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The SOCIETY for POPULAR ASTRONOMY
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Electronic News Bulletin No. 254 2008 October 30
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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://www.popastro.com/



ORIONIDS - FIRST NEWS
By Alastair McBeath, SPA Meteor Section Director

As noted in ENB 253, the Orionid maximum was scheduled to happen
on Monday, October 20, and early indications are Orionid rates were
indeed above normal then, as hoped-for, and that they persisted for
more than one night, just as in 2006 and 2007. Details are still being
established, but preliminary reports on the International Meteor
Organization website (IMO; available via the homepage at
http://www.imo.net ) have so far suggested Zenithal Hourly Rates
(ZHRs) of 30-40 from October 20 to 22, perhaps peaking around 40
on October 21. Initial SPA results indicated ZHRs of ~40-60 on October
20-21 and ~50-70 on 21-22, but these were based on few reports, and
await confirmation. All values may have been affected by the bright
waning Moon. Some early comments indicated brighter Orionids, with
apparently very healthy fireball numbers (meteors of magnitude -3 and
brighter), were spotted by a few lucky observers on October 19-20.
Magnitude distributions for the shower on October 20-21 and 21-22 in
SPA data suggest these were fairly normal by then however, even so,
with the usual smattering of fireballs we would expect. Comments can
be found on the SPA's Observing Forum, at http://snipurl.com/4oyb1,
and also on the UK Weather World's Space Weather Forum, at
http://snipurl.com/4oybv, where there is a fine Orionid image from
October 21-22.


SEPTEMBER METEOR ROUND-UP
By Alastair McBeath & David Entwistle, SPA Meteor Section

The bright-meteor outburst over North America on September 9,
reported last time, was found remarkably weakly in the full set of
September's radio results (see Radio Meteor Observation Bulletin
182 at http://www.rmob.org ). Comparing those datasets which did and
did not show it may suggest that the outburst was due almost
exclusively to bright meteors alone, and that smaller particles producing
fainter meteors (which many radio meteor systems preferentially detect)
were notably absent. Observer-analyst Jeff Brower from Canada has
also asked us to correct his earlier note that his video system recorded
13 meteors of magnitude +1 and brighter between 04:12-12:26 UT on
September 9, to 13 meteors of magnitude -1 and brighter, making the
event still more remarkable!

Nothing further has been established for the widely-seen September
22-23 fireball that may have come down partly over the Borders of
Scotland regrettably, but hard on its heels came another event
observed from multiple sites on September 25-26 around 20:55 UT.
This was due to the re-entry of part of a Russian Proton rocket launched
from Baikonur about twelve hours earlier on September 25. It was
reported to us from six sites in south Wales, southern England, the
Channel Islands and France, and was also imaged from southern
England - see http://snipurl.com/4p014 , on the SPA's Observing
Forum. It was seen from around ten other places in France (thanks to
French meteor expert Karl Antier for this news). Four radio meteor
observers, two each in England and France, recorded a strong signal
probably due to it too. As with most re-entries, the event was unusually
slow-moving for a meteor and long-lasting (in some cases for more
than 30 seconds), and its long path carried it below the horizon for
several witnesses in the British Isles. It peaked around magnitude -6,
and some of the French sightings reported late-stage fragmentation
too. The predicted ground track for the event (which helps explain the
observers' locations) can be found at: http://snipurl.com/4p030 .


EARLY OCTOBER METEOR ROUND-UP
By Alastair McBeath & David Entwistle, SPA Meteor Section

Continuing almost without pause from late September, the first ten days
of October brought a fresh raft of items of meteoric interest. Among
other fireballs (see the Recent Fireball Sightings webpage at
http://snipurl.com/4p03x for the list of those reported to the SPA), there
was a clutch of probably four bright to brilliant ones on October 5-6,
each seen so far from just one place, around 18:28, 19:30, 20:08 and
03:10 UT. This date called to mind the bright-meteor events detected
by European video observers on October 5-6 in both 2005 and 2006
(on which see most recently the report in ENB 206, at
http://snipurl.com/4p0dw ). Whether the 2008 fireballs may have related
to another return is uncertain. Only the 20:08 UT fireball was reported
fully enough to suggest a possible radiant, which perhaps lay
somewhere between Alpha Cephei and Alpha Cygni, on the opposite
side of the pole to that near Draco's tail-tip implicated in the 2005 &
2006 events. Assuming any 2008 recurrence might have repeated
within a similar interval to those two previous returns, it should have
happened on October 5 around 13h-16h UT.

