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The SOCIETY for POPULAR ASTRONOMY
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Electronic News Bulletin No. 258 2009 January 4
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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/



URSIDS 2008 - FIRST FINDINGS
By Alastair McBeath, SPA Meteor Section Director

As in 2006 and 2007, the Ursids again produced a stronger-than-normal
return, possibly with several maxima on December 21-22, and peak
Zenithal Hourly Rates (ZHRs) perhaps up to 35 at best. Apart from the
expected "normal" maximum, due sometime between ~07:30-10:00 UT
on December 22 (as detailed in ENB 256, archived at:
http://snipurl.com/9fyd5 ), two further predictions were made for maxima
on December 22, one by French meteoricist Jérémie Vaubaillon
(around 02:18 UT), the other by Finnish meteor expert Esko Lyytinen (for
circa 05:07 UT). ZHRs for both seemed likely to be roughly 20-30. As
so often for this shower, results till now have been very limited in quantity
thanks to the weather and the shower's proximity to the winter holidays.
Sadly, the UK seems to have missed-out yet again visually.
Consequently, the following discussion is only an initial overview. It will
need checking and correcting as more data comes through (hopefully!).
In particular, the ZHRs should be taken as preliminary estimates only.
Regular Section contributors Jeff Brower (British Columbia, Canada)
and Enrico Stomeo (Italy) provided copies of their data, radio and video
respectively, directly to us, while the remainder were extracted from
notes posted on the Meteorobs Internet Forum, rounded-up and
provided by another long-standing Section correspondent Rich Taibi in
Maryland, USA. These results included video details from Italians
Maurizio Eltri and Roberto Haver, and visual observations made by:
Mark Davis (of the North American Meteor Network, observing from
South Carolina, USA), George Gliba (Maryland, USA), Javor Kac
(Slovenia) and Paul Martsching (Iowa, USA).

The two most detailed video datasets suggested a notable maximum
between approximately 01:30-04h UT on December 22, apparently
strongest in the hour centred at 02:10 UT. However, Jeff's radio data
indicated probable Ursid activity was strengthening from maybe 22h-
23h UT on December 21, and produced a likely first radio peak in the
01h-02h UT interval on the 22nd. Weak possible video sub-peaks
seemed apparent in one dataset each towards 20h and 23h UT on the
21st. Visual ZHRs from 00h-01:30 UT may have been ~20-30, and
perhaps 15-25 from 01:30-03:00. Activity seemed to drop for a time
after this initial main maximum, but may have been rising towards the
end of the night over Europe again, after ~05h. This is uncertain, but
intriguing, because Jeff's radio data showed a strong, sharp peak
around 07h-08h UT on December 22, at a time when visual observers
in North America reported ZHRs around 25-35, rising from ~15-20 at
about 06h and lasting till at least 08:45. Though there are no visual or
video reports to correlate with it as yet, Jeff recorded a further radio
peak at about 18h-20h UT on December 22. There were indications in
some of the visual and video observations that the Ursid magnitude
distributions overall on December 21-22 were brighter than usual,
including a few minor fireballs, which has been allowed-for in computing
all the ZHRs here. Most grateful thanks go to all the named contributors
above for their efforts. All additional Ursid data would be very welcome!


GEMINIDS 2008 - EARLY RESULTS
By Alastair McBeath, SPA Meteor Section Director

Before the Ursids in December, the moonlit Geminid maximum passed
unseen for large swathes of the British Isles, thanks to thick clouds
overnight on December 13-14. As mentioned in ENB 256, its peak was
expected within a couple of hours of 23h UT on December 13. However,
initial International Meteor Organization (IMO) visual results, available
via the homepage at http://www.imo.net , have suggested it was later
than expected, peaking instead between 02:00-03:00 UT on the 14th.
ZHRs may have been inflated in trying to allow for the bright Moon, but
were estimated as ~135 +/- 15. Typically in recent times, the maximum
rate has been about 120. Using shorter observing intervals, the IMO
data indicated the maximum's centre may have been around 02:33 UT,
with ZHRs of ~190 +/- 30, though this value is most uncertain. A
preliminary review of the initial radio results by Assistant Meteor
Director David Entwistle and myself did not suggest an especially clear
maximum signature in most of the data, which we might have expected
had the peak been this strong. Instead, activity seemed to be good for
various parts of December 13-14 when the Geminid radiant was readily-
detectable from different places. We intend a more detailed examination
of the full radio results later. Those few lucky UK observers who could
get out for a time on December 13-14 reported excellent rates of bright
to fireball-class Geminids all night, confirmed by details from elsewhere,
though few fireballs exceeded magnitude -5/-6 in the data as yet.
Observers, visual if not stated, who reported some observations from
the shower, including those from the SPA Forum and UK Weather
Watch's Space Weather Forum, were: Enric Algeciras (Spain; radio),
Jeff Brower (British Columbia, Canada; radio), Willy Camps (Belgium;
radio), David Entwistle (England; radio), Alfred Krohmal (Syzran,
Russian Federation; radio), "Leo" (London), Martin McKenna (Co Derry,
Northern Ireland; visual & imaging), "markt" (West Midlands), Andy
Smith (England; radio), Enrico Stomeo (Italy; video), Dave Swan
(England; radio), Felix Verbelen (Belgium; radio). Many thanks go to all!
The Geminids topic on the SPA's Observing Forum, at:
http://snipurl.com/9fyid has further comments and links to other reports,
including to some of Martin's Geminid photos.


