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PostPosted: Sat Mar 14, 2009 10:09 pm 

Joined: Fri May 16, 2008 10:09 pm
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Location: Headcorn, Kent, England
Electronic News Bulletin No. 263 2009 March 15

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

By Alastair McBeath, SPA Meteor Section Director

Two notable fireballs have been reported from UK sites in the first ten
days of March. The earlier was at 02:54 UT on March 4-5, only seen
from NE Lincolnshire, but also imaged by Klaas Jobse's all-sky camera
in the Netherlands. Unfortunately, sky conditions at both places were
rather poor - you can see how cloudy it was for Klaas on his image at: - so it is probably a measure of the event's
brilliance that it was recorded at all! The start position has not been
well-established so far. It may have been ~100+ km above the Holland-
Belgium border north of Antwerp. The end has been more closely
constrained, at probably ~80 km altitude over the northwest Netherlands,
likely near 52.9°N, 6.2°E. Assistant Meteor Director David Entwistle
has reported a strong radio-meteor echo was detected at about the key
time from four places, two in Belgium, one in England, the other in
Northern Ireland. As usual with radio data, we cannot be certain all four
observers definitely detected this fireball, but it seems plausible most
may have done so.

The second fireball, probably in the magnitude range -6 to -9, was
spotted from eleven sites across southern England and south Wales,
east as far as Hertfordshire, north to Warwickshire, and west as far as
Rhondda Cynon Taf and the south coast of mid Devon. It happened in
the twilight at 18:45 UT on March 10-11. Most of the witnesses were on
the road at the time, so regrettably positional information on the
object's flight is very sketchy. The start may have been somewhere high
above the upper Severn estuary, around Herefordshire-Worcestershire-
Gloucestershire perhaps, and the fireball likely flew from there at an
angle between north-south to northeast-southwest, possibly ending
above Devon-Cornwall, but more likely out over the Channel west of
Start Point. The end especially is little more than a best-guess, however.
It seems to have been quite swift-moving, so it is most unlikely any
meteorites will have survived. Two observers reported the object
fragmented in mid-flight, but the majority saw no such break-up,
possibly because of different viewing angles to the trail. Various striking
colours were noted by different people, commonly blue, green and white
in the head and red, orange or yellow in the tail, and it may have left a
short-lived persistent train. Some of the early sightings and comments
can be found on the SPA's Observing Forum, at: .

Additional sightings of either of these fireballs, any other fireballs
spotted from the British Isles or nearby (a fireball is any meteor that
reaches at least magnitude -3), would be greatly welcomed by the
Meteor Section. See the "Making and Reporting Fireball Observations"
SPA webpage, at: , for information and a
report form.

By Alastair McBeath, SPA Meteor Section Director

This annual Conference is open to all meteor enthusiasts, whether
amateur or professional, theorist or observer. It will be held in Porec, on
Croatia's Istrian Peninsula by the Adriatic Sea, from September 24-27
this year. The booking fee (which includes full board at the conference
hotel, access to all sessions and the excursion, plus a copy of the IMC
Proceedings) is 150 Euros till June 30, after which it rises to 160 Euros.
The IMC's official language is English and although the IMC is the
International Meteor Organization's main meeting each year, you do
not need to be an IMO member to register for, or attend, the IMC. For
further notes, and a link to the IMC registration webpage, see the SPA
Forum topic at: .


A newly-discovered asteroid 2009 DD45 came within 72,000 km
(0.00048 AU) of the Earth on March 2. That's only twice the height of
a geostationary communications satellite. The asteroid is thought to
be 30 to 40 metres across, perhaps similar in size to the Tunguska
impactor of 1908. Although the object passed very close by
astronomical standards, it was still more than 11 Earth radii away.
Statistically, therefore, only one in 11-squared passes -- less than 1%
-- within that distance would result in an actual impact.


The Cassini spacecraft has found within Saturn's G ring a faint
embedded moonlet. Scientists believe that it is a main source of the
G ring and its single ring arc. The G ring is one of the outer
diffuse rings. (Saturn's rings have been named in the order in which
they were they were discovered, and the nomenclature now appears to be
less than systematic; working outwards they are D, C, B, A, F, G and
E.) Within the faint G ring there is a relatively bright and narrow,
250-kilometre-wide arc of ring material, which extends one-sixth of
the way around the ring's circumference. The moonlet moves within
that arc. Previous Cassini plasma and dust measurements already
indicated that the partial ring may be produced from relatively large,
icy particles embedded within the arc, such as the recently recognised

The scientists first saw the moonlet on 2008 August 15, and were able
to confirm it by finding it in two earlier images. They have since
seen it on several occasions. It is too small to be resolved by
Cassini's cameras, so its size cannot be measured directly, but has
been estimated by comparison of its brightness with that of another
small Saturnian moon, Pallene. They have also found that the
moonlet's orbit is being disturbed by the larger, nearby satellite
Mimas, which keeps the ring arc together. The new discovery brings
to three the number of Saturnian ring arcs with embedded moonlets
found by Cassini. The new moonlet may not be alone in the G-ring arc;
previous measurements with other Cassini instruments implied the
existence of a population of particles, possibly ranging in size from
1 to 100 metres. Early next year, Cassini's will be in a position to
take a closer look at the arc and the moonlet.


