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PostPosted: Sun Jan 18, 2009 10:22 pm 

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Electronic News Bulletin No. 259 2009 January 18

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
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By Alastair McBeath, SPA Meteor Section Director

After a fairly quiet December for fireball sightings, other than near
the Geminid and Ursid maxima, IYA2009 has opened with a clutch of
non-Quadrantid fireballs for the UK. Most were reported from single
locations only (see the SPA's "Recent Fireball Sightings" webpage at for details). However, one on January 9-10
was more widely-seen, from at least seven places in western England
and south Wales (Lancashire to Gwent). It happened within eight
minutes of 18:47 UT, and was around magnitude -5 to -8, according to
the more detailed observations. Its possible atmospheric trajectory
has not been firmly-established, but a best estimate from the reports
suggests it may have been moving roughly NE to SW, starting somewhere
high above northwest or central-western Wales, heading out over
Cardigan Bay towards St George's Channel. More accurate positional
data on where the fireball started and ended in the sky from
different locations would be needed to improve this. Most witnesses
described the meteor as slow-moving, and it was visible for probably
3 to 4 seconds or more. Colours reported have included blue, red,
orange and yellow, plus green perhaps in the object's tail. Some of
the sighting reports can be found on the Observing Forum, at, and among the postings on the UK Weather
World's Space Weather Quadrantids topic, at .

Regular ENB readers may recall there was also a bright, UK-seen
fireball on January 9-10 in 2008, around 18:55-19:00 UT (see ENB 236,
archived at ). This seems to be nothing more
than a curious coincidence though, and there is no evidence to link
the two objects beyond their rough timings.

Anyone else who spotted
the 2009 January 9 fireball, or any others - meteors of magnitude -3
or brighter - from the British Isles and nearby is welcome to send a
full report to the Meteor Section as soon as possible. The minimum
details I need from you are:

1) Exactly where you were (name of the
nearest town or large village and county if in Britain, or your
geographic latitude and longitude if elsewhere in the world);

2) The
date and timing of the event; and

3) Where the fireball started and
ended in the sky, as accurately as possible, or where the first and
last points you could see of the trail were if you didn't see the
whole flight.

More advice and a fuller set of items to send are
outlined on the "Fireball Observing" page of the SPA website, at:


By Alastair McBeath, SPA Meteor Section Director

A strong, unusually protracted, Quadrantid maximum seems to have
happened on January 3, judging by the initial "live" International
Meteor Organization's (IMO's) findings, available via the homepage. Visual Zenithal Hourly Rates (ZHRs) were
around 40-60 for much of the European night of January 2-3, but
started rising quickly after 03h UT or so, to be over 100 before
05h. By 09h UT over North America, ZHRs had already crested the usual
peak level of ~120, reaching ~130-150 for a time. Rates then
continued at or above 120 till about 13:30, possibly with two main
peak phases when ZHRs topped-out around 160, centred on ~10:30, and
again for more than half an hour to either side of 13:00. Even by
nightfall over Europe on January 3-4, ZHRs were still just above 100
(albeit the ZHRs were calculated from results collected elsewhere,
because of the very low radiant elevation then from Europe), but
dropped rapidly afterwards, to be back below 30 before 01h UT that
night. The Quadrantid peak was due around 13h UT on January 3 (see
ENB 257, at ), so a lot of this excellent
activity happened before that was due, as well as almost exactly
when it was.

Sadly, and rounding-off a remarkably poor spell for UK
weather throughout the autumn and early winter, very few people in
Britain saw much of the Quadrantids at all, as the comments on the
Quadrantids topics on the SPA's Observing Forum (at ) and on the UK Weather Watch's Space
Weather Forum (address above) helped indicate. Quadrantid data of
some sort, including casual visual watch comments from these two
Forums, has so far reached the SPA from: "@@" (West Midlands), Jeff
Brower (British Columbia, Canada; radio & video), Assistant Meteor
Director David Entwistle (Lancashire; radio), Rob Hale (Cheshire),
Pete Lawrence (West Sussex; imaging - see the SPA Quadrantids topic
for links to Pete's images), "markt" (West Midlands), Dave Mitsky
(eastern USA), Dave Scanlan (Hampshire), Enrico Stomeo (near Venice,
Italy; video), and Rich Taibi (Maryland, USA). Jeff's and David's
radio data featured on the SPA Forum too, while Jeff alerted me to a
new webpage reporting analyzed radio results in graphical form
collected from Japan, with short English notes, at . Rather like the IMO's "live" visual
results, this page needs to be treated with caution, as it is a
preliminary set of findings, but it does give some interesting ideas
to what may have happened. Jeff's and David's analyzed results were
also shown there, albeit uncredited (as the "Canada" and "England"
graphs respectively).

