ENB No. 203 September 3 2006

Current and previous news bulletins from the SPA

Moderators: joe, Brian, Guy Fennimore

Post Reply
Site Admin
Posts: 4382
Joined: Fri Dec 03, 2004 11:24 am
Location: Greenwich, London

ENB No. 203 September 3 2006

Post by joe »

Electronic News Bulletin No. 203 2006 September 3

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/maae7TVabs3yvcixLLVb/

By Alastair McBeath, SPA Meteor Section Director

Mid-July certainly brought an interesting crop of fireballs, as the last
couple of ENBs have demonstrated. Since ENB 202, news has come
in of a meteorite shower that landed in and around Moss, Norway,
around 50 km south of Oslo, on the east shore of the Oslofjord, on
July 14, following a brilliant fireball that produced sonic booms which
was widely-seen across southern Norway. Three meteorites had
been recovered by August 11, weighing roughly 35, 700 and 750g
respectively. Initial analysis showed they were of the very rare C0
carbonaceous chondrite type, of which kind only five other falls have
been recorded. More details, including an image of one of the larger
chunks, can be found at:
http://popastro.c.topica.com/maae7TVabs3ywcixLLVb/ though as noted in
the SPA's General Chat Forum at:
http://popastro.c.topica.com/maae7TVabs3yxcixLLVb/ the ~700g
object was NOT the first European meteorite to crash through a roof
since 1969 (as the Norwegian media reported), since the Glanerbrug,
Netherlands, meteorite fall of 1990 April 7 did the same thing.

This was Norway's second brilliant fireball of the summer. The first
was widely-observed in midnight daytime from the far north (see
ENBs 198 and 199).

Two more European Fireball Network stations caught at least part of
the trail of the July 18-19 fireball, which was seen from across
south-east England, Belgium and the Netherlands, as discussed in
ENBs 201 and 202. Both were in north-west Germany, one at
Herford near Bielefeld, the other at Daun around 85 km south of
Cologne in Rheinland-Pfalz. It is hoped the, now three, photographic
observations will allow an orbit to be calculated for this event.

August too was determined not to be outdone for fireballs over the
UK, with chiefly media reports of a brilliant meteor seen from the
Western Isles off Scotland around 21:20 UT on August 18-19. Initial
claims the meteor was a Kappa Cygnid were based solely on the
date the meteor happened (an easy, but hopelessly unreliable, method
of assigning shower association, though one the media particularly
seem to prefer!). The scant eye-witness data to reach the Section is
so far inconclusive on a possible origin or atmospheric trajectory.

Three further significant events were reported during late August: at
~20:45 UT on August 27-28 from Lancashire; circa 02:06 UT later
that night from Edinburgh (though only a probable persistent train
lasting from at least 02:06-02:09 UT was actually seen; if it was an
ionization train, it must have come from a very bright meteor); and on
August 28-29 at about 21:05 UT. The latter event seems to have
been spotted from four locations so far, in Hull, Staffs, Northants
and Kent, overall suggesting the fireball had a very long path and was
rather slow moving, leaving a persistent train for a short time. It may
have flown high over SE England on a generally north to south track,
starting perhaps over the Leicester-Northants area, and possibly
passing over London, but it likely ended over the Channel or maybe
northern France.

All fireball sightings are welcomed by the Section, particularly those
seen from the UK and places nearby. Details of what information to
send and where to can be found via the Section's "Fireball Observing"
page at: http://popastro.c.topica.com/maae7TVabs3yycixLLVb/

By Alastair McBeath, SPA Meteor Section Director

The moonlit Perseid maximum weekend seems to have passed with
largely cloudy skies across swathes of Britain, judging by reports so
far. Some initial comments can be seen on the SPA's Observing
Forum, at: http://popastro.c.topica.com/maae7TVabs3yzcixLLVb/ including
links to a couple of
Robin Scagell's meteor images on the SPA Gallery Forum.

Positive meteor observations from late July through to the Perseids'
end in late August, including those posted on the Forum, have now
arrived from: Mike Clarke (Nottinghamshire), Mike Feist (West
Sussex), Pam Foster (Perth & Kinross), Dave Gavine (Edinburgh),
'HippyChippy' (Hampshire), Pete Lawrence (West Sussex), Tony
Lawson (Co. Durham), Mike Maunder (Alderney), Gary McGrory
(Ayrshire), Robin Scagell (Devon), Derek Ward-Thompson (SW
France), and myself (Northumberland).

