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The SOCIETY for POPULAR ASTRONOMY
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Electronic News Bulletin No. 278 2009 December 20
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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/ GEMINIDS 2009 - FIRST NEWS
By Alastair McBeath, SPA Meteor Section Director
Early details reaching the Section from the Geminid maximum, due
around 05h UT on December 14 (see ENB 276,
http://snipurl.com/trdma),
have demonstrated the shower produced another excellent return this
year on that night, but perhaps a little earlier than anticipated. The very
preliminary International Meteor Organization (IMO) results on their "live"
Geminids webpage (at:
http://snipurl.com/trdo1 ) have suggested
Zenithal Hourly Rates (ZHRs) were around 100-120 as early as 16h-19h
UT on December 14, and that they continued at only a slightly reduced
level, ZHRs ~90-110, from about 20h to midnight before peaking again
at roughly 120 near 01h. By 05h, they seemed to have fallen back to
about 85, though some reports were still suggesting ZHRs of 70 or so
as late as 15h UT that day. This pattern is liable to continue changing
as fresh results arrive, and the shorter-interval IMO results, while
showing still greater volatility so far (as expected, because of the
smaller amounts of data per analyzed interval), have hinted that peak
ZHRs may have been a little higher than this, maybe around 130-150.
Hopefully, the pattern should gradually become clearer over the next
week or so, as more data come through. Some of the early USA results
(kindly provided to us almost immediately by North American Meteor
Network leader Mark Davis - see
http://www.namnmeteors.org ) have
indicated ZHRs may still have been 90-100+ by 09h-11h UT on
December 14, for instance, which could suggest rather better rates then
than the initial IMO data found.
Reports of how some observers in Britain and nearby fared, can be
found on the Observing Forum's Geminids topic, at
http://snipurl.com/trdoy (including a photographed Geminid trail by
Robin Scagell, and a radio-meteor graph from David Entwistle), and on
the UK Weather World's Space Weather Forum Geminids topic, at
http://snipurl.com/trfis . Combining those with other information arriving
directly at the Section, it seems December 12-13 was the better night
across the UK for those who got any clearer weather at all (and sadly,
not everyone was fortunate), particularly for parts of southwest Scotland,
Northern Ireland, central Wales, western and central to southwestern
England. December 13-14 saw fewer people active generally, mostly
concentrated in parts of southern England, north only as far as mid
Wales in what data has arrived thus far. Overseas colleagues seem to
have struggled with the weather as well, often the case in mid
December across the northern hemisphere, of course, with several
people from the eastern USA and the far southwest of Canada already
having reported-in negatively; clouds and endless, cold rain were not
just affecting the UK, it appears!
Anyone who managed some Geminid observing this year, on whatever
night (including those away from the expected peak) is welcome to
provide a copy of their data to the SPA as soon as possible please,
hopefully allowing a fuller review of the shower next time. There is advice
on what information to send and where to via the Section's homepage,
at:
http://www.popastro.com/sections/meteor.htm .
DECEMBER 3-4 FIREBALL, SOUTHERN ENGLAND
By Alastair McBeath, SPA Meteor Section Director
Eleven definite sightings of a fireball around magnitude -9 or perhaps
brighter have been received from locations in Somerset, Gloucestershire,
Wiltshire, Hampshire, Berkshire, West Sussex and West London so far,
all timed to within five minutes of 20:00 UT on December 3. Some
early details, with links to a few of the initial sightings, can be found on
the Observing Forum here:
http://snipurl.com/trthm . Information derived
from these observations is a little sketchy, but has suggested the
fireball's start was around 90-100 km altitude, somewhere above a
rough area bounded to the east and west by the western Isle of Wight
and the Bournemouth area of Dorset respectively, or a point up to ~15
km north or south of this approximate line. The end could not be firmly-
established, but may have lain within about 40 km of a point roughly
midway between Bridport and Dorchester in Dorset, perhaps around
50 to 60 km altitude. If correct, this would suggest a crude flight direction
aligned somewhere between east-west to southeast-northwest.
