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The SOCIETY for POPULAR ASTRONOMY
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Electronic News Bulletin No. 228 2007 September 16
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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
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/maahShAabBhx5cixLLVb/


ALPHA AURIGID OUTBURST
By Alastair McBeath, SPA Meteor Section Director

Results now confirm that an Alpha Aurigid outburst did occur on
September 1 (which possibility was discussed in ENB 225), a short-
lived, but strong event, with a lot of bright meteors, lasting from
approximately 10:30-12:50 UT, the strongest activity centred
between 11:15-11:19 UT, a little earlier than anticipated. The
predictions were for a peak centred around 11:36 UT +/- 20 minutes,
so the actual peak fell just within that error band.

Visual notes from Assistant Meteor Director David Entwistle
(Lancashire) and myself (Northumberland) overnight on August 31
to September 1 suggested only the usual low Aurigid rates even
towards dawn, something supported by preliminary video results
from Spain issued in IAU Electronic Telegram 1049 (dated 2007
September 3; with thanks to Robin Scagell for forwarding this
information).

The International Meteor Organization's, IMO's, "live" Aurigid data
(accessible from the http://popastro.c.topica.com/maahShAabBhx6cixLLVb/
homepage) has suggested
estimated Zenithal Hourly Rates - ZHRs - of ~60-90 were present
between at least 10:35-11:35 UT on September 1. Though these are
not analysed rigorously enough for scientific use, and change every
time someone adds new results, they can give a useful guide to what
probably happened. The peak rate, lasting just a few minutes, was
~130, centred at 11:17 UT. While these values implied a much
stronger outburst than those previously observed from the Alpha
Aurigids (brief outbursts in 1935, 1986 and 1994 yielded ZHRs of
~30-40, though none was widely-seen; the shower's usual ZHR is
~7), it is important to stress these are a) only estimated preliminary
values, and b) that the visual activity was badly affected by the
bright Moon.

In the radio data so far, from Jeff Brower (British Columbia, Canada),
David Entwistle, Alan Heath (Nottinghamshire), plus notes attributed
to Radio Meteor Observation Bulletin Editor Chris Steyaert based
on details from Willy Camps (Belgium) and Andy Smith (Devon) in
IAU Telegram 1049, a strong, very sharp peak was apparent in the
one-hour interval from 11h-12h UT on September 1, with lesser
activity surrounding that from at least ~10h-13h UT. Jeff very helpfully
made a rapid analysis of his own ten-minute counts, and found a
distinct maximum in activity from 11:10-11:25 UT. Four datasets
covering right across the 11h-12h UT interval gave mean peak times
for the centre of the outburst as between 11:15-11:19 UT, apparently
virtually coincident with the initial IMO visual results. Jeff also
mentioned that a similarly narrow, intense event had been recorded
by Esko Lyytinen (Finland; one of the people who originally forecast
the potential outburst last year) and Felix Verbelen (Belgium), and
that ten-minute counts from Esko and Andy Smith fitted amazingly
well to his own counts for the peak period. Meteor echo numbers
from Jeff's and Esko's data were above half the maximum level for
~56 minutes, about twice the time originally predicted for the
outburst (technically this is the Full-Width-Half-Maximum, FWHM,
time). Though radio rates cannot be converted directly to an
equivalent ZHR value, the radio count profiles do seem to support a
substantial difference during the peak hour to times well outside this,
which may suggest the initial visual ZHR estimates were fairly close
to the actual ones.

More detailed examinations of the radio results by David and Jeff in
the last few days now suggest the actual radio meteor rate may not
have been quite as high as a typical Quadrantid radio maximum
(visual ZHRs ~120), but that the activity was dominated during the
peak hour especially by a notably increased number of very persistent
echoes. Among the early, less formal, radio reports (see the SPA's
Observing Forum topic at
http://popastro.c.topica.com/maahShAabBhx7cixLLVb/ for some of these,
and other Alpha Aurigid notes), there were similar findings of
significant numbers of such radio signatures too. These longer-duration
echoes are thought to be due to bright or fireball-class meteors in
general, while their coincidence with the Alpha Aurigid outburst was
something the initial visual results also tended to concur with. For
instance, IAU Telegram 1049 suggested most meteors were in the
-2 to +3 magnitude range, albeit the moonlight would have made
many fainter meteors than this difficult to spot anyway. Jeff Brower
reported such overdense radio meteor echoes began for his system
at 10:55 UT and lasted till around 11:45 UT, while his automated
fireball patrol video system (minimum meteor magnitude to record
was -3) caught seven fireball events overnight on September 1, all
between 10:55 and 11:59 UT!

