***********************************
The SOCIETY for POPULAR ASTRONOMY
***********************************
====================================================
Electronic News Bulletin No. 298 2010 November 7
====================================================
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/
PLANETS
By Andrew Robertson, SPA Planetary Section Director
By mid-month (November 15) Jupiter, being well past opposition,
culminates at 20h at an altitude of 34° (from my latitude of 52°.5
north). It is still a respectable 45" in diameter at magnitude -2.7.
The SEB is still faded. Uranus, at magnitude 5.8, is 3.5° to the NE
of Jupiter.
Venus is now a morning object; an hour before sunrise (06:15) it is
visible in the SE at an altitude of 9°, but at magnitude -4.5 it is
very prominent. It is displaying a thin 9% crescent and is 54" in
diameter. Above Venus at that time, at an altitude of 24°, is Saturn;
it is magnitude 0.9 and its rings are tilted at 10°.7, so the Cassini
division should be visible provided the seeing is good enough. Saturn
is 3° to the SSE of Porrima (Gamma Virginis).
A selection of members' images/sketches can be seen on the SPA
Planetary Section's Web Page: http://popastro.com/planet/
Any reports of observations would be most welcome via:
METEOR NOTES
Alastair McBeath's meteor notes for November are on the SPA website at
ICE EXISTS NEAR MOON'S SOUTH POLE
University of Arizona
The LCROSS probe, which was deliberately crashed onto the Moon's
surface in 2009 October to raise dust that could be analyzed for the
presence of water ice, has confirmed that frozen water exists just
below the Moon's surface.
The impact site, in the crater Cabeus near the Moon's south pole, was
selected on the basis of data from the Lunar Reconnaissance Orbiter,
whose findings regarding water are now regarded with more confidence.
Previously, scientists thought that ice could only persist in
so-called permanently shadowed regions (PSRs) on the Moon's surface.
Unlike the Earth, the tilt of whose rotational axis ensures that
almost any spot on the surface receives sunlight at some point during
the year, the Moon has an axis that is hardly tilted at all. As a
result, no direct sunlight ever reaches the bottoms of some of the
craters that are close to the lunar poles. At -223°C, those PSRs are
nearly as cold as Pluto, even at noon. But according to the LRO
measurements, there is water even in some areas that are exposed to
the Sun's rays every once in a while, although, conversely, some of the
PSRs turned out to be completely dry.
To trace the abundance of water on the Moon, the spacecraft looked at
neutrons coming from the Moon's surface. Cosmic particles are
constantly bombarding every object in space. Since the Moon lacks a
protective atmosphere, the particles strike the surface at close to
the speed of light. When they collide with the atomic nuclei in the
soil they knock particles off them, mostly protons and neutrons, some
of which escape into space. If some of those particles hit hydrogen
atoms, which are most likely to belong to water molecules, they slow
down dramatically, leaving fewer particles fast enough to escape into
space. By measuring differences in the flow of neutrons coming from
the Moon's surface, researchers were able to infer the amount of water
present in the soil: areas with low neutron radiation indicated water
capturing and retaining most of the neutrons, while areas with high
neutron radiation identified themselves as dry. In the PSRs near the
LCROSS impact site, the soil was found to contain up to 4% of water.
The water might be like some form of ice mixed in with the soil,
possibly similar to terrestrial permafrost.
CASSINI VISITS NINE MOONS IN 62 HOURS
NASA
During a 62-hour period commencing on October 14, the Cassini
spacecraft passed near nine Saturnian moons, sending back a stream of
images. The views of the southern part of Dione's leading hemisphere
(the part of the moon that faces forward in its orbit around Saturn)
and the equatorial region of Rhea's leading hemisphere are more
detailed than the previous images sent by the Voyager spacecraft in
the early 1980s. Of the five big icy moons of Saturn, Dione and Rhea
are often considered a pair, because they orbit close to each other
and are darker than the others. The new images, however, highlight
some differences between them. For example, Rhea shows evidence of
intense cratering all over the imaged region, whereas the
corresponding region of Dione is divided into distinct areas that
exhibit variations in the number and size of preserved craters. In
particular, while parts of Dione are heavily cratered like Rhea, there
are other areas covered by relatively smooth plains. Those areas have
many small craters, but few large impact scars, so they are
topographically younger than the heavily cratered areas. The smooth
plains must have been resurfaced by some event that occurred in
Dione's past but not in Rhea's.
Cassini passed by Saturn's largest moon, Titan, at a distance of
172,000 km from the surface. Then it flew by Polydeuces at 116,000
km, Mimas at 70,000, Pallene at 36,000, Elesto at 48,000, Methone at
106,000, Aegaeon at 97,000, Dione at 32,000, and Rhea at 39,000 km,
distances that are mostly small in comparison with the orbital radii
around Saturn.
