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 Post subject: ENB No. 175 May 22 2005
PostPosted: Sat Dec 03, 2005 8:51 am 
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The SOCIETY for POPULAR ASTRONOMY
***********************************
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Electronic News Bulletin No. 175 2005 May 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/maadxPXabhciUciD1pRb/

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


NO "PRIBRAMIDS" THIS YEAR
By Alastair McBeath, SPA Meteor Section Director

Back in ENB 123, I gave a short update on the 2002 April 6-7 brilliant
fireball over the Austro-German border, which had dropped a meteorite
near Neuschwanstein in Germany, and whose orbit was virtually the same
as that of the Pribram meteorite which fell in what was then Czechoslovakia
on 1959 April 7. In the published reports on the Neuschwanstein
meteorite, it was suggested this and the Pribram fall might be part of a
meteor stream visible from Earth in other years around April 6-8, with a
radiant probably in Coma-Virgo.

Although, as mentioned in ENB 173, several bright fireballs were
reported from Europe, including Britain, in early April 2005 before these
dates, none fitted to the expected "Pribramid" profile. Now, Sirko Molau,
Director of the Video Commission for the International Meteor
Organization (IMO), has released details from European video
observations which confirmed no detectable "Pribramids" were found
emanating from the inferred radiant in mid-southern Coma Berenices this
year. In the first half of April, just over 2% of the video meteors might
have come from near this area, roughly what we would expect by-chance,
and significantly less than the circa 8% of meteors identified as Virginids.
For more details, see the item on video results issued on the IMO-News
e-mailing list for 2005 May 16 (archive available via the IMO's website
at: http://popastro.c.topica.com/maadxPXabhciVciD1pRb/

With only two definite objects reported from this postulated "Coma
fireball stream" in 43 years, we need to keep checking in all years, just in
case.


LYRIDS 2005 UPDATE
By Alastair McBeath, SPA Meteor Section Director

Later in April, the moonlit Lyrids provided a pleasant view for a few lucky
European observers, as commented last time. Zenithal Hourly Rates
(ZHRs) were estimated at 14 +/- 5 between roughly 00h-02h UT on
April 22 in results forwarded to the Section, though this probably did not
represent the main maximum. Fresh video and radio data has come
through since, as discussed here.

Sirko Molau's April video report which discussed the "Pribramids" also
covered the rest of the month, including the Lyrids. Analysing this
European IMO data (which included SPA observer Steve Evans' data,
as noted in ENB 174), he found a suggestion of a possible video peak
around 01h30m +/- 1 hour UT on April 22, with activity seeming to
decline afterwards. It was unclear if the apparently falling rates towards
the end of the night (when moonlight was lessened, but twilight was
increasing) were a genuine feature, or simply resulted from the worsening
sky conditions, however.

The Lyrid radio results have been analysed by the Section this week,
mostly from Radio Meteor Observation Bulletin 141 for April 2005 (see:
http://popastro.c.topica.com/maadxPXabhciWciD1pRb/ with grateful thanks to
Editor Chris Steyaert for
providing a copy immediately they were ready. The contributing observers
included: Enric Fraile Algeciras (Spain), Mike Boschat (Nova Scotia,
Canada), Jeff Brower (Colorado, USA), Gaspard De Wilde (Belgium),
David Entwistle (Lancashire, England), Ghent University (Belgium),
Patrice Guerin (France), Szabolcs Kiss (Hungary), Stan Nelson (New
Mexico, USA), Sadao Okamoto (Japan), Mike Otte (Illinois, USA),
Marcel Schneider (Luxembourg), Andy Smith (Hampshire, England),
Dave Swan (Dorset, England) and Ilkka Yrjola (Finland).

Lyrid rates are rarely strong enough to give an especially clear radio
signature,
but with care, it is often possible to single out likely times when rates were
genuinely higher. A minority of the results with enough reliable comparison
coverage, and for which the Lyrid radiant was sufficiently radio-detectable
at the time, indicated there may have been a weak Lyrid peak between
roughly 01h-03h UT on April 22. However, this was not the main maximum,
which was recorded by most reliable operating systems towards 08h +/-
1 hour UT on the same date. This timing would have been ideal for visual
coverage from North America, but early indications are that weather
conditions were most unhelpful for some of the more regular watchers
there, who might have braved the moonlight under better skies.

The window for the likely Lyrid peak was between 02h30m-13h30m UT
or so on April 22, with an ideal time when higher rates might have occurred
of 10h30m UT. The radio data thus suggests the peak happened slightly
before this ideal, which in turn would imply the peak ZHRs may have been
somewhat below their theoretical best, based on the most recent IMO
report (relevant notes were in ENB 172). Although it is difficult to usefully
calibrate the recorded radio activity to give a ZHR-equivalent estimate,
no especially strong Lyrid signature was found generally across the radio
reports at least.

