ENB No. 179 August 7 2005

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ENB No. 179 August 7 2005

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Electronic News Bulletin No. 179 2005 August 7

Here is the latest round-up of news from the Society for Popular
Astronomy. The SPA is Britain's liveliest astronomical society, with
members all over the world. We accept subscription payments online
using our secure site and can take credit and debit cards. You can
join or renew via a secure server or just see how much we have to
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a Philip's title see the end of this bulletin.

By Alastair McBeath, SPA Meteor Section Director

Four definite sightings of the near-sunset July 16-17, 20:19 UT fireball
have now been received, one from Belgium and three from southern
England, in Somerset, Buckinghamshire and East Sussex, plus the two
radio signals which helped refine the event's timing, as mentioned in ENB
178. Brightness estimates now suggest the event must have been at least
magnitude -8, and was likely significantly brighter. The track probably
passed on a general south to north trend over the southern Channel north
of the Baie de la Seine, perhaps some 40-80 km off the north-east tip of
the Cotentin peninsula of Normandy, northern France. The heights may
have been around 90 to 60 km, but these are only best-estimates.

Further fireballs were spotted: around 21:54 UT on July 23-24 by two
witnesses indoors at the same site in Birmingham; at 23:40 UT on July
30-31 (Wiltshire); and in daylight at 18:45 UT on August 1-2 (Isle of

All additional fireball reports are welcomed by the Section. Information
on what to report and where to can be found on the "Fireball Observing"
page of the SPA website, off the Meteor homepage at:

By Alastair McBeath, SPA Meteor Section Director

The Perseid maximum is now fast approaching, and is due around
17:00-19:30 UT on August 12-13, next Friday evening. The timing is too
early for the UK, as this is still in daylight, and after sunset the shower's
radiant rises to a useful elevation only by about 22:00 UT, though it
improves all night after then. However, the Moon is at first quarter on
August 13, and on nights over the shower's predicted peak, it sets before
22:00 UT for Britain, so creating ideal observing conditions (if skies are
clear!). Even if the maximum does keep to time, Perseid activity should
still be well worth seeing on August 12-13, and indeed for a couple of
nights before and at least a night afterwards, judging by recent past
returns, when Zenithal Hourly Rates (ZHRs) of these swift, often bright,
and commonly trained meteors should be between 40-100 or so.

Although the Perseids' primary peak, which was followed continually
from 1988-2000, recurred in 2004 (when ZHRs reached roughly
180-200 briefly over eastern Europe, as reported in ENB 156), theory
suggests it is unlikely to appear again this year. Any such activity would
fall probably soon after 17:00 UT on August 12, while the "tertiary"
maximum, reported only in 1997-99 results, might happen towards 03:00
UT on August 13, if it recurs at all. Declining Perseid rates can be
followed until August 24 in most years, but the Moon will be an
increasing problem after the peak. More details on all of August's active
meteor showers can be found on the SPA website.

By Jonathan Shanklin, SPA Comet Section Director

Comet 2004 Q2 (Machholz) put on a good show in the early spring, but
comets 2003 T4 (LINEAR) and comet 9P/Tempel rather failed to live up
to expectations as far as visual observation was concerned. Many
members had a look at comet Machholz, particularly when it passed in
front of the Pleiades, and it looks as if it will get into the top
five of visually observed comets. Prospects for the next six months
are not particularly good, though comet 2005 E2 (McNaught) may reach
9th magnitude after Christmas.

On July 4th, comet 9P smashed into the Deep Impact missile, which took
spectacular images before its demise. The images are still being
analysed, but should shed new light on the origin, structure and
evolution of comets. As far as visual observations were concerned,
the comet became more condensed immediately after the impact, but its
total magnitude did not increase significantly. This was roughly what
I predicted on the basis that the impact would not significantly
increase the total area of the comet's surface that was active.
Further news will be published in the astronomical press over the
coming months.

