Society for Popular Astronomy

[joe]

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The SOCIETY for POPULAR ASTRONOMY
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Electronic News Bulletin No. 275 2009 September 22
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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://www.popastro.com/


PERSEIDS 2009 - MORE DETAILS
By Alastair McBeath, SPA Meteor Section Director

Further to the preliminary Perseid results given in ENB 273 (archived at:
http://snipurl.com/s1gfn ), data has continued to arrive, and an updated
assessment of how the shower behaved this year has been possible
very recently. In general, this has confirmed the earlier pattern for
three maxima, on August 12 around 08h-09h UT and a protracted
good-activity spell from roughly 14:30-20:00, followed by a third,
probably strongest, peak around 05:30-06:30 UT on August 13.
However, fresh facets have been suggested, along with some
refinement of part of the earlier information, as discussed below. Note
though that the numerical visual Zenithal Hourly Rate (ZHR) values
remain somewhat uncertain, because of the bright Moon.

New Perseid results and comments have reached the SPA from the
following observers since ENB 273, including three North American
Meteor Network (NAMN; http://www.namnmeteors.org ) watchers,
whose reports fell foul of a computer glitch when NAMN leader Mark
Davis originally tried to send them in. Also given here are the radio
observers whose August reports featured in Radio Meteor
Observation Bulletin (RMOB) 193, available at: http://www.rmob.org ,
submitted by RMOB editor Chris Steyaert. A summary of the
combined Japanese radio results from the shower was made available
too, thanks to SPA Assistant Meteor Director David Entwistle, as
described by observer-analyst Hirofumi Sugimoto, though this
unfortunately did not include the names of the other Japanese
observers involved. In the list below, "R" means radio and "V" visual
results were provided by that individual.

Enric Algeciras (Spain; RMOB; R), Mike Boschat (Nova Scotia,
Canada; RMOB; R), Jeff Brower (British Columbia, Canada; RMOB;
R), Willy Camps (Belgium; RMOB; R), Tibor Csorgei (Slovakia; NAMN;
V), Gaspard De Wilde (Belgium; RMOB; R), David Entwistle (England;
RMOB; R), Dave Gavine (Scotland; V), Bill Godley (Oklahoma, USA;
NAMN; V), Valentin Grigore (Romania; V), Gordon Johns (England; V),
Ken Kennedy (Scotland; V), Tony Markham (England; V), Mikhail
Maslov (Novosibirsk, Russia; NAMN; V), Tom McEwan (Scotland; V),
Mike Otte (Illinois, USA; RMOB; R), Graham Pointer (England; V),
Jean-Louis Rault (France; RMOB; R), Steve Roush (Arizona, USA;
RMOB; R), Wayne Sanders (British Columbia, Canada; RMOB; R),
Andy Smith (England; RMOB; R), Chris Steyaert (Belgium; RMOB; R),
Dave Swan (England; RMOB; R), Dirk Van Hessche (Belgium; RMOB;
R), Maarten Vanleenhove (Belgium; RMOB; R), Felix Verbelen
(Belgium; RMOB; R), John Wardle (England; RMOB; R), Derek Ward-
Thompson & colleagues (France; V).

Professional astronomer Jeremie Vaubaillon made a series of model
calculations soon after the early shower results were in, and found that
various dust trails left behind by the Perseids' parent comet 109P/Swift-
Tuttle could have produced the observed activity in 2009, each trail
named after the AD perihelion return year during which it was laid-
down. A combination of material shed in 1610, 1737 and 1865 would
have given maxima between 06:00-08:00 UT on August 12, while
single-year trails from 1348 and 441 were due to meet the Earth
around 16:55 UT on the 12th and 06:06 UT on the 13th respectively.
None of these gave an especially precise fit to what was observed, but
these trails do seem likely to have been involved in producing at least
part of what happened.