Enrico's video results, plus the limited UK visual comments and
Pete's imaging, all confirmed sharply-rising activity towards the
end of the night on January 2-3. Dave Mitsky's and Rich Taibi's
visual reports from the eastern USA showed the early part of the
good to excellent activity the IMO visual data found, while
suggesting Quadrantid magnitudes were fairly ordinary to
possibly somewhat fainter than usual. This could have affected the
ZHRs, if borne-out by reports from elsewhere, since if many faint
meteors were present, the computed ZHRs may have underestimated the
true activity. The radio results suggested good shower echo-counts
persisted virtually throughout January 3, at best from roughly midday
to 18h UT, though the highest radio rates may have peaked a couple of
hours after the visual ones (the Japanese webpage has an interesting
graph which shows this quite well). The radio details will need
confirming once more data is in, however.

One other facet of the
radio reports, again still unconfirmed, was that Jeff's data and the
Japanese observations seemed to show a minor peak around 18h UT on
January 3. The IMO's visual data is rather limited over this time
unfortunately, and though it has been suggesting a possible short-
lived resurgence in activity, perhaps to ZHRs of ~80-90 around 19:30
on January 3, it is not clear yet whether either of these late
"peaks" resulted from a genuine activity increase, or if they were
simply artefacts of the analyses.

Many thanks to all the contributors
listed above. All further Quadrantid observations gratefully received!


By Alastair McBeath, SPA Meteor Section Director

The recent publication of Radio Meteor Observation Bulletin 185 for
last December (see for the data, the observers,
to whom go fulsome thanks, and their equipment), has allowed a more
detailed appraisal of radio meteor activity during the Ursid and
Geminid showers, to what was discussed in the previous ENB. Fresh
findings from the SPA analyses across both shower peak dates follow.

During the Ursids, there was an indication of a possible minor radio
maximum around 13h-14h UT on December 21, and another at 20h-21h,
roughly coincident with the small Ursid peak found in one video
dataset as reported last time (this has now been shown by a second
detailed video report thanks to Roberto Haver in Italy too).
However, the main active phase in the radio data lasted from about
00h-10h UT on December 22, especially consistently from roughly
midnight to ~05h. Within that interval, the stronger and better-
recorded maxima were between 01h-03h (especially between 01h-02h),
07h-08h, and 09h-10h UT. Activity seemed to be lowest overall during
this time around 06h-07h and 08h-09h UT. There was no evidence to
support the minor peak near 23h UT on December 21, suggested from the
initial video results, but Ursid activity was apparently creating
somewhat increased echo-counts from 20h-24h UT on the 21st even so.
There was a possible further slight radio peak around 15h UT on
December 22, though not later, so no confirmation was practical of
the minor radio maximum from ~18h-20h UT then which Jeff Brower found
in his initial radio report. In general, these results supported
those given in ENB 258, especially for the main maximum period early
on December 22, but the strength of the ~09h-10h UT radio maximum was
unexpected, as there was no corroborating visual evidence from North
America then. In the radio data, this peak seemed similar in strength
to the 02h-03h UT activity. Although radio and visual activity cannot
be directly compared, it is interesting the 02h-03h UT interval
brought visual ZHRs of ~20 +/- 5, and the radio evidence implied the
~09h peak was at least as rich in brighter meteors as either the
~01h or ~07h maxima. Only more data will allow further investigation.

The radio Geminid maximum has proven more difficult to define than
expected, as suggested last time. Just why this was so is uncertain.
With very strong meteor showers, there is sometimes an effect caused
by meteors occurring close together in time, so automated radio
receivers become saturated with echo counts blurring into one another.
This can artificially reduce the total number of echoes recorded
below even normal levels. While this may have contributed to the
difficulties this time, it seems unlikely to have accounted for all
the analysis problems. Overall, most of the operational radio systems
favoured a maximum between 22h UT on December 13 and 05h UT on the
14th, but after allowing for the more favourable radio-observing
circumstances, no better-defined peak than this could be established,
so no confirmation of the very strong visual rates reported
especially between 03h-04h UT on December 14 has been possible this
way. One particularly curious addition is that a significant number
of radio results suggested a weaker peak may have fallen between
roughly 22h-02h UT, perhaps persisting till ~06h-07h, on December
12-13. Some datasets even showed better activity during this interval
than on December 13-14! Last century, it was established that some
mass-sorting of meteoroids had occurred in the Geminid stream, and
that telescopically-faint Geminids, similar to what some radio meteor
systems detect preferentially, seemed to reach maximum approximately
one day ahead of the visual peak. It may be this is what the radio
results picked up in 2008.


