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The SOCIETY for POPULAR ASTRONOMY
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Electronic News Bulletin No. 213 2007 January 21
====================================================

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/maafAZFabv3EOcixLLVb/


SPECIAL MEMBERSHIP OFFER

If you are not already a member of the SPA now is a great time to
join! We are offering to those who receive ENBs and are not already
members a SPECIAL JOINING PRICE of only £12.00, saving £3.00 on the
usual UK annual rate. (Overseas rates vary but discount still applies
-- see our website for details.) You will also receive FREE, THREE
CD-Roms -- 'Window on the Universe' Parts 1 and 2 and 'Window on the
UK'

Join NOW by going to our secure website at www.popastro.com and click
the 'join now' button. To claim the your discount enter ENB017 when
asked for your voucher reference. To join by post send your details
with payment (£12.00 for 1 year or £24.00 for 2 years - UK rate) to
SPA Membership, 36 Fairway, Keyworth, Nottingham, NG12 5DU, quoting
reference ENB017.

Please note: this offer is valid only until 28 February 2007 and does
not apply to renewals of membership.



GEMINID LUNAR IMPACTS
By Alastair McBeath, SPA Meteor Section Director

Although, as noted in ENB 211, the Geminids seem to have been
largely hidden by clouds for British watchers, others elsewhere did
better, including at the NASA Meteoroid Environment Group based
in Huntsville, Alabama, USA. Their video systems watching the
unilluminated part of the lunar disc for impact flashes recorded five
definite Geminids and one "probable" on December 14 last year, a
rate of about one event an hour. The NASA researchers would like
more amateurs to be involved with this work to increase the temporal
coverage, but their long-promised data reduction software to make
the process automatic, thus making this a much more practical
proposition, remains unreleased. They were still hoping it would
become available "in the near future" on January 3 this year. For
more information, see:
http://popastro.c.topica.com/maafAZFabv3EPcixLLVb/ , with grateful
thanks to ENB Editor Clive Down for forwarding details on this
latest report.


EARLY JANUARY FIREBALLS
By Alastair McBeath, SPA Meteor Section Director

The first half of January has brought quite a crop of fireballs to the
Section, though most so far reported just by single witnesses. The
main UK events notified to us included events on January 5-6
around 22:55 UT (mag -3/-9, from West Yorkshire - see:
http://popastro.c.topica.com/maafAZFabv3EQcixLLVb/ on the SPA Observing
Forum for details);
January 7-8 within 15 minutes either side of 23:00 UT (very bright,
seen from Northants); January 13-14 at 04:15 UT (roughly mag
-10/-13, from Suffolk); and January 15-16 at 08:20 UT, a brilliant
object to be spotted so soon before sunrise, seen from South
Lanarkshire.

Several other sightings have come in from the USA as well, the most
notable of which events was a very widely-seen, spectacular,
fragmenting fireball on January 4 at ~13:15 UT (06:15 Mountain
Standard Time). It was observed by witnesses from at least nine states
from Montana south to Arizona and New Mexico, east as far as
Kansas and Nebraska, and was due to the re-entry of the second
stage of a polar-orbiting Russian Soyuz SL-4 rocket, which had
launched the COROT French space telescope from Baikonur on
December 27 last year. There was a report of some fallen debris
from the event over Wyoming, but this has not been confirmed as
yet. Useful links to descriptions of the event, including a map of the
flight and video clips, can be found via
http://popastro.c.topica.com/maafAZFabv3ERcixLLVb/
on the SPA's General Chat Forum. A possible meteorite fall through
a property in New Jersey, USA on January 2 (the identification of
which is most uncertain at present) has been mistakenly linked with
the January 4 re-entry in some reports. The two were entirely
unrelated, as far as is known, however. Notes concerning the
January 2 event can also be traced via the above SPA Forum address.

Fireball reports (meteors of at least magnitude -3) from the British
Isles and nearby are always welcomed by the Meteor Section. Details
of what information is most essential and where to submit it can be
found on the Section's Fireball Observing webpage at:
http://popastro.c.topica.com/maafAZFabv3EScixLLVb/ .


SUPERNOVA REMNANT IDENTIFIED WITH 'GUEST STAR' OF 185 AD
Science Daily

Recent X-ray observations tend to confirm the identification of the
supernova remnant called RCW 86 with one of the earliest historical
records of novae, made by the Chinese in 185 AD. The Chinese noted
that the object sparkled like a star and did not appear to move in the
sky, arguing against its being a comet. Also, it took about eight
months to fade, a reasonable duration for a supernova. RCW 86 had
previously been suggested as the remnant from the 185 AD event, on the
basis of the object's position, but estimates of the age of the
remnant had been about 10,000 years; the new X-ray observations
indicate an age more like 2,000 years and are therefore consistent
with the 185 AD identification. The age estimates are made by
comparing the observed rate of expansion of a remnant with its current
size. It now appears that in many places the expanding RCA 86 remnant
had encountered dense interstellar material that had slowed it down,
but there are places where the expansion has continued relatively
freely and much faster, thereby indicating a much smaller age.