Anyone with still unsubmitted Lyrid observations is very welcome to
provide a copy to the SPA Meteor Section. Details on what to report and
where to can be found off the Section's homepage at:
http://popastro.c.topica.com/maadxPXabhciXciD1pRb/


ETA AQUARIDS - FIRST NEWS
By Alastair McBeath, SPA Meteor Section Director

Eta Aquarid data has come through in the last few days, from visual
reports made by Tim Cooper and Magda Streicher in South Africa, plus
video details from Steve Evans in Gloucestershire, England. Steve caught
two probable Eta Aquarid trails, one each on May 7-8 and 8-9 between
02h30m-02h40m UT, which although rare, do confirm that some meteors
from this source can be seen from Britain, though sensible ZHRs cannot
be computed from such information.

South Africa is better-placed for Eta Aquarid observing, but even so, the
radiant elevation is very poor until only an hour or two before dawn. A
preliminary analysis from Tim and Magda's results suggest the shower
meteors were unusually faint this year. Corrected mean magnitudes for
the Eta Aquarids and early May sporadics were +3.6 and +3.5 respectively.
Normally, we would expect a major shower such as this to have a mean
magnitude significantly brighter than the sporadics. This has created
problems for computing the ZHRs, because it substantially increases the
correction factors (already rather larger than the ideal because of the
relatively low radiant). The likely range of ZHRs for May 4-5, 5-6 and
7-8 was thus estimated instead at roughly 60-100, rather higher than was
anticipated (see ENB 172). Looking at the relative rates on the three nights
available shows the stronger ZHRs were present around 02h +/- 1 hour
UT on May 5, a day earlier than predicted. While fascinating, these are
only first results and all aspects await confirmation from observers
elsewhere. Additional Eta Aquarid results would be gratefully received by
the Section.


ANOTHER SATURN MOON
IAU

Yet another new satellite of Saturn has been discovered; it is
designated S/2005 S 1, and orbits within the Keeler gap in Saturn's
outer A ring. The satellite orbits Saturn every 0.594 day at a
distance of 136500 km.


MARS POLAR LANDER FOUND?
AP

Nearly six years after the Mars Polar Lander failed during a landing
attempt, what may be the wreckage of the spacecraft has been spotted.
The observation came during a re-examination of grainy, black-and-
white images taken by the orbiting Mars Global Surveyor, which
searched for the probe without success in 1999 and 2000. Global
Surveyor will take higher-resolution images later this year in an
attempt to confirm the missing lander's location. The $165 million
Polar Lander was approaching touchdown near Mars' south pole on 1999
Dec. 3 when contact was lost. A NASA team concluded that a rocket
engine shut off prematurely, causing the spacecraft to fall from about
130 feet to almost certain destruction. A re-examination of images of
the surface of Mars taken after the Polar Lander's disappearance has
identified a distinct white patch that could be a parachute. A few
hundred metres away, there is a dark area, possibly a rocket blast
mark, with a tiny white dot in the centre that could be the lander.


STAR ROTATES IN SYNCHRONISM WITH PLANET'S ORBIT
New Scientist

The orbit of an extra-solar planet appears to be synchronized with the
rotation of its parent star. The phenomenon may be common among
massive planets in close orbit around their stars. Many celestial
bodies are thought initially to spin quickly but decelerate over time
owing to the tidal effects of nearby objects. The Moon, for example,
has slowed to the point that it rotates on its axis in the same time
that it takes to orbit the Earth, so it always keeps the same side
facing us. But smaller bodies rarely dictate their hosts' rotation,
unless the two objects are closely spaced and are relatively similar
in mass, such as Pluto and its moon, Charon. Now, a team of
astronomers has observed the phenomenon in a planet--star pair.
The team used Canada's MOST -- Microvariability and Oscillations of
Stars -- satellite to look for reflected light from a planet that was
first detected by the movement that it induces in its host star, Tau
Bootis. The planet appears to be at least 3.5 times the mass of
Jupiter and orbits eight times closer to its star than Mercury does to
the Sun. The team found that the star's own brightness varies
slightly with a period of 3.3 days, the same as the orbital period of
the planet. The brightness variations are tentatively interpreted in
terms of the rotation of the star.


PHOEBE WAS PROBABLY A KUIPER-BELT OBJECT
NASA

Scientists using data collected by Cassini have concluded that
Saturn's moon Phoebe is an interloper to the Saturn system from the
deep outer Solar System. During the spacecraft's encounter,
scientists got the first detailed look at Phoebe, which allowed them
to determine its makeup and mass. From the new information they have
concluded that it has an outer-Solar-System origin, akin to Pluto and
other members of the Kuiper Belt. Phoebe is quite different from
Saturn's other icy satellites, not just in its orbit but in the
relative proportions of rock and ice. It resembles Pluto in that
regard much more than it does the other Saturnian satellites. Phoebe
has a density consistent with that of the only Kuiper-Belt objects for
which densities are known. Phoebe¹s mass, combined with an accurate
volume estimate from images, yields a density of about 1.6 grams per
cubic centimetre, much less dense than most rocks but denser than pure
ice, which is about 0.93 grams per cubic centimetre. That suggests a
composition of ice and rock similar to that of Pluto and Neptune's
moon Triton. Whether the dark material on other moons of Saturn is
the same primordial material as on Phoebe remains to be determined.