UPDATE ON NOVEMBER'S METEOR ACTIVITY
By Alastair McBeath, SPA Meteor Section Director

The Taurid "swarm" return of late October to early November has
continued to prove less obvious than we might have hoped, following the
fireball-rich return of 2005, as last discussed in ENB 256. A review of
the Radio Meteor Observation Bulletin November reports (RMOB 184,
dated November 2008 - see http://www.rmob.org for details, plus the
observers and their radio equipment) indicated some radio datasets
showed mildly enhanced echo counts through to November 6 from the
closing days of October, as noted previously. Counts were particularly, if
not strongly, enhanced on November 4 and 5. Felix Verbelen's counts
of radio meteor echoes lasting more than 2 seconds showed this latter
point most clearly, which inferred somewhat brighter meteors than
normal may have been involved. This seemed to confirm the preliminary
IMO visual findings of enhanced Taurid activity in early November, which
peaked on November 5. Unusual activity seemed not to have continued
much beyond November 6 in the radio data. A note in the IMO's video
meteor report for November (with data chiefly collected in Europe,
posted on the IMO-News and Meteorobs e-mailing lists on December
23) suggested variable Taurid magnitude distributions were present
from late October to November 20, but without a clear pattern, and no
suggestion that the shower as a whole produced more bright meteors
than normal in 2008.

November's RMOB was also thoroughly scanned for the Leonids, to add
to the information on the shower given in ENB 256. As expected from
the visual and preliminary radio news, the majority of results favoured a
strong peak in the 02h-03h UT binning interval on November 17, with
above-normal rates probably due to the Leonids alone lasting from
~01h-10h UT on that date. Activity seemed to decline rather slowly after
the maximum, through till ~04h-05h, but it may have held fairly steady
from ~05h-08h. It then dropped for a time, before rising to produce a
possible minor secondary peak around 10h-11h UT. This could have
been the nodal-crossing peak (the expected 'traditional' maximum -
see the notes in ENB 254, at: http://snipurl.com/9fyx1 ). The IMO's
November video report also mentioned enhanced Leonid activity was
detected from Europe on November 17 from 01:30 to 05:30 UT,
peaking between 02h-03h. No video observations were possible after
05:30 however, and the available data was weather-limited too, unfortunately.

Lastly, further details have continued to appear regarding the
spectacular meteorite-dropping fireball over western Canada on
November 20-21, as featured in the last two ENBs. The ~13-kg
meteorite mentioned last time has now been confirmed as the largest
single surviving part of the event, and with numerous other chondritic
specimens recovered, it seems probable it will set a fresh record for
Canada's largest recorded meteorite fall. For links to reports and
images, plus any further news, see the SPA Forum topic at: http://snipurl.com/9fyyy .


DISTANT PLANET HAS CARBON DIOXIDE ETC
ESA

Scientists using the Hubble telescope have discovered carbon dioxide
and carbon monoxide, methane and water vapour in the atmosphere of a
Jupiter-size planet 63 light-years away.


DIMMEST STARS YET FOUND
NASA/Jet Propulsion Laboratory

Brown dwarfs are objects with masses between those of planets and of
stars; they are not massive enough to ignite the nuclear fires that
power normal stars. The first incontrovertible one was found only in
1995, and astronomers are still finding progressively fainter
examples. A new record has been claimed for the dimmest known
star-like object, by a supposed pair of brown dwarfs. Previously,
astronomers thought the pair of stars was just one typical, faint
brown dwarf, but they have recently concluded that it must be a binary
system although it has not been seen as such. It is called 2MASS
J09393548-2448279 after its entry in the Two-Micron All-Sky Survey.

