It is currently Wed Jun 19, 2019 1:25 am


Post new topic Reply to topic  [ 1 post ] 
Author Message
PostPosted: Tue Mar 18, 2014 11:00 am 
Offline
Site Admin

Joined: Fri Dec 03, 2004 11:24 am
Posts: 4375
Location: Greenwich, London
The SOCIETY for POPULAR ASTRONOMY
Electronic News Bulletin No. 370 2014 February 16

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/


ANATOMY OF AN ASTEROID
ESO
Astronomers using measurements taken with the New Technology Telescope
(NTT) at La Silla in Chile have found evidence that an asteroid has a
varied internal structure: different parts of the asteroid (25143)
Itokawa have different densities. The team has measured the speed at
which that small near-Earth asteroid spins and how that spin rate is
changing over time.
Itokawa is an intriguing object, as it has a strange peanut shape,
revealed by the Japanese spacecraft Hayabusa in 2005. To probe its
internal structure astronomers used images gathered from 2001 to 2013,
by the NTT and other telescopes, to measure its brightness variation
as it rotates. The data were used to derive the asteroid's spin
period and how it is changing over time. In combination with
knowledge of the asteroid's shape, that brought to light the
complexity within its core. The spin of asteroids and other small
bodies in space can be affected by sunlight. That phenomenon, known
as the YORP effect (an acronym for its discoverers), occurs when
absorbed sunlight is re-emitted from the surface of the object in the
form of heat. When the shape of the asteroid is very irregular the
heat is not radiated evenly, and that creates a tiny, but continuous,
torque on the body and changes its spin rate. The astronomers found
that the YORP effect was slowly accelerating the rate at which Itokawa
spins. The change in rotation period is tiny -- a mere 0.045 seconds
per year. But it was very different from what was expected and can
only be explained if the two parts of the asteroid's peanut shape have
different densities. Until now, the properties of asteroid interiors
could be inferred only from rough overall density measurements. The
glimpse into the diverse innards of Itokawa has led to speculation
regarding its formation. One possibility is that it formed from the
two components of a double asteroid after they bumped together and
merged. Finding that asteroids can have inhomogeneous interiors has
far-reaching implications, particularly for models of binary-asteroid
formation.

'ROGUE ASTEROIDS' MAY BE THE NORM
Massachusetts Institute of Technology
To get an idea of how the early Solar System may have formed,
scientists often look to asteroids. Those relics of rock and dust
represent what today's planets may have been like before they
differentiated into bodies of core, mantle, and crust. In the 1980s,
scientists' view of the Solar System's asteroids was essentially
static: asteroids that formed near the Sun remained near the Sun,
while those that formed farther out stayed on the outskirts. But in
the last decade, astronomers have detected asteroids with compositions
unexpected for their locations in space. Scientists considered them
to be anomalous 'rogue' asteroids. But a new map developed by
researchers from MIT and the Paris Observatory charts the size,
composition and location of more than 100,000 asteroids throughout the
Solar System, and shows that rogue asteroids are actually more common
than previously thought. Particularly in the main asteroid belt --
between Mars and Jupiter -- the researchers found a compositionally
diverse mix of asteroids. It has been suggested, unfortunately
without any actual mechanism being proposed, that Jupiter may have
'drifted' closer to the Sun, dragging with it a host of asteroids that
originally formed in the colder edges of the Solar System, before
deciding to move back to its current position. Such a migration may
(so it is said) have simultaneously knocked around more close-in
asteroids, scattering them outward.
To create a comprehensive asteroid map, the researchers first analyzed
data from the Sloan Digital Sky Survey, which uses a large telescope
in New Mexico to observe a lot of galaxies, but included in the survey
are data for more than 100,000 asteroids. The team grouped the
asteroids by size, location, and composition. That last category was
defined by asteroids' origins -- whether in a warmer or colder
environment -- a characteristic that can supposedly be determined by
whether an asteroid's surface is more reflective at redder or bluer
wavelengths. The team then tried to account for observational biases.
While the survey includes more than 100,000 asteroids, they are the
brightest ones. Asteroids that are smaller and/or less reflective
may be overlooked, so an asteroid map based on observations may
unintentionally leave out an entire population. The researchers
determined that the survey was probably complete down to a diameter of
5 km, so they confined their analysis to asteroids above that size.
They grouped them by size and composition, and mapped them into
distinct regions of the Solar System. They observed that for large
asteroids, the traditional pattern holds true: the further from the
Sun, the colder the asteroids appear. But for smaller asteroids, that
trend seems to break down: those that look to have formed in warmer
environments can be found not just close to the Sun, but throughout
the Solar System, and asteroids that resemble colder bodies beyond
Jupiter can also be found in the inner asteroid belt, closer to Mars.

