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 Post subject: ENB No. 216 March 4 2007
PostPosted: Wed Mar 07, 2007 7:32 pm 
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The SOCIETY for POPULAR ASTRONOMY
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Electronic News Bulletin No. 216 2007 March 4
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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
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/maafXVMabwWrHcixLLVb/



FIREBALLS ROUNDUP
By Alastair McBeath, SPA Meteor Section Director

There are now three reports in to the Section of the February 7-8,
circa 19:40-19:45 UT, fireball mentioned last time, the third made
from South Lanarkshire. A preliminary analysis suggests the object
may have flown on a roughly SW to NE trajectory from high above
Cardigan Bay/west Wales, passing NW of Manchester, to end
somewhere over the Leeds-Bradford/east Lancashire/SW North
Yorkshire area.

At least one further significant mid-February fireball was seen
subsequent to those in ENB 215, on February 14-15 around
20:25 UT, as spotted from four locations in England south of North
Yorkshire. The initial sightings can be read at:
http://popastro.c.topica.com/maafXVMabwWrIcixLLVb/
on the SPA's Observing Forum. This meteor was probably over
the southern North Sea off the Belgian coast near Oostende for part
of its trajectory.

A new Special Report has been added to the meteor pages of the
SPA website, on the 2006 November 1-2 fireball (most recently
discussed in ENB 209). Although no clear trajectory could be
established for this event, we were fortunate in that artist Garry
Harwood spotted (and heard!) it from Hyde Park in London. He
made some annotated sketches immediately after the event, and
prepared an excellent painting of what he saw later. Garry has very
kindly made an electronic version of his artwork available to the
SPA, and this image can now be viewed online at:
http://popastro.c.topica.com/maafXVMabwWrJcixLLVb/

The SPA Forum has included a few other possibly fireball-associated
topics in the last month. For instance, February 1 brought a "fireball-
that-wasn't" imaging event for witnesses in Leeds. Long-time readers
of these ENBs may recall how the acceleration contrail from
Concorde catching the setting Sun perfectly was mistaken for
another such "fireball" from south Wales back on 2003 September
24 (last detailed in ENB 136). This time, it seems a bright, partial
sundog was the probable culprit, rather than a daylight fireball. See:
http://popastro.c.topica.com/maafXVMabwWrKcixLLVb/ for further details
and links to some of the
images. More recently, the breakup of a Russian Briz-M auxiliary
fuel tank in Earth orbit has been suggested as a potential future
meteor and fireball "reservoir", albeit not immediately. As regular
Forum contributor "Stella" put it, "The majority [of fragments] are
likely to remain in orbit for decades, or even a century or two, so
patience is required"! Further details are at:
http://popastro.c.topica.com/maafXVMabwWrLcixLLVb/

Fireball sightings (meteors of at least magnitude -3) made from the
British Isles and places adjacent are always welcomed by the Meteor
Section. Notes of what to report and where to can be found on the
Section's Fireball Observing webpage at:
http://popastro.c.topica.com/maafXVMabwWrMcixLLVb/ .


COMA BERENICID VIDEO OUTBURST
By Alastair McBeath, SPA Meteor Section Director

In mid-February news began coming through that a wholly
unexpected outburst had happened in late December from the
normally minor Coma Berenicid (COM) shower, which had been
recorded primarily by automated video meteor camera systems in
Spain. Analysing the data from such systems can be a slow business,
hence the delay in its being recognised and reported.

The COM have been listed among the showers SPA members are
encouraged to observe for more than a decade, but because they
are active from about December 12 to January 23, when the throes
of winter are upon us, and the shower at best was previously thought
to produce a Zenithal Hourly Rate (ZHR) of just 5, observations
of these meteors have tended to be restricted to periods close to
the Geminid and Quadrantid maxima. The most recent International
Meteor Organization examination of them, published last year, found
that the maximum, previously believed to fall around December 20,
seemed to be happening around December 30 instead.

However, the 2006 Spanish-detected outburst split the difference
between these two dates, as it took place on December 24-25
between approximately 01h-06h UT! Of course, this was at about
the worst possible time for visual observers to be likely to confirm it,
and so far, no such reports have come through from that night. The
leader of the Spanish observers, professional astronomer Josep
Trigo-Rodriguez of the Institute of Space Sciences in Barcelona,
indicated that the video records showed a peak between roughly
03:30-04:30 UT, and that the extrapolated visual-equivalent ZHR
estimated from the video results was perhaps of the order of
60 +/- 25.

