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 Post subject: ENB No. 221 May 13 2007
PostPosted: Sun May 13, 2007 10:11 am 
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The SOCIETY for POPULAR ASTRONOMY
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Electronic News Bulletin No. 221 2007 May 13
====================================================


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/maagqFSabyu7ScixLLVb/



FIREBALLS OVER CENTRAL ENGLAND
By Alastair McBeath, SPA Meteor Section Director

A magnitude -3/-4 or brighter fireball was reported from three sites,
in Staffordshire, Lancashire and Hampshire, at 20:58-20:59 UT on
May 3-4. Some information on it can be found on the SPA's
Observing Forum, at: http://popastro.c.topica.com/maagqFSabyu7TcixLLVb/
. Luckily, two of the
observers, one on either side of the object's flight path, were able to
give good positional information on where the meteor appeared in the
sky, and from these, it has been possible to triangulate to an
approximate trajectory, although the start was not well-constrained.
The fireball probably became first visible at around 90 km altitude
somewhere above an area from roughly the southwest shore of The
Wash inland to Oakham in Rutland. It seems to have descended at
a fairly shallow angle to the horizontal from there on a WSW-trending
track, and ended at about 68 +/- 3 km altitude above a point not far
from Redditch in Worcestershire, perhaps quite close to 52.3 deg N,
1.9 deg W. The visible trail may thus have been up to 150 km or so
long. The shallow entry angle and high end-point suggested by this
count against meteorites that survived being recovered, but any that
did land will likely lie at the bottom of the Celtic Sea anyway, perhaps
~100 km south of Cork Harbour in Ireland, projecting on from the
established trajectory. These details are subject to revision if more
observations become available, of course.

Another recent fireball, but so far reported by just one observer in
Hampshire (not the same person who saw the May 3-4 meteor!), was
spotted at 20:12 UT on May 7-8.

Anyone else who saw either of these events, or any other fireballs (a
fireball is a meteor that reaches at least magnitude -3, as bright as
the
planet Jupiter at its best), is invited to send a full report to me at
the
Meteor Section as soon as possible. details of what to send and
where to can be found on the SPA's "Fireball Observing" webpage,
at: http://popastro.c.topica.com/maagqFSabyu7UcixLLVb/


LYRIDS 2007 - MORE NEWS
By Alastair McBeath, SPA Meteor Section Director

Additional reports and analyses have been carried out on the Lyrids
since the report in the last ENB, including some preliminary
International Meteor Organization (IMO) results - see the "live" graph,
updated as fresh reports come in, at:
http://popastro.c.topica.com/maagqFSabyu7VcixLLVb/ . The IMO data have
somewhat
variably indicated a probable maximum with Zenithal Hourly Rates
(ZHRs) of 20-25 around 22:30 +/- 30 mins UT on April 22, but rates
seemed not dissimilar to this level from about 22h-01h UT on April
22-23 overall.

Assistant Meteor Director David Entwistle has carried out a further
assessment of the Radio Meteor Observation Bulletin results (at:
http://popastro.c.topica.com/maagqFSabyu7WcixLLVb/ across the expected
peak, and although most
observing systems recorded their better echo counts on April 22-23,
there is quite a scatter in when the best activity was found. Even so,
a careful examination of the raw counts combined with David's
numerical work does suggest a maximum between about 21h-02h
UT on April 22-23, in-line with the early visual findings. David also
noted that a possible burst of bright meteors with good persistent
trains seemed to have been picked up by at least three radio systems,
Gaspard De Wilde and Willy Camps in Belgium, and Jeff Brower
in British Columbia, Canada, between 07h-08h UT on April 23.
Several other European observers recorded higher counts around this
time, but this need not be too significant, as the ~05h-08h UT period
is one of the more favourable reception times for Lyrids over the
western half of Europe especially. Unfortunately, there are no visual
reports as yet covering this interval on April 23 to confirm the
activity,
or say if it was due to the Lyrids.

One other interesting by-product of David's radio meteor
investigations was the finding of somewhat elevated counts on April
23-25 inclusive during daylight, at a time when the Lyrid radiant was
not readily detectable. This has been found before, most clearly
recently in an SPA analysis from 2003 April, and is probably due to
a combination of rates from two showers with radiants too near one
another to separate by radio observations, the April and Delta Piscids.
Counts were not very high, but it was useful to confirm these showers
remain radio-observable.


NEW E-MAIL ADDRESS FOR ASSISTANT METEOR DIRECTOR
By Alastair McBeath, SPA Meteor Section Director

David Entwistle, our recently-appointed Assistant Meteor Director
with especial responsibility for advising on radio meteor observing,
can now be contacted by e-mail at: <radiometeor@popastro.com>.


CLIMATE CHANGE ON MARS
Nature

Scientists from NASA say that Mars has warmed by about 0.5C since the
1970s. That is similar to the warming experienced on Earth over
approximately the same period, but since there is no known life on Mars
it suggests that rapid changes in planetary climates could be natural
phenomena. The mechanism at work on Mars appears, however, to be
different from that on Earth.

The scientists compared heat maps of the Martian surface from the
Viking mission in the 1970s with maps gathered more than two decades
later by Mars Global Surveyor. They found that there had been
widespread changes, with some areas becoming darker. The darkening is
believed to occur through the action of wind in sweeping rock surfaces
clear of dust. When a surface darkens it absorbs more heat, and the
system has positive feedback, the heat driving up the mean wind speed.
It is speculated that eventually the winds become strong enough to
trigger a global dust storm, such as has repeatedly been seen on Mars
in the past; the storms return relatively light-coloured dust to the
areas previously swept clear, and the cycle begins anew.


