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 Post subject: ENB No. 243 May 11 2008
PostPosted: Sun May 25, 2008 9:23 am 
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The SOCIETY for POPULAR ASTRONOMY
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Electronic News Bulletin No. 243 2008 May 11
===================================================


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/maacvtjaa8Qpbbc8AEAb/


APRIL-MAY FIREBALLS
By Alastair McBeath, SPA Meteor Section Director

Early May has brought a fresh crop of UK fireball observations, with
details on those reported since the roundup in ENB 242 as follows:

Date Time (UT) Magnitude and Notes Observed from
08/04/28-29 ~21:00 Bright Essex
08/05/1-2 22:35 -10/-12?; 3 reports Gwynedd, Cheshire & W Lothian
08/05/2-3 03:30 At least -8; in clouds Devon
08/05/6-7 ~22:17 Very bright; 5 reports W England & Wales

The April 28-29 event may have been a satellite flare, or a point-source
fireball (that is, one heading almost directly towards the observer, so
seeming like a short-lived, very bright point of light). It is not certain if all
three observers saw the same meteor on May 1-2, but the information
so far suggests that is likely. Four of the five witnesses of the May 5-6
event posted some initial notes on the SPA's Observing Forum, at:
http://tinyurl.com/5o2an8 . That meteor may have been trending
generally north to south, perhaps roughly parallel to the British west
coast, but more details are needed to confirm this estimate.

More sightings of these or any other fireballs seen from the British Isles
or places nearby (a fireball is any meteor that reaches at least
magnitude -3) would be welcomed by the SPA Meteor Section.
Details to send are outlined on the "Fireball Observing" page of the
SPA website, at: http://tinyurl.com/l62fh .


LYRIDS 2008
By Alastair McBeath & David Entwistle, SPA Meteor Section

Moonlight and poor weather did nothing to assist observers of the
Lyrids this year, and virtually no positive visual sightings have been
received by the Section so far. Stalwart video observer Enrico Stomeo
in Italy managed some imaging in between clouds on April 19-20,
though Lyrid rates were unimpressive so far ahead of their expected
peak on April 21-22 (as noted in ENB 241; see: http://tinyurl.com/5nchfx ).
However, such problems do not affect radio meteor observing, though
in common with previous years, analysis of the 2008 radio Lyrids
proved challenging. A peak probably due to Lyrid activity was
particularly well recorded by Willy Camps (Belgium), David Entwistle
(England), Pierre Terrier (France) and Felix Verbelen (Belgium). Quite
a number of Belgian observers now rely on the national VVS meteor
observing group's dedicated radio-meteor beacon for their
observations, and these systems recorded a sharp peak lasting only
one or two hours between 01h-03h UT on April 21-22. Observers
elsewhere using longer baselines and more powerful transmitters
recorded increased activity extending over a longer interval, on April 21
and 22. Taking all the currently-available results into consideration,
radio Lyrid activity seemed definitely present between approximately
10:30 UT on April 21, to 00:30 UT on April 23, with the most likely time
for the peak falling between 00:00 and 06:30 UT on April 22. The Lyrid
maximum was predicted to fall sometime between 21h-08h UT on
April 21-22, which broad interval at least was confirmed by the radio
results. It may be possible to narrow the timing further when additional
radio data are available. More information on the radio analysis so far
can be found at: http://tinyurl.com/6llnan .


MARTIAN CLIMATE HAS CHANGED
Brown University

It now seems that Mars' climate has been much more dynamic than has
previously been supposed. After examining high-resolution images
taken last year by the Mars Reconnaissance Orbiter, some researchers
think that ice packs at least a kilometre thick existed along Mars'
mid-latitude belt as recently as 100 million years ago, and they
believe that glaciers flowed in localized areas in the last 10 to 100
million years. They focused on an area called Protonilus Mensae--
Coloe Fossae, which is marked by mesas, massifs and steep-walled
valleys that separate the lowlands in the north from the highlands in
the south. The team looked in particular at a box canyon set in a
low-lying plain. Images show that the canyon has moraines -- deposits
of rocks that mark the limits of a glacier's advance or the path of
its retreat. The rock-deposit lines appear to show that a glacier
flowed up the box canyon, which physically cannot happen. Instead,
the team thought that the ice in the surrounding plain must have grown
higher than the canyon's walls and then flowed downwards onto the top
of the canyon, which had become the lowest point on the ice-laden
land.