Estimates for the visible duration averaged ~4 seconds, but this could
have been longer, maybe up to six or seven seconds, as not all
witnesses saw the entire track. Six reports of some fragmentation during
the object's flight were received, with colours varying from green or
green-white (five reports), to blue-white or orange-yellow (two reports
each), or yellow (one sighting). One observer suggested orange was
present in its tail, while a group elsewhere indicated it was likely the
fragments that were orange, and a short-lived train may have persisted
afterwards (two sightings).
It is possible there were two other UK-visible fireballs that evening, one
around 19:20 UT, the other perhaps near 20:30, plus a fourth event
within half an hour of 22:30, a shadow-castingly bright event seen from
Dorset, but by a witness who unluckily missed the ~20:00 meteor.
Details on the ~19:20 and ~20:30 events await confirmation, however.
All additional sightings of these events, or any other fireballs (meteors of
magnitude -3 or brighter), made from the British Isles and nearby,
would be welcomed by the Section. The minimum details required are:
1) Exactly where you were (give the 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 did not see the whole flight.
More advice and a fuller set of details to send (including an e-mail
report form) are given on the "Making and Reporting Fireball
Observations" page of the SPA website, at:
http://snipurl.com/trfko .
RADIO LEONIDS 2009
By Alastair McBeath, SPA Meteor Section Director
The established visual details for this year's Leonids remain much as
given in the previous ENB, but the arrival of Radio Meteor Observation
Bulletin 196, for November 2009 (RMOB; see
http://www.rmob.org ),
has allowed an appraisal of what the radio observers detected. The list
of contributors active at some stage during the Leonid epoch from this
RMOB were as follows:
Enric Algeciras (Spain), Orlando Benitez (Canary Islands), Michael
Boschat (Nova Scotia, Canada), Jeff Brower (British Columbia,
Canada), Willy Camps (Belgium), Johan Coussens (Belgium), Gaspard
De Wilde (Belgium), David Entwistle (England), Karl-Heinz Gansel
(Germany), Mike Otte (Illinois, USA), Steve Roush (Arizona, USA),
Wayne Sanders (British Columbia, Canada), Andy Smith (England),
Chris Steyaert (Belgium), Dave Swan (England), Istvan Tepliczky
(Hungary), Dirk Van Hessche (Belgium), Felix Verbelen (Belgium), John
Wardle (England).
Unhappily, significant numbers of observers ran into problems during
November, either with adverse weather conditions (storms and aerial-
wrecking gales), computer or electrical faults and loss of transmitter
signals as the apparently inevitable 'digital revolution' continues, aside
from a few minor, normal, interference effects. This, plus the fact the
stronger visual activity from the Leonids happened during the worst
possible observing interval for both Europe and much of North America,
has made interpreting what the radio results showed even more difficult
than usual. However, the relatively few surviving datasets gave evidence
for quite healthy meteor activity from about midnight to 10h, and again
around 12h UT on November 17, and from roughly 01h to 09h UT on
November 18. The closest to a definable peak in all this fell around
03h-05h UT on November 18, but as it was found exclusively in the
European data, and this interval coincided with one of the better daily
periods for radio-Leonid-detection over this region, it cannot be
regarded as especially significant.
Overall, this pattern seemed to have been more determined by the
radiant geometry at the various receiver sites, than any real differences
in the shower's activity. The radio rates near 03h-05h UT on the 18th
being somewhat stronger than in the same interval on the 17th, did
partly fit to the sustained, if modestly-enhanced, visual "tail" to the main
maxima on November 17, which persisted through till roughly 05h UT
on the 18th. Perhaps the oddest feature was how poorly the radio
Leonids were recorded at all this year, even by those systems which
apparently endured fewer observing difficulties, something for which
there is no good explanation (beyond the typical vagaries of radio-
meteor work!).
