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The SOCIETY for POPULAR ASTRONOMY
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Electronic News Bulletin No. 214 2006 February 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
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 http://popastro.c.topica.com/maafIg5abwln5cixLLVb/


SPECIAL MEMBERSHIP OFFER

If you are not already a member of the SPA now is a great time to
join! We are offering to those who receive ENBs and are not already
members a SPECIAL JOINING PRICE of only £12.00 saving £3.00 on the
usual UK annual rate. (Overseas rates vary but discount still applies
-- see our website for details.) You will also receive FREE, THREE
CD-Roms -- 'Window on the Universe' Parts 1 and 2 and 'Window on the
UK'

Join NOW by going to our secure website at www.popastro.com and click
the 'join now' button. To claim the your discount enter ENB017 when
asked for your voucher reference. To join by post send your details
with payment (£12.00 -- 1 year or £24.00 -- 2 years -- UK rate) to SPA
Membership, 36 Fairway, Keyworth, Nottingham, NG12 5DU, quoting
reference ENB017. Please note -- this offer is valid only until 2007
February 28 and does not apply to renewals of membership.



LATE JANUARY FIREBALLS
By Alastair McBeath, SPA Meteor Section Director

Fewer significant fireballs were reported to the Section from the
second half of January than the first (see ENB 213), but the UK ones
included a very bright event around 07:30 UT on January 23-24, not
long before dawn, spotted from Nottinghamshire, Merseyside and
several locations scattered across Wales, and a bright meteor in
evening twilight for a single lucky witness in Powys around 17:30 UT
on January 25-26.

The January 23-24 object seems to have been slow-moving, and was
probably heading roughly north to south over the Irish Sea some way
west of Wales. Some notes about it can be found on the SPA's
Observing Forum, at: http://popastro.c.topica.com/maafIg5abwln6cixLLVb/
including a
link to the BBC News pages, where there is an image which may be
of this event.

Fireball reports (meteors of at least magnitude -3) from the British
Isles
and nearby are always welcomed by the Meteor Section. Notes of
what data is most essential and where to submit it can be found on
the Section's Fireball Observing webpage at:
http://popastro.c.topica.com/maafIg5abwln7cixLLVb/


RADIO QUADRANTIDS 2007
By Alastair McBeath, SPA Meteor Section Director

David Entwistle has kindly forwarded details of his analysis of some
of the better radio meteor results made across the Quadrantid
maximum this year, using a new analysis method which was described
in the International Meteor Organization's (IMO's) journal WGN
last June (Vol. 34, No. 3, pp. 87-92). The method is still somewhat
experimental, and as with all such radio analyses, caution needs to be
exercised due to the difficulties involved in examining this kind of
observation, but David found an average maximum time for the
Quadrantids of around 00:05 UT on 2007 January 3-4, less than half
an hour before the predicted peak (see ENB 209). This is certainly
encouraging, albeit the almost complete absence of any visual results
from the shower this year, due to full Moon and poor winter weather,
means there are few other results available as yet with which to
compare it. The IMO video data for January, expected to be released
in the next couple of weeks, may give more clues, dependent on how
many observers were able to cover the critical interval with their
automated video meteor systems. The results of David's radio analysis
can be seen at: http://popastro.c.topica.com/maafIg5abwln8cixLLVb/


NEW METEOR SECTION ONLINE REPORT FORMS
By Alastair McBeath, SPA Meteor Section Director
Updated versions of both the printable and e-mail text versions of
the meteor report forms are now available from the links at the
bottom of the Meteor homepage,
http://popastro.c.topica.com/maafIg5abwln9cixLLVb/ Please
use these when submitting your meteor watch observations from now
on.


PLUTO PROBE OBSERVES JUPITER
New Scientist

The 'New Horizons' spacecraft, bound for Pluto and possibly other
objects in the outer Solar System, is making a fly-by of Jupiter to
gain speed and test its instruments. It will make its closest
approach on February 28, passing 2.3 million kilometres from Jupiter's
centre, but it took the first of 700 planned observations of the
planet on January 8. In the first 10 days of its observations of
Jupiter, New Horizons found that an area northwest of the Great Red
Spot was unexpectedly tranquil. Pictures from the Cassini spacecraft
in 2000 showed significant turbulence there. Now the area looks more
as it did when Voyager flew by in 1979. Scientists are hoping also to
observe a little red spot that formed fairly recently through the
merger of three smaller storms. New Horizons has already taken a
distant picture of that area, and will get more images when it is
closer.