October 7 brought a world's first event - the predicted atmospheric entry
of an asteroid! Asteroid 2008 TC3 was discovered on October 6 during
routine searching as part of NASA's Catalina Sky Survey for near-Earth
objects, by the Mount Lemmon telescope in Arizona, USA. It was
realised it would hit the Earth, but was small enough to ablate in the
atmosphere and not strike the surface. It arrived close to its expected
place and timing at around 02:46 UT on October 7 over Sudan in
eastern Africa. The brilliant impact flash was claimed as spotted by
the crew of a KLM airliner, and it was imaged by the Meteosat-8
Earth-observing satellite too. Comments and links to various
webpages with further information (including the Meteosat impact
image) can be found via the SPA's General Chat Forum at
http://snipurl.com/4p0mc and http://snipurl.com/4p0mm , plus the UK
Weather World's Space Weather Forum at http://snipurl.com/4p0nq .

The Draconids seem to have produced nothing unexpected around
October 8-10, based on visual results in to the SPA from Martin
McKenna (Co. Derry), "JohnF" (London) and Assistant Director David
Entwistle (Lancashire), plus video results from Enrico Stomeo in Italy.
A few "possibles" were claimed, but at negligible levels.

However, October 8-9 was notable for two further fireballs, one of
magnitude -3/-8 at ~20:52 UT seen from Surrey and Worcestershire
(see http://snipurl.com/4oyl4 on the SPA Observing Forum), the other
of magnitude -6/-8 at 03:08 UT reported from four locations so far, in
Lancashire, West Sussex, Belgium and Holland, from which latter it
was imaged by Klaas Jobse's all-sky fireball patrol camera, as part of
his routine monitoring for the European Fireball Network. A strong
echo-signal in-time to this second meteor was also recorded by ten
radio observers in Belgium, England and France. The earlier fireball
may have flown on a roughly northerly to southerly track above eastern
England, perhaps over Cambridgeshire to Kent, while the 03:08 one
may have passed approximately southeast to northwest from
somewhere high above or near Rouen in northern France, to end over
the Channel some way WNW of Dieppe. Its image can be found on
Klaas' website, at http://snipurl.com/4sau0 .

As always, fresh meteor reports, including fireball sightings made from
within or near the British Isles, are welcomed by the Section. Details to
report can be found on the website, via the meteor homepage at:
http://snipurl.com/4p052 .


MAIN METEOR PROSPECTS FOR NOVEMBER
By Alastair McBeath, SPA Meteor Section Director

The long-lasting pair of minor Taurid showers continue until November
25, reaching maxima around November 5 (Southern Taurids - waxing
crescent Moon) and 12 (Northern Taurids - full Moon), though the
combined effect of both showers is to produce an almost plateau-like
peak between these dates, with combined ZHRs of ~8-10 or so. Lower
rates of these slow, often bright, meteors may be hunted for at other
times during the month when there is no Moon, but as mentioned last
time, 2008 sees the latest prediction for a 'swarm' return by David
Asher of Armagh Observatory. This gives the possibility of unusual
activity from the showers, perhaps from late October through till maybe
mid November, or just at some stage in the first half of November.
Previous 'swarm' returns in 1995, 1998 and 2005 have sometimes
produced persistent ZHRs of ~10-15 through till November 10 (as in
2005) or increased numbers of fireballs (as in 1995 and especially
2005). Even the brightening Moon towards mid month may not spoil
too much of the show if another relatively fireball-rich return happens,
but don't expect too much. For example, the 1998 return produced
ZHRs of ~8-10 only between October 27-31, and without more fireballs
than normal, so only an examination of carefully-made observations
later revealed what had really occurred.

