Society for Popular Astronomy

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The SOCIETY for POPULAR ASTRONOMY
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Electronic News Bulletin No. 284 2010 March 14
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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
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/




INTERNATIONAL METEOR CONFERENCE - REGISTRATION OPEN
By Alastair McBeath, SPA Meteor Section Director

As noted in ENB 276 (at http://snipurl.com/utgjz , the International
Meteor Conference (IMC) is to be held in Britain for the first time later
this year, from September 16 to 19, at Armagh in Northern Ireland.
Registrations are now being taken, and the booking fee (which includes
YHA full board accommodation, access to all sessions and the excursion,
plus a copy of the IMC Proceedings) is 155 Euros till June 30, after
which it rises to 170 Euros. The IMC's official language is English, and
the conference is open to all interested amateur and professional meteor
enthusiasts from around the world.

IMCs are always great fun for anyone with a strong interest in meteors.
There is a daily programme of lectures and poster presentations, dealing
with all branches of meteor astronomy, plus an excursion, but despite
this planned activity, there is always ample time to talk to the many
people present with similar interests, and even to get involved in the
"astro-entertainment", a party evening of songs and sketches. If you still
need persuading, the IMO website also has a whole series of photos and
personal recollections from past IMCs, and the International Meteor
Weekends and Meteor Seminars which preceded them, back to 1979.
From my own attendance at several previous IMCs, there is no other
meteor meeting or conference to compare with it, and I cannot
recommend trying one highly enough!

More information, and online registration details are available on the
International Meteor Organization's website, at: http://www.imo.net/imc2010 .


PTOLEMAEUS AND THE CHAIN GANG
By Peter Grego, SPA Lunar Section Director

Visual lunar observers of the past were a romantic bunch. In addition to
imagining that the large dark patches were seas, bays, lakes and
marshes, and producing a fabulous system of names, they used to call
craters like Tycho, Eratosthenes and Copernicus ‘ring mountains’. Even
larger lunar craters in excess of 70 km with generally low rounded walls
and flattish flooded or partially flooded floors were once called ‘walled
plains’. The most impressive collection of ‘walled plains’ on the Moon’s
near-side dominates the southern central regions. Among them is a
striking north-south ‘chain’ of large craters which comprises the
magnificent Ptolemaeus, Albategnius, Alphonsus, Arzachel, Purbach,
Regiomontanus and Walter. Of these, Ptolemaeus is the main attraction,
particularly when it’s lit up by a low morning or evening Sun. 153 km
across, Ptolemaeus demands the observer’s attention by virtue of its
sheer size, even though it is not the most geologically varied feature on
the Moon. It has a distinctly polygonal outline, and its floor, bounded
by uncomplicated walls, appears relatively featureless in small telescopes
(even when illuminated by a low Sun), save for the 9 km diameter crater
Ammonius in the north-eastern sector of its floor. Through a 150 mm
telescope, observable detail on the crater’s floor includes Ptolemaeus B,
a 15 km diameter ghost ring adjoining Ammonius in the north, along with
lots of dimple craters and a smattering of tiny craterlets on the verge of
telescopic resolution. The region around Ptolemaeus has been sculpted
into a fantastic northwest-southeast pattern by the immense forces
unleashed by the asteroidal impact that formed the nearby Imbrium basin
around 3.8 billion years ago.

This month you can view Ptolemaeus and its ‘chain’ beginning on the
evening of 23 March when it’s lit by a lunar morning Sun. Observations
and images of this feature (along with all other lunar features of course)
are welcomed by the SPA Lunar Section at lunar@popastro.com.


PLANETS
By Andrew Robertson, SPA Planetary Section Director

Mars drops below 10" diameter on 23rd March with a very noticeable
phase of 92% so I would highly recommend taking every opportunity to
view this planet before it gets too small - it's another 2 years (12th Jan
2012 to be precise) before it gets back to 10" in diameter!

