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The SOCIETY for POPULAR ASTRONOMY
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Electronic News Bulletin No. 219 2007 April 15
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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/maageHHabxRzfcixLLVb/


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

Continuing the procession of single-observer fireball sightings since
ENB 218, recently reports have come through as follows: March
26-27, probably between 20:00 and 20:15 UT, a bright fragmenting
event seen from Worcestershire; April 2-3, a clearly brilliant event as
it occurred in full daylight around 17:25 UT, spotted from Norfolk;
two separate events on April 5-6, though both coincidentally timed
at ~22:05 UT, and both of at least magnitude -4, one each from
Caithness and Staffordshire (see:
http://popastro.c.topica.com/maageHHabxRzgcixLLVb/ on the
SPA's Observing Forum for details); April 6-7, within five minutes
of 20:45 UT, probably of magnitude range -4/-6, observed from the
Isle of Man; April 8-9 at 00:11 UT, a fragmenting event of magnitude
-3 or so, reported from Hampshire; and another magnitude -3 or
brighter meteor at 20:15 UT on April 9-10, from Wiltshire.

As always, fireball observations (fireballs are meteors of at least
magnitude -3) made in the British Isles or nearby are welcomed at the
Meteor Section, whether of any of the above objects or not. Notes
on what information to send and where to can be found on the
Section's Fireball Observing webpage at:
http://popastro.c.topica.com/maageHHabxRzhcixLLVb/ .


LYRIDS 2007
By Alastair McBeath, SPA Meteor Section Director

The Lyrid meteor shower will be starting up around April 16 (lasting
till
April 25), and it should peak next weekend, on April 22/23, perhaps
around 22h30m UT, but almost certainly at sometime between
14h45m-01h45m UT then. The maximum comes with a waxing
crescent Moon (first quarter is on April 24) which sets surprisingly
late, between 01h30m-02h00m UT for the UK on April 22/23, but
at least it will be westering and sinking lower by the time the shower
radiant has risen to a usable elevation, after 22h30m UT or so. The
closer the peak falls to 22h30m, the higher its Zenithal Hourly Rates
(ZHRs) are likely to be, perhaps 20-25 or more. The average ZHR
is 18, and it tends to be lower the further the maximum happens away
from this "ideal" time. The peak is often quite short, lasting only a
few
hours, but occasionally more prolonged maxima, lasting for 8+ hours
have been seen, recently in 2000 and 2001, and rare strong ZHRs of
up to 90 (last in 1982 over the USA) may occur too. Thus, when there
is little or no Moon, as to an extent this year, the shower is always
one
to watch. Lyrids are medium-fast meteors, and can be very bright
sometimes. For best results, watch as much clear sky as you
comfortably can, facing away from the Moon but not too near the
Lyrid radiant (which is around the Lyra-Hercules border for the peak)
from about midnight BST onwards. More details, plus a radiant chart,
can be found on April's meteor webpage at:
http://popastro.c.topica.com/maageHHabxRzicixLLVb/ .
Good luck, clear skies, and let me know how your observing went!


PLANETS Of DOUBLE STARS COMMON
Space.com

Astronomers using the Spitzer space telescope have found that
double-star systems are just as likely as single stars to be
surrounded by dusty debris discs. Such discs are believed to be made
up of asteroid-sized rock chunks and other material that might be left
over from planets that might have formed in the systems concerned.
Many stars like our Sun each have at least one stellar companion;
astronomers have theorised that planets could form in certain parts of
binary systems despite the varying gravitational effects, and the new
study provides some support for that idea.

Researchers looked for discs in 69 binary systems more massive and
younger than our Sun and between 50 and 200 light-years away. They
found that about 40% of the systems had discs. That frequency is a
bit higher than that for a comparable sample of single stars.
Surprisingly, most of the debris discs found in the new survey were
around so-called tight binary systems, where the stars are separated
by 500 AU or less. Scientists know of about 50 planets in double
systems, but each of them belongs to one particular component in a
'wide' binary, where the stars are separated by about 1,000 AU and the
second star is enormously further away than the planet is from the
first star. Some scientists had previously argued that planet
formation would be stifled in tight binary systems because of the
large gravitational interactions between the stars.


DUST BLAMED FOR WARMING IN MARS
New Scientist

Using global circulation models similar to those used to analyse the
Earth's changing climate, NASA scientists find that Mars seems to have
warmed by about 0.65°C in the three decades since the Viking mission
first provided detailed mapping of the whole planet. That warming can
be explained entirely by the scouring away of light-coloured dust
from darker areas of the surface, causing an increase in the
absorption of solar radiation. The effect is greatly amplified by
positive feedback: the warmer ground causes stronger winds, which in
turn scour away more of the light dust and lead to greater warming.
It is believed that the mechanism can account for the rapid warming
that has been seen in the disappearing polar caps, which are turning
directly from solid to vapour at a rapid rate.

