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The SOCIETY for POPULAR ASTRONOMY
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Electronic News Bulletin No. 193 2006 March 19
====================================================


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
offer by visiting http://popastro.c.topica.com/maaeBwvabo7zNcixLLVb/

Philip's, a publisher of astronomy books and planispheres for the
amateur astronomer, is sponsoring this bulletin. For information on
Philip's title see the end of this bulletin.


FIREBALLS IN EARLY MARCH
By Alastair McBeath, SPA Meteor Section Director

A magnitude -5/-9 fireball was spotted from Nottinghamshire around
20:22 UT on March 5-6, while another notably bright event seems to
have come down over south-west England, probably within five minutes
of 18:40 UT, on March 10-11. No eye witness sightings of the March
10-11 event have yet been received however, only very vague forwarded
reports from Police and Coastguard sources, which suggested that
fireball
was seen from places on the Hampshire coast westwards, into Somerset,
Devon, Cornwall and points adjacent.

Other observations of these, or any additional bright meteors, should be
sent to the SPA as soon as possible, please. Details of what to submit
and
where to can be found on the "Fireball Observing" page off the meteor
homepage at: http://popastro.c.topica.com/maaeBwvabo7zOcixLLVb/ .

To clarify some recent queries, by international definition, a fireball
is any
meteor which reaches at least magnitude -3 with respect to the stars and
planets (so in other words, a fireball is significantly brighter than
even the
brightest night-time star, Sirius). Jupiter forms a convenient lower end
to
the scale quite often, since at its best, it gets to be about magnitude
-2.9
at its most favourable oppositions. Jupiter is visible from the late
evening
hours just now, and is presently around magnitude -2.3. It will reach
magnitude -2.5 for nearly a month centred on its May 4 opposition this
year. Consequently, for a meteor to be classed as a fireball, it would
need
to be at least a little brighter than Jupiter. Any meteor as bright as
Venus
even at its faintest (around magnitude -3.5) would be a definite
fireball.


APRIL'S LYRIDS
By Alastair McBeath, SPA Meteor Section Director

Lyrid meteors can be seen from April 16-25, and the shower should peak
on April 22, perhaps around 16:30 UT, but more certainly at sometime
between 08:30-19:00 UT on that date. Regrettably, all these timings are
in daylight for Britain, but with a waning crescent Moon rising only
after
the start of morning twilight on nights astride the maximum, it should
be
possible to see something of the shower near then at least. The Lyrid
radiant for the peak is at RA 18h04m, Dec +34 degrees, by the Hercules-
Lyra border but actually in Hercules, just over a Lyre's length (the
distance from Vega to Gamma Lyrae) south-west of Vega. It rises to a
usable elevation by 22:30 UT or so for the UK, and its visibility
improves
throughout the night. Zenithal Hourly Rates (ZHRs) should be around 20-
25 if the peak falls near 16:30 UT, but lower if it happens away from
then,
and the maximum is generally brief, lasting a few hours at most. Rare
longer peaks have been seen though, lasting more than eight hours (as
last
in 2001), and still rarer strong events do occur sometimes (most
recently
in 1982, with ZHRs around 90). Lyrids are medium-fast meteors, and
can be very bright sometimes.

For more information on April's active meteor showers, see the SPA's
monthly meteor notes off the meteor homepage.


NEW DESERT CRATER "KEBIRA" IN EGYPT
By Alastair McBeath, SPA Meteor Section Director

A team from Boston University in Massachusetts, USA, led by "King"
Farouk El-Baz (the same geophysicist who trained the NASA Apollo
lunar astronauts to look for types of crater and volcanic structures on
the
Moon, nicknamed after the then-contemporary Egyptian King Farouk),
has announced the discovery of a new probable impact crater near the
northern tip of the Gilf Kebir highlands in south-west Egypt, near the
Libyan border (around 24 degrees 41' N, 24 degrees 58' E). The 31 km
diameter structure was found in satellite images, and named after the
Arabic word for "large", "kebira", because the team suggested it had
passed unnoticed for so long thanks to its unusual size, apart from the
typical problems in identifying Earth craters thanks to natural erosion.