Observations made by instruments on a US air-force satellite have
shown that the boundary between the Earth's upper atmosphere and space
has moved to extraordinarily low altitudes. The satellite was
designed to study disturbances in the Earth's ionosphere, which is a
gaseous envelope of electrically charged particles that surrounds the
Earth and is important because radar, radio waves, and signals for
global positioning systems can be disrupted by ionospheric
disturbances. The satellite's first discovery was, however, that
the ionosphere was not where it had been expected to be. The
transition between the ionosphere and space was found to be at about
260 miles altitude during the night-time, rising to about 500 miles
during the day. Those altitudes were unusually low compared with the
more typical values of 400 miles at night and 400 miles by day.

New Scientist

It has been proposed that multiple comet impacts around 1500 years ago
may have triggered a 'dry fog' that plunged half the world into famine.
Historical records tell us that from the beginning of 536 March a fog
of dust blanketed the atmosphere for 18 months. During that time, the
Sun (it was said) gave no more light than the Moon, global
temperatures plummeted and crops failed. The cause has been unknown,
but theories have included a great volcanic eruption or an impact from
space. Now scientists have found the first, indirect, evidence that
multiple impacts caused the haze. They found tiny balls of condensed
rock vapour or 'spherules' in debris inside Greenland ice cores dating
back to early 536 AD. Though the spherules' chemistry suggests that
they did not belong to an impactor, they do point to terrestrial
debris ejected into the atmosphere by an impact event. That
represents the first actual geological evidence for an impact in 536.

The fallout material was laid down over several years, and some layers
were particularly densely deposited. That suggests that more than one
impactor was involved -- probably comets, which do tend to fragment.
Two possible submarine craters whose age ranges fit the global dimming
event have been identified -- one is in the Gulf of Carpentaria in
Australia, and the other in the North Sea near Norway. Marine
micro-fossils found with the impact spherules are consistent with an
ocean impact.

Carnegie Institution

It has sometimes been assumed that the small size of asteroids limited
the types of rock that could form in their crusts, but researchers
report that two newly discovered meteorites are ancient asteroid
fragments consisting of feldspar-rich rock called andesite, previously
known only from the Earth. The two light-coloured meteorites were
discovered in a region of the Antarctic ice known as the Graves
Nunatak ice-field. The unusual thing about them is that they have
compositions similar to the Earth's continental crust. Andesite is an
igneous rock common on Earth in areas where colliding tectonic plates
generate volcanoes, such as those of the Andes. The meteorites
contain minerals thought to require large-scale processes such as
plate tectonics to concentrate the right chemical ingredients. In
view of that, some researchers suggested that the meteorites are
fragments of a planet or the Moon, not an asteroid, but analysis of
the meteorites' oxygen isotopes ruled out that possibility, and it
now seems likely that the formation of andesite crust can occur by
processes other than plate tectonics.

Several Solar-System objects, including parent bodies of meteorites,
planets, moons, and asteroids, have characteristic oxygen-isotope
signatures, and just by analyzing the isotopic ratios we can tell
if a meteorite came from Mars, from the Moon, or from a particular
asteroid. One extensively studied parent is the asteroid 4 Vesta.
In the majority of cases the actual location of the parent body is
unknown but, even so, a particular group of meteorites may still be
assigned to the same parent body on the basis of the isotopic ratios.
The ratios in the newly found meteorites are nearly coincident with
those of meteorites from 4 Vesta.

The meteorites' age, more than 4.5 billion years, suggests that they
formed very soon after the birth of the Solar System, making it
unlikely that they came from the crust of a differentiated planet.
The chemical signature of some rare metals, notably osmium, in the
meteorites also points to their origin on an asteroid that was not
fully differentiated. The researchers hypothesize that that the
asteroid had a diameter somewhat larger than 100 kilometres, which
would be sufficient to hold enough heat for the asteroid's rocks to be
partially, but not completely, melted. The asteroid would remain
undifferentiated, but the melted portions could erupt onto the
asteroid's surface to form the andesitic crust.

Harvard-Smithsonian Center for Astrophysics

Jupiter must have gained mass very quickly when it was forming, since
the rest of the material from which it formed probably dispersed in
just a few million years, according to a new study of planet formation
around young stars. Astronomers examined the 5-million-year-old star
cluster NGC 2362 with the Spitzer space telescope, which can detect
the signatures of actively forming planets in infrared light. They
found that all stars with the mass of the Sun or greater have lost
their protoplanetary (planet-forming) discs. Only a few stars less
massive than the Sun still retain their discs. Such discs provide the
raw material for forming gas giants like Jupiter. Therefore, if gas
giants do not form in less than 5 million years they probably won't
form at all. Even though nearly all the discs that could form
gas-giant planets in NGC 2362 have disappeared, several stars in the
cluster have 'debris discs', which indicates that smaller rocky or icy
bodies may still be forming.

