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 Post subject: ENB No. 239 March 2 2008
PostPosted: Sun Mar 09, 2008 12:22 pm 
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Electronic News Bulletin No. 239 2008 March 2

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

By Alastair McBeath, SPA Meteor Section Director

As regular users of the SPA website will be aware, there has been a
number of problems over the past month with the site's service provider.
Though this has nothing to do with the SPA at all, it has prevented or
delayed the usual updates to various parts of the site, including the
Meteor Section's "Recent Fireball Sightings" page. To bring things up
to date in that regard, the following table covers all the fireballs
notified in recent weeks:

Date Time (UT) Magnitude and Notes Observed from
08/02/8-9 ~21:46 -6; imaged Netherlands
08/02/8-9 22:45 -8/-10? Suffolk
08/02/10-11 ~03:00 Bright Hertfordshire
08/02/11-12 ~20:55 -8/-12; 19 reports UK, Channel Islands & Netherlands
08/02/11-12 21:45-21:50 Very bright Kent
08/02/11-12 22:45 +/- 15m -7/-9?; 4 reports SE England
08/02/11-12 ~23:00 Very bright Lincolnshire
08/02/12-13 ~22:15-22:35 -7/-9?; 6 reports England & N Wales
08/02/14-15 ~22:15 -5/-7 Manchester
08/02/19-20 ~23:00 Bright Yorkshire

Unfortunately, despite the additional reports since the previous ENB
(, it has not been possible to further
refine the approximate atmospheric paths for any of these events,
though attempts to secure more details from the observers
continue. The first February 8-9 fireball was imaged by Klaas Jobse's
all-sky camera in Holland, like the first February 11-12 event, and
both can be seen on Klaas's website, via:
. Commentaries and some of the initial sightings from February 11-12
and 12-13 can still be read on the SPA's Observing Forum topic
beginning at:

As ever, observations of any fireballs seen from Britain or places
nearby (a fireball is any meteor of magnitude -3 or brighter), are
welcomed by the SPA Meteor Section, including belated sightings of
any of the above. Advice on details to send me is given on the
"Fireball Observing" page of the SPA website, at: .

By Alastair McBeath, SPA Meteor Section Director

Meteoritic impact flashes on the unilluminated part of the Moon,
recorded by sensitive video cameras, have been reported here from time
to time, since the first such event during the Leonid storm in 1999.
A round-up of impact events prior to NASA's first such successful
recording during the Taurid "swarm" return of late 2005, including
web-links via the SPA Forum, was in ENB 188
( ), while the most recent such notice was in
ENB 213, from results during the 2006 Geminids
( ). More such impacts have been detected by
various observers since, and NASA are now nearing their hundredth such
recording, but an independent observer has just scooped them, by
catching the first impact flash during an eclipse! The event occurred
at 03:19:57.49 UT on February 21, about six minutes before mid-eclipse
in a bay in the southern Oceanus Procellarum. It was caught by an
experienced "lunar meteor" observer, George Varros in Maryland, USA,
using an 8-inch Celestron telescope and a digital video camera. Stills
from the event, plus a link to the full movie, can be found on NASA's
Spaceweather website, for February 23.

By Alastair McBeath, SPA Meteor Section Director

Information and online registration for this year's International
Meteor Conference (IMC) is now available on the International Meteor
Organization's (IMO's) website, at: . The
Conference will be held in Sachticka, central Slovakia, about 8 km
from Banská Bystrica, from September 18-21, and the booking fee (which
includes full board at the conference hotel, access to all sessions
and the excursion, plus a copy of the IMC Proceedings) is 140 Euros
till June 30, after which it rises to 150 Euros. The official language
is English. Although the IMC is the IMO's main annual meeting, and
includes its General Assembly, you do not need to be an IMO member to
register for, or attend, the IMC.

As usual, the IMC will bring together amateur and professional meteor
enthusiasts from around the world. IMCs are always great fun for
anyone with a real interest in meteors. There is a daily programme of
lectures and poster presentations, dealing with all branches of meteor
astronomy, plus the excursion, but despite this planned activity,
there is always ample time to talk to the many people present with
similar interests, and even to get involved in the "astro-
entertainment" party evening of songs and sketches. If you still need
persuading, the IMO website also has a whole series of photos and
personal recollections from past IMCs, and the International Meteor
Weekends and Meteor Seminars which preceded them, back to 1979.

