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Electronic News Bulletin No. 206 2006 October 15

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

By Alastair McBeath, SPA Meteor Section Director

Following the mid September lull noted last time, more fireballs were
reported from late September and early October. These included
events on September 27-28 around 02:50 UT (Co. Durham) and
two on October 2-3, the first at 22:30 UT or so (a rare sighting
between buildings from Central London), the second around
05:10 UT (possibly later, up to ~05:30 UT), a magnitude -5/-9 (?)
meteor spotted from West London and Berkshire. Both initial
reports can be found on the SPA's Forums, the second linked to .

Then October 7-8 produced two fireballs within half a minute for
one fortunate observer in Surrey, who managed to photograph the
second, quite by chance. Both were similarly bright, around
magnitude -4/-6 (possibly brighter; the Moon made the estimates
especially difficult), the first at 22:50 UT, the second at 22:51 UT.
The SPA Gallery Forum topic at has the
imaged meteor and more notes. From preliminary details, it seems
likely this latter meteor was also spotted from Essex (which observer
did not see the first fireball if so). An initial estimate suggests the
22:51 UT fireball was probably high above NW France, maybe
around the Amiens-Arras area, but this will need more information
to confirm.

All fireball sightings, particularly from the UK and nearby, are
welcomed by the Section. Information on what to send and where
to can be found via the Section's "Fireball Observing" page at: .

By Alastair McBeath, SPA Meteor Section Director

Regular ENB readers may recall that October 2005 brought the start
of a busy meteoric autumn with an unexpected outburst of bright
meteors on October 5-6 (see ENBs 184 and 185), from a radiant
near the end of Draco's "tail". Raising the curtain on this autumn's
activity too has been a repeat, with a small outburst of somewhat
brighter than average video meteors recorded over Europe between
00h-04h UT on the morning of 2006 October 6, peaking near the
same relative time as the 2005 event, and from a similar radiant region.

Unfortunately, as last year, there seem to be no confirming visual
observations as yet, and in 2005 only some of the radio meteor
observers detected a very weak signature at about the right time. As it
seems now the 2005 activity was not just a one-off event, observers
need to be alert for future outbursts from this source. The whole
peak interval identified from 2005-06 data will repeat on 2007
October 6 from about 07h to 09h30m UT, which with the Moon
a waning crescent (last quarter October 3, new October 11), makes
observing conditions virtually perfect across North America for
whatever takes place (activity of course is not guaranteed!). This may
give the first real chance for visual observers to attempt to identify
the source too.


Astronomers using the Hubble telescope have obtained images of a dark
spot on Uranus. The University of Wisconsin scientists said that the
feature measures about 1,700 by 3,000 kilometres. There have been
unconfirmed sightings of dark spots on Uranus before, including
sketches made during the early 1900s, low-contrast ultraviolet Voyager
images in 1986, and near-infrared observations taken from the ground
in 1993. However, no previous Hubble images have shown one, so the
present spot probably formed very recently.


Using the Very Large Telescope (VLT) at infrared wavelengths,
astronomers have mapped a disc of gas and dust surrounding the young
star HD 97048, which is thought to have an age of a few million years
and belongs to the Chameleon I dark cloud, a region of star-formation
about 500 light-years away. The star is 40 times more luminous than
our Sun and is 2.5 times as massive. The disc has a radius at least
12 times that of Neptune's orbit and is thought to contain a large
amount of gas, perhaps as much as 10 times the mass of Jupiter. That
is more than thousand times larger than the amounts that seem to be
present in debris discs and Kuiper-belt-like structures that have been
found around older stars such as Beta Pictoris and Vega.

Science Daily

An international team of astronomers based in the Netherlands found
that 'old' stars dominated many large galaxies in the early Universe,
raising the question as to why those galaxies progressed into
'adulthood' so early. Every year only a handful of new stars is born
in galaxies like the Milky Way. To account for the large number of
stars in the Universe today, about 400 billion in the Milky Way alone,
it was thought that the rate of star-formation must have been much
higher in the past. Surprisingly, in this study, astronomers using
the 8.1-m Gemini telescope in Chile report that many of the largest
galaxies in the Universe had a very low star-formation rate even when
the Universe was only about 20% of its present age. The new findings
add to growing evidence that in big galaxies the formation of new
stars was significantly suppressed after an initial period of vigorous


Astronomers have been using the VLT to investigate 'blue stragglers'
in the southern globular cluster 47 Tucanae. Blue stragglers are
unexpectedly young-looking stars found in stellar aggregates, such as
globular clusters, which are known to be made up of old stars. They
are created through the evolution of close-binary-star systems in
which the more massive component, in the normal course of its
evolution, becomes a red giant and sheds much of its material; the
material falls onto its companion, which because of its increased mass
then shines as if it were a hotter and younger star than has any
business to remain in an old cluster. The new study measured the
abundances of chemical elements at the surfaces of 43 blue stragglers,
six of which proved to be under-abundant in carbon and oxygen. The
anomaly is taken to indicate that the material at the surfaces of
those blue stragglers came from the deep interior of a star; it could
reach the surface only during the mass-transfer process occurring
between two stars in a binary system.


