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The SOCIETY for POPULAR ASTRONOMY
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Electronic News Bulletin No. 237 2008 February 3
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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 visiting http://popastro.c.topica.com/maajQGVabEGTCcixLLVb/



MID-JANUARY FIREBALLS UPDATE
By Alastair McBeath, SPA Meteor Section Director

A third multiply-observed mid-January bright fireball was reported to
the Section after the last ENB, seen at around 22:25 UT on January
14/15 from possibly three sites, in Sutherland, West Yorkshire and
perhaps Kent, though it is not certain all these sightings were of the
same meteor. The Sutherland and Yorkshire reports might indicate the
object passed high above north Ireland, however. An analysis of
details provided on the January 9/10, circa 18:55-19:00 UT meteor,
revealed nothing fresh, unfortunately.

Luckily, another analysis, of the January 15/16, ~22:57 UT fireball,
was more fruitful. Eleven definite sightings of this event are now
available, from places scattered across southern England (from Dorset
east to Kent, and north as far as Gloucestershire), plus at Newport in
south Wales. These suggest the meteor peaked at about magnitude -10
to -15, and flew on a generally southwest to northeast trajectory from
over the Channel north of the Cotentin Peninsula of France (perhaps
somewhere on a line from Cherbourg to Bournemouth), ending above
western West Sussex or southeast Hampshire. The start was poorly
constrained, maybe in the 80- 100 km altitude bracket, or perhaps a
little higher, but the end may have been at ~50-60 km altitude,
possibly lower. It almost certainly passed directly over the Isle of
Wight, from where sounds probably relating to the meteor were heard
about a minute after the fireball passed nearly overhead. Solving for
the various possible solutions suggested an entry-angle of between
~15-25 degrees from the horizontal, an atmospheric path length of ~85
to 135 km, and, from the average estimated full visible flight
duration of ~4 seconds, a range of mean atmospheric velocities (not
allowing for deceleration) of ~20-35 km/s, in the "slow" to "medium"
meteor speed categories. Half the witnesses reported the object broke
apart into several fragments (somewhere between two to six main
pieces), while the majority favoured a green or blue colour for the
main body. If any meteorites fell as a result of this event,
projecting on from the possible trajectories could imply landing zones
in Bedfordshire, Cambridgeshire, Suffolk or the North Sea off East
Anglia, at maximum, or perhaps points adjacent but southwest of these
places, though this region is merely a best-estimate from the
available information.

Many thanks go to all the fireball witnesses to submit data on these
three meteors. Observations of any fireballs seen from the UK or
close-by (a fireball is a meteor that reaches at least magnitude -3),
are always welcomed by the SPA Meteor Section, including additional
reports on any of the above three. Advice and the details to send me
are outlined on the "Fireball Observing" page of the SPA website, at:
http://popastro.c.topica.com/maajQGVabEGTDcixLLVb/ .


URSIDS - SECOND UPDATE
By Alastair McBeath, SPA Meteor Section Director

Following the uncertainties about the Ursid activity in December 2007,
discussed most recently in the previous ENB, I have now carried out a
full analysis of the raw radio data covering the shower, between
December 20-24 inclusive, using December's Radio Meteor Observation
Bulletin, RMOB, No. 173 (available at: http://popastro.c.topica.com/maajQGVabEGTEcixLLVb/ ). From
this, December 22 stood out, if rather marginally, in most datasets as
being the more sustainedly active radio meteor day from this interval,
though it did not always produce the highest echo counts. There was no
good evidence to support a likely Ursid maximum around 01:00-03:30 UT
on December 21/22, as was expected from previous years' returns,
although it seems probable Ursid activity was present during that
time, as for most of December 22. Looking nearer the predicted
timings for the possible outburst event, all the results favoured a
peak in probable Ursid activity at some point between 19h-23h UT on
December 22/23, the majority showing a core interval between 20h-22h
UT. A minority also suggested an afternoon UT peak as well, sometime
between 12h-18h UT (possibly beginning around 10h UT), centred on a
mean timing of 14:12 +/- 1h UT. Although the consensus here was not
especially good, this may suggest some elevated Ursid activity was
underway by at least midday UT,and possibly before then. For the
better-established evening maximum, I found a mean timing for the
centre of this at 21:19 +/- 1h UT. This peak was not strong or
especially obvious in any of the results however, nor was there any
good evidence to imply the Ursids showed an unexpected magnitude
distribution overall in 2007. A normal range of meteor brightnesses
seems plausible, with a slight hint that perhaps a few extra, brighter
events may have appeared around 20h +/- 1h UT, though this is
questionable, as such estimates from radio results alone are not
straightforward.

