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 Post subject: ENB No. 225 July 22 2007
PostPosted: Thu Aug 02, 2007 11:08 am 
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The SOCIETY for POPULAR ASTRONOMY
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Electronic News Bulletin No. 225 2007 July 22
====================================================


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/maahaWOabz3TScixLLVb/


ASTEROID 137 OCCULTS STAR ON THE NIGHT OF 23 JULY
Jon Harper, Occultation Section, SPA

Occultation of HD 181938 (SAO 124555, TYC 0464-02162-1), m(v)9.0, by
Asteroid (137) Meliboea, m(v)11.5

This event is due to take place during the night of July 23-24 at
around 01:01 UT on Tuesday 24th in the UK. The asteroid is 2.5
magnitudes fainter than the 9th-magnitude star, so you will see a
definite drop in brightness if you are in the shadow path. The
maximum duration at the centre line is predicted to be around 17
seconds.

The star SAO 124555 is in the constellation of Aquila and lies about
1° to the west of the m(v) 4.6 star Nu Aquilae -- location chart on
SPA Occultation Section site
http://popastro.c.topica.com/maahaWOabz3TTcixLLVb/ It will be
at an approximate azimuth of 210° and an altitude of 32° (Lat N54°,
Long 0°) at the time of the occultation. A special appeal goes out
for observers, especially those living in Northern England (north of
Hull in the east and north of Liverpool in the west), Southern
Scotland (from the Borders to Aberdeen in the east and Oban in the
west), and the whole of Northern Ireland, to watch this star and to
attempt a timing should an occultation occur. You are advised to
observe from between 00:57 UT and 01:05 UT.

For further information please e-mail me at jonvran@aol.com Please
send positive or negative results and timings to the same address.
Report forms can be downloaded at
http://popastro.c.topica.com/maahaWOabz3TUcixLLVb/
For the most up-to-date path and uncertainty margins, please visit
the following sites: Steve Preston's site
http://popastro.c.topica.com/maahaWOabz3TVcixLLVb/
Derek Breit's site (use the zoom, location facility on the left of
the map) http://popastro.c.topica.com/maahaWOabz3TWcixLLVb/


NO COMA BERENICID OUTBURST AFTER ALL?
By Alastair McBeath, SPA Meteor Section Director

Back in ENB 216, I reported that Spanish meteor astronomer Josep
Trigo-Rodriguez had contacted the Section to check whether any
radio meteor results correlated with the detection of an outburst from
the usually minor Coma Berenicid meteor shower (COM) around
01h-06h UT on 2006 December 24-25, recorded by automated
video systems in Spain. Thanks to the excellent efforts of David
Entwistle (now an Assistant SPA Meteor Director) and radio meteor
expert Jeff Brower in Canada, we were quickly able to discover that
only one European radio system operating then showed any sign that
unusual activity had been recorded, while the vast majority found only
the usual, fairly quiet, late December meteor rates. Investigations
continued however, but as time went on, only more negative evidence
came to light, from both radio and other video systems.

Now, in a letter just published in the latest issue of the International
Meteor Organization's journal WGN (Vol.35, No.3, pp.51-52), head
of the IMO's Video Commission Sirko Molau has confirmed that no
COM outburst was recorded by any of the four European IMO
video systems operating simultaneously under clear skies. Instead,
he suggested that the Spanish video systems may have recorded just
a local fluctuation in activity, one of those chance occurrences that
happens from time to time. He went on to mention a suspected new
minor video shower first reported by Japanese observers from a
radiant in Ursa Major around 2006 October 15, which was confirmed
present by IMO video data too, but which apparently the Spanish
video systems failed to detect. This may be because of the different
equipment being operated by these groups. For now though, it seems
increasingly likely the COM did not produce anything untoward last
December 25.