PLANETS ORBITING BINARY STAR
McDonald Observatory, Austin, Texas
Astronomers using observations taken over 20 years by many telescopes
have discovered at least two Jupiter-like planets orbiting the
extremely close binary-star system NN Serpentis. Because of the
gravitational disturbances in a binary, astronomers have not expected
to find planets in such systems. In this case the research team
was able to detect the effects of planets in orbit around the binary
by slight irregularities in the times of the mutual eclipses of the
stars.
The more massive star at the centre of the planetary system is a small
(2.3 Earth radii) and very hot (49,700°C) white dwarf. The other
star in the pair is a modest but larger cool star with a mass only
one-tenth that of the Sun. The Earth lies in the same plane as the
binary-star system, and every 3 hours and 7 minutes we can see the
eclipse that occurs when the larger star moves in front of the smaller
one. The resulting dramatic change in the brightness of the system
acts like a highly precise clock. Regarding the eclipses as ticks of
the clock, the astronomers detected changes in the timings of the
ticks, revealing the presence of two planets orbiting the pair of
stars. The more massive planet is about 5.9 times the mass of
Jupiter, and orbits the binary star every 15.5 years at a distance of
6 AU. Closer in, the other planet orbits every 7.75 years, and is
about 1.6 times the mass of Jupiter. At present no conclusions have
been reached as to the age and origin of the planets, or how they came
to be where they are now, in a system one of whose members recently
passed through the evolutionary stage at which it was a red giant.
MOST MASSIVE NEUTRON STAR YET KNOWN
National Radio Astronomy Observatory.
Astronomers using a new instrument on the Green Bank radio telescope
have discovered the most massive neutron star yet found -- twice the
mass of our Sun. Neutron stars are the super-dense remains of massive
stars that have exploded as supernovae. With all their mass packed
into a sphere only about 25 km across, their protons and electrons are
crushed together into neutrons. A neutron star can be several times
more dense than an atomic nucleus, and a thimbleful of neutron-star
material would weigh more than 500 million tons. That tremendous
density makes neutron stars to be natural laboratories for studying
the densest and most exotic states of matter known to physics.
The scientists used an effect of Einstein's theory of General
Relativity to measure the mass of the neutron star and its orbiting
companion, a white-dwarf star. The neutron star is a pulsar, emitting
lighthouse-like beams of radio waves that sweep through space as it
rotates. The pulsar spins 317 times per second, and the companion
completes an orbit in just under nine days. The pair, 1000 parsecs
distant, is in an orbit seen almost exactly edge-on. As the orbit
carries the white dwarf directly in front of the pulsar, the radio
waves from the pulsar pass very close to it. The close passage causes
them to be delayed, owing to the distortion of space-time produced by
the white dwarf's gravitation. That effect, called the Shapiro Delay,
allowed the scientists to determine the masses of both stars. The
neutron star was found to have the unexpectedly large mass of twice
the Sun's mass, somewhat larger than that of any other neutron star
whose mass has been reliably determined.
BRILLIANT X-RAY EXPLOSION IN MILKY WAY
Penn State University
An X-ray detector on the International Space Station (ISS) recently
observed a great outburst from a previously unknown source in
Centaurus. Astronomers worldwide were quickly alerted, and 9 hours
later the orbiting Swift Observatory was able to measure accurately
the location of the X-ray nova. The Swift observation suggests that
the source is probably a neutron star or a black hole with a massive
companion star, within our own galaxy.
CLUSTERS OF GALAXIES DISCOVERED INDIRECTLY
ScienceDaily
Astrophysicists have discovered 10 new massive clusters of galaxies in
a large, uniform survey of the southern sky. The survey was conducted
by a technique that detects 'shadows' of such clusters on the cosmic
microwave background radiation, a relic of the 'big bang' that gave
birth to the Universe.
The research began in 2008 with a new radio telescope in the Atacama
Desert in Chile -- one of the driest places on Earth. The instrument,
the Atacama Cosmology Telescope (ACT), observes radio waves at the
millimetre wavelengths of the background radiation. Millimetre waves
are easily blocked by water vapour, hence the telescope's siting high
in the Andes at a place where there is very little atmospheric
moisture. The observations showed shadows that indicated the
existence of previously unseen massive clusters of galaxies. Forty
years ago the theoreticians Rashid Sunyaev and Yakov Zel'dovich
predicted the shadow phenomenon, which is now known as the Sunyaev-
Zel'dovich (or S-Z) effect. Shortly thereafter astronomers verified
it by observing shadows cast by previously known clusters of galaxies.