Although the run of strong to storm Leonid returns seen from 1998-2002
is unlikely to repeat again until the 2030s (or perhaps even till next
century), independent model calculations by Russian Mikhail Maslov
and Frenchman Jeremie Vaubaillon have indicated 2008 may bring
good to strong activity. Various possible maxima and strengths have
been proposed. On November 17, UT timings include around 00:22
(Maslov; ZHRs ~130?; brighter-than-average meteors?), 01:32
(Vaubaillon; dust trail left by the shower's parent comet 55P/Tempel-
Tuttle at its 1466 return; ZHRs very uncertain, maybe ~50, perhaps
between ~25-100?) and 09h ('traditional' peak time based on when
the Earth passes nearest the node of the comet's orbit; ZHRs ~15-20?).
On November 18, Jeremie Vaubaillon has suggested we may
encounter the Leonids' 1932 dust trail at about 21:38 UT, perhaps
with ZHRs of ~20. None of these predictions is guaranteed, of course,
nor can other unexpected peaks be ruled-out! The waning gibbous
Moon around Gemini-Cancer on November 17 & 18, is about as
badly-placed as possible for observers, especially because the
shower's radiant rises only by ~23h UT, and reaches a fully usable
elevation after midnight from Britain. Observers trying to catch whatever
the Leonids produce this time will simply have to brave the Moon and
hope for the best, primarily on November 16-17 if you are watching
from the British Isles. Cover as much clear sky as you can comfortably
see, but face away from the Moon, or block it behind some obstruction
like a rooftop or wall. The shower is active from November 10-23,
though the lower rates likely away from the peak night(s) may well
pass unnoticed in the moonlight. Expect very swift, often trained, meteors.

For more on November's likely meteor activity, plus radiant charts for
the Taurids and Leonids, see the monthly meteor page on the SPA
website, at: http://snipurl.com/4oymf . Good luck, and clear skies!


COMET NEWS
By Jonathan Shanklin SPA Comet Section Director

Comet 2008 A1 (McNaught) is slowly moving into UK skies. Although
8th magnitude it is low down in the evening sky, and a difficult target for
large binoculars. Over the coming weeks it will slowly fade, and only
becomes slightly better placed for viewing.

Although fainter, comet 2006 W3 (Christensen) is better placed for
viewing, lying high in the northern sky. Currently 10th magnitude and
still 4 AU from the Sun, it will continue brightening and may reach 7th
magnitude when it reaches perihelion at 3.1 AU in 2009 July.

85P/Boethin, for which an ephemeris appears in Popular Astronomy,
has still not been recovered at this apparition. It seems quite likely
that it was discovered when in outburst, and has possibly disintegrated.
However as we saw with 17P/Holmes, comets can do surprising things,
so it is worth keeping an eye out for developments.

Finder charts can be found at: http://snipurl.com/4oy8k


NO ICE ON MOON AFTER ALL?
New Scientist

A decade ago, the Lunar Prospector spacecraft suggested that the
Moon's poles have large concentrations of hydrogen near the surface,
which could be in the form of frozen water deposited by comets. That
would be very useful for a possible future base on the Moon, providing
water for astronauts and hydrogen fuel for their vehicles. The
Shackleton Crater at the south pole has been a prominent candidate for
a future base station, since it contains a ledge on its rim that would
be a good landing spot. If the crater were also to hold frozen water,
it would be an excellent location. But that possibility seemed to
evaporate when radar signals formerly attributed to water-ice were
also found to reflect off sunlit areas where ice could not survive.
So it had been hoped that the Japanese spacecraft Kaguya, which was
launched in 2007 September, could shed light on the question by
observations from lunar orbit.

