It is currently Thu Jun 04, 2020 8:43 am

Post new topic Reply to topic  [ 1 post ] 
Author Message
PostPosted: Tue Jan 08, 2008 7:46 pm 
Site Admin

Joined: Fri Dec 03, 2004 11:24 am
Posts: 4382
Location: Greenwich, London
Electronic News Bulletin No. 235 2008 January 6

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

By Alastair McBeath, SPA Meteor Section Director

Further to the preliminary Geminid notes last time, the early "live"
International Meteor Organization (IMO) results, accessible via the homepage, which suggested peak Zenithal Hourly
Rates (ZHRs) for the shower may have been well above normal, have
gradually reduced in strength as more data has arrived. The maximum
ZHR has settled near an average of ~120 +/- 6 between roughly
14:30-18:30 UT on December 14-15, with ZHRs in the ~90-110 range
preceding that from approximately 20h UT on December 13-14.
Activity generally declined as December 14-15 progressed after this
early evening peak, much as the preliminary SPA visual results

Assistant Meteor Director David Entwistle has carried out a more
detailed examination of the radio meteor data collected over the shower
now. It appears there were a few problems because of interference, or
system-saturation due to the numbers of Geminid echoes occurring
relatively close together in time, which seem to have been particularly
problematic for North America. Despite this, most radio observers
found a peak sometime between 12h and 17h UT on December 14, the
majority indicating a slow build-up to it, followed by a swifter fall in rates afterwards. Using details from six European Radio Meteor Observation
Bulletin (RMOB; see: ) datasets, David found a
mean maximum time of ~15:39 UT on December 14, with a scatter of
about three hours to either side of this.

Aside from the RMOB observations, two fresh visual reports have
arrived recently from "coldfieldboundary" (Bruges, Belgium) and SPA
Comet Director Jonathan Shanklin (Cambridgeshire). Many thanks as
always to all contributors. Any Geminid observations still to come would
be very welcome. See the pages off the Section's homepage at:
for information on what to send and where to.

By Alastair McBeath, SPA Meteor Section Director

Very late predictions were made barely in advance of the events for
possible outbursts from the Ursids (which we shall look at shortly), and a
theoretical shower called the "Alpha Lyncids", the latter supposedly due
to reach a maximum at 03:40 UT on December 20-21. The existence of
the "Alpha Lyncids" appears to be based on just one 32-minute visual
observation by one observer in 1971! While this 1971 report suggested
unusual meteor numbers coming from a source with a radiant perhaps
around 13h08m RA, +44 degrees Dec on December 20-21, which may
have lasted somewhat longer than the actual observation (beginning
earlier), it seems there was no confirmation of the source then or
subsequently. The UK Weather World's Space Weather Forum topic at: has a little more information on the original
observation, and the 2006 prediction. Aside from bright moonlight, the
weather seems to have been unfavourable for many people that night in
2006, and very few observations have arrived from December 20-21 so
far. These included one set of visual notes from Martin McKenna (Co.
Derry, Northern Ireland), a video report from Enrico Stomeo (Italy), plus
radio details from Jeff Brower (British Columbia, Canada) and David
Entwistle (Lancashire). Enrico found no possible Lyncids at all from 54
recorded trails collected during continuous video recording from 16:42
to 05:23 UT, while Martin saw no suspected Lyncids either, albeit under
a very poor sky, from ~01:35-03h UT (when the weather closed-in
completely). Neither radio system showed a definable signature likely
due only to this possible source, just the usual near-Ursid, later-
December activity, so although further results to arrive will be checked
in case they show anything interesting, it seems the "Alpha Lyncids"
were a complete non-event on the evidence so far. Despite this, a
hearty well done is due to the people who were able to provide their
results so quickly afterwards, since without their efforts, we would still be in the realms of pure speculation about it.

Curiously, there were two UK reports of an apparently unrelated bright
fireball at 23:38 UT on December 20-21, the witnesses in Hampshire
and Ayrshire (both initial reports are on the UKWW Forum topic noted
above), suggesting the event could have been seen from much of the
UK overall, had skies been better that night. If anyone else saw this
meteor, or any other fireballs (a fireball is a meteor that reaches at least
magnitude -3, thus as bright as the planet Jupiter at its very best), who
has not yet done so, please send me a full report as soon as possible.
The details I need, and where to send them, are outlined on the "Fireball
Observing" page of the SPA website, at: .