Cornell University

Astronomers using the big Arecibo radio telescope in Puerto Rico on
February 11 discovered that the 'near-Earth' asteroid 2001 SN263 is
triple. Subsequent radar images have confirmed that the three
objects, about 7 million miles from the Earth, are revolving around
each other. The main body is approximately spherical with a diameter
of roughly 2 km, the larger of its two satellites is about half that
size, while the smallest object is about 1,000 feet across --- the
same size as the Arecibo telescope. Other triple asteroids have been
found in the main asteroid belt between Mars and Jupiter and beyond,
but this is the first near-Earth system, where the actual shapes of
objects can be clearly seen.

Double, or binary, asteroid systems are quite common; about one in six
near-Earth asteroids is known to be binary. The orbits of binary, and
now triple, asteroid systems allow astronomers to determine the masses
of the objects and to assess whether the orbits are stable over
millennia or have formed very recently.


Venus Express has revealed a planet of extraordinarily changeable and
extremely large-scale weather. At visible wavelengths of light
cloud-covered Venus is all but featureless, but in the ultraviolet it
reveals a truly dynamic nature. Bright hazes appear in a matter of
days, reaching from the South Pole to the low southern latitudes and
disappearing just as quickly. During such episodes, the brightness of
the southern polar latitudes increases by about a third and fades just
as quickly. Transient dark and bright markings stripe the planet,
indicating regions where solar ultraviolet radiation is absorbed or
reflected, respectively.

At an altitude of about 70 km and below, Venus's carbon-dioxide-rich
atmosphere contains small amounts of water vapour and gaseous sulphur
dioxide. They are usually buried in the cloud layer that blocks our
view of the surface at visible wavelengths. However, if some
atmospheric process lifts those molecules up above the cloud tops,
they are exposed to solar ultraviolet radiation, which breaks the
molecules, making them highly reactive. The fragments find each other
and combine quickly to form sulphuric acid particles, creating the
haze, in a process that is similar in many ways to the one that makes
smog over cities. Venus Express has made over 600 orbits of the
planet, and scientists are now hoping to be able to identify repeating
patterns of behaviour in the build-up and decrease of the haze layer.


Saturn's largest moon Titan has hundreds of times more liquid
hydrocarbons than all the known oil and natural-gas reserves on the
Earth, according to new Cassini data. The hydrocarbons rain from the
sky, collecting in vast deposits that form lakes and dunes. At a
temperature of minus 179 C, Titan is a far cry from Earth. Instead of
water, liquid hydrocarbons in the form of methane and ethane are
present on the moon's surface, and complex organic molecules (dubbed
tholins) probably make up its dunes.

Cassini has mapped about 20% of Titan's surface with radar. Several
hundred lakes and seas have been observed, with each of several dozen
estimated to contain more hydrocarbon liquid than Earth's oil and gas
reserves. The dark dunes that run along the equator contain a volume
of organics several hundred times larger than Earth's coal reserves.
The question of how much liquid is on the surface is an important one
because methane is a strong greenhouse gas on Titan as well as on
Earth, but there is much more of it on Titan. If all the observed
liquid on Titan is methane, it would last only a few million years,
because as methane escapes into Titan's atmosphere, it breaks down and
escapes into space. If the methane were to run out, Titan could
become much colder. Scientists believe that methane might be supplied
to the atmosphere by venting from the interior in cryo-volcanic
eruptions. If so, the amount of methane, and the temperature on
Titan, may have fluctuated dramatically in Titan's past.

New Scientist

The promising but labour-intensive 'micro-lensing' technique to find
extra-terrestrial planets has netted its first multiple-planet system.
More than 250 planets have been discovered orbiting other stars. Most
were found by the radial-velocity technique, which searches for
tell-tale wobbles in a star caused by the gravitational attraction of
an orbiting planet. Micro-lensing, on the other hand, detects planets
by watching how their gravity bends and focuses the light of a distant
background star. As one star passes by a more distant star as seen
from Earth, the light path from the background star is gravitationally
bent and the star is seen magnified for a period of days to weeks
during the event. If the nearer star has a planet, the planet's
gravity can give an added boost to the background star's light for a
few hours. The events occur randomly and do not repeat themselves,
making finding them very time-consuming. In fact, only four planets
have previously been discovered in that way, but the technique holds
promise because it can detect smaller planets and planets in more
distant orbits than the radial-velocity method, which is best at
detecting massive objects in tight orbits around their host stars.
Now, micro-lensing has revealed two planets around a single star, the
first multiple-planet system discovered with the technique.

In 2006 March/April, a background star about 26,000 light-years away
was observed to brighten and dim over a period of about two weeks.
Additional, smaller bumps complicated the overall rise and fall,
suggesting two massive planets orbited a star about 5000 light-years
distant. One planet appears to be about 71% the mass of Jupiter,
while the other is about 27% Jupiter's mass, or about the same as
Saturn. The more massive one was seen at half the distance from the
star of the lesser one, as Jupiter is placed in relation to Saturn,
but in actual terms the distances are only half as great as those of
our Jupiter and Saturn.

