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Electronic News Bulletin No. 208 2006 November 12

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

Soon after the last ENB was published, information reached the
Section about a loud double sonic boom between 10:30-11:00 UT
on October 26, heard and felt from places near Bude on the north
coast of Cornwall. Unfortunately, only vague media reports are
available as yet (see for the
item suggesting a meteoric sonic boom may have been responsible;
that story has a link back to the original item), so it is not
clear what happened.

There are reports of buildings being shaken by the event, and one
person claimed an existing wall-crack was widened by it, but there
was no seismic signature recorded only ~20 km away at Hartland
Point. Such seismographs tend to record earthquakes, but do
occasionally pick up aerial sonic booms as well, albeit not in this
case. No earthbound explosive cause could be identified by the
local electricity and gas companies or police, and a civil aircraft was
ruled-out too, but claims that a military aircraft cause could be
excluded need to be treated with caution, as the MoD seems to
always deny such reports initially as a matter of routine, though in
the past they have sometimes later admitted their aircraft may have
been involved. A meteoric sonic boom could have produced the
detected effects certainly, but in the absence of any reports of a
bright fireball at the time, this is inconclusive. If anyone has
information, particularly from actual witnesses, or fireball sightings
around this time, it might be possible to define better what took place.

By Alastair McBeath, SPA Meteor Section Director

Unlike this time last year, when we were in the grip of the Taurid
"swarm" return, and fresh fireballs were being reported from virtually
every night between late October to late November, just one fireball
has been recorded by Section contributors since the last ENB, but this
was an impressive magnitude -8/-10 or brighter meteor, spotted so far
by people at four sites scattered over southern England - in Derbyshire,
Suffolk, West Sussex and near Bristol - around 17:30-17:45 UT on
November 1-2. Early indications are the object may have had a
track angled somewhere between NE-SW to E-W, high above the
Berkshire region or nearby, though this needs more data from the
observers to refine and confirm.

Any other sightings of this or different fireballs spotted from the UK
and nearby, would be welcomed by the Section. Information on what
to send and where to can be found via the Section's "Fireball
Observing" page at: .


NASA has selected concept studies for missions that would return a
sample of an asteroid, probe the chemistry of Venus' atmosphere and
reveal the interior structure and history of the Earth's Moon. Also
selected for further study are three missions of opportunity that
would make fresh use of two spacecraft that have completed their
primary objectives.

The Osiris mission would survey an asteroid and return samples to
Earth; the Vesper mission is a Venus chemistry and dynamics orbiter
that would advance our knowledge of the planet's atmospheric
composition and dynamics; and the Grail mission would map the
gravitational field of the Moon to determine the Moon's interior
structure. The Deep Impact eXtended Investigation of comets (DIXI)
mission would use the existing Deep Impact spacecraft to take pictures
of the nucleus of another comet; the Extrasolar Planet Observations
and Characterization (EPOCh) mission would try to use the high-
resolution camera on the Deep Impact spacecraft to search for Earth-
sized planets around other stars; while the Stardust NEXT mission
would use the existing Stardust spacecraft to fly past Comet Tempel 1
and observe changes since the Deep Impact mission visited it in 2005.
In 2005 Tempel 1 made its perihelion approach to the Sun, possibly
changing the surface of the comet.


Astronauts will, after all, service the Hubble Space Telescope in
2008. Without servicing, the observatory is not expected to last more
than two or three more years. Its batteries and gyroscopes, which are
used to point the telescope, are degrading and will be replaced. The
shuttle crew will also install two new instruments -- the Wide Field
Camera 3 (WFC3), and the Cosmic Origins Spectrograph (COS). The new
instruments should improve Hubble's ability to see distant, faint
objects in the early Universe. The servicing mission should extend
Hubble's orbital lifetime to at least 2013, by which time NASA may be
getting close to launching its proposed successor, the James Webb
Space Telescope, which was originally due for launch in 2010.

The Register

A mission to Venus might be able to find out more about the planet's
history than previously thought, as new evidence casts doubt on the
theory that the planet was totally re-surfaced during a cataclysmic
bout of vulcanism 500 million years ago. Scientists at the University
of Minnesota have carried out a new analysis of the surface and have
concluded that no such event occurred.

The age of a planet's surface has sometimes been estimated by counting
craters -- the more craters, the older the surface. By that method of
reckoning, Venus, at 4.5 billion years old, ought to have around 5,000
craters, bit in fact it has only about 1,000, all of which are very
well preserved. That led some scientists to conclude that a single,
massive volcanic event must have covered all the other craters with a
blanket of fresh lava between one and three kilometres deep over most
of the planet. But now some astronomers have reconsidered data from
the Magellan mission and have analysed areas where smooth flat plains
are punctuated by islands of older terrain. By considering how each
island slopes off, they tried to estimate where neighbouring islands
would meet, that is, where the bases of the valleys lay. They found
that the older terrain was covered by a much thinner layer of lava
than had been thought, less than one kilometre. That suggested that
the 'catastrophic eruption' idea could not account for the missing
craters; instead, the researchers concluded that Venus must have been
re-surfaced much more gradually, and that the process has left plenty
of the older surface intact. Parts of the surviving surface could be
as much as a billion years old.


Astronomers using the Very Large Array radio telescope have discovered
ring-like structures around a cluster of galaxies. The discovery
provides tantalizing new information about how such clusters are
assembled, about magnetic fields in the spaces between clusters, and
possibly about the origin of cosmic rays. The newly-discovered ring
segments, some 6 million light-years across, surround the galaxy
cluster Abell 3376, more than 600 million light-years from Earth.
They were revealed because fast-moving electrons emitted radio waves
as they spiralled round magnetic field lines in intergalactic space.