The asteroid-search programmes have thrown up a number of interesting
objects that may or may not be comets. Asteroid 2003 WY25 may be a
fragment of lost comet D/Blanpain, which has not been seen since 1815,
and related to the Phoenicid meteor shower, which put on an intense
display in 1956. There may be another display from the shower this
autumn, but the radiant is too far south for observation from the UK.
It is possible that the fragmentation occurred just before the 1815
apparition of the comet. Asteroid 2005 NA56 may be linked to comet
41P/Tuttle-Giacobini-Kresak, but if so the fragmentation must have
occurred over 500 years ago. The comet experienced a series of
encounters with Jupiter in the sixteenth century, which reduced its
perihelion distance from around 1.5 AU to 1.0 AU. Asteroid 2005 NA82
is in a short-period retrograde orbit and can approach quite closely
to Jupiter, suggesting that it could be an extinct comet. Asteroid
2005 OE is in a highly inclined long-period orbit, with a period of
260 years and perihelion at 2.8 AU.

The SOHO spacecraft is closing in on its 1000th comet, which is likely
to be found in the next month. The vast majority of them are from the
Kreutz group of Sungrazing comets, which can produce spectacular
unaided-eye objects, but none that bright has been seen since 1970. Two
other groups of SOHO comets known as the Marsden and Kracht groups of
Sunskirting comets have tentatively been linked together in an
evolutionary hierarchy of fragmentation. It seems that the Marsden
fragments are in a periodic orbit of about 5.5 years, and the groups
are also linked to comet 96P/Machholz and the Quadrantid and daytime
Arietid meteor showers. Michael Oates has been overtaken as the
leading discoverer by German amateur Rainer Kracht who now has 169
comets compared to Michael's 145. French amateur Xavier Leprette has

University of California

An recently observed explosion on a neutron star halfway across the
Milky Way galaxy was the largest such explosion ever recorded. The
Rossi X-ray Timing Explorer observed that the explosion generated
rapid fluctuations in the X-ray radiation that was emitted. The X-ray
pulses, emitted during each seven-second rotation by the fast-spinning
star, contained the frequency vibrations of the neutron star's massive
quakes. Much as geologists probe the Earth's interior from seismic
waves produced by earthquakes, and solar astronomers study the Sun by
shock waves travelling through it, the X-ray fluctuations should
provide critical information about the internal structure of the
neutron star.

The oscillations began three minutes after a titanic explosion on a
neutron star that, in only a tenth of a second, released more energy
than the Sun emits in 150,000 years. The oscillations then gradually
declined after about 10 minutes. Most of the millions of neutron
stars in our Milky Way galaxy produce magnetic fields that are a
million million times stronger than those of the Earth, but there are
a few, called 'magnetars', with fields a thousand times greater
still. Such fields are so strong that they sometimes buckle the
crusts of neutron stars, causing 'star quakes' that result in the
release of gamma rays. Four such stars are known; they are called
'soft gamma repeaters' by astrophysicists because they flare up
randomly and release a series of brief bursts of gamma rays. SGR
1806-20 (the formal designation of the neutron star that exploded on
2004 December 27, producing a flash brighter than anything ever
detected beyond the Solar System) is one of them. The flash was so
bright that it saturated all X-ray satellites for an instant. The
burst of gamma-ray and X-ray radiation could have come from a highly
twisted magnetic field surrounding the neutron star that suddenly
snapped, creating a quake on the neutron star.

Harvard-Smithsonian Center for Astrophysics

Astronomers were surprised to discover a 25-million-year-old proto-
planetary disc around a pair of red dwarf stars called Stephenson 34,
350 light-years away in Taurus. Dust discs around new-born stars
disappear in a few million years because the material has collected
into full-sized planets. The discovery raises the puzzling question
of why this particular disc has not formed planets despite its
advanced age. Data from the Spitzer Space Telescope show that its
inner edge is about 65 million miles from the binary stars and it
extends to a distance of at least 650 million miles. Additional
material may orbit further out where temperatures are too low for
Spitzer to detect it. The age was estimated by modelling the central
stars within the system, since stars and disc were supposed to be the
same age.