Data from the Spitzer infrared space telescope indicated atmospheric
temperatures of 565 to 635 Kelvin. While that is hundreds of degrees
hotter than Jupiter, it is still very cold as far as stars go.
In fact the object is the coldest star-like one measured so far.
To calculate its intrinsic brightness (candle-power), the researchers
had first to determine its distance. From measurements made at the
Anglo-Australian Observatory in Australia, they concluded that it is
the fifth-closest known brown dwarf to us; it is 17 light-years away,
towards the constellation Antlia. That distance, together with
Spitzer's measurements, showed that the object was both cool and
extremely dim. The brightness was, however, actually twice what would
be expected for a brown dwarf with that particular temperature.
Therefore (the argument runs) it must have twice the surface area; in
other words, it must be twins, with each body shining only half as
bright, and each with a mass of 30 to 40 times that of Jupiter. Both
bodies are a million times fainter than the Sun in total luminosity,
and at least a billion times fainter in visible light alone.


STUDY TRACKS STARS ORBITING MILKY WAY BLACK HOLE
ESO

In a 16-year study made with several ESO telescopes, a team of
astronomers has produced the most detailed view yet of the
surroundings of the super-massive black hole at the centre of our
Galaxy. The research has mapped the orbits of 28 stars, many more
than previous studies. One of the stars has now completed a full
orbit around the black hole known as Sagittarius A* (spoken as
"Sagittarius A-star").

The astronomers observed at infrared wavelengths that penetrate the
dust that blocks the Galactic Centre from view in visible light. They
regarded the central stars as 'test particles' and watched how they
moved around Sagittarius A*. In comparison with previous studies, the
new work improved the accuracy with which the positions of the stars
were measured by a factor of six. The final precision was 300 micro-
seconds of arc. The observations could be used to infer the mass of
the black hole itself, and its distance. They also showed that at
least 95% of the mass sensed by the stars has to be in the black hole
-- so there is comparatively little scope left for other dark matter.
The stellar orbits in the Galactic Centre show that the central mass
concentration of four million solar masses must be a black hole,
almost beyond doubt. The observations also allowed the astronomers to
determine with some precision our distance, 27,000 light-years, from
the centre of the Galaxy.

One particular star, known as S2, orbits the Milky Way's centre so
fast that it completed a full revolution within the 16-year period of
the study. Observing the complete orbit of S2 made a crucial
contribution to the high accuracy reached. It is not understood,
however, how the stars came to be in the orbits in which they are
observed to be today. They are much too young to have migrated far
from their birthplaces, but it seems even more improbable that they
could have formed in their current orbits where the tidal forces of
the black hole must be expected to prevent any gas cloud from
condensing into stars.


DISTANT WATER
NRAO

Astronomers using the 100-m radio telescope in Effelsberg, Germany,
and the Very Large Array (VLA) in New Mexico have detected the radio
spectral lines of water molecules in a galaxy more than 11 billion
light-years away, much further away than water had been seen before.
The galaxy, MG J0414+0534, has a quasar -- a super-massive black hole
powering bright emission -- at its core. In the region near the core,
the water molecules are acting as masers, the radio equivalent of
lasers, to amplify radio waves at a specific frequency. The
astronomers are quoted as saying that their discovery indicates that
such giant water masers were more common in the early Universe than
they are today, although it is hard to see how such a sweeping
generalisation could validly be made from just a single example.
MG J0414+0534 is seen as it was when the Universe was roughly
one-sixth of its current age.

At the galaxy's great distance, even the strengthening of the radio
waves by the masers would not by itself have made them strong enough
to detect with the radio telescopes. However, the scientists had help
from nature in the form of another galaxy, nearly 8 billion light-
years away, located directly in the line of sight to MG J0414+0534.
That intervening galaxy's gravity serves as a lens to brighten the
more-distant galaxy. The gravitational lens produces not one, but
four, images of MG J0414+0534 as seen from here. Using the VLA, the
scientists found the specific frequency attributable to the water
masers in the two brightest of the four images (the other two are
still too faint). The radio frequency emitted by the water molecules
was Doppler-shifted by the expansion of the Universe from 22.2 GHz to
6.1 GHz.

Water masers have been found in numerous nearer galaxies. Typically,
they are thought to arise in discs of molecules closely orbiting
super-massive black holes at the galaxies' cores. The amplified radio
emission is more often observed when the orbiting disc is seen nearly
edge-on. However, MG J0414+0534 seems to be oriented almost face-on
to us, so the water molecules that we are seeing may not be in the
disc; they might be in jets of material being ejected from the
vicinity of the black hole.


Bulletin compiled by Clive Down

(c) 2009 the Society for Popular Astronomy


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