CURIOSITY MARS ROVER FACES MINI SAND DUNE
BBC NEWS
The 'Curiosity' Mars rover is to try to drive over a one-metre-high
dune. The sand bank is currently blocking the robot's path into a
small valley and a route with fewer of the sharp rocks that lately
have been making big dents in the vehicle's aluminium wheels. NASA
engineers will take no risks, however. The rover will be commanded
initially to climb only part way up the dune to see how it behaves.
The team is mindful that the 'Spirit' rover was lost in a sand trap in
2009, and the 'Opportunity' rover, which has just celebrated 10
working years on the planet, very nearly went the same way in 2005
when it became stuck for several weeks in a deep dirt pile. Curiosity
has already had one scuff at the base of the barrier, using a wheel to
test the sand's consistency. The robot would have no problem managing
the incline but mission planners will be concerned about the potential
for any rocks hidden inside the dune to damage or snare Curiosity.
Engineers believe the path ahead between two scarps will be kinder on
the rover's 50cm-diameter wheels, which have been taking a hammering
during the one-ton (only 8 cwt on Mars) vehicle's traverse across the
floor of Mars' equatorial Gale Crater. Recent close-up pictures
reveal multiple punctures, rips and dimples in Curiosity's metal
'tyres'. Getting over the small dune would offer the rover smoother
ground in the future. The next objective is a place where scientists
hope to drill into freshly exposed bedrock and look for traces of any
complex carbon chemistry that might be present. Curiosity's ultimate
goal is to get to the foothills of the big central mountain that
dominates the crater floor, which is still several kilometres away to
the SW. Since landing in 2012 August, Curiosity has travelled almost
5 km.

MARS ORBITER EXAMINES NEW CRATER
NASA
Space rocks hitting Mars excavate fresh craters at a rate of more than
200 per year. A new image from the Mars Reconnaissance Orbiter shows
a crater about 30 metres in diameter at the centre of a radial burst
painting the surface with a pattern of bright and dark tones. The
scar appeared some time between pictures taken of that place in 2010
July and in 2012 May. The new image, which is of higher resolution,
was taken on 2013 Nov. 19.

RED SKIES DISCOVERED ON EXTREME BROWN DWARF
RAS
A peculiar example of a brown dwarf with unusually red skies has been
discovered by a team of astronomers from the University of Hertford-
shire's Centre for Astrophysics Research.
Brown dwarfs straddle the line between stars and planets. They are
too massive to be considered as planets but not massive enough to fuse
hydrogen in their cores and develop into stars. As they have not got
an internal source of energy, they are cold and very faint, and keep
on cooling over time. One called ULAS J222711-004547 caught the
researchers' attention for its extremely red appearance. Observations
with the VLT in Chile have shown that the reason for its peculiarity
is the presence of a very thick layer of dust in its upper atmosphere.
The size of the dust grains influences the colour of the sky. The
atmosphere of that particular brown dwarf appears to contain water
vapour, methane and probably some ammonia but, unusually, it is
dominated by clay-sized particles that are mostly made of mineral
dust, of materials like enstatite and corundum.

OLDEST KNOWN STAR
The Australian National University.
A team led by astronomers at the ANU has observed one of the oldest
known stars in the Universe, which formed shortly after the Big Bang
13.7 billion years ago. It was discovered at Siding Spring
Observatory with the SkyMapper telescope, which is searching for
ancient stars as it conducts a five-year project to produce the first
digital map the southern sky. It is around 6,000 light-years away,
and its composition suggests that it formed in the wake of a
primordial star which had a mass 60 times that of our Sun. It has
been thought that primordial stars died in extremely violent
explosions which polluted huge volumes of space with iron. But the
ancient star shows signs of lighter elements such as carbon and
magnesium, and no sign of iron. That is thought to indicate that the
primordial star's supernova explosion was of surprisingly low energy.

