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 Post subject: ENB No. 218 April2 2007
PostPosted: Tue Apr 03, 2007 8:16 am 
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The SOCIETY for POPULAR ASTRONOMY
***********************************
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Electronic News Bulletin No. 218 2007 April 2
====================================================


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/maaf9EpabxANPcixLLVb/


MORE MARCH FIREBALLS
By Alastair McBeath, SPA Meteor Section Director

The steady trickle of fireball sightings sent in to the SPA has
continued since the last ENB, with a second report of the March
13-14 event, now timed at 23:01 UT, from Hampshire, which
observer estimated the magnitude at about -4/-6. Subsequent solo
reports have arrived from: March 18-19, ~20:40 UT, a very bright
object from Kent; March 19-20, ~23:00 UT, a slow fireball from
Staffordshire; March 22-23, 20:05 UT, an orange-red magnitude
-4/-6 event from Dumfriesshire followed very soon after by another
meteor of magnitude -1/-2 or so, also red coloured; and two separate
fireballs on March 23-24, the first a very bright one seen from
indoors in Lancashire at 19:20 UT, the second an impressive object
spotted around 01:00 UT from Cumbria.

All further observations of these, or any other fireballs (meteors of at
least magnitude -3) from the British Isles or nearby would be
welcomed by the Meteor Section, as soon as possible please. Notes
on what information to send and where to can be found on the
Section's Fireball Observing webpage at:
http://popastro.c.topica.com/maaf9EpabxANQcixLLVb/ .


NEW ASSISTANT METEOR DIRECTOR
By Alastair McBeath, SPA Meteor Section Director

I am very pleased to be able to welcome a fresh face to the running
of the SPA Meteor Section, David Entwistle, who has very recently
joined the team as our second Assistant Director. David has been
enthusiastically meteor observing with us for a good while now, using
visual, imaging and radio techniques, and has become increasingly
involved with the difficult subject of radio meteor analyses in recent
years. David will have particular responsibility for advising
prospective
radio meteor observers about that subject, as well as working on
radio meteor analyses, and giving assistance with some of the
Section's fireball analyses from time to time. If you have any questions
about radio meteor observing at present, David can be contacted
via e-mail sent to me at my usual <meteor@popastro.com> address,
but please make clear that the message is for David in the Subject
line. We hope to organize a separate SPA e-mail address for him
shortly.

Shelagh Godwin will remain as our other Assistant Meteor Director,
responsible for enrolling all new Section members (you can join by
sending Shelagh an A5 SAE with a written request including your name,
address, e-mail address if possible, and SPA number; her postal
address was in the recent SPA News Circular), and sending out
printed copies of Meteor Section publications.

My role too continues as normal, so your meteor observations, fireball
sightings, and questions about such observing or meteor astronomy
more generally, should be sent to me.


METEOR MISSES AIRLINER
By Alastair McBeath, SPA Meteor Section Director

Various reports and comments have been coming through since late
last week about "burning space debris" or a "blazing meteorite" that
supposedly "just missed" a passenger airliner over the South Pacific
some way off New Zealand, en-route from Chile to Auckland. After
sifting the few facts from all the media hyperbole, it's clear this was
a
story of some interest, but apparently not one to cause undue alarm.
The event seems to have occurred around 10 p.m. on March 27 local
New Zealand time. A LAN Chile Airbus 340 pilot reported seeing
one or more bright objects, apparently falling ahead of the aircraft
(though some media summaries suggested another object, or perhaps
part of the flight of just the one, was seen behind the airplane too;
how
the pilot saw both in this case was not mentioned). The pilot was
claimed as estimating the closest approach to the object as less than
10 km, though as this was in the dark, so without any reference
points, how the estimate was made is most unclear. A sonic boom
heard over the noise of the engines was also claimed, though no details
of this could be established. The aircraft was at its cruising height of
about 11 km at the time.

Initial commentators were very quick to blame the unexpectedly early
re-entry of a Russian Progress M-58 cargo craft, twelve hours or so
ahead of schedule, but as this was still attached to the ISS at the time
of the incident with the aircraft, that would have been remarkable
indeed! The object instead seems to have been a very substantial
natural fireball, and chances-are that it was a lot more than 10 km from
the airplane. Exceptionally rarely, such incoming bodies have been
observed as still glowing to as low as 10 or 15 km or so above the
surface, but in general, even very bright fireballs usually extinguish
well
above this - typically between 20-50 km altitude or more. This may
have been one of those very rare closer approaches however, and if
the sonic boom was from the fireball, that would suggest it survived to
below 30-40 km altitude at least. To complete the story, the aircraft
was reported as having landed safely at its scheduled time without
further incident. For more details, see the links from:
http://popastro.c.topica.com/maaf9EpabxANRcixLLVb/ on the UK Weather
World's Spaceweather
Forum.


COMET C/2007 E2 (LOVEJOY)
Spaceweather.com

This looks as if it may be a nice comet in the morning sky after about
April 11 and in the evening sky a week or so later, with the optimum
time being about April 22 when it will be near Altair and will be 11º
altitude at midnight and at its brightest (about mag 7.5). On May 5
it will be quite close to M92. It was discovered on March 15 from
Australia by Terry Lovejoy using, remarkably, not a telescope but an
off-the-shelf digital camera.