The bright-meteor nature of the event was supported as well by
numerous reports from the western USA, including photos and
videos of some of the brightest. A three-page photo-gallery with
other reports is available on the SpaceWeather.com website, under
the archives for early September - see for instance the link from:
http://popastro.c.topica.com/maahShAabBhx8cixLLVb/ which has a splendid
"creaky movie" of one
spectacular event right at 11:17 UT, crossing above the bright Moon!

Away from this main interval, the IMO visual data suggested Alpha
Aurigid ZHRs were of fairly negligible proportions, as far as the
moonlight allowed, though the radio results continued to indicate
somewhat elevated count levels for an hour or more afterwards, albeit
without the probable "bright meteors" component, which may account
for the apparent drop in visual rates, as the meteors returned to the
more typical, fainter, Alpha Aurigid brightness regime.

Many thanks go to all who have contributed some notes directly or
via the SPA's Forums, particularly David Entwistle, for making time
to get his radio results online so rapidly, and Jeff Brower, again for
his rapid response in getting material online, and subsequent
discussions. Any further results on the shower would be most welcome!


SPECTACULAR NEW MEXICO FIREBALL IMAGED
By Alastair McBeath, SPA Meteor Section Director

The http://popastro.c.topica.com/maahShAabBhx9cixLLVb/ homepage for
September 15 had an
all-sky movie and details of a superb magnitude -15 meteor that had
shot across New Mexico, USA around 09h UT (3 a.m. local summer
time) on September 13. Early comments suggested it may have been
re-entering space-junk, but this is unconfirmed, and from the object's
apparent speed on the movie, a natural fireball seems a far more
plausible explanation. More details are hoped-for on the event once
further witness sightings have been recovered and analysed.


"SKY LANTERNS" ARE NOT FIREBALLS!
By Alastair McBeath, SPA Meteor Section Director

The recent discussions at:
http://popastro.c.topica.com/maahShAabBhyacixLLVb/ on the SPA'S
Observing Forum have highlighted a growing problem with "sky
lanterns" this year, enough to indicate they are becoming unfortunately
common. There was a sighting of three slow objects seen in formation
on August 11-12 from Harrogate for instance, which has turned out
to be a group of such "lanterns" (thanks to Tony Bills of Harrogate
AS for these details), plus more recently what appears to be another
one, reported by a group of eleven people in Worthing, West Sussex
on September 8-9.

These objects are lightweight, tissue-paper hot-air balloons, about a
metre tall, with a naked-flame burning wick suspended in a small tray
below them. They are used to "celebrate" various events, being lit and
released to go where the wind takes them, creating an obvious fire
risk in the process. They have so far been reported as UFOs, mystery
lights and fireballs, as regrettably, they appear to be capable of
reaching heights above some of the lower clouds (thus presumably
creating a minor aviation hazard as well).

To tell them apart from genuine fireball-class meteors (any meteor
of magnitude -3 or brighter), or other astronomical targets like
artificial
satellites, the best way is to examine any similar "mystery lights" with
good binoculars. This should enable an easy confirmation of what they
were. Anyone who has no time to get their binoculars into action before
the object(s) vanished will likely have seen a genuine meteor (unless
the wind was particularly strong at the time, thus whipping the blazing
lantern smartly across the sky). Natural meteors rarely last more than
a few seconds up to a few tens of seconds (very rarely), though a
man-made re-entry fireball might last for a minute or two.

In all cases, if you are not sure whether what you saw was a fireball,
send me as full a description as possible, including where you were,
the date and time of your sighting, and where the object's visible track
started and ended in the sky. More details of what to record and
where to submit your data are on the SPA's "Fireball Observing"
webpage, at: http://popastro.c.topica.com/maahShAabBhybcixLLVb/ .


NEW STARS FOUND IN GALAXY
Keck Observatory

Edwin Hubble once called IC 10 "one of the most curious objects in the
sky". New observations, obtained with Hubble and the Keck telescope in
Hawaii, of that faint, low-mass dwarf galaxy show a small region which
is the site of a vigorous star-formation event that took place within
the last 10 million years. Astronomers have known that IC 10 has more
of the rare objects called Wolf-Rayet stars than all other nearby
dwarf galaxies combined. Wolf-Rayet stars are extremely hot blue
stars losing mass to the interstellar medium at an enormous rate.
There are two types, whose spectra are dominated by carbon and
nitrogen respectively. Nearly all the IC 10 W-R stars seem to be of
the carbon variety. The new images are centred on a bright star first
thought to be the most luminous Wolf-Rayet star in IC 10, but they
show it to be actually a small cluster of stars. The distance to IC
10 has been confirmed to be about 2.4 million light-years, as already
suggested by previous estimates.