Although ground investigations will now be needed to confirm the
structure's origin, and to try to date it, it has already been mentioned
as
perhaps associated with the extensive nearby strewnfield of Libyan
Desert
Glass, a roughly 80 km x 25 km oval area whose long axis trends
approximately north-south, beginning at the northern edge of the Gilf
Kebir. This Glass occurs as fragments of translucent yellow to pale
green
high-silica material scattered over the desert, and although not
absolutely
certain, it is thought to have been produced in a high-temperature
event,
possibly an Earth-impact, but perhaps more probably a Tunguska-like
airburst. No definite conclusion has been reached about the cause as
yet.

Two other impact craters are known to lie within 140 km west of the
Libyan Desert Glass field, in east Libya, called the BP and Oasis
structures, whose respective centres are close to 25 degrees 19' N, 24
degrees 20' E, and 24 degrees 35' N, 24 degrees 24' E. The BP
structure is some 2.8 km in diameter while Oasis is about 11.5 km in
size.
Both have been dated as created ~120 million years ago, significantly
older than the estimated age of ~30 million years for the Libyan Desert
Glass fragments, so they cannot be associated with the Glass's
formation.

Useful links to the Kebira crater's discovery announcement can be found
via the SPA's General Chat Forum at:
http://popastro.c.topica.com/maaeBwvabo7zPcixLLVb/ , while a
detailed summary of information on the Libyan Desert Glass, the BP and
Oasis impact structures is in pp.152-160 of Joe McCall's "Tektites in
the
Geological Record", published by the Geological Society, London, in
2001.


A LUNAR OCCULTATION OF THE BRIGHTEST STAR!
By Jon Harper (Occultation Section)

2006 March 29

The path of this total eclipse begins at the most easterly point of
South America, crosses the Atlantic into Africa, and continues in a
north-easterly direction to the Mediterranean and Turkey. It then
proceeds across the eastern edge of the Black Sea, touching the
northern shore of the Caspian Sea, before ending at sunset on the
Steppes of Central Asia. For those not travelling abroad to watch
totality, the best place in the UK to observe the partial phase will
be Dover, where at 10.34 UT, about 39% of the south-eastern portion of
the Sun's disc will be covered. At Blackpool, the magnitude of the
eclipse is smaller, with only 22% cover, and at Londonderry a mere
16.5% is hidden. The eclipse will be of a similar magnitude in
Scotland.

At Scarborough on the North Yorkshire coast, midway between London and
Edinburgh, the contact times are as follows:

First Contact: 9h 51m 25s UT
Maximum Phase (0.243 of Sun's diameter covered): 10h 36m 13s UT
Last Contact: 11h 21m 53s UT

People requiring specific times for their locations should get in
touch with the Director.

The following solar eclipse in the UK is again a partial one, due to
take place during the morning of 2008 August 1.

Remember, as with all solar eclipses, in no circumstances should
you look at the Sun directly, either with the unaided eye or through
optical instruments. The safest method of observing the Sun is by
projecting its image onto a card.


ECLIPSE WEBCAST
By Peter Grego

I am planning a solar-eclipse webcast on my website at
www.lunarobservers.com on 2006 March 29, 09:45 to 11:20 UT.
Instrument used will be a 200mm SCT (Meade LX90) with Inconel solar
filter. Camera: ToUcam PCV740.


JUPITER'S NEW RED SPOT
NASA

Jupiter is growing a new red spot that is officially named `Oval
BA'. It is about half the size of the famous Great Red Spot and
almost exactly the same colour. Oval BA first appeared in 2000 when
three smaller spots collided and merged. A similar merger centuries
ago may have created the original Great Red Spot, a storm twice the
size of the Earth and at least 300 years old. At first, Oval BA
remained white, the same colour as the storms that combined to
create it, but in recent months it has changed to brown and then red.