X-ray observations strongly suggest a recent collision and merger of
two or more smaller clusters. Such a phenomenon is among the most
energetic events in the Universe after the Big Bang. Only a tiny
fraction of the total energy of such a collision, if transferred to
electrons, would cause them to emit the radio waves observed by the
VLA. This is the first observational evidence for a shock wave around
a massive galaxy cluster, and the discovery may throw some light upon
the thin gas between the galaxies, and also upon the magnetic fields
on the outskirts of such clusters -- magnetic fields whose origin is

In addition, the scientists speculate that violent regions like those
in Abell 3376 may be sites from which cosmic rays originate. Cosmic
rays are protons or atomic nuclei accelerated to nearly the speed of
light, and shocks such as those found in the collisions of galaxy
groups may be able to provide the enormous energies required -- the
most energetic cosmic-ray particles detected on Earth have energies
about 100 million times greater than anything achieved by man-made
particle accelerators.


Scientists using the Swift satellite have observed a stellar flare so
powerful that, had it been on our Sun, it would have triggered a mass
extinction on Earth. It occurred last December on a star slightly
less massive than the Sun, in the binary system II Pegasi which lies
at a distance of about 135 light-years from Earth. It was about a
hundred million times more energetic than a typical solar flare.
Solar flares originate in the corona, the outermost part of the Sun's
atmosphere, where the temperature is about two million degrees. They
are manifested as a burst of radiation across much of the electro-
magnetic spectrum, from low-energy radio waves up to high-energy
X-rays. The X-ray emission can last up to a few minutes on the Sun;
on II Peg it lasted for several hours. The flare involves a shower
of electrons raining down from the corona onto the photosphere,
heating the coronal gas to temperatures that normally exist only deep
inside the Sun. Scientists think that the twisting and breaking of
magnetic field lines lacing through the corona generates the particle
acceleration and flaring.

The flaring star in II Peg is 0.8 times the mass of the Sun; its
companion is 0.4 solar masses. The stars are quite close to one
another, only about seven stellar radii apart, so there are strong
tidal forces that cause them to rotate in synchronism with the 7-day
period of the orbital revolution -- much faster than the Sun. Fast
rotation is conducive to strong stellar flares. The key finding in
the II Peg flare was the detection of higher-energy X-rays. Swift's
Burst Alert Telescope usually detects gamma-ray bursts, which are
thought to arise from star explosions and mergers. The II Peg flare
was energetic enough create a false alarm for a burst detection.
Scientists quickly knew that it was a different kind of event,
however, when the flare overwhelmed Swift's X-ray telescope, a second


Our Milky Way Galaxy is surrounded by a number of dwarf satellite
galaxies, which because of their loosely rounded shapes are referred
to as 'dwarf spheroidal' galaxies. Faint and diffuse, they are a
thousand times fainter than the Milky Way itself, making them the
least luminous galaxies known. Cosmological models assert that small
galaxies formed first, and later assembled into larger systems like
our Galaxy. Since the Universe initially contained only hydrogen and
helium, dwarf galaxies should have the lowest heavy-element content.

A survey has recently been made with the VLT by a big international
consortium of astronomers to measure the heavy-element abundances in
over 2000 individual giant stars in the Fornax, Sculptor, Sextans and
Carina dwarf spheroidal galaxies. Whilst the average abundances of
elements in the dwarf galaxies are comparable with those seen in the
Galactic halo, the former are lacking the very-metal-poor stars that
are seen in the Milky Way -- the two types of systems, contrary to
theoretical predictions, are essentially of different descent. The
results rule out any merging of the nearby dwarf galaxies as a
mechanism for building up the Galactic halo, even in the early history
of the Universe, and so are inconsistent with current cosmological

University of Cambridge

The University of Cambridge and the Kavli Foundation have announced
their intention to establish a new institute at the University of
Cambridge to probe the beginnings of the cosmos. Led by Professor
George Efstathiou, the Kavli Institute for Cosmology will be
supported by a multi-million-dollar endowment from the Kavli
Foundation which is dedicated to advancing scientific knowledge 'for
the benefit of humanity'. The researchers of the new institute will
seek to advance our knowledge and understanding of the Universe,
bringing together scientists from Cambridge's Institute of Astronomy,
the Cavendish Laboratory (the Department of Physics) and the
Department of Applied Mathematics and Theoretical Physics.

Sloan Digital Sky Survey

A team from the Sloan Digital Sky Survey (SDSS-II) and Fermi [US]
National Accelerator Laboratory has announced its discovery of the
brightest known image of a galaxy from the early Universe. While
furious star-formation makes the galaxy luminous, it enters the record
books because the gravity of a foreground galaxy acts as a natural
telescope, focusing its light for us. The newly discovered galaxy,
seen as an arc of four elongated images that encircle the foreground
lens, offers a rare window into the state of the Universe two billion
years after the Big Bang. Astronomers discovered the arc whilst
searching more than 70,000 SDSS-II images for merging pairs of
galaxies. Follow-up observations confirmed that the arc consists of
four lensed images of a galaxy at a red-shift of 2.73; this equates to
a distance of 11.2 billion light-years. Theoretical modelling
indicates that gravity has enhanced the galaxy's brightness by more
than a factor of 10. While earlier surveys detected more than 1,000
such distant, highly red-shifted galaxies, they are generally too faint
for detailed study, even with the largest telescopes.

Bulletin compiled by Clive Down

(c) 2006 the Society for Popular Astronomy

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