Scientists look forward to measurements to be made in Jupiter's
so-called magnetotail, a region of sulphur and oxygen ions
originating from the volcanic moon Io. The charged particles get
trapped in Jupiter's magnetic field, then blown by the solar wind into
a tail that stretches hundreds of millions of kilometres behind
Jupiter -- practically to Saturn's orbit. After its closest approach,
New Horizons will keep making measurements of the magnetotail until
June. Mission managers estimate that it could fly one-quarter of the
length of the tail. In addition, it will make a detailed search for
satellites around Jupiter with its telephoto camera. It will also get
a nearly-edge-on view of the tenuous ring system, which it will map in
3D; scientists hope to determine which of Jupiter's dozens of moonlets
create the rings.

The main point of flying past Jupiter, however, is to get a boost in
speed. By a clever use of Jupiter's gravity, the probe's speed will
be increased by 4 km/s, reducing by three years its travel time to
Pluto. So far, New Horizons has remained quite close to its intended
trajectory, and has not needed to call on the 25 kilograms of fuel
(out of its initial total of 77 kg) reserved to correct any
deviations. Now, that extra propellant promises to be available to
take it, after Pluto, to other objects in the ring of trans-Neptunian
bodies known as the Kuiper Belt.


DISC OF MATERIAL ENCIRCLES MIRA B
California Institute of Technology

It has been reported that material from the well-known evolving star
Mira is being captured into a disc around Mira B, its companion.
Located 350 light-years away in the constellation Cetus, Mira made
history 400 years ago upon the discovery of its variations in
brightness. Visible to the unaided eye for a month or two at a time, it
becomes 100 times fainter and disappears from view, only to reappear
again, on an 11-month cycle. Although Mira was once a star somewhat
like the Sun, it is now in a late stage of its evolution as a giant
star and is expelling its outer layers at a rate of one Earth-mass
every seven years. If Mira were a single star, all that material
would dissipate into space. Mira, however, has a companion star in
an orbit with a period of about 1,000 years, and the companion, Mira
B, has a gravitational field that catches nearly 1% of the material
lost from Mira A.

By using specialized high-contrast techniques at the 10-m Keck I
telescope in Hawaii and the 8-m Gemini South telescope in Chile,
observers discovered heat radiation coming not only from Mira B
itself but also from a location offset from Mira B by a distance
equivalent to the radius of Saturn's orbit. The intense radiation
from Mira A, 5,000 times brighter than the Sun, heats the edge of the
disc to about the Earth's temperature and causes it to glow in the
infrared. The researchers found that the material was indeed the edge
of a disc and not just a local condensation in the wind from Mira A.
By modelling the way in which the outflow from Mira A is captured,
the researchers were also able to confirm that Mira B is simply an
ordinary star like the Sun, although only about half as massive.
Eventually Mira A will have expelled all of its tenuous outer layers,
and what is left will appear as a white dwarf about one million years
from now.


NEW DISTANCE ESTIMATE FOR ORION NEBULA
Topix.net

The distance to the Orion Nebula was previously estimated at about
1,500 or 1,600 light-years, but now astronomers at Keele University
say that it is actually closer than that. They studied 34 stars
formed in the nebula, and compared their rotational velocities with
their periods of rotation to deduce their size. It was then
possible to derive their intrinsic magnitudes and compare them with
the apparent magnitudes to show that the true distance of the Orion
Nebula is 'only' 1,300 light-years. The new distance increases the
estimated age of the Nebula's stars to 1.5 million years -- still
very young.


DISTANT STAR CLUSTERS FOUND BEHIND NEARBY ONE
University of California

Astronomers have discovered the most distant population of star
clusters so far identified, hidden behind one of the nearest such
clusters to Earth. At a distance of more than a billion light-years,
the newly discovered star clusters probably exemplify what similar
systems in our own Galaxy once looked like. However, because a
billion years is hardly a tenth of the ages that globular clusters
are supposed to have, it is not to be expected that there have been
significant changes in their characters or appearance in that time.

The study began as an investigation of a globular star cluster known
as NGC 6397; at about 8500 light-years it is one of the closest such
clusters. The Hubble telescope was used to image a small field within
the cluster. In the background, however, was a population of stars
and galaxies which included a large elliptical galaxy that contains
several hundred globular clusters. Although each of the clusters
probably contains hundreds of thousands of stars, they are so far away
that each cluster appears as a single faint point of light in the
Hubble image. In fact, a single giant star in NGC 6397 appears 10
million times brighter than one of the distant globular clusters. The
distance of the elliptical galaxy hosting the globular clusters was
estimated from its red-shift, and showed that the globular clusters
are the most distant so far identified.