TITAN PROBABLY HAS LIQUID LAKES
NASA

Radar images from a recent fly-by provide convincing evidence for
large bodies of liquid on Saturn's satellite Titan. Radar-dark
patches are interpreted as lakes on the basis of their very low radar
reflectivity and morphological similarities to terrestrial lakes,
including smoothness, associated channels, and location in topographic
depressions. At least 75 radar-dark patches were seen, ranging from 3
to more than 70 km across.


DYING GALAXY DESTINED TO BE REBORN
New Scientist

About 20 small galaxies are known to exist around the Milky Way. Most
fall into one or other of two main categories: dwarf spheroidals,
which are dead because they lack the gas needed for making new stars,
and dwarf irregulars, which have plenty of gas and show signs of
ongoing star-formation. Some astronomers have suggested that dwarf
galaxies can switch back and forth between the two types. In the
irregular phase, abundant gas fuels rapid star-formation. But the
newly formed stars then sterilise the galaxy when some of them explode
as supernovae and blow away its gas. The galaxy's gravity later pulls
the gas back in to fuel a new cycle of star-formation. Now, new
observations have bolstered that idea by showing that a gas cloud
expelled from one such galaxy is moving so slowly that it will
eventually revive the galaxy by falling back into it.

The cloud concerned is in the vicinity of an object called the Phoenix
galaxy, which lies about 1.4 million light-years from Earth, has a
mass of about 33 million Suns, and may be a satellite galaxy of the
Milky Way. Although the Phoenix is spheroidal, with no sign of
current star-formation, Hubble observations of the colours of 22,000
of its stars are interpreted as showing that it underwent a burst of
star-formation 50 million years ago. If the gas cloud was expelled by
that burst, its current position suggests that it is moving too slowly
to escape the galaxy for ever; the galaxy's gravity will pull most of
the gas back in a few hundred million years from now, providing enough
raw material for a fresh burst of star-formation.


HALO OF M31
BBC News

Astronomers have found an enormous halo of stars around the Andromeda
galaxy (M31), which suggests that it is as much as five times as big
as was previously thought. In fact the outlying parts of Andromeda
are so vast that they nearly overlap those of our own Galaxy.
Theories of galaxy formation predict that the halo of a large galaxy
is the first component to form, with the disc and central bulge
developing some time later.

Studying the Milky Way's halo is difficult because the Earth is
buried within the galaxy; and the haloes of distant galaxies are
impossible to study because astronomers cannot see individual stars.
Andromeda is at the perfect distance, about two million light-years:
it is just far enough away for astronomers to see the whole galaxy,
and just close enough for them to observe individual stars. A team
from the University of California at Santa Cruz has been able to
detect a sparse population of red giant stars smoothly distributed
around Andromeda out to a distance of 500,000 light-years from the
centre. Stars in the outer region were found to have low abundances
of heavy elements, comparable with abundances of Milky-Way halo stars.
According to the hypothesis of steady enrichment of heavy elements
over cosmic time, low abundances imply great age. as is to be expected
for halo stars.


3-D MAP OF DARK MATTER
Science Daily

Astronomers claim to have made a three-dimensional picture of the dark
matter in the Universe, the material that has been thought to
represent much of the total mass and has defied any description or
successful scientific probe ever since its existence was proposed
in the 1930s. Astronomers used the Hubble telescope to measure the
shapes of half a million distant galaxies. The light from the galaxies
passed through the intervening dark matter, being deflected slightly
as it travelled through space. The researchers reckoned that they
could interpret the subtle distortions in the shapes of the galaxies to
reconstruct the distribution of intervening mass along each line of
sight. The resulting map shows a loose network of filaments that grew
over time and intersect in massive structures at the locations of
clusters of galaxies. It stretches halfway back to the beginning of
time and suggests that dark matter has grown increasingly clumpy as it
collapses under gravity.


PROBABLE BLACK HOLE IN GLOBULAR CLUSTER
Science Daily

Astronomers using data from the XMM-Newton satellite say that they
have found a stellar-mass black hole in a globular star cluster in NGC
4472 (M49), a galaxy about fifty million light-years away in the Virgo
Cluster. They surprised themselves by finding it so quickly: they
were preparing for a search of thousands of globular clusters in the
hope of finding just one black hole, but they found one in only the
second globular cluster observed. They say that there is little doubt
that the object is a black hole -- it is too bright, and varies by too
much, to be anything else.