University of Hawaii

An international group of astronomers has reported that the Sun-like
star Tau Bootis, which is visible to the unaided eye and is only 51
light-years away, reversed its magnetic field north to south at some
time during the last year. It has been known for many years that the
Sun's magnetic field changes its direction every 11 years, but this is
the first time that such a change has been observed in another star.
The astronomers, who used of Canada-France-Hawaii telescope on Mauna
Kea, caught the reversal of Tau Bootis in only two years of
observations; possibly the event occurs more frequently on that star
than on the Sun, and the astronomers hope to continue to monitor it to
see how long it will be before the reversal occurs again. Magnetic-
field reversals on the Sun are closely linked to the varying number of
sunspots seen on the Sun's surface. The last solar minimum (the time
when number of sunspots was the lowest and the magnetic reversal
occurred) was in 2007. The first sunspot of the new cycle appeared
this January.

Tau Bootis has a giant planet (about 6.5 times the mass of Jupiter)
orbiting it at only one twentieth the distance between the Sun and the
Earth; it appears that the tidal torques between star and planet are
such that the surface of the star co-rotates with the planet's orbital
motion, in the same way as the Moon co-rotates with its orbit around
the Earth so we see only one side of it.

Chandra X-ray Center

Scientists have reported the possible detection of a binary-star
system that was later destroyed in a supernova explosion. Near the
position of a recently detected supernova, they discovered its
possible progenitor in images taken by the Chandra X-ray telescope
more than four years before the explosion. The supernova, known as SN
2007on, was identified as a Type Ia supernova. Astronomers generally
agree that Type Ia supernovae are produced by the explosion of a
white-dwarf star in a binary-star system, but they are not agreed as
to whether the explosion is caused by a collision between two white
dwarfs or because a white dwarf became unstable by accreting too much
material from a companion star. If the supernova explosion is caused
by material falling from a companion star onto the white dwarf, fusion
of that material on the surface of the star should heat the star and
produce a strong source of X-radiation before the explosion. When the
supernova explosion occurs, the white dwarf is expected to be
completely destroyed and then would be undetectable in X-rays. In the
merger picture, the intensity of X-ray emission before the explosion
is expected to be much weaker.

There appears to have been a fairly strong X-ray source at
approximately the position of SN 2007on 4 years before the explosion.
The small number of X-ray sources in the field implies that there is
only a small chance of an unrelated source being so close by
coincidence. Also, the X-ray source has properties similar to those
expected for fusion on a white dwarf, unlike most X-ray sources in the
sky, so the evidence seems to favour the accretion picture. However,
in follow-up studies with higher-quality optical images, there
appeared to be a small but significant difference between the
positions of the supernova and the X-ray source, so the X-ray source
may, after all, not represent the progenitor.


Ulysses, the mission to study the Sun's poles and the influence of our
star on surrounding space, is coming to an end. After more than 17
years in space -- almost four times its expected lifetime -- the
mission is finally succumbing to its harsh environment and is likely
to finish in the next month or two. Ulysses is a joint mission
between ESA and NASA. It was launched in 1990 from a space shuttle
and was the first mission to study the environment of space above and
below the poles of the Sun. The reams of data that Ulysses has
returned have changed the way scientists view the Sun and its effect
on the space surrounding it.

Ulysses is in a six-year orbit around the Sun. Its long path through
space carries it out to Jupiter's orbit and back again. The further
it gets from the Sun, the colder the spacecraft becomes. If its
temperature drops to 2 degrees C, its hydrazine fuel will freeze.
That has not been a problem in the past because it carries heaters to
maintain a workable on-board temperature. The spacecraft is powered
by the decay of a radioactive isotope, and over the 17 years the power
it has been supplying has been steadily dropping. Now, the spacecraft
no longer has enough power to run all of its communications, heating
and scientific equipment simultaneously. Scientists expect certain
parts of the spacecraft to reach 2 C pretty soon. Frozen hydrazine
will block the fuel pipes, making the spacecraft impossible to
manoeuvre. In an attempt to solve the problem, the project team
approved a plan temporarily to shut off the main spacecraft
transmitter to release 60 watts of power that could go to the heater,
and to turn it back on again from time to time when data were to be
transmitted. Unfortunately, during the first test of the method in
January, the power to the transmitter failed to turn back on.

The SPA Electronic News Bulletins are sponsored by the Open University.

Bulletin compiled by Clive Down

(c) 2008 the Society for Popular Astronomy

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