight observing
by someone from Siemens in Germany, operating a system once
overnight only in May. That system had recorded similar activity levels
to what a visual observer might have seen, so we were hopeful the
daytime operation might be equally successful, as seems to have been
the case. Laurence is still working on the analysis however!

Many thanks and well done to everyone who has sent in some notes,
and especially those who have provided full observing reports, so far.
Anyone with results still to submit, particularly full meteor watch
observations, should please do so as soon as possible.

The main UK Forum topics with Perseid reports are at:

SPA - http://popastro.c.topica.com/maahHAjabAZEEcixLLVb/ ; and UKWW -
http://popastro.c.topica.com/maahHAjabAZEFcixLLVb/

while the IMO "live" data and graphs are at:
http://popastro.c.topica.com/maahHAjabAZEGcixLLVb/ .


LARGEST KNOWN EXOPLANET FOUND
The Register

Astronomers have discovered the biggest transiting exoplanet yet.
Orbiting a star in the constellation of Hercules, planet TrES-4 is 70
per cent bigger than Jupiter, but is less massive; it is roughly as
dense as cork. Its gravity has only the most tenuous grasp on its
upper atmosphere: the team that made the discovery at the Lowell
Observatory suggests that the planet probably has a diaphanous tail of
material spiralling towards its parent star. TrES-4 appears to be
something of a theoretical problem, since it is larger relative to its
mass than current models of superheated giant planets can presently
explain.

Like all transiting planets, TrES-4 betrays its existence by causing
an observable dip in its parent star's brightness each time it passes
between the star and our telescopes. It is about 1400 light-years
from us, and orbits its parent star in 3.5 days at a distance of about
4.5 million miles -- so close that its surface is extremely hot,
around 1,600 Kelvin.


LARGEST MERGER OF GALAXIES
New Scientist

Researchers at the Harvard-Smithsonian Center for Astrophysics have
found the largest galaxy merger so far recognized. It involves a
quartet of galaxies at the centre of a cluster known as CL0958+4702,
which lies about 5 billion light-years away in Ursa Major. Three of
the merging galaxies are probably comparable in mass with the Milky
Way, while the other may be about three times as massive. Using
infrared observations from the Spitzer space telescope and optical
images from the WIYN Observatory in Arizona, the team also noticed a
fan-shaped plume of old red stars trailing about 360,000 light-years
from the merger, apparently tossed out of the galaxies as they
spiralled towards each other. Eventually, about half of those stars
will probably fall back into the merged galaxies, while the other half
will remain outside it. Interestingly, the four merging galaxies are
made of old, red stars, suggesting that each had lost the gas
necessary to form new stars long beforehand, within 5 billion years of
the Big Bang. That agrees with other recent observations showing that
galaxies within clusters (which typically contain hundreds of
galaxies) have fewer young stars than those lying outside clusters.


GOOGLE EARTH LOOKS TO THE SKY
Web User

A new feature that allows you to view the sky has been added to Google
Earth. By choosing Switch to Sky from the View drop-down menu in
Google Earth, you can access the Sky feature, which allows you to view
and navigate through 100 million individual stars and 200 million
individual galaxies. Sky consists of seven layers of information that
illustrate celestial bodies and events, including constellations,
Hubble telescope imagery, planets, and the life of a star. You will
need the latest version of Google Earth to run the Sky feature.
http://popastro.c.topica.com/maahHAjabAZEHcixLLVb/


CLOSEST NEUTRON STAR TO EARTH?
Science Daily

Canadian and U.S. scientists have discovered what might be the closest
neutron star to the Earth, probably between 250 and 1000 light-years
away. Although most neutron stars are accompanied by remnants of the
supernova explosion that created them, or a close stellar companion,
or exhibit radio pulsations, the scientists say that the newly
discovered neutron star has none of those characteristics. It is only
the eighth such isolated neutron star to have been discovered. The
discovery was reported by astronomers from McGill University, who
first noticed the star from its X-ray emissions.


COMET-LIKE TAIL TRAILS MIRA
NASA

The space-based 'Galaxy Evolution Explorer' has observed Mira Ceti in
the course its ongoing sky survey in ultraviolet light, and shown it
to look like a comet with a gargantuan tail. Mira is a fast-moving
red giant about 400 light-years away, and is the archetypical
long-period variable star; it sheds massive amounts of surface
material as a stellar wind. The tail material is thought to have been
shed over the past 30,000 years. Some astronomers are suggesting that
Mira's tail offers an opportunity to study how stars like our Sun die
and ultimately seed new stars. Compared to other red giants, Mira is
travelling unusually fast, at about 130 km/s with respect to the
average of the stars in our locality in the Galaxy. Gravitationally
bound in an orbit with Mira is a small, distant companion thought to
be a white dwarf.


RINGS OF URANUS SEEN EDGE-ON
RAS

For the first time since their discovery in 1977, the rings of Uranus
are presented edge-on to the Earth. Some of the world's major
telescopes have been observing Uranus during the current ring-crossing
window, and are watching mutual occultations and eclipses of the
satellites. The Earth's motion round the Sun results in there being
not one but three occasions when the ring-plane passes exactly through
the Earth - on 2007 May 3 and August 16 and 2008 February 20.