Astronomers have published maps made from a new survey, known as the
2MASS Redshift Survey (2MRS), which combines two-dimensional positions
and colours from the Two-Micron All-Sky Survey (2MASS) with redshifts
of 25,000 galaxies over most of the sky. The detailed maps show the
'local' cosmos out to a distance of 600 million light-years,
identifying all the major superclusters of galaxies and voids. The
most massive supercluster is 400 million light years away and 20
million light-years across, and is named after its identifier, the
American astronomer Harlow Shapley. The 'Great Attractor'
supercluster, which is a third of the distance of Shapley, plays a
bigger role in the motion of our Galaxy. According to the team, our
Milky Way galaxy, its sister galaxy Andromeda and other neighbouring
galaxies are moving towards the Great Attractor at about 400 km/s.
The researchers established that the Great Attractor is indeed an
isolated supercluster and is not part of Shapley.


The Hubble telescope has discovered 16 extra-solar planet candidates
orbiting stars in the crowded central region of our galaxy 26,000
light-years away. The tally is consistent with the number of planets
expected to be uncovered from such a distant survey, on the basis of
exoplanet detections in the solar neighbourhood. Five of the new
planet candidates represent a new extreme type not found in any nearby
searches: they whirl around their stars in less than one Earth day.
The shortest orbital period is only 10 hours; the planet concerned is
only 740,000 miles from its star and must be very hot.

New Scientist

A new study makes a bid to explain loops of gas that exist above the
Galactic plane near the centre of the Milky Way. The tube-like
structures may be responsible for the formation of star clusters near
the Galaxy's centre and may also be related to the region's
unexpectedly strong magnetic field. In 2003 astronomers finished a
survey, made with a radio telescope in Chile, that showed two
loop-shaped structures within about 1000 parsecs (1 pc = 3.26
light-years) of the Galaxy's centre. The team believes that the loops
formed in the same way that glowing arches called prominences do on
the Sun -- by the stretching and bending of magnetic field lines.
The origin and structure of the Galaxy's magnetic field are not
understood, but the field lines appear to lie in the same plane as the
Galactic disc.

Now, the team has modelled on a computer a field structure that
appears to be able to produce gas loops similar to the ones observed.
In the model, small vertical hills in the initially horizontal field
lines cause gas to start flowing down into the valleys between them.
With less gas at the tops of the hills, the magnetic field there
becomes free to expand upwards even more, leading to great loops. The
model accounts for the loops' size and mass -- they are about 300 and
500 pc long and have a combined mass of about 170,000 Suns.

The model also explains the observed speed of the gas as it falls down
the sides of the loops. The motion of the gas in each loop carries
roughly the same amount of kinetic energy as is produced in a
supernova explosion. The pooling of the gas at the bottoms of the
loops could provide the raw material for stars to form, but because
the gas is crashing down with so much energy the turbulence it creates
would tend to prevent the gas clouds from condensing into stars unless
the clouds were very massive. Thus clusters can form only from very
massive gas clouds and are very rare, but when they do form they must
be very massive and rich. Indeed, some star clusters observed near
the centre of the galaxy *are* very dense, such as the Arches cluster,
which contains about 150 massive stars.


A number of UK astronomers has joined a group of US and German
institutions to exploit an advanced new telescope, Pan-STARRS, which
is sited on the Hawaiian island of Maui and is equipped with what is
claimed to be the world's largest digital camera. While monitoring
the sky to look for near-Earth asteroids, Pan-STARRS will build up the
most detailed image yet of the sky in general. It will enable
astronomers to investigate small Solar-System objects and identify new
supernovae and other objects of interest.


Scientists analyzing astrometric data from the Hubble telescope have
shown for the first time that the orbit of an extra-solar planet is
aligned with its star's circumstellar disc of dust and gas, as of
course is only to be expected. The planet, detected six years ago,
orbits the nearby Sun-like star Epsilon Eridani. The research team
determined the planet's mass and its orbit, which proved to be
co-planar with the disc. The planets in our Solar System share a
common alignment, indicating that they were created at the same time
in the Sun's disc. But the Sun's debris disc dissipated long ago,
whereas Epsilon Eridani is relatively young and still retains its
disc. The planet, a gas giant, orbits its star every 6.9 years and is
the nearest known planet outside our own Solar System.

Bulletin compiled by Clive Down

(c) 2006 the Society for Popular Astronomy

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