The detailed International Meteor Organization's (IMO's) "live" Perseid
results (at http://www.imo.net/live/perseids2009 ), have tended to show
mostly quite subtle changes to the pattern noted last time. ZHRs of 100+
have continued to feature from about 07:30-08:30 UT on August 12,
peaking at ~150-160 between 08:05-08:15 UT or so, with a protracted
spell of ZHRs ~130-170 from roughly 14:30-20:00 UT on the same
date, observed chiefly from Far Eastern locations. European ZHRs on
August 12-13 have now suggested the better activity that night, ZHRs
~70-100, was found predominantly before 23:30 UT, with rates between
~50-75 after then through to approximately 01:50. Activity started to
increase again from about 02:00 on August 13 however (indeed the
02:00 datapoint suggested a brief ZHR of ~150 then, with ZHRs of
70-90 in the half-hour to either side of it), followed by another possible
peak when ZHRs reached ~140 near 04:20 UT. ZHRs of ~140-180
were found between 05:05-05:20, and pushed up to ~200 from
05:35-06:30, at highest still ~225 around 06:30 UT. ZHRs remained
close to 145 till 07:00, dropping slowly afterwards to be below 100
shortly before 08:00, and fell steadily after this to be just 25-30 by
nightfall over Europe again on August 13-14. The SPA visual results
have remained essentially unchanged from the ENB 273 report.

David Entwistle and I have examined various elements of the radio
data since the shower, and I completed a thorough review of all the
available information late last week. The main findings were as follows,
remembering that virtually all the radio results were given as meteor-
echo counts per one-hour interval only (the timings in this paragraph and
the next thus indicate the start and end for all the periods involved, and
are given solely in UT, so for example, "07h-12h" means "07:00-12:00
UT"). Radio meteor activity was registered at notably above-normal
levels for most of the time from 05h on August 12 to 15h on August 13.
A sharp, strong first radio maximum was apparent in most datasets
from 08h-09h on August 12, surrounded by a period of better activity
lasting from 07h-12h, perhaps including a lesser peak around 11h-12h.
After a couple of relatively less-active hours, a second, ill-defined,
maximum spell was apparent from ~14h-20h. There may have been
two better phases within this, around 14h-17h and 19h-20h, but these
were not especially clear-cut. Another more protracted period of
significantly good radio rates was then present between 23h-09h on
August 12-13, though the possible 20h-23h "gap" in good activity may
be illusory. A third maximum, apparently equally strongly-detected to
the first, fell on August 13 in the 03h-05h interval (with slightly lower
activity surrounding this from 01h-06h, perhaps strongest in the
04h-05h data-bin). A fourth maximum followed from 07h-08h, apparently
only marginally weaker than that around 03h-05h, and possibly simply
the latter part of this whole extended peak spell that started around 14h
on the 12th. An additional, more isolated, and probably weaker, peak
was suggested as having happened at 13h-14h on August 13, as
found in some data from all three main geographic regions involved,
possibly tailing off till as late as 15h.

Radio meteor analyses are never easy, but there were particular
difficulties in interpreting these results, because many datasets were
collected from western Europe, from where the daily peak in sporadic
activity typically falls around 04h-08h, plus the analyses tend to rely on
comparing results made at the same time for a day or two to either side
of any suspected event. As good Perseid activity happened around
these same times on August 12 and 13, and for much of the time
between, it was difficult to be sure sufficient allowance had been made
for these factors. Also, there were problems with system-saturation for
a number of radio observers, where the radio echo counts were
artificially reduced because too many echoes were occurring close
together in time, so overlapping one another, and not being recorded
each as a separate event. Even so, there were some striking
coincidences with what the visual results suggested - especially the
August 12, ~08h event, the protracted "Far Eastern" visual peak later
on the 12th, plus the activity in the 04h-05h interval and its surrounding
~01:30-08:00 spell on the 13th - as well as oddities where no such
mutual support seemed present, such as the poor match between the
strongest visual ZHRs near 06:30 on August 13, and the radio peaks
then, which preferred the 03h-05h and 07h-08h data-collection bins.

One final new item concerns a recent addition to the SPA's Perseids
Observing Forum topic, at http://snipurl.com/s1gh2 , added by David
Entwistle. This is a composite image showing 54 Perseids all captured
on August 12-13 by Pierre Martin in Ontario, Canada. A further posting
by "GeorgeC" added a graphic demonstrating how nicely these meteor
tracks all contributed to indicating exactly where the Perseid radiant
was that night.

Once more, my most grateful thanks go to all our contributing
observers and correspondents from the Perseids this year for their
splendid efforts. If anyone still has Perseid observations to submit,
please send them in with all speed.