ELECTRICAL STORM ON SATURN
NASA

There is a powerful electrical storm raging on Saturn, with lightning
bolts 10,000 times more powerful than those found on Earth. Storms on
Saturn have diameters of several thousand kilometres, and radio
signals produced by their lightning are thousands of times more
powerful than those produced by terrestrial thunderstorms. The radio
waves were first detected on 2007 November 27; Cassini's imaging
cameras did not show the storm until about a week later. There were
similar storms in 2004 and 2006; each lasted for nearly a month, but
this storm is longer-lived by far. The new storm is located in
Saturn's southern hemisphere where the previous lightning storms were
observed by Cassini. Every few seconds it gives off a radio pulse
lasting for about a tenth of a second, which is typical of lightning
bolts and other electrical discharges. Amateur astronomers can see
the storm and have watched it over its five-month lifetime.


PULSATIONS DISCOVERED IN NEW TYPE OF WHITE DWARF
McDonald Observatory

Most stars end their lives as white dwarfs, just remnants left when
all the nuclear fuel in the stars' cores has burned. Until recently,
astronomers knew of only two types of white dwarf stars: those that
have an outer layer of hydrogen (about 80%), and those with an outer
layer of helium (about 20%), whose hydrogen shells have somehow been
stripped away. Then in 2007, a third type was discovered, the 'hot
carbon white dwarfs', which have had both their hydrogen and helium
shells stripped off, leaving their inner carbon layer exposed.

Astronomers calculated that pulsations in such stars were possible.
Just as geologists study seismic waves from earthquakes to learn what
goes on in Earth's interior, so astronomers can study the changes in
light from a pulsating star to learn something about its interior.
The McDonald observers used the 82-inch reflector to look for
pulsators among carbon white dwarfs. They discovered one about 800
light-years away in the constellation Ursa Major, about ten degrees
east-northeast of Mizar, the middle star in the handle of the Plough.
Its light intensity varies regularly by nearly two per cent about
every eight minutes. It has about the same mass as our Sun, but its
diameter is smaller than the Earth's. It has a surface temperature of
19,500 C, but despite its much higher temperature it is only 1/600th
as bright as the Sun owing to its much smaller surface area.


COMPACT GALAXIES IN EARLY UNIVERSE
STSI

Astronomers looking at galaxies in the Universe's distant past have
found nine young, compact galaxies, each with about 200 billion times
the mass of the Sun. The galaxies, each only 5,000 light-years
across, are a fraction of the size of today's galaxies but contain
approximately the same number of stars. Each could fit inside the
central hub of our Milky Way galaxy. The astronomers used the Hubble
telescope and the Keck Observatory in Hawaii to study the galaxies as
they existed 11 billion years ago, when the Universe was less than 3
billion years old; they are still speculating as to how they might
have formed.


PLAN TO SEND A PROBE TO THE SUN
Johns Hopkins University

The Johns Hopkins University Applied Physics Laboratory (APL) is to
send a spacecraft closer to the Sun than any probe has gone
previously, in an effort to find out more about the solar wind that
influences everything in our Solar System. The Solar Probe mission
will observe from a vantage point within the Sun's corona -- its outer
atmosphere -- where the processes that heat the corona and produce
solar wind occur. At its closest approach Solar Probe will fly past
the Sun at 125 miles per second, protected by a carbon-composite heat
shield that must withstand up to 1400 C and survive blasts of
radiation and energized dust at levels well beyond those experienced
by any previous spacecraft.

Scientists have thought about such a mission for more than 30 years,
running into seemingly insurmountable technological and budgetary
limitations. But now an APL-led team has completed a design study for
NASA, and is to design and build the spacecraft on a schedule to
launch it in 2015. The compact, solar-powered probe would weigh about
half a ton; preliminary designs include a 9-foot-diameter, 6-inch-
thick solar shield filled with carbon foam. Two sets of solar arrays
would retract or extend as the spacecraft swings toward or away from
the Sun during several loops around the inner Solar System, making
sure that the panels stay at the proper temperatures and power levels.
Solar Probe will use seven Venus fly-bys over nearly seven years to
shrink its orbit round the Sun, coming as close as 6.6 million
kilometres to the Sun, far within the orbit of Mercury and about eight
times closer than any spacecraft has come before. At its closest
passes the spacecraft must survive solar intensity more than 500 times
what spacecraft experience while orbiting the Earth.


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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