By Alastair McBeath, SPA Meteor Section Director

The badly-moonlit Ursid maximum was due around 01h-03h UT on
December 21-22, as noted in ENB 232 (see: ),
but late predictions appeared of a possible further peak, perhaps giving
ZHRs of ~40-80 at some stage from ~20h-22h UT on December 22-23,
the strength and timing not entirely consistent between all sources to
mention it. A few visual reports appeared subsequently, from people
with better skies chancing the bright moonlight, including on the
UKWW Forum topic mentioned under the "Alpha Lyncids" notes above,
and on the IMO-News and Meteorobs e-mail listings. Quite a number of
these tended to suggest generally low Ursid activity was seen around
the possible December 22-23 outburst time, but the often poor skies
meant ZHR numbers could have been considerably inflated above their
observed values, albeit not especially reliably. Unfortunately, the
outburst prediction date meant most visual observers ignored the
normal peak night of December 21-22, so there was no comparison
data for what occurred then under similarly moonlit conditions, meaning
the significance of the activity on December 22-23 was especially
difficult to judge. The IMO's "live" Ursid page (off the IMO homepage)
did initially suggest a ZHR peak around 21:15 UT on the proposed
outburst night, but with more data available as time has gone on, it
seems as if ZHRs of ~20-35 may have persisted from around 11h-22h
UT on December 22-23 at least. Unfortunately, there were virtually no
data from outside this interval, so again, it is very hard to say how this
possible peak compared to the expected "normal" maximum night's
activity. David Entwistle's initial review of the early radio results (three
full European datasets) found no clear pattern in the probable Ursid
signature this year, and that overall, the shower's activity may have been
somewhat less than in 2005 or 2006. Different systems suggested
Ursid rates were better on one of December 21, 22 or 23, but without a
definite consensus for any date. Early comments from the IAU (IAU
Electronic Telegram 1188, kindly forwarded by SPA Vice-President
Robin Scagell) proposed confirmation of the December 22-23 peak
based on two radio datasets, one set of video results and the initial
IMO visual notes. This may have been a little premature however, as
one of the radio observers, regular Section correspondent Jeff Brower,
reported transmitter problems on December 21-22, which may have
made his December 22-23 results seem suggestive of a peak that night
incorrectly. Investigations continue to try to clarify what took place, so all further Ursid reports would be most welcome!


Astronomers are monitoring the trajectory of an asteroid estimated to
be 50 m across that is expected to cross Mars' orbital path late this
month. Observations indicate the object may pass within 30,000 miles
of Mars at about 11h UT on Jan. 30. At present asteroid 2007 WD5 is
about half-way between the Earth and Mars. It was discovered on 2007
Nov. 20 by the Catalina Sky Survey and put on a 'watch list' because
its orbit passes near the Earth's. Further observations gave
scientists enough data to determine that the asteroid was not a danger
to Earth, but could potentially impact Mars. That makes it a member
of an interesting class of small objects that are both 'Near-Earth
Objects' and 'Mars-crossers'. With the present uncertainties about
the asteroid's exact orbit, there is a 1-in-75 chance of 2007 WD5
impacting Mars. It has been estimated that impacts by bodies of the
size of 2007 WD5 occur on Mars every thousand years or so and may
create craters about half a mile across. The Mars rover 'Opportunity'
is currently exploring a crater approximately that size.

Science Daily

Using observations from the VLT, astronomers have been able to
determine the site of a flare on a young sunlike star, about 30
million years old, located 150 light-years away. The astronomers
observed the star BO Microscopii, nicknamed 'Speedy Mic' because of
its fast rotation and location in the constellation Microscopium,
during two consecutive nights in 2006 October, with a spectrograph on
the VLT and simultaneously with the XMM-Newton X-ray satellite. Using
a technique called Doppler imaging, the astronomers constructed images
of the surface of the star, detecting the presence of several spots.
A few are near the visible pole, while most are asymmetrically
distributed at mid-latitudes. The X-ray observations identified
several flares, which are sudden major releases of energy. The point
of origin of one of them could be pinpointed on the surface of the
star. The flare, lasting about 4 hours, was a hundred times more
energetic than a large solar flare and considerably larger than solar
coronal loops. Unlike on our Sun, the site of the observed flare did
not correspond to that of any of the detected spots, but was in a
portion of the star's surface away from the main concentration of spot

Brigham Young University

Images from Cassini's radar instrument have shown the existence of
mountains on Titan, Saturn's largest moon. They are thought most
likely to be made of water-ice and are not very high, at most 2000 m.
Competing (but not mutually exclusive) possible explanations for their
apparently somewhat uniform heights are that they have been subject to
similar amounts of erosion, that they are roughly the same age, or
that the materials are behaving in a way that prevents them from
growing any taller. Before Cassini, scientists assumed that most of
the topography on Titan would be impact structures, but the new
findings suggest that the mountains were formed by tectonic processes.


Star formation involves the presence of dust, radiating heat that
arises from the compression of a gas cloud and enabling it to collapse
and ignite nuclear reactions in its core. We see dust being ejected
by dying Sun-like stars, but when the Universe was young there would
have been no such source, and it has been supposed without proof that
supernovae could have produced a lot of dust. They could have
produced dust early on, but their progenitor stars would still have
had to form without dust. Now, the Spitzer spacecraft's infrared
detectors have found 10,000 Earth-masses of dust in the well-known
supernova remnant Cassiopeia A, which is close enough to study in
detail. A spectrographic map reveals the quantity, location and
composition of the supernova remnant's dust, which includes proto-
silicates, silicon dioxide, iron oxide, pyroxene, carbon, aluminium
oxide and other compounds. The map of the dust matches perfectly
that of the gaseous ejecta from the explosion.