MARS' SOUTH-POLE ICE
Science Daily

New measurements by the Mars Express spacecraft of Mars' south polar
region indicate extensive frozen water. The polar region contains
enough frozen water to cover the whole planet in a layer approximately
11 metres deep. That new estimate comes from mapping the thickness of
the ice. The Mars Express orbiter's radar instrument has recorded
more than 300 virtual slices through layered deposits covering the
pole to map the ice. The radar sees through icy layers to the lower
boundary, which is as deep as 3.7 kilometres below the surface. The
instrument is also mapping the thickness of similar layered deposits
at the north pole of Mars.

Polar layered deposits hold most of the water known to exist now on
Mars, though other areas of the planet appear to have been very wet at
times in the past. Understanding the history and fate of water on
Mars is the key to whether Mars could ever have supported life, since
all known life-forms depend on liquid water. The layered deposits
extend beyond and beneath a polar cap of bright-white frozen carbon
dioxide and water at Mars' south pole. Dust darkens many of the
layers. However, the strength of the echo that the radar receives
from the rocky surface underneath the layered deposits suggests that
the composition of the layered deposits is at least 90% frozen water.
One area with an especially bright reflection from the base of the
deposits puzzles researchers. It resembles what a thin layer of
liquid water might look like to the radar instrument, but the
conditions are so cold that the presence of melted water is deemed
highly unlikely.


KUIPER BELT OBJECT BROKEN UP BY MASSIVE IMPACT
Caltech

Caltech astronomers say that an entire family of bodies seems to
have originated from a catastrophic collision involving the KBO
object 2003 EL61 at about the time that the Earth was forming. They
base their assumptions on similar surface properties and orbital
dynamics of smaller fragments still in the general vicinity. They
conclude that 2003 EL61 was spherical and nearly the size of Pluto
until it was hit by a slightly smaller body about 4.5 billion years
ago, leaving behind the egg-shaped body we see today and a couple of
moons, as well as many more fragments that left the vicinity
altogether.


SUPERNOVA PRECEDED BIRTH OF SOLAR SYSTEM?
Science Daily

A team of planetary scientists from the University of Tokyo has
proposed that the molecular cloud that gave birth to the Sun existed
near a star of more than 20 solar masses which underwent a supernova
explosion in which the exploding star's inner regions mixed and some
of the material was ejected, while the rest fell back onto the
collapsing core. The researchers say that the supernova's shock wave
would have compressed the molecular cloud, initiating the cloud's
collapse. The supernova would have had to be about 10 light-years
away for the shock wave to have been strong enough to compress the
molecular cloud but not so strong as to shred it.


FINGERPRINTING STAR CLUSTERS IN THE MILKY WAY
ESO

The formation and evolution of our Galaxy is one of the major problems
of astrophysics. Now an international team of astronomers, using
observations made with ESO's Very Large Telescope, has tried to use
the chemical compositions of stars in 'open' clusters to shed light on
the formation of our Milky Way. Open star clusters are composed of a
few tens up to a few thousands of stars that are gravitationally bound
together, and they span a wide range of ages, from a few million up to
several billion years. The astronomers determined the abundances of a
number of chemical elements in each of a dozen red giants in the old
open cluster Collinder 261, located about 25,000 light-years from the
Galactic Centre. They found that all the stars that they observed in
that cluster share the same chemical signature. That homogeneity is
taken to indicate that the chemical information survived through
several billion years, and that all the stars in the cluster must have
formed from the same primordial cloud. A comparison with the Hyades
open cluster, and the group of stars moving with the bright star
HR 1614, shows that those clusters, each internally homogeneous,
exhibit abundances that differ from cluster to cluster, indicating
that each cluster formed in a different primordial region, from a
different cloud with a different chemical composition. If it turns
out that most clusters have their own distinctive chemical signatures,
it might pave the way to the chemical tagging of stars in our Galaxy
to common formation sites and thus cast some light on the history of
the Milky Way. It would be unwise to be too optimistic too soon,
however, on the present basis of only three clusters, since it is
already known that the stars in certain globular clusters, notably
Omega Centauri, have heterogeneous chemical abundances.


CASSINI IMAGES HEXAGON FEATURE ON SATURN
ESA

A hexagonal feature encircling the north pole of Saturn, already
imaged by the Voyager 1 and 2 spacecraft over 20 years ago, is still
to be seen in recent Cassini images. A second hexagon, significantly
darker than the historical feature, is also visible in the Cassini
pictures. The hexagon is similar to the Earth's polar vortex, which
has winds blowing in a circular pattern around the polar region, but
on Saturn the vortex has a hexagonal rather than circular shape, and
is nearly 25,000 kilometres across. The new images taken in thermal-
infrared light show that the hexagon extends much deeper into the
atmosphere than previously expected, some 100 kilometres below the
cloud tops. Within the hexagon lies a system of clouds which has not
been visible to Cassini's visual cameras, because the hexagon is under
the cover of the long polar night, which lasts about 15 years. The
infrared mapping spectrometer can image Saturn in both daytime and
nighttime conditions and see deep inside. As winter wanes over the
next two years, the feature may become visible to the visual cameras.



Bulletin compiled by Clive Down

(c) 2007 the Society for Popular Astronomy


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