Despite these trying radio circumstances, and the fact most of our
contributing observers by all methods were not lucky in catching the
very best from the shower this time, my most grateful thanks go again
to everyone who provided results to us.
EARTH'S ATMOSPHERE CAME FROM SPACE?
National Geographic News
A new study proposes that the gases that make up Earth's atmosphere
came from a swarm of comets, not from volcanoes as has been thought.
The new theory came about after scientists discovered that pristine
samples of the elements krypton and xenon, recently collected from
deep within the Earth, have the same chemical make-up as ancient
meteorites.
Most of the gases in the air we breathe originated in the solar
nebula, the cloud of gas and dust that formed the Sun and planets.
The gases became gravitationally bound to the young Earth and were
then transported into the Earth's interior -- leaking out over the
aeons through vulcanism and cracks in the Earth's crust. It is true
that volcanoes emitted some gases, but now it is being suggested that
that contribution was insignificant. Scientists studied krypton and
xenon because they are 'noble' gases, so called because they do not
associate chemically with most other elements. As a result, most of
the Earth's krypton has remained unchanged since its arrival on our
planet. The team claims that our atmosphere formed when gas- and
water-rich comets bombarded the Earth shortly after its formation.
APPEARANCE OF IAPETUS EXPLAINED
Southwest Research Institute
Analysis and modelling of Cassini imaging and heat-mapping data have
confirmed and extended previous ideas that migrating ice, triggered by
infalling reddish dust that darkens and warms the surface, may explain
the two-toned appearance of Saturn's moon Iapetus. Shortly after he
discovered Iapetus in 1671, the French-Italian astronomer Giovanni
Domenico Cassini noticed that the surface is much darker on its
leading side than on the opposite trailing hemisphere. Images from
Voyager and Cassini have shown that the dark material on the leading
side extends onto the trailing side near the equator. The bright
material on the trailing side, which consists mostly of water ice and
is 10 times brighter than the dark material, extends across the north
and south poles onto the leading side.
Findings made by Cassini's cameras during the spacecraft's close
fly-by of Iapetus on 2007 September 10 and on previous encounters show
that both the bright and dark materials on Iapetus' leading side are
redder than similar material on the trailing side, suggesting that the
leading side is coloured (and slightly darkened) by reddish dust that
Iapetus has swept up in its orbit around Saturn. This observation
confirms an old idea that Iapetus' leading side has been darkened
somewhat by infalling dark dust from an external source, perhaps from
one or more of Saturn's outer moons. The dust may be related to the
giant ring around Saturn recently discovered by the Spitzer space
telescope. However, the new images show that infalling dust cannot be
the sole cause of the extreme global brightness dichotomy. It is
impossible that the very complicated and sharp boundaries between the
dark and the bright regions are formed by simple infall of material.
Close-up images provide a clue, showing evidence for thermal
segregation in which water ice has migrated locally from sunward-
facing (warmer) areas to nearby poleward-facing (colder) areas,
darkening and warming the former and brightening and cooling the
latter.
Cassini's infrared observations in 2005 and 2007 found that the dark
regions reach temperatures high enough (-144C) to evaporate many
metres of ice over billions of years. Iapetus' long rotation period,
79 days, contributes to such 'warm' temperatures by giving the Sun
more time to warm the surface each day than on faster-rotating moons.
The infalling dust darkens the leading side of Iapetus, which
therefore absorbs more sunlight and heats up enough to trigger
evaporation of the ice near the equator. The evaporating ice
recondenses on the colder and brighter poles and on the trailing
hemisphere. The loss of ice leaves dark material behind, causing
further darkening, warming, and ice evaporation on the leading side
and near the equator. Simultaneously, the trailing side and poles
continue to brighten and cool owing to ice condensation until Iapetus
ends up with extreme contrasts in surface brightness in the pattern
seen today.