Josep contacted the SPA to find out what the radio meteor results that
night had suggested. Thanks to invaluable help from Meteor Section
stalwart David Entwistle and Section correspondent Jeff Brower
(himself a highly experienced radio meteor observer active that night,
in British Columbia, Canada), drawing on the Radio Meteor
Observation Bulletin data for December (see:
http://popastro.c.topica.com/maafXVMabwWrNcixLLVb/
plus other results, we were able to quickly reach a surprisingly
negative
general conclusion, that very little evidence pointed to a strong
meteoric
event during the video event's timing. Just one of eight viable radio
datasets collected during the 01h-06h UT interval, where the COM
radiant was above the horizon, gave a clear signature indicative that
something unusual was potentially underway meteorically then (that
of Gaspard de Wilde's system in Belgium), but that one did give a
peak around 03h-04h UT on December 25. Investigations continue,
so if anyone has any still-unsubmitted meteor data from 2006
December 24-25, please contact the Section to report it as soon
as possible.


MSF ANTHORN
By Jon Harper, Occultations Director

The 60-KHz time transmissions from MSF Rugby will end on March 31.
However, the transmissions will continue from Anthorn near the Scottish
border (Lat N 54° 55'. W 3° 15'). At the moment test transmissions are
in progress from Anthorn, and the schedule involves the shutting down
of the MSF signal from Rugby for periods of time during the day. For
further information, and the testing schedule, go to the following
site: http://popastro.c.topica.com/maafXVMabwWrOcixLLVb/ For time
reporting
of occultation events, it will be necessary to list MSF Anthorn
instead of MSF Rugby as from 0h UT on April 1.


ACTION PLAN FOR KILLER ASTEROIDS
BBC News

The threat of an asteroid hitting the Earth is being taken more and
more seriously as more and more near-Earth objects (NEOs) are found.
At the moment, NASA tries to track all objects more than 700 m in
diameter and is monitoring 127 NEOs that have might have a possibility
of hitting the Earth. The US Congress has set a new goal, to track all
NEOs down to 70 m in diameter. A draft UN treaty to specify what
should be done if an asteroid were found to be on a collision course
with Earth is to be drawn up this year. The document would set out
global policies including who should be in charge of plans to deflect
any object. It is the brainchild of the Association of Space
Explorers, a professional body for astronauts and cosmonauts. The
association has asked a group of scientists, lawyers, diplomats and
insurance experts to draw up the recommendations. The group will have
its first meeting in Strasbourg in May this year. It is hoped that the
agreed document will be presented to the UN in 2009.


QUASAR SUPERCLUSTERS FOUND
Princeton University

Using a map of more than 4,000 very distant quasars, scientists of the
Sloan Digital Sky Survey (SDSS-II) have shown that the quasars are
strongly clumped. The strong clustering is thought to suggest that
the quasars lie within massive concentrations of dark matter.
Previous maps showed that more nearby quasars cluster like normal
galaxies, but the clustering in the new map is ten times stronger.


FASTEST SPINNING NEUTRON STAR
ESA

Astronomers using the Integral gamma-ray observatory think that they
have detected the fastest-spinning neutron star yet discovered,
rotating 1122 times every second. The star, known by its catalogue
designation XTE J1739-285, was discovered on 1999 October 19 by the
Rossi X-Ray Timing Explorer (RXTE) satellite, but later it seemed to
have faded out. In 2005 August, while Integral was monitoring the
relevant area of sky, XTE J1739-285 started to come back to life.
About a month later Integral discovered the first short bursts of
X-rays from the object. Together the two satellites recorded about
twenty bursts between September and November.

When a neutron star is in orbit with another star, its strong
gravitational field can pull in gas that is lost from the other star.
It coats the surface of the neutron star, and when the coating
reaches a depth of between 5 and 10 metres, the gas ignites in a
thermonuclear explosion. This massive release of energy generally
lasts from several seconds to several minutes and a burst of X-rays is
produced. Previous observations of other neutron stars have shown
that the X-rays emitted during bursts display oscillations that
correspond to the rotation rates of the stars. XTE J1739-285's
brightest burst, which RXTE recorded on November 4, exhibited
oscillations with a frequency of 1122 Hz, nearly twice the previous
fastest, 619 Hz.

Certain astronomers have estimated that the fastest a neutron star
could spin is 760 Hz, but if the new observations are confirmed, they
will presumably have to admit to error. But even neutron stars can't
spin as fast as they like. If one were to spin arbitrarily fast --
and their equatorial speeds can be a significant fraction of the speed
of light -- even the extreme gravity of the star would be unable to
hold matter to the surface and the star would break up. The exact
break-up speed depends on factors that are not yet known.