JUPITER INCREASES RISK OF COMET STRIKE
New Scientist

According to a new study that flies in the face of conventional
wisdom, Jupiter does not protect the Earth from comet strikes but
actually has the opposite effect. A 1994 study showed that if Jupiter
were somehow replaced by a much smaller planet like Uranus or Neptune
it would lead to many more long-period comets hitting the Earth, but
a new study by astronomers at the Open University indicates that if
there were no planet at all in Jupiter's orbit the Earth would
actually be safer from impacts. The contradictory results arise
because Jupiter affects comets in two different, competing ways. Its
gravity helps to pull comets into the inner parts of the Solar System,
where they have a chance of hitting the Earth, but also clears away
Earth-threatening comets by ejecting them from the Solar System
altogether. According to the new study, the worst case for the Earth
is when Jupiter is replaced by a planet with about the mass of Saturn.
Such a planet is fairly capable of putting comets into an Earth-
crossing orbit, but still has some difficulty ejecting them, so
they will stay in Earth-crossing orbits for a much longer time. The
projected result was more than three times as many impacts as in the
real Solar System.


VOID IN SPACE IS OF UNPRECEDENTED SCALE
New Scientist

Radio astronomers at the University of Minnesota have been studying
data from a survey carried out by the Very Large Array radio telescope
in New Mexico. In the direction of the 'WMAP cold spot' -- an
unexplained anomaly in the map made by the WMAP satellite of the
cosmic microwave background -- they saw few or no radio sources in a
volume that is about 280 megaparsecs or nearly a billion light-years
in diameter. The lack of radio sources implies that there are no
galaxies or clusters in that volume, and because dark matter is
usually found to be associated with luminous matter the region
presumably lacks dark matter too. The void is about 6 to 10 billion
light-years away, in the direction of the constellation Eridanus, and
is much bigger than any found previously.


TWIN MARS ROVERS RESUME WORK
NASA

After six weeks of inactivity during dust storms that limited solar
power, both Mars rovers, Spirit and Opportunity, have resumed driving.
Opportunity advanced 13 metres toward the edge of Victoria Crater on
August 21. Mission controllers were taking advantage of the gradual
clearing of dust from the sky while also taking precautions against
build-up of dust settling onto the rover. With the improved energy
supplies, both rovers are back on schedule to communicate daily.
Opportunity had previously been conserving energy by going three or
four days between communications. On Spirit, dust on the lens of the
microscopic imager has slightly reduced image quality from that
instrument, although image calibration can compensate for most of the
contamination effects. The team is experimenting to try to dislodge
the dust from the lens. Spirit drove 42 centimetres in reverse on
August 23 to get into position for photographing a rock that it had
examined with its spectrometer.


NEUTRON STARS WARP SPACE-TIME
NASA

X-ray astronomers have seen Einstein's predicted distortion of
space-time around three neutron stars. Using XMM-Newton, they
observed the binary system Serpens X-1, which contains a neutron star
with a stellar companion, and two other systems. They studied a
spectral line from hot iron atoms that are whirling around in a disc
just above the neutron star's surface at 40% of the speed of light.
Previous X-ray satellites detected iron lines around neutron stars,
but they lacked the sensitivity to measure the shapes of the lines in
detail. Astronomers found that the iron line is broadened
asymmetrically by the gas's extreme velocity, which smears and
distorts the line because of the Doppler effect and beaming effects
predicted by Einstein's special theory of relativity. The warping of
space-time by the neutron star's powerful gravity, an effect of the
general theory of relativity, shifts the neutron star's iron line to
longer wavelengths. Scientists have seen such asymmetric lines from
many supposed black holes, but this is the first confirmation that
neutron stars can produce them as well. It shows that the way neutron
stars accrete matter is not very different from that of black holes,
and it provides a new tool to probe Einstein's theory. Also, since
the innermost part of the disc obviously can't orbit any closer than
the neutron star's surface, the measurements give a maximum size for
the neutron star. The neutron stars can be no larger than 18 to 20.5
miles across, results that agree with other types of measurements.


VOYAGERS MARK 30 YEARS IN SPACE
Science Daily

NASA is celebrating three decades of flight of the two venerable
Voyager spacecraft as they head towards interstellar space. They were
launched on 1977 August 20 and September 5, and continue to return
information from distances more than three times farther away than
Pluto. During their first dozen years of flight, the Voyagers made
detailed explorations of Jupiter, Saturn, and their moons, and
conducted the first explorations of Uranus and Neptune. They showed
in unprecedented detail Jupiter's turbulent atmosphere, which includes
dozens of interacting hurricane-like storm systems, and erupting
volcanoes on Jupiter's moon Io. They also showed waves and fine
structure in Saturn's rings from the gravity of nearby moons. Since
then, the Voyagers have remained operational and have been probing the
Sun's outer heliosphere and its boundary with interstellar space.
Voyager 1 is currently the most distant man-made object, at a distance
from the Sun of about 15.5 billion kilometres; Voyager 2 is at about
12.5 billion kilometres. In late 2004, Voyager 1 began crossing the
Solar System's final frontier, called the heliosheath. It is
turbulent area, approximately 14 billion kilometres from the Sun,
where the solar wind slows as it impinges upon the thin gas that fills
the space between stars. Each spacecraft carries five fully
functioning science instruments that study the solar wind, energetic
particles, magnetic fields and radio waves as they cruise through that
otherwise unexplored region of deep space. The spacecraft are too far
from the Sun to use solar power; they run on less than 300 watts,
provided by long-lived radioisotope thermoelectric generators.




Bulletin compiled by Clive Down

(c) 2007 the Society for Popular Astronomy


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