MIZAR/ALCOR SYSTEM IS SEXTUPLET
Science Daily
Until light pollution got so bad in recent years, it was obvious even
to the layman that one of the principal stars in the Plough is, in
fact, two stars quite close together. The bright one is Mizar; its
companion Alcor is now invisible to the naked eye from many locations
owing to its relative faintness. Mizar is itself now recognized as a
pair of binaries -- what was once thought of as a single star is
actually two pairs of stars orbiting one another. Alcor has sometimes
been considered a fifth member of the system, orbiting far away from
the Mizar quadruplet.
Now, astronomers have discovered that Alcor is also actually two
stars, and is apparently gravitationally bound to the Mizar system,
making the whole group a sextuplet. The researchers were actually
looking for planets when they found a faint M-type dwarf star almost
hidden in the glare of Alcor. Not only did the project reveal the
image of the star, but its presence was able to explain slight
deviations in movement that scientists had noticed in Alcor. In
addition, it explains the unexpectedly high levels of X-rays coming
from Alcor -- dwarf stars naturally radiate high levels of X-rays.
Some astronomers have questioned whether Alcor is truly a part of the
system made up of the Mizar group of stars, because Alcor's motion is
not identical with that of the Mizar group. However, the team says
that indeed Alcor is part of the same system, and that the influence
of the newly discovered companion is partly responsible for Alcor's
unexpected motion.
ALLEGED EXOPLANET DOES NOT EXIST
NASA/JPL-Caltech
A proposed planet near a star some 6 parsecs away may not exist
after all. The finding is also a strike against a planet-seeking
strategy called astrometry, which measures the side-to-side motion of
a star on the sky to see whether any unseen bodies might be orbiting
it. Ground-based astrometry has been used for more than a century,
but none of the extrasolar planets it has detected has been verified
in subsequent studies. In May, astronomers at the Jet Propulsion
Laboratory in California, using a telescope at the Palomar
Observatory, raised fresh hopes for the technique when they announced
an exoplanet, six times more massive than Jupiter, orbiting VB10, a
star about one-thirteenth the mass of the Sun,. However, astronomers
from the Georg-August University in Gottingen, Germany, who used the
radial-velocity technique, which has found most of the extrasolar
planets detected so far, at the VLT, found nothing. Radial-velocity
measurements are typically made in the visible part of the
electromagnetic spectrum, but as VB10 gives most of its light as
infrared radiation, the VLT observers operated in the infrared.
The astronomers would definitely have seen significant variation in
the data if the planet were there. In a rearguard action, the JPL
astronomers claim that the radial-velocity technique only rules out
the presence of any planet that is at least three times more massive
than Jupiter, adding that the method "limits certain orbits for
possible planets".
But Alan Boss, an exoplanet enthusiast at the Carnegie Institution,
points to the notorious episode in 1963, when Dutch astrometrist Piet
van de Kamp claimed that two planets were orbiting Barnard's Star -- a
finding disproved a decade later. The dispute over the VB10 planet,
says Boss, "is another example of how hard it is to detect extra-solar
planets by astrometry from the ground". Astronomers expect astrometry
to work much better above the distorting effects of the atmosphere.
Two space missions in preparation -- ESA's GAIA, due to be launched in
2012, and NASA's Space Interferometry Mission, of indeterminate launch
date -- will use the technique to search for planets as small as the
Earth around Sun-like stars. More significantly, astrometry can yield
the mass of a planet, whereas radial velocity can put only a lower
limit on it.
CYGNUS X-3
ScienceDaily
The enigmatic binary-star system known as Cygnus X-3 has fascinated
astronomers for decades. It is thought to be either a small black
hole or a neutron star and an ordinary, albeit massive, star orbiting
one another. Now, a team of researchers has detected high-energy
gamma-rays from the system. The findings may provide a new window on
how Cygnus X-3 accelerates charged particles to enormous energies.
