PLANETS
By Andrew Robertson, SPA Planetary Section Director
Jupiter is now at a respectable altitude (in the early hours) for the
first time in quite a few years. In the last couple of weeks I have
observed it visually between 2 and 4am BST. I realise not everyone
can get out at that time, but if you are able to it's well worth the
effort. It is a very dynamic planet with a wealth of detail (which is
always changing), easily discernible even in small telescopes. I
never tire of looking at that planet just watching different details
pop into view in moments of better seeing. Because it rotates in just
under 10 hours you can observe different features over consecutive
nights. Frequently when a feature does come back into view it will
have changed or moved slightly. I'm now starting to get some
excellent images and sketches from SPA members. A bright Moon doesn't
interfere with observing/imaging Jupiter, in fact some of the best
views are obtained in twilight. Jupiter is currently at magnitude,
-2.5 shining like a beacon in the east at 12° altitude at midnight
BST. By 2am it's at 29° in the ESE and by 4am it's at 45° altitude in
the SE.
Any reports of observations would be most welcome via:
http://popastro.com/planet/contact/COMET GARRADD BRIGHTENS
By Robin Scagell
A comet discovered in 2009 by Australian amateur astronomer Gordon
Garradd is currently visible from the UK for most of the night, moving
slowly west through Delphinus and Sagitta during the month. At
magnitude 7, it might seem easy to observe, but the object is quite
small so at least a medium-sized telescope and fairly dark skies are
needed for good views. However, it can be glimpsed with binoculars
that have at least 10 x magnification, and preferably more. Details
of its position and magnitude are updated by Comet Section director
Jonathan Shanklin on the Comet Section website -- scroll down to Comet
Ephemerides. Or you can use the charts at
http://www.popastro.com/news/newsdetail.php?id_nw=64to locate it. The first one shows its track for August compared with
the constellations, then when you have picked out its location use
your binoculars or finder to pinpoint it using the more detailed maps.
Remember that the positions are shown for 0 hours UT on the dates in
question, so if you are observing in the late evening, the comet will
have moved almost to the next position.
'DAWN' REACHES VESTA
NASA
Finally we can see the real face of Vesta, asteroid number 4,
discovered on 1807 March 29 by Olbers. It was photographed on July 9
by the Dawn probe, after a journey of almost four years. An image was
taken from a distance of 41,000 km and shows a great deal of surface
detail, even though the resolution is only 3.8 km/pixel. At first
glance, Vesta resembles many of the other minor bodies in the Solar
System, particularly some of the satellites of the giant planets with
similar diameters of around 500 km. Dawn has now been placed into a
stable orbit about the asteroid, at a distance of 16,000 km. It
will stay in orbit around Vesta for a year, after which it will leave
for its second target, the dwarf planet Ceres (ex asteroid number 1),
where it will perform a similar manoeuvre to that at Vesta.
NEW SATELLITE OF PLUTO FOUND
Astropublishing
During an observing campaign aimed at searching for possible rings
around Pluto, a team of researchers using the Wide-Field Camera 3 on
the Space Telescope has found a new satellite. Provisionally called
P4, it has a diameter of roughly 20 km and its orbit lies between
those of two other small moons, Nix and Hydra, that together with the
larger Charon, make up, for now, the satellite system of Pluto. The
new discovery strengthens the hypothesis that the system was formed as
the result of an impact between the primitive Pluto and another body
of similar size. It looks less likely that the moons are the result
of gravitational capture of bodies that formed elsewhere.
PAIR OF WHITE DWARFS ON COLLISION COURSE
Smithsonian Institution
Astronomers using the MMT telescope on Mt. Hopkins, Arizona, have
discovered a pair of white dwarfs spiralling into one another at
breakneck speeds. The stars are so close to each other that they make
a complete orbit in just 13 minutes, travelling at a relative speed of
600 km/s, but they are gradually slipping closer together. In about a
million years they will merge and possibly explode as a supernova.
The brighter one contains about a quarter of the Sun's mass compacted
into a Neptune-sized ball, while its companion has more than half the
mass of the Sun and is Earth-sized. Their mutual gravitational pull
is so strong that it deforms the lower-mass star by 3%. If the Earth
bulged by the same amount, we would have tides 120 miles high.
The stars are much too close together to distinguish photographically,
but their relative motions can be measured spectroscopically. Their
orbit is oriented such that they eclipse each other every 6 minutes.
The eclipses provide a very accurate measure of the orbital period.
General relativity predicts that moving objects create ripples in the
fabric of space-time, called gravitational waves. The waves are
supposed to carry away energy, so the stars ought to inch closer
together and orbit each other faster and faster. Gravitational waves
have never yet been detected, but their existence can be tested by
measuring the change in the separation of the two stars. Because they
don't seem to be exchanging mass, the system is an exceptionally clean
laboratory to perform such a test.