The current mean temperature on the equator of Mars is 69 degrees
below zero Fahrenheit. Scientists have long thought that Mars was
once temperate enough for water to have existed on the surface, and
for life possibly to have evolved. Now Caltech and MIT scientists
report that Martian meteorites demonstrate that at least several rocks
originally located near the surface of Mars have been freezing cold
for four billion years. Their work is a novel approach to extracting
information on the past climate of Mars through the study of Martian
meteorites. In fact, the evidence shows that during the last four
billion years, Mars is likely never to have been sufficiently warm for
liquid water to flow on the surface for extended periods of time.
That implies that Mars has probably never had a hospitable environment
for life to have evolved. The work involves two of the seven known
'nakhlite' meteorites and the celebrated ALH84001 meteorite that some
optimists once claimed to show evidence of microbial activity on Mars.

Using geochemical techniques, scientists reconstructed a thermal
history for each of the meteorites to estimate the maximum long-term
average temperatures to which they were subjected. They did that by
estimating the total amount of argon still remaining in the samples.
Argon is present in the meteorites as well as in many rocks on Earth
as a natural consequence of the radioactive decay of potassium. As a
noble gas, argon is chemically unreactive, and because the decay rate
is precisely known, geologists have measured argon as a means of
dating rocks. However, argon is also known to leak out of rocks at a
temperature-dependent rate, so from the amount remaining in the rocks
an inference can be made about the maximum heat to which the rock has
been subjected since the argon was first made. The cooler the rock
has been, the more argon will have been retained. It turned out that
only a tiny fraction of the argon that was originally produced in the
meteorite samples has been lost, and calculations suggest that the
Martian surface has been in deep-freeze for most of the last four
billion years.


Astronomers using the XMM-Newton space observatory have found that a
star called SN 1979C that exploded in 1979 is as bright today in
X-rays as it was when it was discovered years ago, a surprise because
such objects usually fade rapidly. The scientists can document a
unique history of the star, both before and after the explosion, by
studying rings of light spreading from the blast, similar to counting
rings in a tree trunk. Among the interesting finds is the history of
the star's stellar wind dating back 16000 years before the explosion.
Such a history is not even known about our Sun. Also, the scientists
could measure the density of the material around the star. The
lingering mystery, though, is how this star could fade away in visible
light yet remain so radiant in X-rays. Supernovae are typically half
as bright after about ten days and fade steadily after that,
regardless of the wavelength. SN 1979C has in fact faded in optical
light by a factor of 250, becoming barely visible with a good amateur
telescope. In X-rays, however, it is still the brightest object in
its host galaxy, M100, in the constellation Coma Berenices. SN 1979C
appears to have originated from a star of about 18 solar masses that
produced fierce stellar winds that blew into space for millions of
years, creating concentric rings. The X-rays -- produced after the
explosion when the supernova shock caught up with the stellar wind and
heated it to a temperature of several million degrees -- illuminated
16000 years' worth of stellar activity.

New Scientist

Astronomers have used the Galaxy Evolution Explorer (GALEX)
ultraviolet space telescope to study the properties of 300 nearby
galaxies. Optical images show the galaxy NGC 4625, which lies 31
million light-years away, to be smaller than its neighbour NGC 4618,
but GALEX revealed it to be larger. The spiral arms were bright in
ultraviolet light because they are made up of hot, newborn stars. The
stars in the arms appear to be about 1 billion years old, while those
in the galaxy's centre are about 10 billion years old. The stars in
NGC 4625's spiral arms are significantly younger than those in most
spiral galaxies, including our Milky Way. Those galaxies formed
within the first 2 billion years after the Big Bang. They have been
more or less continuously producing stars in their arms ever since,
with most of the star births taking place billions of years ago, so
the entirely young arms of NGC 4625 suggest that they began to take
shape only recently, mimicking the form of older galaxies. But unlike
those early galaxies, which are difficult to observe because the
Universe has expanded in the intervening ages, NGC 4625 galaxy is
comparatively nearby, so astronomers can see its features. The arms'
delayed development means that for billions of years there was
probably nothing happening that could trigger the formation of the
spiral arms. Then, the adjacent galaxy NGC 4618 may have sparked the
intense star birth by gravitationally disturbing NGC 4625.