Coverage on the maximum night was practical only from a few places
in Britain, and the often moonlit data available are not sufficient to
compute reliable Zenithal Hourly Rates (ZHRs) from, much as
expected in advance because of the Moon. However, this information
does seem to infer a peak probably before midnight UT on August
12-13, possibly even a little earlier than predicted, as rates seemed
to decline after 00h, and not simply due to increased moonlight
problems, as these should have been partly offset by the improving
radiant elevation. Estimated ZHRs suggest peak activity was at about
normal levels, maybe 90-120 at best. Any additional results would
still be most welcome!

By Alastair McBeath, SPA Meteor Section Director

NASA released details on August 23 of a possible originating object
for the intense meteoroid bombardment their Mariner 4 probe to
Mars underwent after its 1965 July 14 Martian fly-by, on 1967
September 15, in the space between Mars and Earth. The
storm-strength meteoroid peppering lasted roughly 45 minutes,
damaging the probe's surface and temporarily knocking it out of
orientation. As it was running short of fuel, and was not intended to
carry out any tasks by that stage of its mission, this was not an
especial problem, but the event, reckoned as surpassing any recorded
Leonid meteor storm seen from Earth, was a complete surprise.

In 2005, Bill Cooke, who heads NASA's Meteoroid Environment
Office, suggested the event might have been due to an old, decayed,
"D"-class comet, and asked Paul Wiegert of the University of Western
Ontario to look into it. Wiegert's investigations suggested the most
likely candidate of the known D-comets was D/1895 Q1 (Swift),
named after the famous comet-discoverer Lewis Swift (1820-1913),
whose most well-known comet, the first he found, is 109P/Swift-Tuttle,
parent of the Perseid meteor shower. Swift's 1895 comet was the
eleventh of his thirteen comet discoveries, and one made entirely
by-chance while trying to determine the position of a nebula he had
recently found. As he wrote of this lucky find in "Popular Astronomy"
- not the SPA magazine! - of 1897 (volume 4, pp.138-139), "It is as
if a blind man were to fire a gun into the air and bring down a bird",
rather in the fashion of Mariner 4's running into the meteoroid stream.

Comet D/Swift was estimated as having an orbital period of about five
years, but since it was last seen in early 1896, it has never been
recovered, and may have broken up, hence the "D/" prefix. If so, this
may be where all the particles Mariner 4 encountered came from.
Paul Wiegert's calculations suggested the place where the comet's
nucleus should have been was roughly twenty million kilometres from
the spaceprobe, not far on a Solar System scale, though its associated
meteoroid stream must have passed very much closer to the probe
to produce the observed effect. Unfortunately, Comet D/Swift's orbit
is not especially well-known due to its short visible lifetime, but
checking is underway to see if any earlier 19th century observations of
it exist, not identified at the time, to try to refine the orbit
further, and
confirm whether this was the stream Mariner 4 chanced-upon.

By Alastair McBeath, SPA Meteor Section Director

If predictions were correct, the generally minor Alpha Aurigid meteor
shower should have peaked around 06h30m UT on September 1 this
year, probably producing ZHRs of ~5-10, much as in most years.
However, a few past returns have brought rare higher rates. Estimated
ZHRs from brief outbursts in 1935, 1986 and 1994 were 30-40 or
so, for instance. Unfortunately, this short-lived nature and the general
lack of meteor observations during late August and September, mean
details about the outbursts remain uncertain. The shower has been
linked to long-period Comet Kiess of 1911, which has an orbital
period estimated at ~2000-2500 years. Material left along the orbit
can be perturbed by the gas giant planets Jupiter and Saturn however,
hence the past outbursts.