NASA KILLS OFF ASTEROID MISSION
New Scientist

NASA has confirmed that the `Dawn' mission to study two of the largest
main-belt asteroids, Vesta and Ceres, has been cancelled. The mission
had been in development for more than four years but had overrun
budget and experienced many technical problems. NASA approved the
mission in 2001 December as the ninth in its Discovery programme,
which works under the `better, faster, cheaper' motto. It was
originally scheduled to be launched this June on a journey to study
the 550-km-diameter Vesta and the 950-km Ceres in 2011 and 2015
respectively. The cancellation leaves NASA with no current asteroid-
studying mission.


FORECAST FOR NEXT SUNSPOT CYCLE
NCAR

Solar minimum took place during 2006 February when the Sun was devoid
of spots all month. According to a computer model of solar dynamics
developed at the [US] National Center for Atmospheric Research (NCAR),
the next sunspot cycle will be 30-50% stronger than the last one and
begin as much as a year late. Predicting the Sun's cycles accurately,
years in advance, would help societies plan for active bouts of solar
storms, which can slow satellite orbits, disrupt communications, and
bring down power systems. The forecasts are generated, in part, by
tracking the sub-surface movements of the sunspot remnants of the
previous two solar cycles.


POTENTIAL LIQUID WATER ON ENCELADUS
NASA

The Cassini spacecraft may have found evidence of liquid water
reservoirs on Saturn's moon Enceladus. The images show icy jets and
towering plumes ejecting huge quantities of particles at high speed.
The jets might be erupting from near-surface pockets of liquid water
above 0 degrees Celsius, like cold versions of the Old Faithful geyser
in Yellowstone National Park in the US. Scientists previously knew
that active vulcanism exists on Jupiter's moon Io and possibly
Neptune's moon Triton, as well as on the Earth. In the spring of
2008, scientists will get another chance to look at Enceladus when
Cassini is due to fly within 350 km of it.


EXTREME HELIUM STARS MAY BE DOUBLE DEGENERATES
New Scientist

The Hubble Space Telescope has revealed chemical evidence for the idea
that a rare type of hydrogen-depleted supergiant star is created
through the merger of two white dwarfs. Scientists have located 21
so-called `extreme helium stars' in the Galaxy. They are unusually
luminous stars that are much larger and hotter than the Sun despite
being less massive. Their name reflects their abundance of surface
helium and peculiar dearth of hydrogen.

Since the discovery of the first extreme helium star in 1942, two
theories have come to dominate the discussion of their origin. One,
dubbed the final-flash (FF) model, suggests that an outer helium
layer of a cooling white dwarf ignites, producing an extra thermal
pulse that balloons the star into a giant. In such circumstances, an
extreme helium star might result as the giant then contracts.
The alternative theory, known as the double-degenerate (DD) model,
begins with a binary star system involving a helium-rich white dwarf
and a more massive carbon&oxygen-rich white dwarf orbiting one another
for billions of years. If the two eventually got too close, the
smaller star would rapidly be broken into a disc, and the larger star
would consume it, becoming a supergiant star enriched in surface
helium.

Now astronomers from the Indian Institute of Astrophysics have
published chemical abundances for 17 extreme helium stars and found
that they largely match the DD model's predictions. They used
Hubble's imaging spectrograph to make new measurements of seven stars
in the ultraviolet, and made additional optical measurements with the
McDonald Observatory's 2.7-m telescope in Texas and the 2.3-m
Vainu Bappu telescope in India. They measured the stars' surface
abundances of 18 elements, including the heavy elements yttrium and
zirconium, and claim that they match what would be expected from the
DD model.