SHORT GAMMA-RAY BURST CAUGHT
NASA

Scientists have, for the first time, determined the location of a
gamma-ray burst that lasted only 50 milliseconds. It is thought by
some that the burst marks the birth of a black hole, and certain
astronomers are speculating on what may have caused it -- perhaps a
collision of two older black holes or two neutron stars. Gamma-ray
bursts have been called the most powerful explosions in the Universe.
Bursts lasting more than two seconds have been observed by satellites
such as Swift, built to detect and quickly to locate the flashes.
Some of the scientists who work in the relevant field are convinced
that short and long bursts arise from two different catastrophic
origins. The longer bursts appear to be from explosions of massive
stars in very distant galaxies. Short bursts had remained elusive
until May 9, when Swift detected the recent flash. Swift autonomously
locked onto the location in less than a minute, and its X-ray
telescope detected a weak afterglow that faded away after about five
minutes. Its UV/optical Telescope did not see any afterglow, and
ground-based telescopes have not detected one, though afterglows from
long bursts linger for days to weeks. The burst appears to have
occurred near a galaxy that has old stars and is relatively nearby.
That is consistent with the speculation that short bursts come from
older, evolved neutron stars and black holes.


STARS NEAR GALACTIC BLACK HOLE
New Scientist

A group of young stars has been found in close proximity to the giant
black hole that has been thought to exist at the centre of our Galaxy.
It is the second such group to be found. Two years ago, astronomers
found the first cluster of young stars 0.7 light-years from the black
hole. How they got there is a question, because a black hole's
gravity ought to tear apart the clouds of gas and dust from which new
stars form. The newly identified group of five young stars, found by
astronomers using the Keck I telescope in Hawaii, is even closer to
the Galactic Centre -- just 0.26 light-years away. The stars appear
to be only about 10 million years old.


MARS' SOUTH POLE
NASA

Scientists think that they have solved a long-standing problem by
finding that the reason why Mars' southern polar cap is offset from
the actual south pole is because of two different polar climates.
Weather generated by the two Martian regional climates creates
conditions that cause the southern polar ice to form a cap whose
centre lies about 93 miles from the actual south pole. The scientists
found that the location of the two major surface depressions, Hellas
and Argyre, in the southern hemisphere of Mars is the root cause of
the two distinct climates, as they create winds that establish a
low-pressure region over the permanent ice cap in the western
hemisphere. Just as on Earth, low-pressure weather systems are
associated with cold, stormy weather and snow. On Mars, the two
basins anchor the low-pressure system that dominates the southern
polar ice cap and keep it in one location. According to the
scientists, the low-pressure system results in white fluffy snow,
which appears as a very bright region over the ice cap, whereas 'black
ice' forms in the eastern hemisphere, where Martian skies are
relatively clear and warm. The eastern hemisphere of the south polar
region gets very little snow, and clear ice forms over the Martian
soil there.


WOLF--RAYET STAR HAS 10-HOUR PERIODICITY
Universite de Montreal

The MOST space telescope has given astronomers a new headache about a
Wolf--Rayet star called WR123, located about 19,000 light-years away
in the constellation Aquila. Wolf-Rayet stars have long been known to
exhibit complex, seemingly chaotic, brightness variations associated
with the turbulent high-speed winds that they eject into space. But
the nearly continuous coverage possible with the MOST satellite has
revealed a periodicity -- a stable variation repeating every 10 hours.
There is no satisfactory explanation of such a period. Ideas might be
(1) the rotation of the star itself, (2) the orbit of another small
star around WR123, or (3) vibrations in the structure of WR123 that
are transmitted to its dense enveloping wind. All those ideas seem
equally unacceptable. If WR123 is spinning at that rate, the
`centrifugal force' would be expected to exceed the star's gravity and
cause it to break up. A tight binary system would have to be so tight
that the companion would be orbiting *inside* the star itself. If
pulsations are to be the right answer, the theoreticians will have to
re-write the book completely on that class of massive stars.



NEXT BULLETIN:

The ENB editor is taking a short break in warmer climes and the next
bulletin will not be issued until June 26.


PHILIP'S NEW TITLE

NEW EDITION OF PHILIP'S GUIDE TO THE NIGHT SKY (48-page
paperback, £4.99, ISBN 0540087017). SIR PATRICK MOORE takes
the novice astronomer on a guided tour of the stars and constellations of
the northern hemisphere. An accessible work, clearly and concisely
written.


Bulletin compiled by Clive Down

(c) 2005 the Society for Popular Astronomy


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