RECENT FIREBALLS
By Alastair McBeath, SPA Meteor Section Director

Since the Perseids produced their usual clutch of fireballs - meteors of
magnitude -3 or brighter - in mid August, just a few more probable or
definite such events have been reported to us from sites in the British
Isles and nearby, most of which are listed on our Recent Fireball
Sightings webpage, http://snipurl.com/s1m0a . Of some concern is that
numbers of "sky lanterns" mistaken for genuinely meteoric fireballs
have remained quite high, since they were last discussed here (in ENB
270, at http://snipurl.com/s1n2p ), but thankfully more amateur
astronomers are becoming aware of these man-made objects, how
they can appear and behave, which in turn is helping to guide novices
and more casual witnesses in identifying what they may have seen,
through Internet sites like the SPA's Forums.

Of the genuine fireball-class meteors lately, one that was not given on
the Recent Fireball Sightings page, because it was likely just too far
away to have been seen from Britain (and no UK reports on it were
received), was observed from places in eastern France, Belgium and
the Netherlands at 19:59 UT on August 15-16. French colleague Karl
Antier reported it was estimated at around magnitude -7/-10, and its
flight lasted eight seconds, an unusually long time for a natural meteor.
Karl also mentioned the event had been caught on an automated video
system in central France, run by Tioga Gulon, which video can be seen
via: http://snipurl.com/s1ner .

More recently, a particularly brilliant fireball featured in media notices
as having been seen from various places in Ireland on September 3-4,
likely sometime between roughly 20:00 and 20:15 UT. Unfortunately,
but as commonly happens with fireballs reported just by the media,
details on the event have been extremely sketchy so far. This BBC
News webpage, http://snipurl.com/s1mw1 , despite its vagueness, has
as much information as any.

The latest British fireball sighting to reach the SPA was from North
Yorkshire, of a magnitude -5 or so meteor that occurred within ten
minutes of 23:30 UT on September 9-10.

Anyone who saw one or more of these fireballs, or any others, from the
British Isles recently, is welcome to send a full report to the Meteor
Section as soon as possible. The minimum details needed are:

1) Exactly where you were (give the name of the nearest town or large
village and county if in Britain, or your geographic latitude and longitude
if elsewhere in the world);

2) The date and timing of the event (please ensure these are in UT =
GMT, so subtract one hour from current clock time, BST, to get UT. Do
not forget the date changes at UT midnight!); and

3) Where the fireball started and ended in the sky, as accurately as
possible, or where the first and last points you could see of the trail
were if you did not see the whole flight.

More advice and a fuller set of details to send (including an e-mail
report form) are given on the "Making and Reporting Fireball
Observations" page of the SPA website, at: http://snipurl.com/s1jjo .


LATE JULY METEOR UPDATE
By Alastair McBeath, SPA Meteor Section Director

Fresh results have come through since the initial ENB 273 report on
the Delta Aquarids and Alpha Capricornids from late July, including
from the following additional contributors, to whom go fulsome thanks
for their work (see the Perseid report above for abbreviations). The
data from the German Arbeitskreis Meteore group (AKM; see
http://www.meteoros.de ) arrived this week in their journal "Meteoros"
Vol. 12, No. 9, kindly provided by Ina Rendtel.

Pierre Bader (Germany; AKM; V), Tibor Csorgei (Slovakia; NAMN; V),
Mikhail Maslov (Novosibirsk, Russia; NAMN; V), Sven Näther
(Germany; AKM; V), Jürgen Rendtel (Canary Islands & Germany; AKM;
V), Frank Wächter (Italy; AKM; V), Sabine Wächter (Italy; AKM; V).

In general, the initial findings for the Delta Aquarids were similar to
those in ENB 273, with an ill-defined peak around July 29-30 and 30-
31, though the mean ZHRs have reduced slightly, to 17 +/- 3. ZHRs
seemed to have been 10 or more between roughly July 25-26 to 31-
32. A few more Alpha Capricornids have been added than were
available originally, yielding ZHRs of ~4-6 from July 24-25 to 31-32,
perhaps marginally better on July 28-29, but this remained uncertain,
and the question of whether Alpha Capricornid visual activity can really
be separately defined from the overlapping shower radiant of the
Antihelion Source meteors, continues unresolved.