SUMMER METEOR PROSPECTS
By Alastair McBeath, SPA Meteor Section Director

Full Moon in late July sees off the late July meteor shower maxima from
the Delta Aquarids around July 28 (Zenithal Hourly Rates, ZHRs,
expected under good skies would be around 15-20 otherwise), and the
much less active, but sometimes fireball-producing Alpha Capricornids
on July 30-31 or so. The other former Aquarid showers once thought
active in July-August have now been subsumed into the new Antihelion
Source at this time of year. For more details on the late July meteor
activity, including radiant charts, see July's meteor webpage at:

http://popastro.c.topica.com/maahaWOabz3TXcixLLVb/ .

The loss of the late July shower maxima does mean August brings an
excellently moonless Perseid peak, due on August 12-13 between
about 05:00-07:30 UT. Though this is too late for UK visual observers,
radio observers here should still be able to follow events (interference
permitting!), because the shower's radiant first reaches a useful
elevation by ~22h UT, and improves all night after then, to culminate
after dawn, at circa 06h. No especially strong Perseid activity has been
predicted for 2007, so ZHRs of the usual ~90-100 may be anticipated
near the peak (thus perhaps ~60-80+ for Britain overnight on August
12-13). If the shower behaves as usual, activity should be rewarding
for at least a couple of nights before, and perhaps a night after August
12-13 as well, with ZHRs of 40-60 or so. Lower Perseid activity is
already underway (the shower began on July 17), and can be followed
through to August 24. Perseids are swift, often bright, and commonly
trained.

As August draws to a close, there is the possibility the normally-minor
Alpha Aurigids may produce one of their stronger returns. This was
first suggested last August by astronomers Esko Lyytinen and Peter
Jenniskens (see ENB 203), but it has recently been refined somewhat
by including simulations by French meteoricist Jeremie Vaubaillon. The
peak is still expected probably within 20 minutes of 11:36 UT on
September 1, but the latest work very carefully made no mention of
anticipated activity levels, after some heavy criticism of Jenniskens'
earlier suggestion that strong to storm Alpha Aurigid rates were likely
to manifest. They still might, but nothing is guaranteed in meteor
work! Previous Alpha Aurigid outbursts have yielded ZHRs around
30-40, though none was widely-seen, while the shower's usual activity
is nearer 7. If another better event does happen in 2007, there is the
possibility rates could be higher, maybe even significantly higher, than
these earlier outbursts, while the 2006 research indicated a good
chance for many bright meteors during the encounter. Sadly, whatever
occurs will be accompanied by a waning gibbous Moon just four days
past full, plus only British radio observers will be able to cover the
predicted daylight peak time, if it proves accurate. Despite this, and
the
moonlight difficulties, observing overnight on August 31- September 1
would be worthwhile from the UK, just in case something unexpected
happens ahead of the suggested peak. The radiant is usefully visible
after about 23h UT from Britain, so if clearer skies manifest and you
would like to try for the shower, watch as much clear sky as you
comfortably can facing away from the Moon, and hope for the best!

More information on August's meteor activity, including radiant charts
for the more active sources, is available on the SPA website at:

http://popastro.c.topica.com/maahaWOabz3TYcixLLVb/ .

Good luck, clear skies, and let me know how your summer observing
went!


ASTRONOMERS LOOK FORWARD TO HERSCHEL
RAS

The Herschel Space Observatory is to be launched by the European Space
Agency in 2008. It is named after William Herschel, who in 1800 made
the first detection of infrared radiation, some 19 years after he
discovered the planet Uranus. It will be the largest astronomical
telescope yet flown in space, with a aperture of 3.5 metres, and will
carry three scientific instruments -- SPIRE (the Spectral and
Photometric Imaging Receiver), HIFI (the Heterodyne Instrument for the
Far Infrared) and PACS (Photodetector Array Camera and Spectrometer).
They are designed for the far-infrared and sub-millimetre wavelength
bands that cannot be seen from the ground because the Earth's
atmosphere is opaque at those wavelengths.