UNDERGROUND WATER RESERVOIRS ON MARS?
New Scientist

Apparent dried-up rive-beds and other evidence have been held to imply
that Mars once had enough water to fill a global ocean more than 600
metres deep, together with a thick atmosphere of carbon dioxide that
kept the planet warm enough for the water to be liquid. Now, however,
Mars is very dry and has a thin atmosphere. Some scientists have
proposed that Mars lost its water and CO2 to space as the solar wind
stripped molecules from the top of the atmosphere. Measurements by
Russia's Phobos-2 probe in 1989 hinted that the loss was quite rapid,
but now the Mars Express spacecraft has indicated a rate of loss that
is much lower. Its measurements suggest that the whole planet loses
only about 20 grams per second of oxygen and CO2 to space, only about
1% of the rate inferred from Phobos-2 data. If the same rate has been
maintained throughout Mars' history, it would have removed only a few
centimetres' depth of water and a thousandth of the original CO2.
Either some other process removed the water and CO2 or they are still
present and hidden somewhere on Mars, presumably in underground
reservoirs.

Pictures from the now-lost Mars Global Surveyor suggested that
liquid from sub-surface sources had gushed down slopes on Mars in
recent years, so it seems possible that there is some water existing
in liquid form even now. However, the researchers point out that
other mechanisms, such as asteroid and comet impacts, might have
removed water and CO2 from Mars, or the solar wind might have blown
off whole chunks of atmosphere rather than individual molecules.


ROSETTA OBSERVES ASTEROID PREMATURELY
The Register

The spacecraft 'Rosetta' is primarily intended to observe Comet 67P
Churyumov-Gerasimenko, which it will not reach until 2014. Before
then, it will pass close to two asteroids -- a small one, 2867 Steins,
at a distance of only 1700 km on 2008 September 5, and a 100-km one,
21 Lutetia, at 3000 km on 2010 July 10; much sooner, on the 27th of
this month, it will pass by Mars, but not so much to observe Mars as
to obtain additional speed by utilising the planet's gravity.
Asteroids, like comets, are supposed to offer clues as to conditions
in the early Solar System, so observations of them promise to add to
the scientific return of the Rosetta mission. Rosetta has started
observing Lutetia already; it cannot resolve any surface detail but is
only monitoring its apparent magnitude, with the intention of
determining the orientation of its rotational pole. Its rotation
period is already known -- it was discovered to be 8.172 hours by
Russian scientists observing from the ground years ago.


NEW STAR DISCOVERED IN SOUTHERN CROSS
Science Daily

A research team at Swarthmore College discovered a previously unknown
companion to the bright star Beta Crucis in the Southern Cross. The
companion star was discovered accidentally while the research team was
using the orbiting Chandra X-ray Observatory to study the X-rays
emitted by Beta Crucis itself. The astronomers were surprised to see
two strong X-ray sources where only one had been expected.


HUBBLE'S MAIN CAMERA BROKEN
The Register

Hubble's main camera, the Advanced Camera for Surveys (ACFS), has shut
down after an electrical failure. The camera went offline last year
after a problem with its power supply. That was eventually resolved,
but this time most of the damage appears permanent: NASA says that
only one of the ACFS's three sub-cameras is likely to be restored.
The ACFS was installed during the 2002 servicing mission. Its three
cameras observed in the ultraviolet, visible and infrared wavelength
regions, and its installation effectively doubled Hubble's field of
view. The camera's three channels took in wide-field and high-
resolution pictures, as well as a dedicated channel for observing
our own Solar System. NASA speculates that it will be able to reboot
that last-named channel -- the solar blind -- but says that the
wide-field and high-resolution channels are almost certain to remain
offline.

Since its installation, the camera has sent back some truly remarkable
images and has made a great contribution to science. It has been the
most frequently demanded instrument on the observatory. Hubble is
long overdue for its next service, and is scheduled to be attended by
astronauts in 2008 September. NASA had hoped that that mission would
be able to repair the ACFS properly, but that looks unlikely now.
Instead, the mission will carry out its other objectives -- installing
the new wide-field camera and the 'Cosmic Origins' spectrograph, as
well as new batteries and gyroscopes.


Bulletin compiled by Clive Down

(c) 2007 the Society for Popular Astronomy


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