The spacecraft contains a camera that can obtain images of the Moon's
surface even in the near-total darkness of its south pole. The inside
of the crater receives no direct sunlight, but for a short period
during summer time in the Moon's southern hemisphere (November and
December in the Earth's calendar), a small part of its rim catches
some sunlight, which is then scattered to the crater floor. Japanese
scientists analysed pictures of the crater taken at such a time. The
images resolve objects as small as 10 metres across. They provided a
full profile of the crater, including details of tiny craters on its
floor and two landslides from the inner wall. The most striking
feature was what was missing. If there had been ice, there would have
been brighter reflections from its surface, but none was visible.
Instead, the images showed just dull lunar soil. That does not
completely rule out the possibility of frozen water within the crater
-- it could be buried, or the ice crystals could be dirty and mixed
with particles of soil. But there may be no water at all, and the
hydrogen could be combined in another compound like methane. Ice
particles trapped within the lunar soil could still be useful for a
human base station, but that would depend on the difficulty of mining
the mixture and extracting the water.


PHOBOS PROBABLY MADE OF RUBBLE
ESA

Mars has two small moons. The larger one, Phobos, is an irregular
lump of rock measuring 27 by 22 by 19 kilometres. It has been
observed in a series of close encounters by the Mars Express
spacecraft, and is now considered almost certain to be a rubble pile
rather than a single solid object. The pictures taken by the
spacecraft enable an accurate 3-dimensional model of Phobos to be
made, so that its volume can be determined with some precision.
During one of the nearest encounters, the spacecraft's radio signals
were monitored from the Earth to record the changes in frequency
brought about by Phobos' gravitational acceleration of Mars Express,
to enable the calculation of the precise mass of the moon. When the
team has finished doing the sums putting the mass and volume data
together, it will know the density, which will be an important clue
as to how the moon was formed. Previously, radio tracking from the
Soviet Phobos 88 mission and from other spacecraft orbiting Mars had
provided the most accurate mass. The team's current mass estimate
for Phobos is about one-billionth the mass of the Earth. Preliminary
density calculations suggest that it is 1.85 grams per cubic
centimetre, which is very similar to that of some asteroids.
Asteroids that share Phobos' density are known as D-class. They are
believed to be highly fractured bodies containing caverns and voids
because they are not solid but are just collections of pieces weakly
held together by gravity, 'rubble piles'. Spectroscopic data from
Mars Express and previous spacecraft show that Phobos has a
composition similar to that of such asteroids. That suggests that
Phobos, and probably Deimos too, are captured asteroids. However,
one circumstance remains difficult to explain in that picture:
usually, asteroids are captured into just random orbits around the
planet concerned, but Phobos orbits above Mars' equator -- a very
specific case.


OUTER SOLAR SYSTEM NOT SO CROWDED
Harvard-Smithsonian Center for Astrophysics

The Taiwanese-American Occultation Survey (TAOS) spent two years
periodically photographing portions of the sky to look for small
bodies orbiting beyond Neptune, in a region of the Solar System called
the Kuiper Belt. The survey looked for Kuiper Belt objects (KBOs)
with sizes between 3 and 28 kilometres. Since such objects are too
small to see directly, the survey watched for stars to dim as KBOs
passed in front of and occulted them. After accumulating more than
200 hours of data (only 100 hours' work a year, a duty cycle of little
over 1%) watching for stellar flickers lasting a second or less, TAOS
had not observed any occultations.

The Kuiper Belt contains objects in a range of sizes -- a few large
ones (the 'dwarf planets' Pluto, Eris, Makemake and Haumea) and many
more smaller ones. The commonness of a given size might offer a clue
as to the history of planet formation and dynamics. In particular,
the size distribution of KBOs may reflect a history of agglomeration,
in which colliding objects tended to stick together, followed by
destructive collisions, where collisional velocities were high enough
to shatter the rocks involved. Astronomers wondered whether they
would find more and more objects at smaller and smaller sizes, or
whether the distribution levelled out. Unless there has been some
miscalculation over the sensitivity of the TAOS observational
procedures, the fact that no occultations were seen sets an upper
limit to the number density of KBOs in the relevant size range.
The outer Solar System now appears not to be as crowded as some
theories suggest, perhaps because small KBOs have already stuck
together to form larger bodies or frequent collisions have ground them
down into even smaller bits below the threshold of the survey.