OUTFLOW FROM NEAR BLACK HOLE
Harvard-Smithsonian Center for Astrophysics

An international team of astronomers has studied the outflow of
material from the vicinity of the black hole at the centre of the
galaxy NGC 4051. It found that gas was escaping from much closer to
the hole than previously thought. The outflow source is located about
1 light-day from the hole --- about five times the distance of Neptune
from the Sun. The team also estimated that only 2 to 5 per cent of
the accreting material is thrown back out.


ANOTHER PLANET DISCOVERED
Harvard-Smithsonian Center for Astrophysics

Astronomers have found the most massive known transiting extrasolar
planet. The gas-giant planet, called HAT-P-2b, has more than eight
times the mass of Jupiter. It orbits the F-type star HD 147506, an
8.7-magnitude object about 440 light-years away in the constellation
Hercules. Brightness measurements during transits show that HAT-P-2b
is about 1.18 times the size of Jupiter. Although it has an orbital
period of only 5.63 days, that is the longest period known for a
planet that transits in front of its star. An intriguing feature of
HAT-P-2b is its highly eccentric (e = 0.5) orbit. Gravitational
forces between star and planet tend to circularise the orbit of a
close-in planet, and all other known transiting planets have circular
orbits.


JAMES WEBB SPACE TELESCOPE
Science Daily

NASA has approved 10 new technologies for use in the James Webb space
telescope to be launched in 2013. The approval came a year ahead of
schedule and includes several technologies not used previously in
space. One example is the telescope's microshutters -- tiny doorways,
the width of a few hairs, that will allow scientists to block unwanted
light and view distant stars and galaxies. NASA said that the early
approval may reduce the risk of increased costs and schedule delays.


EUROPEAN PLANET HUNTERS
New Scientist

European astronomers say that their new space telescope, called COROT,
is proving 10 times as sensitive as expected. The realisation came as
astronomers analysed the first data from COROT, which was launched on
2006 December 27. After 60 days of initial observations, two possible
planets stood out strongly in the raw data. A follow-up campaign of
observations from ground-based telescopes across Europe showed that
one of the candidates was indeed a planet, of 1.3 Jupiter masses,
orbiting its host star in 1.5 days. The other object was a previously
unknown red dwarf star in orbit around a larger, yellow star.

Even before final processing of the observations, COROT exceeded all
expectations. The astronomers say that, when they have written the
software to enable the final refinements to be made, COROT may be
performing up to 30 times better than its design specification. There
has obviously been a serious miscalculation in the planning of the
spacecraft, but for once it is in the favourable direction. During
its three-year mission, COROT will monitor tens of thousands of stars.
Working at its newly estimated sensitivity, it may be able to find
Earth-sized planets in the 'habitable zones' of red dwarf stars, with
orbital periods of about a fortnight.


MERCURY HAS MOLTEN CORE
NRAO

Scientists have found that Mercury probably has a molten core.
Mercury is one of the least-understood of the planets in our Solar
System. Its distance from the Sun is just over one-third that of the
Earth, and it has a mass only 5.5% of the Earth's. Only about half of
Mercury's surface has been photographed by a spacecraft, Mariner 10,
in 1974. Mariner 10 also discovered that Mercury has a weak magnetic
field, about 1% as strong as the Earth's. That discovery spurred a
scientific debate about the planet's core. Planetary magnetic fields
are usually thought to be caused by an electromagnetic dynamo in a
molten core. However, Mercury is so small that most scientists
expected its core to have cooled and solidified long ago. Those
scientists speculated that the magnetic field seen today may have been
frozen into the planet when the core cooled.

Whether the core is molten or solid today depends greatly on its
chemical composition, which can provide important clues about the
processes involved in planet formation. To answer the question, the
scientists used a radar technique to measure, with an unprecedented
precision of one part in 100,000, the rate at which Mercury spins on
its axis. Tiny variations in its spin rate, caused by solar
gravitational effects, were calculated to be twice as large if the
core were liquid than they would be if Mercury had a solid core. The
measured variations are best represented by a core that is at least
partially molten.


BRIGHTEST-EVER SUPERNOVA SEEN
University of California-Berkeley

A supernova first observed last September is the most luminous ever
seen, according to University of California astronomers, and may be
the first example of a type of massive exploding star rare today but
possibly common in the very early Universe. The explosion was a
hundred times more energetic than a typical supernova. Unlike typical
supernovae that reach a peak brightness in days to a few weeks and
then dim into obscurity in a few months, SN2006gy took 70 days to
reach maximum brightness and stayed brighter than any previously
observed supernova for more than three months. Nearly eight months
later, it still is as bright as a typical supernova at its peak,
outshining its host galaxy 240 million light-years away. Astronomers
estimate the star's mass at between 100 and 200 times that of the Sun;
such massive stars are very rare.

The star that produced SN 2006gy apparently expelled a large amount of
mass before exploding. Its rapid mass loss is reminiscent of the
current behaviour of Eta Carinae, a so-called luminous blue variable
which, at 100 to 120 solar masses, is one of the most massive stars in
our Galaxy, and might possibly be getting ready to explode in a
similar manner.


Bulletin compiled by Clive Down

(c) 2007 the Society for Popular Astronomy


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