Space Telescope Science Institute

The Hubble telescope has been surveying the complete sample of stars
known to be nearer than 10 parsecs (32.6 light-years). Part of the
intention is to discover and characterize 'missing' members of the
sample. The sample includes 239 known red dwarf stars (normal stars
that are about half the diameter and a fifth ofthe mass of the Sun and
with much lower surface temperatures), and there are 12 known brown
dwarfs. Only two brown dwarfs were found as companions to normal
stars. Since brown-dwarf binaries do exist, the fact that there are
very few binaries whose components lie on opposite sides of the
hydrogen-burning limit -- the division between normal stars and brown
dwarfs -- must be seen as significant, although what the significance
actually is remains unknown.


Observations made with the Spitzer telescope are interpreted as
indicating the existence of the remains of shredded asteroids around
six dead white-dwarf stars. Spitzer's infrared spectrograph observed
dusty discs around eight white dwarfs and found that the dust contains
a glassy silicate mineral similar to olivine and commonly found on
Earth. The Spitzer data also suggest that there is no carbon in the
rocky debris. The gravitational tides that could be raised by a white
dwarf in a rocky body that got too close would be enough to tear that
body apart. It is being proposed the asteroid-like bodies have met
such a fate within the last million years in the cases of the white
dwarfs recently investigated by Spitzer. The amount of material is
such that in one case it might have constituted an asteroid 200 km in
diameter. So far, the results suggest that the same materials that
make up the Earth and our Solar System's other rocky bodies could be
common in the Universe.

Iowa State University

As the Sun and other stars revolve around the centre of the Milky Way,
we cannot see the spiral arms directly, but have to rely on indirect
evidence to find them. In visible light, the Milky Way appears as an
irregular, densely populated strip of stars. Dark clouds of dust
obscure the Galaxy's central region, so it cannot be observed in
visible light; if it were not for the obscuring clouds its brightness
would be comparable with that of the Moon and be a great hindrance to
astronomers. Infrared light, however, can penetrate the dust clouds,
so astrophysicists have used satellite-infrared data to model the
distribution of molecular gas in the Galaxy and thereby to map the
Galaxy's spiral arms.

The stars in the Milky Way are thought to be distributed as a disc
with a central bulge dominated by a bar-shaped arrangement of stars.
Outside the central area, stars are located along spiral arms. In
addition to the two main spiral arms in the inner Galaxy, there are
thought to be two weaker arms which end about 10,000 light-years from
the Galaxy's centre. (The Sun is about 25,000 light-years from the
Galactic centre.) One of the weaker arms has been known for a long
time, but there has been concern over its large deviation from
circular motion, which is now attributed to gravitational effects of
the newly identified central bar. The other weak arm, on the far side
of the Galaxy, was recently found in gas data. The discovery of that
second arm was something of a relief, affirming that the inner Galaxy
is indeed quite symmetrical in structure as had been supposed.


In some regions of prolific star-formation in the Galaxy there are
cosmic masers, areas where gas molecules are strengthening naturally-
occurring radio emission in the same way as lasers strengthen light
beams. By repeatedly measuring maser positions very accurately by
radio interferometery using intercontinental baselines, at times when
the Earth is at opposite sides of its orbit around the Sun, radio
astronomers can measure parallaxes (and thereby distances) for objects
at great distances in the Galaxy. Some of such direct distance
measurements differ from earlier, indirect measurements, sometimes by
as much as a factor of two. The star-forming regions harbouring the
cosmic masers define the spiral arms of the Galaxy, so the
measurements are helping to improve our understanding of the structure
and motions of the Galaxy. They also indicate that the Milky Way is
rotating somewhat faster than had been thought previously, such that
the circular velocity in the vicinity of the Sun is more like 260 km/s
rather than the 200 km/s that has long been accepted. The increase
implies that our Galaxy is correspondingly more massive, so it is now
seen as being on a par with the Andromeda Nebula.


Spirit and Opportunity approach the fifth anniversaries of their
landings on Mars. No one expected, when they landed early in 2004,
with a three-month nominal service life, that they would still both be
operating in 2009, The rovers have made important discoveries about wet
and violent environments on ancient Mars and have returned a quarter of
a million images, driven more than 21 kilometres, climbed a mountain,
descended into craters, struggled with sand traps and ageing hardware,
survived dust storms, and relayed a great deal of data via the Mars
Odyssey orbiter.

Web User

The Large Hadron Collider, the world's biggest particle accelerator,
may be started again by the summer. Soon after it was switched on in
September last year, it suffered a catastrophic malfunction whereby
super-cold helium leaked into the system. Many of the magnets used to
accelerate the particles needed to be repaired as a result, at a cost
of around £20m.

Bulletin compiled by Clive Down

(c) 2009 the Society for Popular Astronomy

The Society for Popular Astronomy has been helping beginners to
amateur astronomy -- and more experienced observers -- for more than
50 years. If you are not a member then you may be missing something.
Membership rates are extremely reasonable, starting at just £16 a year
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My astro blogs.. | Practical Astronomy magazine

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