JAPAN LAUNCHES MOON PROBE
Yahoo

Japan's space agency has launched its much-delayed lunar probe SELENE.
The launch of the $279 million probe has come four years behind the
agency's original schedule. Japan launched a Moon probe in 1990, but
that was a fly-by mission, unlike SELENE, which is intended to orbit
the Moon. It cancelled another Moon shot, LUNAR-A, that was to have
been launched in 2004 but had been repeatedly postponed because of
mechanical and fiscal problems. According to Japan's space
agency. the SELENE project is the largest lunar mission since the
U.S. Apollo programme in terms of overall scope and ambition,
outpacing the former Soviet Union's Luna programme and NASA's
Clementine and Lunar Prospector projects. It involves placing the
main satellite in orbit at an altitude of about 60 miles and deploying
two smaller satellites in polar orbits. Researchers will use data
gathered by the probes to study the Moon's origin and evolution. The
main orbiter will remain in its orbit for about a year.


ALTERNATIVE TO ADAPTIVE OPTICS
BBC News

A collaboration between Cambridge University and Caltech has developed
a system called 'Lucky' to obtain some astronomical pictures with
excellent angular resolution. They were acquired with the 200-inch
telescope on Palomar Mountain in California, and are claimed to be
twice as sharp as those from Hubble. Pictures taken by Hubble are
normally much better than images from ground-based telescopes because
the Earth's atmosphere has a distorting effect. The Lucky camera
partly overcomes the problem by a software system that watches the
image on a very short time-scale, and saves image frames obtained at
the best moments. It then sums together all the saved frames to
produce the final image. The team leader, Dr. Craig Mackay of
Cambridge, remarks that images produced by space telescopes are of
extremely high quality but their resolution is limited by the sizes of
the telescopes. "Our technique can do well when the telescope is
bigger than Hubble and has intrinsically better resolution."


VENUS EXPRESS
The Register

Sweltering in four times the radiation that its sister craft, Mars
Express, receives, Venus Express is celebrating its 500th day around,
and 500th orbit of, our twin planet. Although most of the data that
have been sent back are still being digested, there have already been
some interesting discoveries. The planet's atmosphere is much more
changeable than scientists thought. Recent images have shown the
atmospheric structure to change almost daily, although there are some
enduring patterns. The vortices at the poles are fascinating for
astro-meteorologists. The giant double storms, spanning 2000 km, have
been seen at both north and south poles, and changes have been seen in
them between successive orbital passes. Venus Express is operating in
an incredibly harsh environment, but the modifications to the Mars
Express design on which it was based have worked well. Engineers say
that the craft is stable. One limitation is the speed at which data
can be transmitted back to Earth. Last month, Venus was at inferior
conjunction and the craft could send data back at maximum speed, but
when Venus is on the other side of the Sun, data rate will drop to 22
kb/s.


THE ASTEROID THAT MAY HAVE KILLED OFF THE DINOSAURS
New Scientist

An origin has been suggested for the asteroid that hit Earth 65
million years ago and has been considered responsible for wiping out
the dinosaurs. Astronomers know of more than 40 families of asteroids
that are fragments of shattered larger bodies, and can calculate when
the break-ups happened. Earlier this year, researchers from the
Southwest Research Institute in Boulder, Colorado, identified a new
group which they named the Baptistina family after a 40-km asteroid
that is its largest known member. The dinosaur-killer may well have
been a lost member of that family, formed by a collision in the inner
part of the asteroid belt 160 million years ago. The team has
calculated that a 10-km asteroid, one of roughly 300 chunks of the
original 170-km body, could have collided with the Earth. Other
fragments may have hit Venus, they suggest, and could have been
responsible for the formation of Tycho, the youngest prominent crater
on the Moon. The composition of Baptistina matches that of impact
debris found on Earth.


HST LOSES ANOTHER POINTING GYRO
New Scientist

Another pointing gyroscope has failed on the Hubble telescope, leaving
it with two gyros in operation and a third available as a spare, but
managers believe that the telescope will survive until the space
shuttle services it for the last time a year from now. Hubble uses
gyros to point and stabilise itself in space, but the devices have
been a continuing problem. There are actually six; it has operated
with three, but to keep the telescope working until the final shuttle
servicing mission engineers devised a way for it to operate on two
instead. It switched to the two-gyro mode in 2005, and engineers have
since thought how to allow it to make observations with only a single
gyro.