The IMO "live" visual results have a webpage for the Delta Aquarids, at
http://www.imo.net/live/sdaquariids2009/ , but very curiously, this has
suggested peak ZHRs were around 40 +/- 6 on July 28, substantially
higher and differently-timed to what the more limited SPA data have
indicated. The IMO ZHRs were probably inflated by assuming a lot
more faint Delta Aquarids were present than was really the case,
given that the July IMO video results (published on the IMO-News e-mail
list on September 4, and also given in German in the AKM's journal
mentioned above) showed quite normal video activity, similar to that
seen over the previous decade. The IMO video results suggested a
peak on July 28-29 as well, unlike the long-term average date of July 30.
These same video results found an Alpha Capricornid peak on July 29,
but with relative video rates less than one-third those of the Delta
Aquarids.

Intriguingly, the IMO video results since 1998 have suggested both the
Delta Aquarids and Alpha Capricornids exhibit a slowly-decreasing
atmospheric velocity in their meteors with time, so they seem to be
moving slower towards the ends of their activities in late and mid
August respectively, than near their late to mid July starts. The
difference for the Delta Aquarids was from approximately 46 km/sec in
July to 38 km/sec in August, while that for the Alpha Capricornids was
from ~28 km/sec to 21 km/sec. The Delta Aquarid findings appear to
be backed up by video results from the SonotaCo video network in
Japan, though those suggested a rather smaller difference in the fall,
from ~43 km/sec to 39 km/sec. Why this should be so is presently
unexplained, but the confirmation for the Delta Aquarids by two
independent datasets hopefully rules-out a systematic error in one or
other analysis technique. The differences, though fairly small,
depending on which dataset is more nearly correct, might be
discernible by very experienced visual observers who routinely
estimate meteor apparent velocities, though most visual meteor
watchers are unlikely to notice them.


PROSPECTS FOR THE 2009 ORIONIDS & LEONIDS
By Alastair McBeath, SPA Meteor Section Director

With an impending break in the regular ENBs till late November now,
these two major showers form the main meteoric highlights during that
period. More details on them, with radiant charts and information on the
other known showers active simultaneously, can be found on the
monthly meteor activity webpages, off the Meteor homepage, at
http://www.popastro.com/sections/meteor.htm . The November page
will be available from mid October.

The main Orionid maximum is due on October 21, when the radiant is
near Orion's "Club" asterism, an area of sky usefully observable for
meteor work from about 23h UT onwards. An IMO analysis some years
ago suggested Orionid ZHRs could be around 30 at best this year, at
their latest, possibly cyclical, activity peak, between roughly 2008-2010.
In 2006 to 2008, abnormally strong Orionid returns occurred, with ZHRs
of 40-70 on two or three consecutive dates across the predicted peak.
Another IMO analysis after the 2006 event indicated no good likelihood
for similarly protracted, enhanced rates to still happen this year, so it
will be interesting to discover what does transpire. Even in a normal
year, the build-up to and fall-away from the Orionid maximum tends to
be fairly gentle, with ZHRs of ~15 or more persisting from
approximately October 18-23. In addition, a sub-peak, with ZHRs
similar to the normal main maximum, has happened in the past on
October 17-18, though definitely reported from only two years so far,
1993 and 1998. With new Moon on October 18, conditions could
scarcely be more perfect for covering whatever near-maximum Orionid
activity comes-by this time.