STARDUST FINDINGS MAY ALTER VIEW OF COMET FORMATION
Reuters

Particles from Comet Wild-2 that were collected and returned to Earth
in a capsule from the Stardust spacecraft show dozens of minerals that
form only in extreme heat -- a finding that complicates theories about
how the Solar System formed. The grains include a titanium-vanadium-
nitrogen mineral that forms only in temperatures higher than 1,100
degrees Celsius. The minerals must either have formed in the hottest,
innermost region of the nebula that eventually became our Solar
System, or have come from another star. If they were formed in our
Solar System, then they would have had to be closer than Mercury to
the Sun to form, and no mechanism has been identified that would
transport them far outwards to reach the Kuiper Belt region.
Researchers plan extensive studies to try to determine the chemical
histories of the sample particles, which eventually will reveal
whether the grains were heated by the Sun or another star. Between
150 and 200 samples from the comet are currently circulating among
scientists and research labs around the world. Next month, work
begins on another set of samples collected during the mission,
interstellar dust grains. Unlike the comet samples, the bits of
interstellar dust picked up during Stardust's travels are tiny.
Scientists plan an Internet-based detection programme of volunteers
who will use their home computers to scrutinize images and try to
identify any particles.


NEPTUNE-SIZE PLANET FOUND
New Scientist

A Neptune-size planet has been discovered in the outskirts of a
planetary system 9000 light-years away. It is the second known planet
of its kind. Around 170 extra-solar planets have been discovered so
far, most of them gas giants like Jupiter circling nearby stars. The
majority have been found because their gravity makes their parent
stars wobble. The new planet was discovered by an alternative
technique called microlensing which detects planets around much more
distant stars. Microlensing can occur when one star passes directly
in front of another, as seen from Earth.

In 2005 April, an astronomical collaboration called OGLE noticed a
bright microlensing event in the central bulge of the Milky Way.
Analysis of nearly 1500 images suggests that the lensing (foreground)
star is about half as massive as the Sun and has a Neptune-mass
planet. The planet lies about 2.7 times as far from its star as the
Earth lies from the Sun, and the astronomers estimate that its
temperature is -200°C. The new planet has no giant Jupiter-like
siblings.


DARK MATTER IN DISTANT GALAXIES
ESO

An international team of astronomers has observed several dozen
distant galaxies to try to shed new light on how galaxies that are far
away -- and thus seen as they were when the Universe was significantly
younger -- evolve into ones like those nearby. In particular, they
wanted to study the importance of dark matter in galaxies. In nearby
galaxies, there seems to be about 30 times as much mass in dark matter
as there is mass in stars. The astronomers discovered that as many as
40% of distant galaxies were `out of balance' -- their internal
motions were very disturbed -- a possible sign that they are still
showing the aftermath of collisions between galaxies. When they
limited themselves to only those galaxies that have apparently reached
equilibrium, they found that the relationship between the dark matter
and the stellar content did not appear to have changed significantly
during the last 6 billion years.


NEXT BULLETIN DELAYED

Owing to the solar eclipse and consequential holidays, the next
bulletin will not be issued till April 16.




PHILIP'S RECENT TITLES:

Philip's The Sky at Night Volume 2 is the latest volume in Sir Patrick
Moore's series of essays written to accompany the BBC television
series of the same name. It tracks developments in astronomy,
astrophysics and space exploration in the period from 2001 November
to 2005 March -- £9.99
Philip's Stargazing 2006 by Heather Couper and Nigel Henbest - £6.99
Published last year:
Philip's Solar System Guide by Peter Grego contains an abundance of
information and images, and is a practical and colourful introduction to
our corner of the Universe. It describes how to observe not only the
planets but also the Moon, Sun, comets, meteors, asteroids and other
objects found within our Solar System -- £9.99

Philip's Solar System Observer -- a pack for the amateur Solar-System
observer. It contains three items for exploring and enjoying our
corner of the Universe: Philip's Solar Observer's Guide, Philip's Map
of the Solar System and Philip's Solar System Phenomena poster --
£12.99

For more information on those and other Philip's titles please visit
www.philips-maps.co.uk or call 020 7644 6935 for a catalogue.




Bulletin compiled by Clive Down

(c) 2006 the Society for Popular Astronomy


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