VISTA FINDS 96 STAR CLUSTERS HIDDEN BEHIND DUST
Physics.org
Using data from the VISTA infrared survey telescope at the Paranal
Observatory, an international team of astronomers has discovered 96
new open clusters, invisible in previous less-sensitive surveys,
hidden by the dust in the Milky Way.
THE ORIGIN OF COSMIC DUST
Astropublishing
Thanks to observations made with the Herschel space telescope of the
supernova 1987A, it seems that an explanation may have been found as
to why very distant, and so very young, galaxies are found to be
particularly rich in dust. The dust is actually made up of tiny
grains that are typically much smaller than a familiar terrestrial
speck of dust, being closer to the size of a smoke particle, and are
composed of heavy elements such as carbon, silicon, oxygen and iron.
They are released in the supernova explosions of dying, massive stars.
However, until now it appeared that the quantity of dust produced by
supernovae was insufficient to explain the amounts of dust observed in
the primordial galaxies. That was largely owing to limitations in
instrumentation, but Herschel has allowed a group of astronomers from
the University College London to discover a surprisingly large amount
of dust associated with SN 1987A in the Large Magellanic Cloud. The
amount of dust in SN 1987A, about one solar mass, is up to 1000 times
the mass estimated by previous studies, and demonstrates that the
amount of dust observed in primordial galaxies could be consistent
with the amount produced by the supernova explosions of the first
generation of giant stars (over 10 solar masses), that ended their
lives 'just' a few hundred million years after the Big Bang.
The data collected by Herschel are also surprising because the
estimated temperature of the dust, between 16 and 23 Kelvin,
is about a twentieth of the temperatures derived from previous
data at shorter wavelengths. That implies that the dust plays a key
role in the formation of new stars, by cooling clouds of interstellar
gas, thus allowing them to collapse under gravity. In the absence of
such cooling, a cloud which is undergoing gravitational contraction
heats up, and the additional pressure may halt further collapse. The
formation of a dense nucleus that will become a star would be
inhibited. So the presence of dust generated by supernovae has
probably influenced the evolution of galaxies from a very early stage.
WHAT ACTIVATES A SUPERMASSIVE BLACK HOLE?
ESO
A new study combining data from the VLT and the X-ray satellite
XMM-Newton suggests that activity associated with black holes in the
centres of galaxies was not turned on by mergers between galaxies, as
had been previously thought. Some astronomers believe that at the
heart of most large galaxies there is a supermassive black hole with a
mass millions, or sometimes billions, of times that of the Sun. In
many galaxies, including our own Milky Way, the central black hole is
quiet, but in some, particularly early on in the history of the
Universe, there is intense radiation given off by material as it falls
into the black hole.
Astronomers have now looked in detail at more than 600 active galaxies
in an extensively studied patch of the sky called the COSMOS field.
As expected, they found that extremely brilliant active nuclei were
rare, while the bulk of the active galaxies in the past 11 billion
years were only moderately bright. But there was a surprise: the new
data showed that the majority of the commoner, less-bright active
galaxies, even in the far past, were not triggered by mergers between
galaxies. The presence of active galactic nuclei is revealed by the
X-rays emitted from around the black hole, which were picked up
XMM-Newton. The galaxies were subsequently observed with the VLT,
which was able to measure their distances. When combined, the
observations allowed the team to make a three-dimensional map showing
where the active galaxies lie.
The astronomers could see how the galaxies were distributed and
compare the distribution with theory. They could also see how the
distribution changed as the Universe aged, from about 11 billion years
ago to almost the present day. The team found that active nuclei are
mostly found in large massive galaxies with lots of dark matter. It
had been expected that, if most active nuclei were a consequence of
mergers and collisions between galaxies, they would be found in
galaxies of moderate mass, but the team found that most active nuclei
occur in galaxies with masses about 20 times larger than the value
predicted by merger theory.
OXYGEN MOLECULES DISCOVERED IN SPACE
NASA
Astronomers using Herschel have found oxygen molecules in the Orion
star-forming complex. The discovery has prompted researchers to look
for oxygen molecules in other star-forming regions. Individual atoms
of oxygen are common in space, particularly around massive stars, but
molecular oxygen has eluded astronomers until now. The team proposes
that oxygen is locked up in water ice that coats tiny dust grains, and
that the oxygen detected by Herschel in Orion was formed after
starlight warmed the icy grains, releasing water, which was converted
into oxygen molecules.
JUNO SPACECRAFT LAUNCHED TO JUPITER
NASA
The solar-powered Juno spacecraft has begun its five-year journey to
Jupiter. It will orbit the planet's poles 33 times and use its
instruments to probe beneath the obscuring cloud cover to learn more
about Jupiter's structure, atmosphere and magnetosphere, and look for
a potential solid core.
Topic: August Astronomy Bulletin (Read 877 times)