Theoretical calculations by astronomers Peter Jenniskens and Esko
Lyytinen concerning such perturbed stream trails has suggested next
year may bring another Alpha Aurigid outburst, but maybe of unusually
strong proportions, with many bright meteors. The peak is expected
only about an hour before the one usually observed, centred at
11:37 UT on 2007 September 1, according to these researchers. At
the IAU General Assembly in Prague on August 18, Jenniskens
announced he anticipated ZHRs to be between 400-1000+ for the
probably short-lived peak of the outburst, though Lyytinen has been
a great deal more cautious in his public comments, saying he
anticipates something between a moderate to good shower, but he
does not entirely rule out a possible storm-strength maximum rate.

Of course, this peak timing is in daylight for Britain, but will favour
in the extreme western parts of North America and the eastern North
Pacific Ocean particularly. Unfortunately, the waning gibbous Moon
will be just four days past full on 2007 September 1, so will be
beautifully on-view for most of the night then anyway, and will cause
a lot of problems for accurate estimates of whatever activity the
shower produces. Even so, if there are strong to very strong rates
of bright meteors, the Moon may be less of a nuisance than it might
at first seem, as some of the moonlit Leonid storm peaks around the
millennium demonstrated. We must wait and see!


The Hubble space telescope has for the first time identified the
parent star of a distant planet discovered through gravitational
microlensing. Microlensing occurs when the gravitational field of a
foreground star amplifies the light of a background star that
momentarily aligns with it. The particular character of the light
magnification can reveal clues to the nature of the foreground star
and any associated planets. However, without identification and
characterization of the foreground star, little can be said about
the accompanying planet.

The newly discovered host star, catalogued as OGLE-2003-BLG-235L/
MOA-2003-BLG-53L, has a planetary companion that was discovered in
2003 through ground-based gravitational microlensing observations.
A planetary companion of a foreground star can produce additional
brightening of the background star. The additional brightening can
reveal the planet, which is otherwise too faint to be seen by
telescopes. The Hubble images allowed the research team to resolve
the background source star from its neighbours in the very crowded
star field in the direction of the centre of our Galaxy. The star
appeared to be about 20% brighter than expected; the additional
brightness is most likely from the foreground lens star, which hosts
the planet. Hubble could not resolve the two stars, but, by taking
multiple images through differently-coloured filters, it recorded a
colour offset in the overlapping images of the two stars. That is
possible because the foreground star is redder than the background
star. From its colour, the researchers were able to make a crude
estimate of the type of the star, and thereby obtain its distance as
19,000 light-years and the planet's mass as 2.6 Jupiter masses. The
characteristics of the lensing event show that the planet is in a
Jupiter-sized orbit around its parent red star.

Chandra X-Ray Center

A critically important number that specifies the expansion rate of the
Universe, the so-called Hubble constant, has been independently
determined by the Chandra X-ray Observatory. The Hubble constant is
calculated by measuring the speed at which objects are moving away
from us and dividing by their distance. The usual methods of
estimating it rely upon measuring the apparent brightness of standard
objects whose absolute luminosities ('candle-powers') are known and
are supposed to have remained constant throughout the age of the
Universe. Optimist have thought in recent years that the value of the
constant is known to about 10%, at 72 +/- 8 km/s per megaparsec. Now,
by a combination of X-ray data from Chandra with radio observations of
galaxy clusters, distances have been estimated to 38 galaxy clusters
ranging from 1.4 to 9.3 billion light-years. The results give a
Hubble constant of 77 km/s per megaparsec, with an uncertainty of
about 15%, thereby reinforcing other recent values. The implied age
of the Universe is between 12 and 14 billion years.

Ohio State University

Certain astronomers have suggested that the Triangulum Galaxy (M33),
or at any rate one binary-star system in it, is about 15% further away
from us than has been thought. That would imply that the Hubble
constant should be correspondingly reduced and that the Universe could
be 15% bigger and older. The astronomers studied two of the brightest
stars in M33, the components of a binary system in which one star
eclipses the other every five days. They determined the masses of the
components, and from that they guessed the candle-power of those stars.
Then the comparison between the intrinsic brightness and the apparent
brightness told them how far away the stars were. It was 15% further
than they expected, about 3 million light-years. The margin of error
was claimed to be 6%, but there might be merit in waiting a bit before
altering the Universal distance scale to suit the findings on one
binary system; the star's masses may have been determined quite
accurately, but their luminosities are only conjectural.

