Topic: Late February Astronomy Bulletin

[Clive]

FIRST LARGE X-RAYFLARE OF THE NEW SOLAR CYCLE
Spaceweather.com

Sunspot 1158 has produced the strongest solar flare in more than four
years.  The eruption, which peaked at 0156 UT on Feb. 15th, registered
X2 on the Richter scale of solar flares.  NASA's Solar Dynamics
Observatory recorded an intense flash of extreme-ultraviolet
radiation.  X-flares are the strongest type of solar flare, and this
is the first such eruption of the new Solar Cycle 24.  In addition to
flashing the Earth with UV radiation, the explosion also shot a
coronal mass ejection (CME) in our direction.


STARDUST NExT MEETS ITS SECOND COMET
NASA

Seven years ago the 'Stardust' spacecraft visited Comet Wild 2 out
beyond the orbit of Mars, capturing a thimbleful of comet dust in its
collector.  Two years later it dropped the sample in the Utah desert.
It has led to a revision of some ideas about comets.  Because comets
form in the ultra-frigid region beyond Neptune, scientists expected
the non-icy parts of the comet to be made up of particles that flowed
into the Solar System from outside.  Instead, it turned out that
nearly everything bigger than a micron in diameter was formed in the
inner Solar System, at very high temperatures.  The material must
somehow have been carried out beyond the planets and incorporated
there into comets.

Stardust had enough fuel left for another venture, and it was
re-programmed to visit Comet Tempel 1, the comet that was observed and
deliberately bombed by the Deep Impact mission in 2005.  The craft was
rather crudely re-named 'Stardust NExT', the new word standing for
'New Exploration of Tempel 1'.  The encounter took place on Feb. 14.
The spacecraft could not take a sample of Tempel 1, because its
collector was returned to Earth following the encounter with Wild 2.
At Tempel 1 it took photos of the crater formed during the Deep Impact
mission - something that Deep Impact itself was prevented from doing
by the cloud of debris which obscured its view of the crater.

Stardust started out with about 18 gallons of hydrazine fuel for its
thrusters.  Now, two missions and about 3600 million miles later,
there is perhaps a cupful of fuel left, not enough for any further
meaningful operations, so the office-desk-sized spacecraft will have
to continue to orbit the Sun on its own as a dead piece of space junk.
The junk includes two microchips bearing the names, in microscopic
type, of more than 1 million people who signed up before the launch.


ISOLATING THE THICK STELLAR DISC OF ANDROMEDA
RAS

Spiral structure dominates the appearance of most large galaxies, with
roughly 70% of all stars contained in a flat stellar disc.  The disc
structure contains the spiral arms traced by regions of active star-
formation, and surrounds a central bulge of old stars at the core of
the galaxy.  Observations of our own Milky Way and other nearby
spirals have led to a belief that such galaxies typically possess two
stellar discs, both a 'thin' and a 'thick' disc. The thick disc
consists of older stars whose orbits take them along paths that extend
both above and below the more regular thin disc.  The thin stellar
discs that we typically see in Hubble imaging result from the
accretion of gas towards the end of a galaxy's formation, whereas
thick discs are produced in a much earlier phase of the galaxy's
existence, so they may be tracers of the processes involved in
galactic evolution.  It is only now that astronomers, using the Keck
telescope to measure the radial velocities of individual stars in the
Andromeda galaxy, have been able to identify the existence there of a
thick disc and to assess the respective diameters and heights of the
two overlapping discs and the elemental abundances of their
constituent stars.

Currently, the process of formation of the thick disc is not
understood.  Previously, the best hope for comprehending that
structure was by studying the thick disc of our own Galaxy, but much
of it is obscured from our view.  The discovery of a similar thick
disc in Andromeda, our nearest large spiral neighbour, offers a much
clearer view.  Astronomers will try to determine the properties of the
disc across the full extent of the galaxy and look for signatures of
events that may be connected to its formation.