PLANETS IN COLLISION?
UCLA

Astronomers have been studying a star known as BD +20 307, which is in
the constellation Aries and is surrounded by about a million times
more dust than exists around our Sun. They expected BD +20 307 to
prove to be a young star, with the massive dust ring signalling the
final stages in the formation of a planetary system. A major revision
of ideas was called for last May, when Carnegie astronomers showed
that BD +20 307 is actually a close binary system, composed of two
stars, both very similar in mass, temperature and size to our own Sun,
orbiting about their common centre of mass every 3.42 days. The
patterns of element abundances in the stars indicate that they are
several billion years old, like our Solar System. The origin
suggested for the extraordinary quantity of dust, orbiting the binary
pair at about the same distance as Earth and Venus are from our Sun,
is a collision between two terrestrial planets. That would have had
to have happened quite recently by astronomical standards, no more
than a few hundred thousand years ago, because at such distances from
a star small dust particles get pushed away by stellar radiation while
larger pieces get reduced to dust in collisions within the disc and
are then pushed away. A serious objection to the idea of a major
collision is, however, that it seems most unlikely that bodies that
have orbited stably for billions of years would suddenly decide to
collide vigorously just now, but no more plausible idea has been put
forward so far.


MASSIVE DOUBLE STAR SYSTEM
ESO

A new image of the star-forming region Gum 29 shows that a small
cluster of stars, only 1 to 2 million years old, called Westerlund 2
includes one of the most massive double-star systems known. Gum 29
is a region of hydrogen gas that has been stripped of its electrons
(ionised) by the intense radiation of the hot young stars at its
centre. Astronomers call that an HII {'aitch-two') region, and this
particularly fine example is over 200 light-years across. The latest
measurements indicate its distance as about 26,000 light-years,
placing it towards the outside edge of the Carina spiral arm of the
Milky Way.

Previous observations have shown that a pair stars on the south-
preceding side of the cluster are particularly massive. They have
masses of 82 and 83 times that of our Sun and orbit one another in
approximately 3.7 days. They are both Wolf-Rayet stars -- massive
stars nearing the end of their lives, expelling vast quantities of
material as their swansong. X-ray observations show that streams
of material from each star continually collide, creating a blaze of
X-ray radiation.


FIRST GAMMA-RAY-ONLY PULSAR
NASA

A pulsar is a rapidly spinning neutron star, the crushed core left
behind when a massive star explodes. Astronomers have catalogued
nearly 1800 of them. Although most of them have been found through
their pulses at radio wavelengths, some also beam energy in other
forms, including visible light and X-rays. Now the orbiting Fermi
gamma-ray telescope has discovered a pulsar that seems to pulse only
in gamma-rays. The object lies within a supernova remnant known as
CTA 1, about 4600 light-years away in the constellation Cepheus. It
emits 1000 times the energy of our Sun. and its lighthouse-like beam
sweeps across the Earth every 316.86 milliseconds. Fermi scans the
entire sky every three hours and detects photons with energies ranging
from 20 million to more than 300 billion times the energy of visible
light. The instrument sees only about one gamma-ray per minute from
CTA 1, but that is enough for scientists to piece together the neutron
star's pulsing behaviour, its rotation period, and the rate at which
it is slowing down.

A pulsar's beams arise because neutron stars possess intense magnetic
fields and rotate rapidly. Charged particles stream outwards from the
star's magnetic poles at nearly the speed of light to create the
gamma-ray beams Fermi sees. Because the beams are powered by energy
drawn from the neutron star's rotation, the pulsation period gradually
increases as the neutron star spins down. In the case of CTA 1, the
rotation period is increasing by about 12 microseconds a year.



The SPA Electronic News Bulletins are sponsored by the Open University.

Bulletin compiled by Clive Down


(c) 2008 the Society for Popular Astronomy


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