Herschel should help to elucidate problems of star formation, which
occurs deep inside clouds of gas and dust, from which no visible light
can emerge but far-infrared light can get out. Herschel's instruments
will also be used to investigate the planets, comets and satellites of
our own Solar System.


AKARI MAPS WARM UNIVERSE
RAS

A team of Japanese and European astronomers has re-mapped the whole
sky at infrared wavelengths. The new map, produced by the AKARI
surveyor, is far sharper than its most recent predecessor, completed
by the IRAS satellite in 1984. AKARI uses a telescope with a 68.5-cm
mirror to observe at near-, mid- and far-infrared wavelengths. AKARI
was launched on 2006 February 21, and on current projections the
liquid helium that keeps the detectors cold will last until at least
2007 September 9, giving the primary mission a lifetime of about 550
days. Thereafter the satellite can continue operating to some extent
in the near infrared by the use of mechanical coolers.


GIANT OUTER EXTRA-SOLAR PLANETS RARE
University of Arizona

Astronomers conducting a survey for planets round nearby stars have
found that extra-solar planets more massive than Jupiter are rare far
out from the stars. University of Arizona astronomers and their
collaborators from the European Southern Observatory, Max Planck
Institute for Astronomy at Heidelberg, Italy's Arcetri Observatory,
the Keck Observatory and the Harvard--Smithsonian Center for
Astrophysics just concluded a 3-year survey using direct-detection
techniques sensitive to planets far from their stars. They looked at
54 young nearby stars that were thought to be among the best
candidates for having detectable giant Jupiter-like planets at
distances beyond 5 astronomical units (AU), or the distance between
Jupiter and the Sun.

Since 1995, astronomers using the radial-velocity method have found
more than 230 'super Jupiters' orbiting very close to their parent
stars. However, that method is most sensitive to planets close to
their stars, and reveals little about extra-solar planets farther out.
Astronomers need to use other techniques to find extra-solar planets
beyond 5 AU so that they can assess what the 'average' planetary
system looks like, and whether ours is a typical solar system. The
3-year survey did not turn up even one giant extra-solar planet.
Astronomers were surprised in the early days of planet finding to
discover a population of planets more massive than Jupiter and closer
in than Mercury, taking only a few days to orbit their host stars.
Now they are surprised that there aren't large numbers of giant
planets orbiting at large distances from their stars.


SIGNS OF WATER BEYOND SOLAR SYSTEM
Science Daily

Astronomers think that they have detected water vapour in the
atmosphere of the giant planet HD 189733b, which lies 60 light-years
away in the constellation of Vulpecula. The planet appears slightly
larger at wavelengths that correspond to water vapour, suggesting
that that substance is present in its atmosphere. The findings
contradict earlier studies showing no evidence of water. However,
the earlier studies looked at light emitted from the day side of the
planet, while the new research used a different method that measured
light transmitted through the outer edges of the planet's atmosphere.

There is of course no particular significance in the detection of
water vapour -- it is a simple molecule derived from elements known
to be abundant and so is likely to be formed anywhere that is cool
enough for the molecule not to be thermally disrupted. It does not
argue for the existence of life. It has long been observed -- and
much more definitely than in the case of the planet that has been
observed recently -- in the outer parts of the atmospheres of cool
stars.


GREAT CANARY TELESCOPE
BBC Online

One of the world's largest optical telescopes has been completed.
Installed on a 2,400-m peak on the Canary Island of La Palma, the
Great Canary Telescope (GTC) has a 10.4-m mirror. If the initial test
run is successful, GTC's team expects it to be up and running for the
scientific community within the next 12 months. The enormous array
has taken seven years to construct; its installation has been hampered
by poor weather and the logistical difficulties of transporting
equipment to such an inaccessible location.