The most recent failure occurred on September 1. The gyro had been
operating for more than six years, a lifetime considered well above
average, when a critical wire broke. One of the two remaining gyros
in operation is fairly new, but the second has operated for about four
years, and the reserve has run for about six years. The servicing
mission, now scheduled for launch on 2008 September 10, will replace
all six gyros. But if they were all to fail before that, the
telescope would naturally stabilise itself gravitationally, so the
shuttle could safely capture it for repair. Plans for the servicing
mission include an ambitious series of five space-walks. Priorities
in addition to gyro replacement include replacing Hubble's two
230-kilogram batteries, and installing two new instruments -- the
'cosmic origins spectrometer' and 'wide-field camera 3'. If
astronauts complete those essential tasks, they will turn to repairing
Hubble's highest-resolution instrument, the 'advanced camera for
surveys', and the imaging spectrograph, which failed in 2004 August.
At present the only instruments operating on the telescope are the
'wide-field planetary camera' and the 'near-infrared camera and
multi-object spectrometer'.


MORE SMALL GALAXIES DISCOVERED AROUND THE MILKY WAY
Keck Observatory

There is a theory called the 'cold dark matter model', which purports
to explain the growth and evolution of the Universe. It implies that
large galaxies like the Milky Way ought to be surrounded by swarms of
up to several hundred satellite objects known as dwarf galaxies.
However, until recently, only 11 such companions were known to be
orbiting the Milky Way. To explain the large discrepancy, theorists
suggested that while hundreds of dwarf galaxies near the Milky Way may
indeed exist, the majority might have few, if any, stars. If so, the
galaxies would be comprised almost entirely of dark matter -- a type
of matter that has gravitational effects on ordinary atoms, but which
does not produce any light (not very remarkable -- a pencil, for
example, has just such properties, although it is not to be concluded
galaxies are likely to be made of pencils!). But proving the existence
of a large number of nearly invisible galaxies has seemed problematic.

Recently, several additional dwarf galaxies have been discovered in a
survey known as the Sloan Digital Sky Survey, and astronomers have
used the Keck telescope to study eight of them. Repeated radial-
velocity measurements of a total of several hundred stars in the
galaxies have enabled internal velocity dispersions of only 4 to 7
km/s to be derived -- far smaller than in galaxies such as the Milky
Way, in which the Sun is circulating with a velocity of 220 km/s --
and very comparable with the velocity dispersions of globular star
clusters. Knowledge of the velocity dispersions made it possible to
estimate the total mass of each galaxy; the masses proved to be much
smaller than expected, of the order of 10,000 times smaller than that
of the Milky Way. The formation of such small galaxies is not
understood theoretically, so it is not possible to say how many stars
might be expected to form in such objects or, therefore, how many such
dwarf galaxies we might expect to be able to see. All that can be
said is that, by increasing the number of known dwarf galaxies
associated with the Milky Way, the new research narrows the gap
between the 'cold dark matter' theory and observations, and we have
learnt a little about the properties of such galaxies, including the
fact that their masses can be even smaller than was previously
realised.


EARTH MIGHT SURVIVE SUN'S EXPANSION
The Register

Astronomers have discovered a planet that seems to have survived the
evolution of its star as a red giant, suggesting that the Earth could
do the same. The planet is a gas giant at least three times as
massive as Jupiter, and orbits about 150 million miles from a faint
star known as V 391 Pegasi, about 4,500 light-years away. Before the
star became a red giant and lost half its mass, the planet must have
been about as far from it as the Earth is from the Sun. The star is
now about half as massive as the Sun, burning helium into carbon; it
will eventually settle into senescence as a white dwarf. Meanwhile,
it pulsates with a periodicity of about 6 minutes. Subtle modulations
in the 6-minute cycle have provided the evidence that the star is in a
three-year orbit with a massive planet.


PLANET-MASS OBJECT ORBITING NEUTRON STAR
NASA

Using the Swift and Rossi X-ray Timing Explorer (RXTE) satellites,
astronomers have discovered an object with a minimum mass about 7
times the mass of Jupiter, orbiting a rapidly spinning pulsar every
54.7 minutes at an average distance of only about 230,000 miles
(slightly less than the Earth-Moon distance). The system was
discovered when Swift detected an outburst of X rays and gamma rays in
the direction of the Galactic Centre in Sagittarius. Periodic timing
anomalies in the X-ray pulses demonstrated the presence of the orbiting
companion. Because the orbital inclination of the system is unknown,
the companion's actual mass cannot be calculated, but it is unlikely
to exceed 30 Jupiters.





Bulletin compiled by Clive Down

(c) 2007 the Society for Popular Astronomy


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