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The SOCIETY for POPULAR ASTRONOMY
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Electronic News Bulletin No. 186 2005 December 4
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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/maaeg58abmzc8cixLLVb/

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.


AURORAL ACTIVITY
by Ian Brantingham SPA Solar Director

Sunspot 826 has grown very large, and is approaching the centre of the
sun's disk. 2 M class flares fired off on 2nd, so expect auroral activity
from the 3rd onwards. Also, a coronal hole is causing increased solar
wind speeds at the moment, so we've got 2 chances, provided you get
some clear sky.


YET MORE NOVEMBER FIREBALLS
By Alastair McBeath, SPA Meteor Section Director

Aside from the spate of Taurid, and then Leonid, fireballs mentioned last
time, additional fireball reports have come in to the Section since. Some
of these were Taurids, and a few more probable Leonids, but several of
the most recent ones seem to have been sporadics. Observations of one
fireball or more are in the files now from almost all nights between
October 26-27 and November 24-25 made by witnesses in the UK (the
vast majority), Europe or the USA, an unprecedented spell in the Section's
records. Of the sightings since the ENB 185 reports were prepared, the
most significant was a brilliant event spotted from sites scattered between
Aberdeenshire south to South Wales, around 07:10-07:15 UT on
November 22-23. Four definite observations are available now, but any
more would be very welcome, whether of this event or not. Some early
notes and discussion of the November 22-23 event is on the SPA
Observing Forum topic "Possible Meteorite Sighting", while information
on what to report after seeing a fireball, and where to, is on the SPA
"Fireball Observing" webpage, off the meteor homepage at:
http://popastro.c.topica.com/maaeg58abmzc9cixLLVb/ .


METEOR PROSPECTS FOR DECEMBER
By Alastair McBeath, SPA Meteor Section Director

Overall, these are not good, with both the main shower maxima troubled
to a greater or lesser extent by bright moonlight. Full Moon on
December 15 in Taurus-Gemini is extremely bad news for dark-sky
Geminid observing. However, the shower's strength means some of its
best should still survive this year. The Geminids are due to reach their
maximum on December 13-14, between roughly 02h-07h UT. This
timing is excellent for British watchers, as the radiant around the peak,
near Castor (Alpha Geminorum), is nicely on-view virtually all night,
culminating around 02h UT. Highest Zenithal Hourly Rates (ZHRs) should
be about 120 judging by recent returns, so with luck and clear skies,
observed Geminid counts might be approaching a meteor a minute or so
for much of the night, despite the Moon.

Activity remains good for a night or two before, and sometimes a night
after, the maximum in an average year, so something of them might
survive the moonlight onslaught, even if clouds intervene on the maximum
night. Geminids are medium speed and often bright, though few leave
persistent trains. For best effects, face away from the Moon, while still
watching as much clear sky as you comfortably can. If you can hide the
Moon behind something like a wall or a fence, so much the better.

Ursid activity is usually most likely to be seen for a night or two over its
peak, this year scheduled for about 13h-15h UT on December 22, in UK
daytime. ZHRs at best may be between 10-50 or so (they were briefly
~30 in 2000), though only at very rare returns do they exceed ~10-15.
No ZHR of 50 has been seen since 1986. The radiant is near Kochab,
the brighter of the two "Guard" stars in Ursa Minor, so is circumpolar
from Britain, but highest towards dawn. The waning gibbous Moon rises
about 22h-23h UT for British sites on December 21-22 and 22-23.
Dark-sky observing well before moonrise on December 22-23 might
catch the declining tail of the maximum, with luck. Ursid meteors are
chiefly faint and of slow to medium speed.

More details on December's meteor showers can be found on the
monthly meteor activity page of the SPA website, off the meteor
homepage.


19 GRAVITATIONAL LENSES FOUND
The Register

Astronomers using the Hubble space telescope have identified 19 new
examples of gravitationally lensed galaxies. Among the new examples
are eight so-called Einstein rings, in which ideally an image of a
hidden galaxy is stretched in a complete circle around the lensing
object. In actual fact a whole ring has never been observed: usually
it is just an arc, but in a few cases the image extends to as much as
a semicircle or more. Gravitational lensing takes place when a
sufficiently massive object lies between the Earth and a very distant
galaxy. The gravity of the intermediate object bends light from the
object behind it around itself, making it visible from Earth. It
normally takes the form of an arc or of multiple images of the
otherwise hidden object around the lensing object. When the two
objects are lined up exactly, an Einstein ring is formed. From a
study of the arcs and rings the researchers try to calculate the
masses of the lensing galaxies. That information permits the
mass-to-light ratio of the galaxies to be estimated -- a matter of
interest because many galaxies seem to have much larger masses than
would be expected from their luminosities. If enough gravitational
lenses can be found, including sufficiently distant ones, it may be
possible to see whether the distribution of visible and invisible mass
changes with cosmic time, and so to test the idea that large galaxies
form from collision and mergers of smaller ones.