The new modelling shows that the heating produced by those changes is
of the same order of magnitude as that required for the rapid removal
of the polar ice. The model predicts that the winds will build up so
much that at some point they will trigger a global dust storm such as
has sometimes been seen on Mars, redistributing the light dust over
most of the surface and starting the process over again. While the
dust redistribution may be unique to Mars, the Earth may have
analogous feedback processes that can amplify changes in surface
reflectivity -- in this case, mostly based on changes in sea ice and
snow cover.


STAR'S DOUBLE EXPLOSION
New Scientist

This item refers to a star, in a galaxy 77 million light-years away,
that survived a massive explosion only to be destroyed in a second
blast just two years later. The star appears to have been a
Wolf-Rayet object, a type of very hot star which begins its existence
with more than 40 times the mass of the Sun. It first exploded on
2004 October 20, when it was so bright that the amateur astronomer who
discovered it initially mistook it for a supernova. The 2004
explosion was not fatal, but the star underwent a second explosion on
2006 October 11, when it was indeed a supernova, which was named
SN 2006jc.

That was the first time that astronomers have witnessed a star suffer
a pair of explosions, with the second one being a supernova. Indirect
evidence suggests that something similar happened in one other case,
however. Astronomers studying the expanding blast wave from a
supernova called 1994W found signs that it had ejected material in a
major outburst about 1.5 years earlier, but that original blast was
not observed directly. The highly unusual demise of SN 2006jc has
aroused the curiosity of astronomers, who have followed the evolution
of the supernova with a variety of telescopes. It seems certain the
first explosion must somehow be connected with the star's destruction
two years later.


SATELLITES OF JUPITER AND SATURN, RING OF URANUS
IAU

The IAU has approved the following new designations and names of
satellites of Jupiter and Saturn:

Jupiter XLIX Kore = S/2003 J 14

Saturn XXXVI Aegir = S/2004 S 10
Saturn XXXVII Bebhionn = S/2004 S 11
Saturn XXXVIII Bergelmir = S/2004 S 15
Saturn XXXIX Bestla = S/2004 S 18
Saturn XL Farbauti = S/2004 S 9
Saturn XLI Fenrir = S/2004 S 16
Saturn XLII Fornjot = S/2004 S 8
Saturn XLIII Hati = S/2004 S 14
Saturn XLIV Hyrokkin = S/2004 S 19
Saturn XLV Kari = S/2006 S 2
Saturn XLVI Loge = S/2006 S 5
Saturn XLVII Skoll = S/2006 S 8
Saturn XLVIII Surtur = S/2006 S 7

The IAU has designated the Uranian ring 1986 U the 'zeta ring'.


'YOUNG' STARS MAY REALLY BE ANCIENT
New Scientist

A new study claims that 'young' stars that seem to have formed
impossibly close to our Galaxy's supermassive black hole could in fact
be ancient interlopers merely masquerading as youngsters. Several
clusters of what appear to be massive young stars have been found just
a few dozen light-years from the black hole at the centre of the
Galaxy. However, that is puzzling, since some astronomers think that
the black hole's intense gravity should rip apart gas clouds before
they have a chance to condense and form stars. At the same time, such
massive stars are too short-lived to have survived a journey from much
farther out.

Now, US astronomers have proposed that the clusters are actually old
and look young only because they are collecting a lot of fresh gas in
the region. They believe that the clusters migrated to the Galactic
Centre from elsewhere, gradually spiralling inwards as they lost
energy owing to the drag exerted by stars and gas that they
encountered in their orbits. Although most of the stars in each
cluster would be ejected in the migration process, the cluster's inner
core could survive all the way to the black hole's neighbourhood.
Once there, white dwarfs and neutron stars, which are known to collect
in the centres of massive star clusters, could absorb material from
nearby gas clouds. They would heat up and glow where the gas fell on
them, making them appear as bright as young, massive stars. The idea
avoids a problem associated with the concept that the clusters formed
where they are now. Unless such star-formation began only recently,
successive generations of stars over the Galaxy's lifetime would have
left behind a lot of heavy elements near the Galactic Centre --
something that is not seen there.


WATER DETECTED ON DISTANT PLANET
BBC News

Water has been detected in the atmosphere of a planet outside our Solar
System. The planet, known as HD 209458b, is a Jupiter-like gas giant
located 150 light-years from Earth in the constellation Pegasus. Other
scientists, however, reported in February that they were unable to find
evidence of water in the planet's atmosphere, or in another Jupiter-
like planet, so the question may not be definitely settled.

Water vapour was expected to be present in the atmospheres of most
known extra-solar planets, even those that orbit more closely to their
parent stars than Mercury is to our Sun. For the majority of
exoplanets, their close proximity to their parent stars has made
detecting water and other compounds difficult. The identification
reported here depends on the fact that, as seen from Earth, HD 209458b
passes directly in front of its star in every 3.5-day revolution. As
it does so, its atmosphere absorbs different amounts of starlight at
different wavelengths of light. In particular, absorption by water in
its atmosphere makes the planet appear larger in a specific part of the
infrared spectrum than at wavelengths in the visible part.



Bulletin compiled by Clive Down

(c) 2007 the Society for Popular Astronomy


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