ENB No. 195 April 30 2006

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ENB No. 195 April 30 2006

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Electronic News Bulletin No. 195 2006 April 30

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/maaeKLGabqb0ocixLLVb/

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

By Alastair McBeath, SPA Meteor Section Director

Conditions seem to have been fairly unhelpful in the UK for the Lyrids
year. For instance, I spotted just a single Lyrid casually around 01:15
on April 23-24 in clear, but too hazy, skies, and saw nothing in a very
hazy sky around 02:30 UT the previous morning here in Northumberland.
Neither night was good enough for proper meteor watching unfortunately.
There were a few casual sightings made from elsewhere. See for instance
the SPA Forum topics on the Lyrids:


and Comet 73P/Schwassmann-Wachmann 3 (page 5):


though the most detailed results so far are some video observations from
Enrico Stomeo in Italy, made on April 20-21, well before the expected

The preliminary International Meteor Organization visual results were
issued in a special shower circular on April 25 (see:
These indicated a maximum probably about as predicted, with Zenithal
Hourly Rates of ~17 +/- 3 near 15:30 UT on April 22. The expected
ideal maximum time was predicted for an hour later than this, but no
are available covering that as yet.

Anyone with unsubmitted meteor reports from the shower is invited to
send them to the SPA Meteor Section as soon as possible. Advice on
what to report and where to can be found via the meteor homepage at:
http://popastro.c.topica.com/maaeKLGabqb0scixLLVb/ .

New Scientist + editing

Vega is the second-brightest star in the northern hemisphere of the
sky. Because it passes near the zenith of observatories at north-
temperate latitudes and has a seemingly simple and characteristic
early-type spectrum, it has very often been used as a comparison or
standard star in spectroscopic work. It is also one of the few stars
whose brightnesses have been calibrated against an absolute laboratory
source and so are known in terms of ordinary physical units and not
just astronomical magnitudes. Its spectrum has moderately narrow
lines, which have long been recognized as indicating that it has an
equatorial rotational velocity whose projection on the line of sight
is a modest 18 kilometres per second or thereabouts. About 20 years
ago, when Vega's spectral lines were examined with high spectral
resolving power and comprehension, they were noticed to have unusual
profiles, being almost flat-bottomed, and the favoured explanation was
that the star is actually rotating very rapidly but seen almost
pole-on. Recently the USNO 'Prototype Optical Interferometer' in
Arizona, which can achieve such high angular resolution on the sky as
to be able to 'see' the discs of stars, has been used to determine in
detail the distribution of brightness over Vega's surface. The
results have been interpreted as confirming that Vega is presented
almost pole-on to our view and that it is rotating at about 90% of
the speed at which it would fly apart. The poles are more than 2000°C
hotter than the equator. The uneven temperature and fast rotation
imply that Vega is not a suitable star to be used as a standard of
comparison for other stars, as its spectrum cannot be matched by any
simple model. Furthermore, the rapid rotation means that the observed
composition of the star does not apply just to its surface layer, as
the star must be well mixed. That has repercussions on estimates of
its age, which have been revised from about 350 million years to about
570 million.


The Venus Express has returned the first-ever images of the south-pole
area of Venus. They were taken from a distance of about 200,000
kilometres during the spacecraft's initial 'capture orbit' after its
arrival on April 11, and they show surprisingly clear structures and
unexpected detail. Scientists are especially intrigued by a dark
vortex almost directly over the south pole, a previously suspected but
until now unconfirmed structure that corresponds to a similar cloud
structure over the north pole. The spacecraft operators are working
to a plan to lower the apocentre during successive orbital loops round
the planet, until on May 7 the craft should attain its final 24-hour
polar orbit, ranging from 66 000 to 250 kilometres above Venus. The
pictures can obviously be expected to show much more detail as the
spacecraft gets closer to Venus.

New Scientist

Astronomers have found what they interpret as two black holes orbiting
one another 100 times closer than any previously seen. When two
galaxies collide, any black holes at their cores are thought to fall
towards the centre of the resulting larger galaxy, go into orbit
around each other, and eventually merge. A binary system was found
with black holes within 3000 light-years of each other in 2002, and
earlier in April another was announced at a separation of 28,000
light-years. Now, radio astronomers using the Very-Long-Baseline
Array have found what appear to be two black holes within 24 light-
years of one another.

The objects are buried within a blob-shaped galaxy called 0402+379,
which is about 470 million light-years away. Both appear to be
actively devouring their surroundings. The astronomers who observed
them spectroscopically with the Hobby-Eberly telescope in Texas say
that the objects are indeed orbiting each other and have a combined
mass of 150 million Suns, but another astronomer cautions that the
spectrum attributed to a second black hole might simply be due to gas
sloshing around the first.


Supermassive black holes are the 'most fuel-efficient engines' in the
Universe, according to observers who used the Chandra X-ray
observatory to study nine supermassive black holes at the centres of
elliptical galaxies. The black holes, suggested to be two to three
billion times the mass of the Sun, are relatively old and generate
much less radiation than quasars, the fast-growing black holes seen in
the early Universe. The researchers said that the Chandra findings
show that most of the energy released by matter falling towards a
supermassive black hole is in the form of high-energy jets travelling
outwards at nearly the speed of light. The researchers were surprised
to discover that the black holes are all producing much more energy in
jets of high-energy particles than in visible light or X-rays. Some
of the gas first drawn in may be blown away by the energetic activity
before it gets too close to the hole, but a significant amount must
eventually approach the event horizon, where it is used with high
efficiency to power the jets.


Astronomers using the Arecibo 1000-foot radio telescope have detected
a neutral-hydrogen gas cloud in an area that spans 200,000 light-
years. The dark cloud lies at a distance of 147 million light-years
near NGC 1156, an irregular galaxy in Aries. The search covered a
field of 2 by 2.5 degrees, but no starlight was seen in the area
containing the neutral hydrogen. The source was missed in previous
searches as it appears not to contain many bright stars, but the area
surrounding NGC 1156 probably contains a lot of dust, which absorbs
starlight and prevents it from reaching optical telescopes. Optical
observations are now needed to verify that the object is a bona fide
dark galaxy.


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: 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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