Overall, this may suggest that the International Meteor Organization's
(IMO's) 'live' Ursid visual results, which suggested best Zenithal
Hourly Rates (ZHRs) of about 35 +/- 5 around 21:15 UT on December
22/23, while possibly inflated because of the bright moonlight, could
be treated as a useful working upper limit to this maximum's
activity. More recently, IMO Video Commission Director Sirko Molau
indicated good Ursid activity was present in the European automated
video meteor observations between 15:30-23:00 UT on December 22
(posted on IMO-News, January 17), perhaps at best from 17h UT onwards,
though he was unable to suggest a more probable maximum from his
preliminary review. While the radio results, as so often, are somewhat
tentative, thanks to problems in making the analysis, it is
interesting that the radio mean peak timing was so nearly coincident
with the probable visual maximum, as both were achieved independently
of one another. This may be about as close to the reality of what
happened as can be achieved without more good-quality (especially
visual or video) results. It seems to support the idea that an Ursid
maximum away from its normally-expected time, and roughly coincident
with the predictions for a possible outburst peak on December 22/23,
did happen, albeit the ZHRs were probably less strong than had been
hoped-for.


ECLIPSE WEBCAST
By Peter Grego (SPA Lunar Section Director)

Join SPA Lunar Section Director Peter Grego at www.lunarobservers.com
for a LIVE WEBCAST of the total eclipse of the Moon on February 21,
from 01:30 to 05:15 UT (if the event is clouded out a real-time
computer simulation of the eclipse will be broadcast). Peter will be
using a 200-mm SCT and a Philips ToUcam Pro, and the view will take in
the entire lunar disc. First contact with the Earth's pale grey outer
penumbral shadow occurs at 00:37 UT, enveloping the Moon within an
hour. Since the penumbra is faint, all that is likely to be noticed
during that period is a slight darkening of the Moon's leading
(left-hand) edge. At 01:43 the Moon makes first contact with the
umbra, the darkest part of the shadow. Totality starts at 03:01, when
the Moon is completely immersed in the umbra. Given good conditions,
the Moon will be visible with the unaided eye because sunlight is
refracted by the Earth's atmosphere onto the Moon, giving it a reddish
hue. At some eclipses the Moon appears a bright orange at totality,
while at others the Moon assumes a rich brown colour. Totality lasts
for 50 minutes, making it the deepest eclipse visible from the UK
until 2011 June 15. At 03:51 the Moon's leading edge emerges from the
umbra into the relative brightness of the penumbra, ending totality.

During the eclipse the Moon is in Leo, close to Regulus and a few
degrees away from Saturn. From the UK, the Moon remains fairly high,
with an altitude of around 44 degrees at first umbral contact, 33
degrees at mid-totality (03:27) and 18 degrees at last penumbral contact
(05:09).

Steadily-held binoculars are the best instruments with which to enjoy
lunar eclipses. Most viewers prefer to gaze at these events without
worrying about recording them, but some enjoy noting the definition of
the umbra's edge and the colour of the Moon, along with timing the
contact between the umbra and certain prominent lunar features.
Estimations of the totally eclipsed Moon's brightness may be made
using binoculars held the wrong way round, by comparing the Moon's
small image with a star or planet. Comparison stars include nearby
Regulus (mag 1.35) and Saturn (mag 0.2), Procyon (mag 0.38) and Spica
(mag 0.98).