LIGHT FROM EXTRASOLAR PLANETS
NASA

The Spitzer space telescope has obtained enough vestiges of spectra
from planets outside our Solar System, known as exoplanets, to
identify signatures of molecules in their atmospheres. Spectra were
obtained of two gas-giant planets, HD 189733b in the constellation
Vulpecula and HD 209458b in Pegasus. The planets concerned are
periodically eclipsed by their stars, and their spectra were
represented by the small differences between spectra obtained during
eclipse and outside eclipse. The technique works only at infrared
wavelengths, where the planet is brighter than in visible light and is
less overwhelmed by the glare of its star.

The data indicate that the two planets are drier and cloudier than
predicted; theorists who thought that they would have lots of water
in their atmospheres were surprised when none was found around either
planet. In addition, HD 209458b showed hints of tiny sand grains,
called silicates, in its atmosphere. In previous observations of
HD 209458b, the Hubble telescope measured changes in the light from
the star, not the planet, as the planet passed in front. The spectra
showed absorption lines, of elements such as sodium, oxygen and
carbon, that were imposed upon the starlight as it passed through the
outer atmosphere of the planet on its way to us.


SATELLITES OF TRANS-NEPTUNIAN OBJECTS
IAU

Astronomers using the Hubble telescope have discovered satellites
orbiting four large trans-neptunian objects including (55637) 2002
UX_25, (90482) Orcus, 2003 AZ_84 and (50000) Quaoar.


POSSIBLE CRATER ON TITAN
New Scientist

The surface of Saturn's moon Titan is almost unblemished by impact
scars. So far, only three features have been unambiguously identified
as craters, while about a dozen others are considered to be
candidates. The dearth of craters is puzzling, since it had been
expected that meteoroid impacts would have created hundreds that
would still be visible today. Maybe slushy volcanoes, as well as
hydrocarbon rain and soot, are depositing new material on the moon's
surface, covering up existing craters. Now, radar images taken by the
Cassini spacecraft during a fly-by on January 13 show the northern
half of what might be a large crater. The semi-circular structure,
180 km across, has some crater-like features, such as a rim and a
possible peak in its centre. Smooth deposits may have covered the
inside of the crater, giving it a dark appearance in the radar images,
while the 'ejecta blanket' thrown up during the supposed impact may
explain the bright ring around the crater itself. However, other
aspects of it are enigmatic. Some dark features -- which may have
been created by a liquid -- near the northeast side of the rim appear
to be concentric with the rim. That is unusual, because if liquid
fills up inside a crater and breaches its rim, it usually creates a
radial, spoke-like feature. If it is not a crater, the suspiciously
circular feature could be a volcanic caldera, a depression created
when lava drains away and a volcano collapses. If it is a crater, the
degradation of its rim suggests that it might be old.


TITAN'S LARGEST LAKE RIVALS CASPIAN SEA
New Scientist

A very large lake may have been observed on Titan. If it is indeed
filled with liquid, the 1100-kilometre-long feature would be the
largest yet found on the moon. It appears as a dark area in an image
taken by the Cassini spacecraft of Titan's north polar region on
February 25. It has a surface area slightly smaller than the Caspian
Sea, which is the largest lake on Earth. At -180°C, Titan's surface
is far too cold for liquid water; instead, liquid methane, perhaps
with some liquid ethane mixed in, is thought to fill the moon's
apparent lakes.


SUPERNOVA SOURCE KEEPS BRIGHTENING
Science Daily

SN 1987A in the Large Magellanic Cloud is the nearest supernova
detected since the invention of the telescope. Almost 20 years after
the outburst, XMM-Newton observed the stellar remnant in X-rays on
January 17. Continuously brightening since its first detection in
X-rays by ROSAT in 1992, it now outshines all other X-ray sources in
its immediate neighbourhood and it is more than ten times brighter
than in the first observations of XMM-Newton in 2000. Observations
across the whole electromagnetic spectrum have revealed a detailed
picture of the circumstellar medium produced by the stellar wind from
the massive progenitor star during its supergiant phase before it
exploded. The X-rays we see mainly originate from the interaction of
the supernova shock with that circumstellar medium.


EUROPE APPROVES MERCURY MISSION
ESA

Although NASA has its Messenger spacecraft headed towards Mercury,
the European Space Agency is planning a mission of its own called
BepiColumbo. The agency recently announced that it has 'adopted' the
BepiColumbo mission. Developed in partnership with Japan, BepiColumbo
is scheduled to be launched in 2013 and to arrive 6 years later. The
mission is actually to consist of two spacecraft, one orbiter for
planetary studies and another for magnetospheric studies. The Mercury
Planetary Orbiter (MPO) will be developed by ESA, while the Mercury
Magnetospheric Orbiter (MMO) will be created by the Japan Aerospace
Exploration Agency (JAXA). A single vehicle will carry both to
Mercury.




Bulletin compiled by Clive Down

(c) 2007 the Society for Popular Astronomy


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