The gamma-rays, the most powerful type of electromagnetic radiation,
were detected by the Italian gamma-ray satellite AGILE (Astro-
rivelatore Gamma ad Immagini Leggero). From those observations a
clockwork pattern of the gamma-ray emission was noted, which always
seems to occur just before the onset of the powerful radio jets.
Cygnus X-3 is a strange case indeed, being one of the brightest radio
sources in the Galaxy except when it descends into a radio-quenched
state. Now the extremely energetic gamma-rays have been observed
during the low state. That may be indicating the preparation of the
major radio flare, which follows just days after, when the source
shoots up energetic radio jets from the core of the compact object.
The new gamma-ray findings might also shed light on how distant
quasars, powered by supermassive black holes, pump even greater
amounts of energy into space. Micro-quasars such as Cygnus X-3 permit
studies of jet phenomena such as dominate the most luminous quasars'
emission. Because the emissions from micro-quasars vary on time-
scales of days to weeks rather than the decades of quasar emissions,
they present opportunities to learn about quasar activity -- always on
the assumption that the two types of object are worked by analogous
mechanisms.
The very complex behaviour of Cygnus X-3 requires monitoring
throughout the electromagnetic spectrum from radio to X-rays and
now including also gamma-ray emission. Micro-quasars have strong
magnetic fields which can store enormous amount of energy. During
gamma-ray flares the stored energy can accelerate charged particles to
very high energies, which prompts them to emit gamma-rays. Then
radio-emitting blobs are pushed out of the system, producing the major
radio flares.
HST REVEALS MOST DISTANT GALAXIES YET SEEN
RAS
Using the recently updated Hubble telescope (HST), two teams of UK
astronomers have identified galaxies which are likely to be the most
distant yet seen. The UK teams analysed infrared images from the new
'Wide Field Camera 3' instrument installed on HST during the 2009
servicing mission. The expansion of the Universe causes the light
from very distant galaxies to appear redder, so having a new camera
which is very sensitive in the infrared allows us to identify
galaxies at greater distances than was previously possible. The
new images include the region of sky known as the Hubble Ultra-Deep
Field, which astronomers analysed 5 years ago from visible-light
images. Astronomers can now look even further back in time,
identifying galaxies when the Universe was only 5% of its current age
-- within 1 billion years of the Big Bang.
As well as identifying potentially the most distant objects yet, the
new HST observations present a puzzle. Astronomers know that the gas
between galaxies in the Universe was ionized early in the history of
the cosmos, but the total light from the newly observed galaxies does
not seem to be sufficient to achieve that. The researchers are
looking forward to seeing these objects more clearly in the years
ahead. The new observations from HST are likely to be the best Hubble
will ever take, but the very distant galaxies they have now discovered
will be studied in detail by Hubble's successor, the James Webb Space
Telescope, supposed to be launched in 2014.
PETITION BY SWANSEA ASTRONOMICAL SOCIETY
Swansea Astronomical Society has occupied the Marina Towers
Observatory site on the Swansea foreshore for 16 years. It has
reluctantly decided that it cannot renew its lease for the site with
the City and County of Swansea owing to the increased costs and
charges proposed by the Council. The Society has hitherto received
financial support from the Council; however, with the proposed
withdrawal of that support, the Society, as a registered charity, is
unable to finance a service for the community of Swansea in the form
of regular public and educational events at the site. During the past
year the Society opened the Observatory and its Exhibition Room on 44
occasions to the public and schools from Swansea and surrounding
districts. Anyone wishing to sign a petition to keep Swansea
Observatory open may do so by clicking on the Number 10 petition
regarding the Marina Towers (as featured in the December edition of
Astronomy Now). The web address is:
http://snipurl.com/trxhh The
deadline for signing up is January 23.
Bulletin compiled by Clive Down
(c) 2009 the Society for Popular Astronomy