MERCURY'S VOLCANIC PAST REVEALED
BBC Online

A fly-by by the 'Messenger' probe has revealed evidence of widespread
vulcanism on the planet Mercury. Evidence from the Mariner 10 probe
launched in the 1970s provided only tenuous evidence for volcanic
activity. In addition, only 45% of Mercury's surface had previously
been mapped; Messenger has already covered a further 30% of the
planet. The spacecraft has also discovered a feature that scientists
dubbed The Spider, which is unlike anything seen on Mercury before, or
for that matter on the Moon. It lies in the middle of a large impact
crater called the Caloris basin and consists of more than 100 narrow,
flat-floored troughs radiating from a 40-km central crater. The
Spider has a crater near its centre, but whether that crater is
related to the original formation or came later is not clear.


EUROPEAN PROBE AIMS FOR MERCURY
BBC News

The European Space Agency has signed an industrial contract to build a
probe named BepiColombo to send to Mercury in 2013, to arrive in 2019.
The £260m deal will lead to the production of spacecraft components in
Germany, Italy, France and the UK. Researchers hope that by following
hard on the heels of NASA's Messenger, BepiColombo can help tie down
the answers to the questions that still remain over how the planet
came into being. The mission is a joint endeavour with Japan which
will be responsible for the Mercury Magnetospheric Orbiter that will
investigate the planet's magnetic field with its five on-board
instruments. Europe will produce a Mercury Planetary Orbiter that
will be equipped with 11 instruments. Flying in a polar orbit, it
will study Mercury for at least a year, imaging the planet's surface,
generating height profiles, and collecting data on Mercury's
composition and extremely tenuous atmosphere.


THE SUN HAS A TWIN 220 LIGHT-YEARS DISTANT
NASA

Astronomers have identified a yellow star that they say is the nearest
yet seen to being a twin to our own Sun. Its name is HD 101364 and it
lies 220 light-years away. The star's mass, temperature, and chemical
composition appear to match the Sun's exactly, although the star may
be slightly more luminous than the Sun. Since Sun-like stars brighten
as they age, that suggests that the star may be a billion years older
than the Sun.


NEUTRON STARS CAN BE MORE MASSIVE
Cornell University

Neutron stars can be considerably more massive than previously
believed, and it is more difficult to form black holes, according to
new research developed by using the Arecibo Observatory in Puerto
Rico. Astronomers had thought the neutron stars needed a maximum mass
between 1.6 and 2.5 suns in order to collapse and become black
holes. However, this new research shows that neutron stars remain
neutron stars between the mass of 1.9 and up to possibly 2.7 suns.
The matter at the centres of neutron stars is the densest in the
Universe. It is one to two orders of magnitude denser than matter in
the atomic nucleus.

From 2001 until 2007, astronomers examined a binary pulsar called M5
B, in the globular cluster M5, which is located in the constellation
Serpens. A pulsar is a strongly magnetized neutron star that emits
large amounts of electromagnetic radiation, usually from its magnetic
poles. As in the case of a lighthouse, distant observers perceive a
sequence of pulsations, which are caused by the rotation of the
pulsar. In the case of M5 B, the radio pulsations arrive at the Earth
every 7.95 milliseconds. The pulsations were recorded with accurate
timing information, which was used to determine the orbital motion of
M5 B about its companion, which in turn allowed the astronomers to
estimate the mass (1.9 solar masses) of the pulsar.


MILKY WAY'S BLACK HOLE PROBED MORE CLOSELY THAN BEFORE
New Scientist

Astronomers have detected radio emission coming from within 30 million
kilometres of the dark object, thought to be a black hole, that lies
at the centre of the Galaxy. Previously, astronomers could see no
closer than 100 million kilometres from the object, called SgrA*. The
new observation reaches to within three times the radius of the hole's
event horizon, the boundary within which any matter, light or
radiation is prevented from escaping. The radio waves were picked up
last April by three separate observatories in Hawaii, Arizona and
California that were linked together to form in effect a telescope
4500 kilometres across, operating at the very short radio wavelength
of 1.3 millimetres, which penetrates the shroud of gas that lies
between the Earth and the Galactic Centre. The radio emission must be
coming from hot gas that was probably blown off massive stars. It is
not yet clear, however, whether that gas will be irrevocably sucked
into the hole, or is in the process of being blasted out again.




Bulletin compiled by Clive Down


(c) 2008 the Society for Popular Astronomy


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