Saturn on the other hand comes to opposition on 22nd March reaching a
respectable altitude of 39 degrees in the constellation of Virgo. Had a
quick look at Saturn on Sunday night 7th March; poor seeing, had a low
power (x135) as I'd been Galaxy hunting and was just 'passing through'
when I noticed a faint smudge at the edge of the field. Closer inspection
revealed this to be a mag 11 almost 'edge on' galaxy NGC 4179. I've
seen plenty of planetary conjunctions before but not a planet and a galaxy.
I made a sketch more to record the event than any artistic talent! Sketch
made at 2330 hours. Whilst both in the same field of view at x135 I could
see a bright equatorial band on Saturn, the shadow of the rings on the
globe and in the galaxy could see a brighter core and a narrow elongated
halo. Tethys, Rhea and Titan were visible just to the right of Saturn in the
sketch. You can view the sketch on the SPA forum courtesy of Peter
Grego: http://snipurl.com/ur8nc Wonderful sight, especially as both
objects have an elongated appearance and were at different orientations
to each other. I should add that I was using my 12" Dall-Kirkham
Cassegrain - you do need a bit of aperture to view a faintish galaxy near
a bright object such as a planet. Peter then realised that as Saturn was
passing through Virgo there would be lots of opportunities to view
Saturn in the vicinity of Galaxies. You can view an excellent sketch of his
the following night of Saturn amid galaxies in Virgo also on the forum:
http://snipurl.com/ur6kk

Finally, Venus is getting higher in the West after sunset (12 degrees
altitude on the 14th and 15 degs 2 weeks later).


EVIDENCE FOR ICE ON THE MOON
NASA

India's Chandrayaan-1 spacecraft has detected ice deposits near the
Moon's north pole. During the past year, Chandrayaan-1's radar mapped
the Moon's permanently shadowed polar craters that are not visible
from the Earth. The radar uses the polarization properties of
reflected radio waves to characterize surface properties. It found
water ice in more than 40 small craters ranging in diameter from 2 to
15 kilometres. Although the total amount of ice depends on its
thickness in each crater, it is estimated that there could be at least
600 million tons of ice. Some scientists claim that the picture
emerging from recent missions indicates that water creation,
migration, deposition, and retention are occurring on the Moon.


MOST EXTREME WHITE-DWARF BINARY SYSTEM
University of Warwick

An international team of astronomers has shown that the two stars in
the binary HM Cancri definitely revolve around each other in a mere
5.4 minutes. This makes HM Cancri the binary star with by far the
shortest known orbital period. It is also the smallest known binary.
The binary separation is no more than a quarter of the distance from
the Earth to the Moon. The system, which is at a distance of 5000
parsecs (1 pc = 3.26 light-years), consists of two white dwarfs.

HM Cancri was first noticed in 1999 as an X-ray source showing a
5.4-minute periodicity, but it has not been clear whether that is the
actual orbital period of the system. It is so short that astronomers
were reluctant to accept that possibility. Now the Keck telescope has
been used to measure the radial velocities of the stars and to show
that they do indeed vary in the 5.4-minute period. The observations
of HM Cancri were difficult because the object is very faint
(magnitude 21) and its extremely short period meant that very short
exposures were needed to avoid excessive phase smearing.


AGE OF COMETARY MATERIAL
Science Daily

Though comets are thought to be some of the oldest and most primitive
bodies in the Solar System, new research on Comet Wild 2 indicates
that inner-Solar-System material was transported to the comet-forming
region at least 1.7 million years after the formation of the oldest
Solar-System solids. The research by Lawrence Livermore scientists
provides the first constraint on the age of cometary material from a
known comet. The Stardust mission, which was launched to Comet Wild 2
in 1999, was designed on the premise that comets preserve pristine
remnants of materials that helped to form the Solar System. It
extended a retractable device containing cells filled with a material
called aerogel, a porous substance designed to trap dust particles.
In 2006, Stardust returned with the first samples from a comet.
Though the mission was expected to provide a glimpse into the early
Solar System by returning a mix of Solar-System condensates, amorphous
grains from the interstellar medium and true stardust (crystalline
grains originating from distant stars), the initial results painted a
different picture. Instead, the comet materials consisted of
high-temperature materials including calcium-aluminium-rich inclusions
(CAIs), which are the oldest objects formed in the solar nebula and
are common in meteorites.


PROBE MAY ALSO HAVE RETURNED COSMIC DUST
BBC News

Scientists may also have identified two specks of interstellar dust in
the material collected by Stardust. The discovery was made by a
member of the public, using the Stardust@Home internet application,
which invited participants to search the aerogel collection medium for
tiny particles of the dust. The researchers have so far analysed
magnesium, aluminium, iron, chromium, manganese, nickel, copper and
gallium from the particles. Though prized by the Stardust team,
interstellar dust is a nuisance in optical astronomy, because it can
obscures objects they want to observe.