The newly opened Southern African Large Telescope (SALT) boasts a
segmented primary mirror with -- in the longest dimension -- a
diameter of 11 m. The Hobby-Eberly in Texas also has an 11-m mirror;
however, the Keck twins in Hawaii, which have mirrors 10 m across,
have a slightly larger light-collecting area. The twins can also be
used together to act as an interferometer, allowing them to mimic for
some purposes an 85-m telescope. Those US telescopes are rivalled in
power by Europe's own Very Large Telescope, sited in Chile, which
includes four separate 8.2-m telescopes; they too will soon be able
to work as one, mimicking a telescope that is 200 m across. The Large
Binocular Telescope in Arizona uses two 8.4-m mirrors side by side to
achieve an effective 11.8-m diameter. All such telescopes will be
dwarfed in the next decade if plans to build instruments with mirrors
30-60 m across come to fruition.


MARTIAN ICE SWAPS POLES EVERY 25,000 YEARS
The Register

Researchers investigating the different types of ice at the Martian
poles entered new data from the Mars Express mission into a model of
the planet's climate. Then, adding in details of the planet's slow
precession, they ran the clock back 21,500 years to a time when the
northern summer took place when Mars was closest to the Sun, the exact
opposite of the situation today. As time passed, the model showed
water-accumulation rates shifting across the globe. Water at the
north pole became unstable and vaporised easily, moving to the
southern hemisphere where it recondensed and froze on the surface.
There, over the course of 10,000 years, it formed an ice cap up to six
metres thick. Run the clock forward towards today, and the opposite
starts to happen: the ice at the south vaporises and shifts on the
winds to the north. The process was interrupted about 1,000 years
ago, the researchers say, when for an unknown reason a layer of carbon
dioxide ice formed a protective layer over the ice, preventing further
erosion.

The model helps to explain newly discovered deposits of ice at the
southern pole, observed by the OMEGA instrument early on in the Mars
Express mission. The European Space Agency says that the "perennial
deposits of water-ice" have built up on top of million-year-old
layered terrain, and argues that their presence is evidence for
recent glacial activity.


SUPERNOVA THEORY STRENGTHENED
Astronomy

Type Ia supernovae are extremely luminous and have been supposed to be
very similar to one another, and on that basis they have been used
extensively as 'standard candles' to estimate distances, but their
nature
and governing physics have remained very poorly understood. In the
most widely accepted model the pre-explosion white dwarf orbits
another star which continuously loses mass, feeding it to the white
dwarf, which explodes when its mass exceeds a critical value.

Astronomers using the VLT have been looking at SN 2006X, a Type Ia
supernova that exploded 70 million light-years away in the spiral
galaxy Messier 100. They observed material that was probably ejected
from the giant star (the companion to the now-exploded white dwarf)
before the explosion took place. The material probably forms a series
of shells having a radius of the order of 0.05 light-years, or 3,000
times the distance between the Earth and the Sun. It is moving with a
velocity of 50 km/s, implying that the material would have been
ejected some 300 years before the explosion. Such a velocity is
typical for the winds of red giants. The system that exploded was thus
most likely composed of a white dwarf that hoovered up much of the
material lost by its red-giant companion. The astronomers are hoping
that what they have witnessed in this one case can be taken as
representative of Type Ia supernovae in general.


STILL ANOTHER SATURN MOON
IAU

The Cassini imaging-science team reports the discovery of S/2007 S 4,
a satellite orbiting in the region between Saturn XXXII (Methone) and
Saturn XXXIII (Pallene). A search of other Cassini images generated a
number of additional detections spanning more than three years.
S/2007 S 4 is located approximately 3400 km beyond Saturn XXXII, but
still interior to the orbit of Saturn XXXIII, suggesting that the
three may be part of a larger group of satellites in that region.
Preliminary estimates suggest that S/2007 S 4 has a radius of about
1 km.


SPA MEMBER DISCOVERED SUPERNOVA SN 2007ck

It is pleasing to learn that one of the supernovae mentioned in the
ENB 224 article 'Two Supernovae in One Galaxy' was discovered by SPA
member Tom Boles. Tom has discovered no fewer than 106 such objects
to date!




Bulletin compiled by Clive Down

(c) 2007 the Society for Popular Astronomy


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