BBC News

Astronomers at the University of Toronto have discovered a companion
to a 'planetary-mass object' or orphan planet -- one that has no star
around which to orbit. Both objects have masses similar to those of
extra-solar giant planets, usually found in orbit around a star. The
researchers discovered the companion candidate in an optical image
taken with ESO's 3.5-m New Technology Telescope on La Silla, Chile,
and investigated it further with the 8.2-m Very Large Telescope on
Paranal. Those follow-up observations confirmed that both objects are
young, at the same distance, and much too cool to be stars. From
theoretical models, the astronomers estimate that they have about 14
and 7 times the mass of Jupiter. The newborn pair, barely a million
years old, has a separation about six times the distance between the
Sun and Pluto, and is located in the Ophiuchus star-forming region
approximately 400 light-years away. It is the first planetary-mass
object to be resolved into a double. The existence of such a wide
pair with such a small total mass and consequently weak gravitational
binding sets useful constraints on theories of their origin.

New Scientist

Astronomers combing through 89 hours of observations from the Rossi
X-ray Timing Explorer think that they detected 58 minuscule trans-
Neptunian objects (TNOs) between 20 and 100 metres in size. What the
astronomers actually saw in the records, which were all of a distant
X-ray source called Scorpius X-1, were sudden momentary dips in the
X-ray brightness. The best idea that they could think of by way of
explanation was that the dips, which mostly lasted only 2 or 3
milliseconds, were caused by transits of TNOs, which would be only of
the order of 50 metres across if they were at the assumed distance of
43 Astronomical Units. Such objects would be much too small to detect
directly with any telescope. If there were really so many of them
transiting a very small X-ray source, the total number of such objects
would have to be very formidable.

Science Daily

There is no formal definition of a 'Sungrazing comet,' but the term
typically refers to the Kreutz-group comets, which have a perihelion
distance of less than 0.01 of an Astronomical Unit. The 1000th
Sungrazer is the 1185th comet discovered in data from the SOHO LASCO
or SWAN instruments (the other 185 are not members of the Kreutz
group). The faint object is officially designated C/2006 P7 (SOHO) by
the Minor Planet Center of the International Astronomical Union.
Before the launch of SOHO in 1995 December, only some thirty members
of the Kreutz group were known. All 1000 Kreutz comets are believed
to be fragments of a single great comet observed in c. 371 BC by
Aristotle and Ephorus, and the fragments themselves continue to
fragment, making more Sungrazing comets.

Australian National University

The Universe has used up about 20 per cent of its normal matter, or
original fuel reserves, according to findings from a survey of the
'nearby Universe' by an international team of astronomers involving
researchers at the Australian National University. The survey
suggests that about 20 per cent of the normal matter or fuel that was
produced at the Big Bang 14 billion years ago is now in stars, a
further 0.1 per cent lies in dust expelled from massive stars (and
from which solid structures like the Earth and its people are made),
and about 0.01 per cent is in super-massive black holes. The survey
data, which constitute the 'Millennium Galaxy Catalogue', were
gathered by telescopes in Australia, the Canary Islands and Chile, and
include over ten thousand giant galaxies. According to the survey
leader Dr Simon Driver of St Andrews University, the remaining
material is almost completely in gaseous form lying both within and
between the galaxies, forming a reservoir from which future
generations of stars may develop. The catalogue has estimates of the
distribution of each galaxy's stars between its central bulge and its
surrounding disc-like structure. Roughly half of the stars appear to
reside in bulges and the other half in discs.

Science Daily

The International Astronomical Union (IAU) has downgraded the status
of Pluto to that of a 'dwarf planet'. The decision means that only
the rocky planets of the inner Solar System and the gas giants of the
outer system will hereafter be designated as planets. The ruling
effectively settles a year-long controversy about whether the body
officially called 2003 UB313 would have planetary status. Somewhat
larger than Pluto, the body has been informally known as Xena since
the formal announcement of its discovery on 2005 July 29 by Caltech
planetary scientist Mike Brown. "I'm of course disappointed that Xena
will not be the tenth planet, but I definitely support the IAU in this
difficult and courageous decision", said Brown. "It is scientifically
the right thing to do, and is a great step forward in astronomy.
Pluto would never be considered a planet if it were discovered today,
and I think the fact that we've now found one Kuiper-belt object
bigger than Pluto underscores its shaky status."