NEW CLASS OF SUPERGIANT BINARIES
ESA

Astronomers using the Integral gamma-ray observatory have discovered a
new class of binary stars, which display periods of enhanced X-ray
emission. The new class of double-star systems consist of a very
compact object that produces recurrent X-ray outbursts, and a very
luminous 'supergiant' companion. The compact object can be an
accreting body such as a black hole, a neutron star or a pulsar.
Only a dozen X-ray binary stars containing supergiants had previously
been detected. Actually, scientists thought that they were rare,
since stars in supergiant phases have very short lifetimes. However,
it now seems that transient supergiant X-ray binary systems may be
much more abundant in our Galaxy than previously thought.


DWARFS FOUND IN WAKE OF COLLIDING GALAXIES
New Scientist

The vast majority of local galaxies are dwarfs, with only something
like a thousandth of the mass of our galaxy, the Milky Way. It is not
clear how dwarf galaxies form. Some may have condensed directly from
primordial gas soon after the Big Bang, but astronomers doubt whether
they could have survived the collisions that probably occurred
frequently in the early Universe. Now, a team from Cornell University
is using the Spitzer space telescope to study dwarf galaxies that
definitely were born when two larger galaxies collided. They form in
long, tail-like structures but are so faint that only about a dozen
had previously been observed. The Cornell team has identified 15 such
dwarf galaxies around a pair of merging galaxies called NGC 5291 that
lie 200 million light-years away. The galaxies are strung along two
arcs of stars and gas stretching about 240,000 light-years behind each
of the two larger galaxies. Previous ultraviolet measurements had
suggested that the arcs contained knots of star formation, and Spitzer
confirmed that, finding that the modest objects are actually
powerhouses of star formation containing about 200 million stars that
are just a few million years old. The researchers also discovered
that the merger-induced dwarf galaxies have a telltale infrared
spectrum. They are now searching for that signature in large infrared
sky surveys to try to estimate what fraction of other dwarf galaxies
formed in the same way.


MORE PROBLEMS FOR JAPANESE PROBE
AFP

Japan's space agency says its Hayabusa spacecraft successfully landed
on the asteroid Itokawa and almost certainly collected samples from
it. The probe is on a mission to bring back material from Itokawa to
help scientists learn more about how the Solar System was created. It
could also provide information that might be helpful for any future
effort to deflect a celestial object on a collision course with Earth.
The craft fired a small metal ball at the asteroid's surface to stir
up material for collection. Although researchers will not know for
sure whether it did pick up material until the craft returns to Earth
in 2007 they seem confident that it worked. But there now appears to
be a problem with one of the thrusters designed to control its
attitude, and the return journey cannot commence unless engineers can
point the craft's antenna towards the Earth. There will be a delay of
three years if it misses a planned departure time in mid- December,
when the relative positions of the Earth and the asteroid are suitable
for the return trip.


STELLAR SURROUNDS PROBED
ESO

Astronomers using the Very Large Telescope Interferometer, which
combines the light from two or three of the 8.2-m 'unit telescopes',
thereby creating what is in effect for interferometric purposes a
telescope of 40 to 90 metres' aperture, have observed two stars
unprecedented detail.

A first group of astronomers studied the young 10-solar-mass object
MWC 297, which is in a very early stage of its life. It is more than
800 light-years away and hidden by a large amount of gas and
dust. They found the object to be surrounded by a proto-planetary
disc extending to about the size of our Solar System, but truncated in
its inner part out to about half the distance between the Earth and
the Sun. They also found it to be surrounded by an out-flowing wind,
the velocity of which ranged from about 70 km/s near the plane of the
disc to 600 km/s in the polar regions.
Another team studied the surroundings of a star entering the last
stages of its life. The star is a B[e] supergiant that is 10,000
times more luminous than our Sun and is 8,000 light-years away.
Structures on scales as small as 1.8 thousandths of an arcsecond could
be seen. The circumstellar envelope around the supergiant appeared to
be non-spherical, most probably because the star is also surrounded
by an equatorial disc made of hot dust and has a strong polar wind.


PLANET ORBITING RED DWARF
ESO

Astronomers have discovered one of the least-massive exoplanets found
so far, with the HARPS instrument on the ESO 3.6-m telescope in Chile.
The host star, Gl 581, is 20 light-years away in Libra, and has a
mass of only one-third the mass of the Sun. Such red dwarfs are at
least 50 times fainter than the Sun and are the most common stars in
our Galaxy: there are 80 of them among the 100 stars closest to the
Sun. Previous observations of about 200 red dwarfs revealed only two
with planets. The newly found planet is at least 17 times the Earth's
mass, or about the mass of Neptune -- one of the smallest masses
known. As in most other cases, however, the mass quoted is a minimum
value, and has to be divided by the sine of the orbital inclination
angle, a number that is not determined, cannot be more than 1 and can
be a lot less, so nobody can be sure what the real mass of the planet
actually is, only the lower limit. The planet is only 6 million
kilometres, also divided by the sine of the inclination, from its host
star, and completes an orbit every 5.4 days.




PHILIP'S NEW 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 the most important 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.
Stargazing 2005 was a popular addition to Philip's astronomy list last
year, and the 2006 edition of this month-by-month practical guide to
the changing night sky is expected to be equally well received. - £6.99
Published this month:
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 brand-new pack for the amateur
Solar-System observer. It contains three essential 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) 2005 the Society for Popular Astronomy


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