New Scientist

Astronomers using the Keck II telescope in Hawaii to make new
observations of the motions of stars in the most distant outskirts of
the spiral galaxy M31 have discovered that it is much bigger than was
previously thought. They found that the movement of the sparse
smattering of far-flung stars is actually synchronized with the rest
of the galaxy's stars, rotating in an orderly way around its centre.
The stars had been seen before, but astronomers had assumed they were
captured fragments of other galaxies that would retain their own,
essentially random, stellar motions. It is now estimated that the
disc of the galaxy is 220,000 light-years across.

New Scientist

Astronomers mapping the distribution of hydrogen gas within the Milky
Way, a project known as the Southern Galactic Plane Survey, recently
discovered another arm of our own Milky Way galaxy. The structure
consists of an arc of hydrogen gas 77,000 light-years long and a few
thousand light-years thick running along the galaxy's outermost edge.

BBC Online

Photographs of a giant patch of frozen water nestled within an unnamed
impact crater on Mars have been taken by a camera on board Mars
Express. The ice disc is located on Vastitas Borealis, a broad plain
that covers much of Mars' far-northern latitudes. The existence of
water on Mars boosts the chances that manned missions can eventually
be sent there. The highly visible ice is in a crater 23 miles in
diameter, with a maximum depth (the crater, not the ice) of about 6000
feet. Scientists believe that the water ice is present all year round
because the temperature and pressure are not sufficient to allow it to
change state. Researchers studying the images are sure that it is not
frozen carbon dioxide (CO2), because CO2 ice had already disappeared
from the north polar cap at the time the image was taken.

Various sources

Astronomers have identified a Kuiper-belt object which is larger than
Pluto and three times as far from the Sun as Pluto. It measures
between 2,600 and 3,000 km in diameter, and has an orbital period of
560 years. Officially designated 2003 UB313, and now nicknamed Xena,
it was discovered at the Gemini Observatory in Hawaii. Although some
astronomers claim that the object is a planet, such a classification
is likely to be extremely contentious.

Amateur observers have discovered another large trans-Neptunian object
with a 30-centimetre telescope in Mallorca. The first data made
public about the object, designated 2003 EL61, suggested that it could
be up to twice the size of Pluto, but more sober assessments make it
about 70% of Pluto's diameter. The object was discovered when the
observers reviewed observations that they had made in 2003. Then they
scoured archives and found the object in images dating back to 1955
that allowed the orbit to be accurately calculated. The object is
about 51 Astronomical Units from the Sun and comes as close as 35 AU,
while Pluto is at an average distance of about 39 AU. The plane
of the orbit is tilted by 28° with respect to the orbital plane of
most planets. making it even more off-kilter than Pluto, which orbits
in a plane tilted by 17°.

New Scientist

Some molecular building blocks of life had already formed by the time
the Universe was only a quarter of its present age, new observations
by the Spitzer telescope reveal. The telescope observed eight
galaxies at an average distance of about 10 billion light-years and
its spectrometer showed the signature of complex molecules in two of
the galaxies. The molecules, called polycyclic aromatic hydrocarbons
(PAHs), each contain about 100 carbon and hydrogen atoms.


£4.99, ISBN 0540087017). SIR PATRICK MOORE takes the novice astronomer
on a guided tour of the stars and constellations of the northern
hemisphere. An accessible work, clearly and concisely written.

Bulletin compiled by Clive Down

(c) 2005 the Society for Popular Astronomy

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