According to Brown, the decision will pose a difficulty for a public
that has been accustomed to thinking for the last 75 years that the
Solar System has nine planets. In fact, the public has had some
experience with the demotion of a planet in the past, although not in
living memory. Astronomers discovered the asteroid Ceres on 1801
January 1 -- literally at the turn of the 19th century. Having no
reason to suspect that a new class of celestial object had been found,
scientists designated it the eighth planet (Uranus having been
discovered some 20 years earlier). Soon several other asteroids were
discovered, and those, too, were summarily designated as newly found
planets. But when astronomers continued finding numerous other such
bodies in the region (there are thought to be millions), the
astronomical community in the early 1850s demoted Ceres and the others
and coined the new term 'asteroid'. The IAU now says that the Solar
System has eight planets and (so far) three dwarf planets -- Ceres,
Pluto and 2003 UB313.

New Scientist

Four new satellite galaxies of the Milky Way have been discovered,
bringing the total known to about 20. The pace of new discoveries
suggests that many more such satellites remain unknown. The
satellites are dwarf galaxies a few hundred to a few thousand
light-years across. The tiny galaxies are thought to be the building
blocks of large galaxies, such as our own Milky Way which is about
100,000 light-years across. The small galaxies are faint and
difficult to observe behind the throngs of foreground stars in the
Milky Way. Just two years ago, only 10 satellite galaxies were known,
with the exact classification of some objects in dispute. Now, thanks
to new observing techniques and detailed sky maps such as the Sloan
Digital Sky Survey (SDSS), that number has doubled. Astronomers use
SDSS to look for the particular types of stars expected to lie in
dwarf galaxies, then detect the dwarfs as slight 'overdensities' of
those types of stars. The four new discoveries were made by
astronomers at the University of Cambridge. Named after the
constellations in which they were found -- Coma Berenices, Canes
Venatici II, Hercules, and Leo IV, all of them are between roughly
100,000 and 500,000 light-years away. The largest and smallest are
Hercules and Coma Berenices, which are about 1000 and 200 light-years
across, respectively. Like most of the other dwarfs discovered by
SDSS, the new finds are much smaller and fainter than the 10 dwarfs
that were known previously.

Science Today

Until now, scientists had been aware only of the clouds in lower
reaches of the atmosphere. Mars Express has now seen a fleeting layer
of clouds, most likely composed of carbon dioxide. at an altitude
between 80 and 100 kilometres. The new high-altitude cloud layer may
have implications for landing on Mars, as it suggests the upper layers
of Mars' atmosphere may be denser than was previously thought. That
will be an important piece of information for future missions if they
rely on friction in the outer atmosphere to slow down spacecraft (a
technique called aerobraking), either for landing or going into orbit
around the planet.


A weak but abnormally long-lasting gamma-ray burst (GRB) has given
astronomers an unprecedented start-to-finish view of an exploding
star. Ground- and space-based telescopes studied the blast in detail
at gamma-ray to radio wavelengths. Scientists now suspect that such
weak bursts may outnumber more powerful ones by as much as 10 to 1.
Usually, such events are not detected until after the supernova has
brightened substantially at optical wavelengths, many days after the
initial explosion, but on this occasion astronomers were able to study
the remarkable event from the very beginning.

On February 18, the Swift satellite sensed a rise in gamma rays from
the constellation Aries. Within 20 seconds, the spacecraft reported
the burst's location to astronomers and slewed its instruments towards
the source. The burst lasted about 35 minutes -- about 100 times
longer than typical bursts associated with supernovae. It was also
just 1 per cent the brightness of GRBs seen in the distant Universe,
which places it in a sub-class known as X-ray flashes. After
two-and-a-half minutes, Swift's telescopes identified the blast's
X-ray and ultraviolet counterparts. They coincided with a dwarf
galaxy about 500 million light-years away. That places the burst some
25 times closer than typical GRBs. On February 20, two days after the
GRB, a brightening type Ic supernova began to be seen.

Bulletin compiled by Clive Down

(c) 2006 the Society for Popular Astronomy

Post Reply