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 Post subject: ENB No. 262 March 1 2009
PostPosted: Sun Mar 01, 2009 12:02 pm 
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Electronic News Bulletin No. 262 2009 March 1

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
at 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

By Alastair McBeath, SPA Meteor Section Director

Although February has been fairly quiet for UK fireball observations, as
indicated by our Recent Fireball Sightings webpage (at ), this has not been the case elsewhere. Indeed
February 13-14 especially proved quite a global date for imaged
fireballs, with spectacular events caught at 20:03 (from Italy; magnitude
about -17!), 20:26 (Italy), 21:52 (Italy), 02:11 (France), around 03h
(Texas, USA) and 05:16 UT (Italy once more). The 20:03 UT Italian
meteor and the Texas fireball at least were both initially suspected of
having dropped meteorites, and it seems now the first meteorites may
have been recovered from the Texan fall. The French image was made
from Normandy, and with visual sightings from Paris and the area
north of there, it is possible this 02:11 UT event might have been seen
from southern Britain as well, but no reports of it have arrived from here
so far. Links to sites with images of all these fireballs, plus more details
(notably on the Texas event) can be found on the SPA's General Chat
Forum, at .

Another possible meteorite-dropping brilliant fireball came down over
Finland at 21:39 UT on February 16-17. Again this was recorded on
video, and searches were underway soon afterwards in the hopes of
recovering any meteorites before fresh snow fell there. As with the
cluster of fireballs in mid January (see ENB 260, archived at ), there is no evidence as yet to suggest any of
the February fireballs were related to one another, other than by their
coincidentally happening relatively close together in time. Grateful
thanks go to our meteor-expert correspondents Ferruccio Zanotti (also
one of the lucky Italian video observers!), Karl Antier and Esko Lyytinen
(who caught the Finnish fireball on video) for details and comments on
the Italian, French and Finnish events respectively.

Assistant Meteor Director David Entwistle has posted some additional
notes to the Observing Forum's topic on the Canadian fireball and
meteorite fall of last November 20, at . The fall
is now called the Buzzard Coulee meteorite, from the place near which
the objects fell, and David drew attention to three professional papers
to be presented at the 40th Lunar and Planetary Science Conference
in Texas in late March, concerning the chemistry and structure of the
H4 chondrites recovered, and the observed characteristics of the
originating fireball. This fireball last featured in ENB 258 ( ).

David added a note to the Forum's topic on the predicted fireball over
Sudan of last October 7 too (this was most recently mentioned in ENB
255, ; the Forum topic is at: [www_popastro_com] ), with a link to a
preliminary report in the online New Scientist that suggested meteorite
fragments had been recovered associated with this fireball. A team of
searchers led by Dr Muawia Shaddad from Khartoum University was
credited with the find, using data from NASA to locate the probable fall
region. No details on the nature of the fragments are yet available,

Fireball reports made from the British Isles and nearby are always
welcomed by the Meteor Section. A fireball is any meteor that reaches
at least magnitude -3; Venus, the brilliant planet currently dominating
the evening sky, is presently magnitude -4.8. The information to send
me is described on the new-look "Making and Reporting Fireball
Observations" page of the SPA website, at: .
A verbal description which contains all the essential details is fine, but
for those who prefer a more structured approach, a new e-mailable
fireball report form is also available.


Here and now, we are used to the idea that even the nearest stars are
light-years away from the Sun, but scientists at the University of
Bonn think that things were very different in the early Universe. In
particular, ultra-compact dwarf galaxies (UCDs), a recently discovered
class of object, may have had stars packed together a thousand times
more closely than in the solar neighbourhood. UCDs were discovered in
1999. They are about 60 light-years across, which is less than
1/1000th the diameter of the Milky Way. Astronomers believe that UCDs
were created when more normal galaxies collided in the early Universe.
But oddly, UCDs clearly have more mass than the light from the stars
that they contain would imply.

Sometimes, exotic dark matter has been suggested to explain the
apparently missing mass, but it is now not thought to gather in
sufficient quantities within a UCD. The astronomers think that at one
time, each UCD had an incredibly high density of stars, with perhaps a
million in each cubic light-year. The stars would have been close
enough to merge from time to time, creating many much more massive
stars in their place. Those more massive stars consume hydrogen much
more rapidly, before ending their lives in supernova explosions. All
that then remains is either a super-dense neutron star or sometimes a
black hole. So in today's UCDs, a good part of their mass is made up
of such dark remnants, largely invisible to Earth-based telescopes but
fossils of a more dramatic past. To have such vast numbers of stars
packed closely together is quite unlike anything we see today. An
observer on a hypothetical planet inside a UCD would have seen a
'night' sky as bright as day on Earth.