Using the Very Large Telescope, astronomers have made observations
of the atmosphere of Pluto. They found unexpectedly large amounts
of methane in the atmosphere, and also discovered that the atmosphere
is hotter than the surface by about 40 degrees, although it still
reaches only a frigid minus 180 degrees Celsius. Those properties of
Pluto's atmosphere may be due to the presence either of patches of
pure methane or else of a methane-rich layer covering the surface.
Pluto, which is about a fifth the size of the Earth, is composed
primarily of rock and ice. As it is about 40 times further from the
Sun than the Earth on average, it is very cold, with a surface
temperature of about minus 220 degrees Celsius.

It has been known since the 1980s that Pluto has a tenuous atmosphere,
which consists of a thin envelope of mostly nitrogen, with traces of
methane and probably carbon monoxide. As Pluto moves away from the
Sun during its 248-year orbit, its atmosphere gradually freezes and
falls to the ground. In periods when it is closest to the Sun -- as
it is now -- the temperature of the solid surface rises, causing the
ice to sublimate into gas. Until recently, only the upper parts of
the atmosphere of Pluto could be studied. By observing stellar
occultations, when the planet as it moved across the sky passed in
front of a background star, astronomers were able to demonstrate that
Pluto's upper atmosphere was some 50 degrees warmer than the surface,
or minus 170 degrees Celsius. Those observations could not shed any
light on the atmospheric temperature and pressure near Pluto's
surface, but the new observations made with an infrared spectrograph
have indicated that the atmosphere as a whole, not just the upper
layers, has a mean temperature of minus 180 degrees Celsius, and so it
is indeed 'much hotter' than the surface. The infrared observations
also indicate that methane is the second-most-common gas in Pluto's
atmosphere, representing 0.5% of the molecules.

Science Daily

Intergalactic space appears to be filled with a haze of tiny, smoke-
like 'dust' particles that dim the light from distant objects and
subtly change their colours, according to a team of astronomers from
the Sloan Digital Sky Survey. Galaxies contain lots of dust, most of
it formed in the outer regions of dying stars. The surprise is that
dust is observed hundreds of thousands of light-years outside the
galaxies, in intergalactic space.

The Sloan team considered the colours of distant quasars whose light
passes in the vicinity of foreground galaxies on its way to the Earth.
Dust grains block blue light more effectively than red light; it
appears that quasars are reddened by intergalactic dust, and the
reddening extends up to ten times the radii of the foreground galaxies
themselves. Supernova explosions and outflows from massive stars
drive gas out of some galaxies and the gas may carry dust with it, but
it is also possible that the dust may be pushed directly by the
radiation pressure of starlight.


GLOBE at night, the international star-counting programme, starts on
Monday, 16 March, 2009, a key activity during this International Year of
Astronomy (IYA2009). Running between 16 and 28 March, it is a digital
effort to obtain precise measurements of urban dark skies around the
world using sky-quality meters. It is an excellent opportunity for people
to get outside and see the night sky. Even from towns and cities it is
possible to see Orion, and the information obtained from everyone who
takes part will allow astronomers to build up a map of light pollution
around the UK, and worldwide.

The constellation of Orion is used to gauge the magnitude of a dark
sky (how dark the sky is). Through counting the number of stars in
Orion’s constellation visible to an unaided eye, you can conclude
whether your sky has a measly magnitude of 1 (lucky to see even a few
stars, normal in urban sprawls like London) or anything up to magnitude
7 (so many stars you lose count, possible in unspoilt natural beauty like,
for example, The Shetland Islands).

For more information, and to learn how to make and report
measurements, see . To make a measurement,
you must wait for astronomical twilight (approximately 20.30 in the UK
this week) for the sky to be properly dark, look in a south westerly
direction and look for three bright stars close together in a straight line.
If you can spot it, you’ve found Orion’s belt. Go to
for further tips.

Bulletin compiled by Clive Down

(c) 2009 the Society for Popular Astronomy

The Society for Popular Astronomy has been helping beginners to
amateur astronomy -- and more experienced observers -- for more than
50 years. If you are not a member then you may be missing something.
Membership rates are extremely reasonable, starting at just £16 a year
in the UK. You will receive our bright quarterly magazine Popular
Astronomy, regular printed News Circulars, help and advice in pursuing
your hobby, the chance to hear top astronomers at our regular
meetings, and other benefits. The best news is that you can join
online right now with a credit card or debit card at our lively

Kevin Brown, SPA webmaster
My astro blogs.. | Practical Astronomy magazine

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