Texas Tech University

After studying more than 20,000 stars, researchers conclude that our
disc-shaped galaxy has two spherical haloes of stars left behind when
their original galaxy was either assimilated or dissolved into our
own. The stars in the haloes are among the oldest in the Universe.
Astronomers have suggested for some time that an outer halo existed,
but they had only small samples of stars in their studies. The new
research is based on a much larger sample and shows that there is
definitely a second halo orbiting retrograde to the direction in which
the disc of the Galaxy is rotating. If it were a part of the original
formation of our galaxy, it should obviously orbit in the same
direction. The inner halo of stars is more flattened, and orbits
slowly but in the same direction as the disc. It is not clear whether
the inner halo arose from mergers of small satellite galaxies or as
part of the overall formation of the galactic disc.

The outer halo, however, seems to be composed of a population of stars
which were stripped from smaller galaxies that orbited counter to the
rotation of the disc. While small galaxies which orbit with our
Galaxy's rotation tend to fall rapidly into our Galaxy, the retrograde
satellite galaxies dissolve and their stars are spread throughout the
outer halo. The stars in that halo have proved to have smaller
abundances of heavy elements such as calcium and iron than those in
the inner one. The difference in chemical composition, as well as in
orbital characteristics, indicates that two separate populations of
stars exist in the halo of the Milky Way; the most likely origin of
the outer-halo stars is in small, disrupted, satellite galaxies which
did not share the chemical history of the Milky Way Galaxy.

ETH Zurich/Swiss Federal Institute of Technology

An international team of astronomers has for the first time been able
to detect the visible light that is scattered in the atmosphere of an
exoplanet. They observed the cool dwarf star HD 189733, which is 60
light-years away in the constellation Vulpecula and has a planetary
companion, discovered two years ago, that transits across its disc.
The companion is a 'hot Jupiter' that circulates very close to the
star. The astronomers used a 60-cm telescope, on La Palma and
belonging to the Royal Swedish Academy of Science, by remote control.
They enhanced the brightness of the planet with respect to that of the
star by a polarimetric technique slightly analogous to that by which
polarizing sunglasses reduce glare. They discovered that polarization
peaks near the moments when half of the planet is illuminated by the
star as seen from the Earth. Such events occur twice during the
orbit, similar to half-moon phases. The polarization indicates that
the scattering atmosphere is considerably larger (>30%) than the
opaque body of the planet seen during transits, and most probably
consists of particles smaller than half a micron, for example atoms,
molecules, tiny dust grains or perhaps water vapour, which was
recently suggested to be present in the atmosphere. Such particles
effectively scatter blue light, in exactly the same scattering
process that creates the blue sky of the Earth's atmosphere.
The scientists were also able for the first time to discover the
orientation of the planet's orbit and trace its motion in the sky.

New Scientist

Planets are thought to form as dust collides and sticks together in
so-called proto-planetary discs around young stars. Observations have
shown that the discs tend to dissipate within the first 10 million
years of a star's life, suggesting that planets must take shape before
that time. But until now, no extra-solar planets had been found
around stars young enough still to have discs. That might be because
most planet searches have excluded young stars, whose pulsations can
mimic the velocity variations caused by potential planets.

Using spectroscopic measurements taken with a 2.2-metre telescope at
La Silla Observatory in Chile, researchers at the Max Planck Institute
observed the star TW Hydrae (TW Hya). They found in the star's
spectra a disturbance every 3.56 days that did not correspond to signs
of the star's activity, suggesting that the repeating signal was
indeed caused by an orbiting planet. The planet appears to be quite
massive, nearly 10 Jupiters. It also orbits extremely close to the
star -- 10 times closer than Mercury's distance from the Sun, within
the inner rim of the star's dusty disc. The researchers believe the
planet formed farther away from the star -- as if between the orbits
of the Earth and Jupiter in our Solar System -- where there was more
material from which it could grow. Then, as it lost energy through
gravitational interactions with gas in its natal disc, it moved to its
present location over the course of 100,000 years or so, stopping when
it reached a region cleared of gas.

The fact that the planet was found around a star estimated to be 10
million years old "gives a real upper limit to the timescales of
planet formation and migration", the researchers write in their study.
The planet is in a position comparable with all of the other close-in
Jupiters, so the astronomers conclude that such planets need to be
made and to migrate close to the star within 10 million years. Other
scientists, however, argue that giant planets can form in just a few
thousand years, collapsing quickly from a clump of gas and dust in the

By Bob Mizon

The BAA Campaign for Dark Skies is conducting a UK-wide survey on
light nuisance and light-pollution-related problems. Please spare a
few moments before Jan. 25 to look at, and if appropriate, respond

The SPA Electronic News Bulletins are sponsored by the Open University

Bulletin compiled by Clive Down

(c) 2008 the Society for Popular Astronomy

 Profile Send private message  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 1 post ] 

All times are UTC

Who is online

Users browsing this forum: No registered users and 2 guests

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You can post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group