The first gamma-ray burst to be seen at high resolution from the Fermi
gamma-ray space telescope had the greatest total energy, the fastest
motions and the highest-energy initial emissions ever seen. That
explosion, designated GRB 080916C, occurred on 2008 Sept. 16 in the
constellation Carina. Fermi's other instrument, the gamma-ray burst
monitor, simultaneously recorded the event. Together, the two
instruments provided a view of the blast's initial, or prompt, gamma-
ray emission at energies between 3,000 to more than 5 billion times
that of visible light. Gamma-ray bursts are the Universe's most
luminous explosions. Astronomers believe most of them occur when
massive stars run out of nuclear fuel. As a star's core collapses
into a black hole, jets of material blast outward at nearly the speed
of light. The jets bore all the way through the collapsing star and
continue into space, where they interact with gas previously shed by
the star and generate bright afterglows that fade quickly. The
first thing astronomers try to do after a gamma-ray burst is scramble
to detect the fading afterglow, whose optical spectrum can indicate
the distance to the blast site. That is crucial information to enable
calculation of a burst's power. Nearly 32 hours after the blast, a
group at the Max-Planck Institute found the afterglow of GRB 080916C.
Working quickly, before it could fade away, they measured the
afterglow's spectrum with the 2.2-m telescope at the European Southern
Observatory in Chile. According to their data, the explosion took
place 12.2 billion light-years away. With the distance known, Fermi
team members calculated that the blast would have exceeded the power
of approximately 9,000 ordinary supernovae if the energy were emitted
equally in all directions. That is a standard way for astronomers to
compare events even though gamma-ray bursts emit most of their energy
in tight jets. Coupled with the Fermi measurements, knowledge of the
distance also helps determine the speed of the gamma-ray-emitting
material. Within the jet of this burst, gas bullets must have moved
at least 99.9999 percent the speed of light. This burst's tremendous
power and speed make it the most extreme recorded to date.

Carnegie Institution

The Giant Magellan Telescope (GMT) Corporation has announced that an
agreement has been made to construct and operate the GMT at Las
Campanas Observatory in the Chilean Andes. It is to have seven
co-mounted 8.4-metre primary mirrors and an adaptive secondary system,
which should give it the resolving power of a single 24.5-metre
(nearly 1000-inch) primary mirror. Construction will begin in 2012
and is scheduled for completion around 2019.

BBC News

NASA and the European Space Agency have decided to forge ahead with an
ambitious plan to send a probe to Jupiter and its icy moons Europa and
Ganymede. The proposal could be the agencies' next 'flagship'
endeavour, to follow on from the successful Cassini-Huygens mission
to Saturn. Officials had been considering the Jupiter mission along
with a venture to Saturn's moons Titan and Enceladus. Although the
Jupiter-system mission has been chosen for an earlier flight
opportunity, a Saturn-system mission clearly remains a high priority
for the scientific community.

The team suggests that the US and Europe both send orbiters. NASA
would despatch the Europa orbiter and ESA the Ganymede one. The two
spacecraft would occasionally conduct joint observations, but only
NASA's probe would spend time around Europa, which is known to have a
severe radiation environment. A previous ESA feasibility study into a
Europa mission gave spacecraft orbiting that moon a lifetime of just
66 days. NASA plans to use specific shielding to protect sensitive
electronic systems; it is confident now that its spacecraft could
operate for several months in orbit and obtain complete coverage both
of the surface and the interior. The two spacecraft would end their
missions by crashing into their respective moons.

BBC News

An innovative UK launcher concept is to get 1m euros from the European
Space Agency. The Skylon space-plane would take off from a
conventional aircraft runway, carry over 12 tons into orbit and then
return to land on the same runway. The money will help prove the
vehicle's core technologies, including its Sabre air-breathing rocket
engine. Alan Bond, owner of the company behind the project, believes
that its reusable launcher could fly within 10 years. The Holy Grail
to transform the economics of getting into space is to use a truly
re-useable space-plane capable of taking off from an airport and
climbing directly into space, delivering its satellite payload and
automatically returning safely to Earth. The Skylon technology is
part jet engine, part rocket engine. It burns hydrogen and oxygen to
provide thrust, but in the lower atmosphere the oxygen is taken from
the atmosphere. At high speeds, that requires the engine to cope with
1,000-degree gases entering its intake.

Bulletin compiled by Clive Down
(c) 2009 the Society for Popular Astronomy

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