The sensitivity and resolution of the ACT now makes it practical to
reverse the procedure -- to search the background radiation for
shadows that indicate the presence of unseen clusters. The 'shadows'
that the ACT mapped are not shadows in the traditional sense, as they
are not caused by the clusters blocking radiation from another source.
Rather, the hot gases within the clusters cause a tiny fraction of the
background radiation to be shifted to higher energies, leaving
shortfalls that appear as shadows in one of the ACT's observing
wavelengths.
EVIDENCE OF WARMING IN EARLY UNIVERSE
RAS
A team of astronomers has found evidence that the Universe may have
gone through a warming trend early in its history. They measured the
temperature of the gas that lies between galaxies, and found an
indication that it had increased during the time when the Universe was
one-tenth to one-quarter of its current age. Early in the history of
the Universe, the majority of matter was not in stars or galaxies, but
was spread out in a very thin gas that filled all of space. The team
measured the temperature of the gas from the absorption lines that it
superimposes on light from background quasars.
The quasar light was more than ten billion years old by the time it
reached the Earth. Each intergalactic gas cloud through which it had
passed left its own mark, and the cumulative result is like a fossil
record of temperature in the early Universe. Rather as the Earth's
past climate can be studied from ice cores and tree rings, the quasar
light contains encrypted information on the temperature history of the
cosmos. One billion years after the Big Bang, the gas was a 'cool'
8,000°C. By three and a half billion years the temperature had risen
to at least 12,000°. The warming trend is counter-intuitive -- as the
cosmos expands, the gas ought to cool down through the normal process
of adiabatic expansion. Quasars were the probable source of the heat
that warmed the intergalactic gas. Over the relevant period of time,
quasars were becoming much more common; they were emitting huge
amounts of energetic ultraviolet light. which would have stripped the
electrons from helium atoms in the intergalactic gas, freeing the
electrons to collide with other atoms and heat up the gas. When most
of the helium atoms had been stripped, the gas started to cool down
again; it is suggested that that occurred after the Universe was a
quarter of its present age.
'DEAD' SPACECRAFT WOKEN UP
NASA
A pair of spacecraft that were supposed to be dead a year ago are
flying to the Moon for a mission in lunar orbit. The story begins in
2007 when NASA launched a fleet of five spacecraft into the Earth's
magnetosphere to study the physics of geomagnetic storms.
Collectively, they were called THEMIS; the outermost members of the
quintet were identified as P1 and P2. The mission was going well,
except for one thing: occasionally, P1 and P2 would pass through the
shadow of the Earth. The solar-powered spacecraft were designed to go
without sunlight for as long as three hours at a time, but as the
mission wore on their orbits evolved and by 2009 P1 and P2 were
spending as much as 8 hours a day in the dark and the two spacecraft
were running out of power. They still had an ample supply of fuel,
however -- enough to go to the Moon -- and NASA decided to utilise
them for a different project. The mission was given a new name,
ARTEMIS, after the Greek goddess of the Moon (it is also a rather
contrived acronym for a long-winded title). The spacecraft are now at
two of the five Lagrange points in the Earth--Moon system -- places
where the gravity of the Earth and Moon balance, creating a sort of
gravitational parking spot. P1 reached the L2 Lagrange point on the
far side of the Moon on 2010 August 25, and P2 arrived at the opposite
L1 point on October 22.
Because they lie just outside the Earth's magnetosphere, Lagrange
points are excellent places to study the solar wind. Sensors onboard
the ARTEMIS probes have in-situ access to solar-wind streams as they
approach our planet. Moreover, working from opposite Lagrange points,
the two spacecraft will be able to measure solar-wind turbulence on
scales never sampled by previous missions. ARTEMIS will also try to
explore the Moon's plasma wake -- a turbulent cavity carved out of the
solar wind by the Moon itself. Another target of the ARTEMIS mission
is the Earth's magnetotail. The Earth's magnetic field is elongated
by the action of the solar wind, forming a tail that stretches to the
orbit of the Moon and beyond. Once a month, around the time of Full
Moon, the ARTEMIS probes will follow the Moon through the magnetotail
for in-situ observations. Scientists are particularly hoping to catch
some magnetic reconnection events in the magnetotail, events that are
analogous to solar flares, albeit on a much smaller scale.
Bulletin compiled by Clive Down
(c) 2010 the Society for Popular Astronomy
--
Good Clear Skies
--
Astrocomet
--
Colin James Watling
--
--
Real Astronomer and head of the Comet section for LYRA (Lowestoft and Great Yarmouth Regional Astronomers) also head of K.A.G (Kessingland Astronomy Group) and Navigator (Astrogator) of the Stars (Fieldwork)
--
--
No comments:
Post a Comment