PROBABLE BLACK HOLE IN DWARF GALAXY
Science Daily

Scientists studying the nuclei of dwarf galaxies, which are thought to
develop from globular clusters, discovered that one particular dwarf
elliptical galaxy, VCC128, in the Virgo cluster, has a double nucleus.
They think that the double nucleus is made up of two points of light
from stars collected at opposite edges of a ring surrounding a black
hole. Using the 3.5-m telescope at the Apache Point Observatory in
New Mexico, they found that the nucleus is a ring of stars at least 1
billion years old, so the system seems to be very stable. The
researchers believe the black hole has a mass at least equal to the
ring of stars surrounding it, ranging from 1 million to 50 million
times the mass of our Sun.


NO PLANETS UNLESS THEY FORM VERY EARLY
Science Daily

Observations from the Spitzer space telescope indicate that gas-giant
planets either form within the first few million years of a Sun-like
star's life, or not at all. Astronomers searched for warm gas close
to 15 different Sun-like stars, most with ages of 3 to 30 million
years. All of them -- including those as young as a few million years
-- had less than 10 per cent of Jupiter's mass in gas around them, so
there can never be gas-giant planets like Jupiter and Saturn around
those stars unless indeed they have already formed.


SUPERNOVA MAY HAVE TOPPLED 'PILLARS OF CREATION'
The Register

The famous 'Pillars of Creation', the subject of one of the best-known
of Hubble's images, may already have been blown apart by a supernova.
We won't see their destruction here on Earth for another thousand
years, but the astronomers making the claim estimate that the massive,
star-forming pillars that make up the Eagle Nebula were obliterated
almost 6000 years ago. Infrared images show that cool dust makes up
most of the nebula, but there is an area of much hotter gas.
Astronomers suggest that the gas has been heated by a nearby supernova
explosion, some 8000 or 9000 years ago, and around 2000 light-years
from the famous Pillars. The explosion might have been seen from
Earth between one and two thousand years ago. From our perspective
the edge of the shock wave has still to reach the pillars, but
commentators say that when it hit, the wave would have crumbled the
towers, exposing the newly born stars within them. The catastrophe
probably triggered the birth of additional new stars.


LIGHT ECHO FROM MILKY WAY'S BLACK HOLE?
Chandra X-Ray Center

Astronomers using the Chandra X-ray Observatory think that they have
uncovered evidence of a powerful outburst from the black hole at the
Milky Way's centre. A light echo was produced when X-ray light
generated by gas falling into the supermassive black hole, known as
Sagittarius A*, was reflected off nearby gas clouds. While the
primary X-rays from the outburst would have reached the Earth about 50
years ago, the reflected ones took a longer path and arrived when
Chandra was looking. Chandra has detected small recent outbursts from
the hole, but the one implied by the echo was about 1,000 times
brighter and lasted well over 1,000 times longer than any of the
recent ones.


MARS PROBE MAY HAVE FOUND LOST ROVER
New Scientist

The Mars Reconnaissance Orbiter, which arrived at the planet last
March, has so far observed four spacecraft on the planet's surface --
the current rovers (Spirit and Opportunity), and the twin 30-year-old
Viking landers. Now it has been looking at yet another lander lying
lifeless on its surface: Mars Pathfinder, which operated for three
months in 1997. It could see scattered hardware from the mission,
including the parachute and backshell it used during its descent a
decade ago; it may also have found the mission's tiny rover,
Sojourner, which appears to have crawled towards Pathfinder after the
lander had already died. The lander and some of the components had
been seen previously from orbit, by the now-lost Mars Global Surveyor
spacecraft. However, the current orbiter has better resolution of
just under 30 cm.


EIGHT NEW DWARF GALAXIES ORBITING MILKY WAY
Sloan Digital Sky Survey

An international team of researchers has discovered seven -- and
perhaps eight -- new satellites of the Milky Way. The seven new Milky
Way satellites all lie in the area of sky around the North Galactic
Pole surveyed by 'SDSS-II'. There are two new dwarfs in the
constellation of Canes Venatici, one in Bootes, one in Leo, one in
Coma Berenices, one in Ursa Major and one in Hercules. The eighth and
newest discovery may be the most intriguing. Named Leo T, it is about
1.4 million light-years away, on the fringes of the Milky Way's
gravitational influence. It may be a 'free-floating' Local Group
dwarf, rather than a satellite of the Milky Way. In addition to its
greater distance, Leo T is distinct from the other seven discoveries
in that it has populations both of fairly old stars (more than five
billion years old) and comparatively young ones (less than one billion
years old). It also appears to have neutral hydrogen gas, so its
star-forming days may not be over.




Bulletin compiled by Clive Down

(c) 2007 the Society for Popular Astronomy


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