SPA SOLAR SECTION 2013 December
By Geoff Elston, SPA Solar Section Director
December was a fairly quiet month in terms of solar activity.
In white light some fairly complex groups were seen but they were
comprised of fairly small sunspots and were not seen with the unaided
eye. In H-alpha there was a lot of plages associated with the spot
groups, some long dark filaments and a few strong flares.
Rotations 2144, 2145. The Mean Daily Frequency rose slightly, up from
5.26 in November to 5.66 in December. The Relative Sunspot Number went
up a little from 80.47 to 81.92. The stormy weather across much of
the UK had some impact on observations, and we lost 5 days to cloud
wind and rain. Well done to Jonathan Shanklin and Alan Heath each of
whom observed the Sun on 23 days, and Brian Gordon-States who observed
on 19 days, in December.
WHITE-LIGHT ACTIVITY. Nearly all the sunspot activity seems to have
been confined to the southern hemisphere in the first week of
December. On the 8th groups AR 1909 and AR 1915 were seen nearing the
W limb, and AR 1916 was not far behind. AR 1916 was pretty complex
in structure (AR 1909 was flare-active too according to the
Spaceweather.com website). It was not visible to the unaided eye but I
did count some 21 spots/pores in the whole group. AR 1912, a single
spot, lay farther east, and AR 1917 was just by the E limb and had 3
distinct umbrae in the leader spot and some fainter following pores.
AR 1918 was on the E limb and would become more easily visible by 10th
and 11th. By the 19th there were several spots on the disc. ARs 1920
and 21 were approaching the W limb, faculae were seen preceding the
spots, but AR 1928 took centre stage as another complex group. It was
not seen with the unaided eye but it did show several umbrae within the
leader spot and a trail of smaller spots and pores. It was also
flare-active. Towards the east were four more active regions but of
those AR 1931 was noticeable for showing the Wilson Effect well. It
was a similar view on the 22nd, AR 1928 was nearing the W limb and
still complex in structure, but another group, AR 1934, had just come
over the E limb. On the 28th AR 1934 was still showing quite a
complex structure, and AR 1936, a group of small spots and pores, was
near the CM. In that group some 13 spots and pores were counted, and
by the following day the total had grown to 16. MDF: 5.66 R: 81.92
H-ALPHA ACTIVITY
A long convoluted filament was observed reaching away westwards from
an arched-type prominence on the E limb on the 1st. By the 4th the
filament had left the limb and moved westwards. There were other
filaments and plages associated with ARs 1908 and 09. A very long
curved filament was observed stretching northwards away from spot
group AR 1912. On the 17th AR 1928 was surrounded by plages and a
convoluted filament was just to the south of the sunspot group.
Plages and filaments were also seen around sunspot groups AR 1917, 20
and 21. Former Section Director Richard Bailey just caught sight of a
very faint western prominence on the 20th, and after increasing the
sensitivity of his imaging camera discovered a quickly changing and
very tall loop prominence. Four images were taken in about 35 minutes
from 1034 to around 1109 UT, and during that time he noticed quite a
few sections of the prominence fall back towards the solar surface.
Flares were reported on the 21st (at 1035 UT) and 22nd (0935, and a
weaker one at 1005). The SE limb had a low but long prominence on the
25th. By the 29th all the sunspots were strung out along the southern
hemisphere. Several filaments and some extensive plages were visible
around the spots.
MDF (P): 7.78
Owing to a mistake in totalling up the MDF (P) I need to revise the
totals for September, October and November. They should be 7.93, 8.49
and 9.24.

Bulletin compiled by Clive Down
(c) 2014 the Society for Popular Astronomy
The Society for Popular Astronomy has been helping beginners in
amateur astronomy -- and more experienced observers -- for more than
60 years. If you are not a member then you may be missing something.
Membership rates are extremely reasonable, starting at just £18 a year
in the UK. You will receive our bright bi-monthly magazine Popular
Astronomy, help and advice in pursuing your hobby, the chance to hear
top astronomers at our regular meetings, and other benefits. You can
join online right now with a credit card or debit card at our lively
website: http://www.popastro.com
________________________________________


Top
 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:  
cron
Powered by phpBB® Forum Software © phpBB Group