Although the run of strong to storm Leonid returns seen from 1998-
2002 is unlikely to repeat again until the 2030s (or perhaps even till
next century), independent model calculations by various theoreticians
have indicated 2009 may bring strong to possibly storm-proportion
rates, with various maximum timings and strengths proposed, due
primarily to dust trails left by the shower's parent comet 55P/Tempel-
Tuttle at its 1466 and 1533 returns. The better peaks are forecast to
occur between roughly 20:40 to 22:00 UT on November 17. However,
this may not be the only interesting period. The 1466 trail may
produce ZHRs above 20 from about 06:30 UT on November 17 till
00:30 UT on November 18, with a denser dust region likely producing
ZHRs above 40 from circa 16h-23h UT on the 17th. This denser 1466
region will probably combine with the 1533 trail to push ZHRs up
perhaps towards 130-150 at some stage between 21h-22h UT that
day. One meteor analyst, Jeremie Vaubaillon, found there may be a
chance of very strong peaks around 21:44 (ZHR ~950+) and 21:51 UT
(~600), which could combine to give a rate perhaps in the 1000-1500
range briefly. Other submaxima may occur as well, on November 17
around 07:26 (ZHRs maybe ~200+) and 09h UT (~25-30), and on
November 18, at about 00:04 (~15) and 19h UT (~10-15, probably of
faint meteors). The Earth passes closest to the node of the comet's
orbit near 15h UT on November 17, perhaps with ZHRs of ~10-20 then.
Clearly, the evening to early morning UT hours of November 17-18 will
create most interest for watchers, but none of these predictions is
guaranteed of course, nor can other unexpected peaks be ruled-out.
Whatever takes place, new Moon on November 16 ensures perfect
Leonid viewing conditions.

The shower's radiant rises only by ~23h UT, and reaches a fully usable
elevation after midnight from Britain. This will mean British sites may
miss the very strongest Leonid activity, and watching from the UK will
probably be most rewarding towards dawn on November 16-17, plus
around and shortly after radiant-rise on November 17-18, but coverage
at any time when the radiant is readily-seen on these nights, and
perhaps others, would be important as well, and could catch any
unanticipated peaks. There is the slim chance that if storm-level activity
should manifest as predicted on November 17, one or two Leonids
might be seen around then from Britain, even though the radiant will still
be below the horizon here. A few, very rare, meteors from a given
shower can still just graze the meteor layer, and so theoretically be
seen from a surface site, where the radiant is less than about 10°
below the horizon, a circumstance that will apply for the Leonids at the
predicted storm-peak time from the more southerly parts of Britain
especially. As Leonids are very swift meteors, about as rapid as
meteors can be, and still be members of the Solar System, they ablate
somewhat higher in the atmosphere than other meteors, which works to
increase slightly the chances for such "sub-horizon" activity to happen.
This may mean most observers in the British Isles have at least an
outside chance to spot one or maybe more, should a storm happen
around 21:45-21:50 UT. Any such meteors will be moving away from
where the sub-horizon Leonid radiant is, naturally, but they will have far
longer paths than would be expected, perhaps streaking across much
of the sky, and with a very good chance of leaving a persistent, glowing
train after they have vanished. This may mean they appear to be
moving slower than Leonids "should do", so do not be fooled!

Good luck, and clear skies!


MINI-COMETS EJECTED BY COMET HOLMES IN ITS OUTBURST
RAS

Astronomers have discovered that multiple fragments were ejected
during the outburst of Comet 17P/Holmes in 2007 October, when the
small (3.6-km) body brightened by nearly a millionfold in less than a
day. The astronomers examined a sequence of images, taken with the
Canada-France-Hawaii telescope in Hawaii on nine nights in 2007
November; they used a digital filter, called a Laplacian filter, that
enhances sharp discontinuities within images and made it possible to
recognize faint small-scale features that would otherwise be hard to
detect against the bright background of the expanding comet. They
found that numerous small objects had moved radially away from the
nucleus at speeds up to 125 m/s. The objects were too bright to be
just bare rocks, but were more like mini-comets, creating their own
dust clouds as ice sublimated from their surfaces.

While cometary outbursts are common, their causes are unknown. One
possibility is that internal pressure built up as the comet moved
closer to the Sun and sub-surface ices evaporated. The pressure
eventually became too great and part of the surface broke away,
releasing a cloud of dust and gas, as well as larger fragments.
However, the solid nucleus of Comet Holmes survived the outburst and
continued on its orbit, seemingly unperturbed, just as it did in the
analogous outburst that led to its discovery in 1892. Comet Holmes
has an orbital period of about 6 years, and travels from the inner
edge of the asteroid belt to beyond Jupiter. The comet is now moving
away from the Sun but will return to perihelion in 2014. Images and
animations can be downloaded at http://snipurl.com/rvmvz .


NEW IMAGES OF MARS
JPL, Pasadena, California

Thousands of new images from the Mars Reconnaissance Orbiter show a
wide range of gullies, dunes, craters, areological layering, and other
features. The orbiter recorded the images from April until early
August of this year. The camera team at the University of Arizona,
Tucson, makes several new images available each week and periodically
releases much larger sets, such as the batch posted on September 2.
Each complete image from the camera covers a strip of Martian ground
6 km wide, about 2--4 km long, and show details as small as 1 metre
across. The new images are available at http://snipurl.com/rqcrs


JUPITER CAPTURED COMET FOR 12 YEARS IN MID-20TH CENTURY
RAS

Comet 147P/Kushida--Muramatsu was captured as a temporary satellite of
Jupiter in the mid-20th century and remained trapped in an irregular
orbit for about twelve years. There are only a few comets known to
have been captured as temporary satellites, and the capture duration
in the case of Kushida-Muramatsu, which orbited Jupiter between 1949
and 1961, is the third-longest. An international team modelled the
trajectories of 18 'quasi-Hilda comets' -- objects with the potential
to go through a temporary capture by Jupiter that results in them
either leaving or joining the Hilda group of objects in the asteroid
belt. Most of the cases of temporary capture in the modelled
trajectories were fly-bys, where the comets did not complete a full
orbit. However, the team used recent observations that tracked
Kushida-Muramatsu over nine years to narrow down the diversity of the
possible orbital paths for the comet over the previous century.
In all the variants, Kushida--Muramatsu completed two full revolutions
of Jupiter, making it only the fifth captured orbiter to be identified.

Asteroids and comets can sometimes be distorted or fragmented by tidal
effects induced by the gravitational field of a capturing planet, or
may even impact upon the planet. The most famous victim of both those
effects was Comet Shoemaker--Levy 9, which was torn apart on passing
close to Jupiter and whose fragments then collided with that planet in
1994. Previous computational studies have shown that Shoemaker--Levy
9 may well have been a quasi-Hilda comet before its capture by
Jupiter. The object that impacted upon Jupiter this July, causing the
new dark spot, may also have been a member of the class, even if it
did not suffer tidal disruption like Shoemaker--Levy. The team has
also confirmed a future moon of Jupiter. Comet 111P/Helin--Roman-
Crockett, which orbited Jupiter three times between 1967 and 1985,
will complete six laps of the planet between 2068 and 2086.


CRATERS ON VESTA AND CERES COULD HOLD KEY TO JUPITER'S AGE
RAS

Crater patterns on Vesta and Ceres could help to show when Jupiter
began to form during the evolution of the early Solar System. A study
modelling the cratering history of the two largest objects in the
asteroid belt, which are believed to be among the oldest in the Solar
System, indicates that the type and distribution of craters would show
marked changes at different stages of Jupiter's development. The
study, carried out by scientists at the Italian National Institute for
Astrophysics in Rome, explored the hypothesis that one or both objects
formed during Jupiter's formation by modelling their cratering
histories. Their simulation described Jupiter's formation in three
stages: an initial accretion of its core followed by a stage of rapid
gas accretion, in turn followed by a phase where the gas accretion
slowed down while the planet reached its final mass. During the last
two phases Jupiter's gravity started to affect more and more distant
objects. For each of the phases, the team simulated how Jupiter
affected the orbits of asteroids and comets from the inner and outer
Solar System, and the likelihood of them being moved onto collision
paths with Vesta or Ceres.

Their model suggested that the stage of Jupiter's development made
big differences to the speed of impacts and the origin of potential
impactors. When Jupiter's core approached its critical mass, it
caused a sharp increase in low-velocity impacts from small, rocky
bodies orbiting nearby to Vesta and Ceres, which led to intense and
uniform crater-distribution patterns. Such low-speed collisions may
have helped Vesta and Ceres gather mass. Once Jupiter's core had
formed and the planet rapidly accreted gas, it deflected more distant
objects onto a collision course with Ceres and Vesta and the impacts
became more energetic. Although rocky objects from the inner Solar
System were the dominant impactors at that stage, the higher energies
of collisions with icy bodies from the outer Solar System made the
biggest mark.

The third stage of Jupiter's formation was complicated by a period
known as the Late Heavy Bombardment, which occurred around 4.1 to 3.8
billion years ago. During that time a significant number of objects
from the outer Solar System were injected into orbits crossing those
of the giant planets and may have reached the asteroid belt. In
addition, Jupiter is thought to have migrated in its orbit around that
time, which would have caused an addition flux of impactors on Vesta
and Ceres. The team will have occasion to reconsider their results
when the 'Dawn' space mission reaches Vesta in 2011 and then continues
for a rendezvous with Ceres in 2015. Dawn will gather information on
the structure and surface morphologies of the two asteroids and send
back high-resolution images of the crater patterns.


SPOT ON DWARF PLANET
RAS

Haumea is an object that orbits the Sun beyond Neptune, in the
so-called Kuiper belt. It is the fourth-largest known Kuiper-belt
object (KBO) after Eris, Pluto and Makemake. Those large KBOs,
together with main-belt asteroid Ceres, are now officially called
dwarf planets. Because it is so far away, Haumea is visible only as
a rather uninformative point of light. Most of what little we know
about it is derived from its brightness variations. Because of its
rotation and elongated shape, Haumea brightens and dims periodically
as it reflects more and less sunlight. The period tells us that it
rotates in 3.9 hours -- faster than any other large object in the
Solar System -- and the amplitude of the variation tells us how
elongated Haumea is. It is estimated to be approximately an
ellipsoid, 2000 by 1600 by 1000 km, whose shape balances gravitational
and rotational accelerations. Haumea may have been spun up by a
massive impact in the distant past. The shape and rotation period
imply that Haumea has a density 2.5 times that of water. Since we
know from spectroscopic observations that Haumea is covered in water
ice, its high density implies that Haumea must have a rocky interior,
in contrast to its icy surface. Photometry shows two maxima and
two minima of brightness as the oblong object rotates. They are not
exact duplicates of one another, as would be expected from a uniform
surface: there must be differences in reflectivity between different
azimuths. The differences are not quite the same in infrared
wavelengths as they are in visible light, and show that the darker
azimuth is slightly redder than the rest of the surface. The reason
for the non-uniformity of surface brightness and colour is presently
a matter for speculation.


NASA APPROVES X-RAY SPACE MISSION
Science Daily

NASA recently said that it hopes to launch the 'Nuclear Spectroscopic
Telescope Array' (NuSTAR) mission in 2011 August. NuSTAR will carry
the first high-energy-X-ray focusing telescopes into orbit, providing
deeper, clearer views of energetic phenomena such as black holes and
supernova explosions than previous X-ray instruments.


HUBBLE OPENS NEW EYES ON THE UNIVERSE
NASA

The first pictures have been received from the refurbished Hubble
telescope; astronauts installed new instruments during the servicing
mission in May. The new imaging camera can observe across a wide
swath of the electromagnetic spectrum, from the ultraviolet to the
near infrared. The telescope's new instruments are more sensitive and
can observe significantly more efficiently than previous generations
of Hubble instruments.


ASTRONOMER'S SUPERNOVA-DISCOVERY RECORD

A Suffolk astronomer has broken a long-standing world record by
identifying his 125th supernova. Tom Boles, 65, runs the Coddenham
Observatory, which has three robotically-controlled telescopes that
scour the night sky looking for supernovae. The eccentric Bulgarian-
born astronomer Fritz Zwicky has held the record for 36 years after
discovering 123 supernovae before his death in 1974 but Mr Boles has
now leapt ahead of him after his latest discovery in August. He said
his state-of-the-art equipment regularly examined a range of 12,000
galaxies, and his long-standing ambition was to find a supernova in or
close to our own Galaxy.


LEEDS ASTROMEET
Rod Levene

This year's annual 'Astromeet' is on Saturday October 7, and is rather
a special one, being our 150th anniversary. Speakers include Dame
Jocelyn Bell, Dr. Monica Grady, Prof. Mike Edmunds, Dr. Allan Chapman,
and Prof. Alan Watson. The venue is The Clothworkers Hall, School of
Music, University of Leeds. £10 at the door (students half price).
Further information at: leedsastronomy.org.uk


NEXT BULLETIN

Owing to holidays, the next scheduled bulletin will not appear until
November 22.


Bulletin compiled by Clive Down

(c) 2009 the Society for Popular Astronomy