FIRST OF MISSING PRIMITIVE STARS DISCOVERED
Harvard-Smithsonian Center for Astrophysics.

Astronomers have discovered a relic from the early Universe -- a star
that may have been among the second generation of stars to form after
the Big Bang. Located in the Sculptor dwarf galaxy some 90,000
parsecs away, the star has a chemical make-up remarkably similar to
that of the Milky Way's oldest stars. There is a theory that our
Galaxy grew to its current size by swallowing dwarf galaxies, small
galaxies with just a few billion stars, compared to the hundreds of
billions in the Milky Way. If dwarf galaxies are indeed the building
blocks of larger ones, then the same kinds of stars should be found in
both, especially old, metal-poor stars. (To astronomers, 'metals'
means chemical elements heavier than hydrogen and helium.) Because
they are products of stellar evolution, metals were rare in the early
Universe, and so old stars tend to be metal-poor. Old stars in the
Milky Way's halo can be extremely metal-poor, with metal abundances
only a thousandth of those in the Sun, which is a typical younger,
metal-rich star.

Surveys over the past decade have failed to turn up any such extremely
metal-poor stars in dwarf galaxies, however. The Milky Way seemed to
have stars that were much more primitive than any in the dwarf
galaxies. If dwarf galaxies were the original components of the Milky
Way, then they ought to have similar stars. The team suspected that
the methods used to find metal-poor stars in dwarf galaxies were
biased in a way that caused the surveys to miss the most metal-poor
stars. They developed a method to estimate the metal abundances of
large numbers of stars at a time, making it possible to cut corners in
the search for the most metal-poor stars in dwarf galaxies. Among
stars they found in the Sculptor dwarf galaxy was an 18th-magnitude
one which spectroscopy with the Magellan telescope in Chile showed to
have a metal abundance 6,000 times lower than that of the Sun, five
times less than in any other star found so far in a dwarf galaxy. The
researchers expect that further searches will discover additional
metal-poor stars in dwarf galaxies, although the distance and
faintness of the stars pose a challenge for current optical
telescopes. The next generation of extremely large telescopes should
open up a new window for studying the growth of galaxies through the
chemistries of their stars.


ASTRONOMERS DISCOVER THAT ANCIENT GALAXIES ARE MERGING
Penn State University

Astronomers using the Hubble telescope have discovered that a
collection of small, ancient galaxies, called the Hickson Compact
Group 31 (HCG 31), about 50 Mpc away (Megaparsecs; 1 Mpc = 1 million
parsecs = 3.26 million light-years) is finally coming together into
one larger galaxy after 10 billion years. Most other small galaxies
in the Universe came together into larger galaxies billions of years
ago, but the galaxies within HCG 31 have been interacting for only a
few hundred million years. The new observations have allowed the team
to estimate when the encounter began and to predict a future merger.
The galaxies have been distorted by their gravitational effects on
each other. The HCG 31 group of galaxies is also aglow with a
firestorm of star birth, which is triggered when hydrogen gas is
compressed by the close encounters between galaxies and then collapses
to form stars. Everywhere in HCG 31 there are batches of young star
clusters and regions brimming with star birth. The observations
indicate that the brightest clusters, groups of at least 100,000
stars, are less than 10 million years old. The stars are formed from
an abundance of hydrogen gas, but a measurement of the gas content
shows that very little has been used up -- proof that the
star-formation is a recent event. This is a clear example of a group
of galaxies on its way towards a merger. The galaxies are relatively
small, comparable in size to the Large Magellanic Cloud, a satellite
galaxy of our Milky Way. Their relative velocities, measured in
previous studies, are only about 60 km/s, and it seems likely that the
system will merge into a single elliptical galaxy in another billion
years.


GALACTIC LENSES MEASURE AGE AND SIZE OF UNIVERSE
DOE/SLAC National Accelerator Laboratory

Researchers have been trying to measure the size and age of the
Universe, and how rapidly it is expanding, by the use of gravitational
lensing which enables them to measure the distances light travelled
from a bright, active galaxy to the Earth along different paths.
By understanding the time it took to travel along each path and the
effective speeds involved, they could infer not just how far away the
galaxy lies but also the overall scale of the Universe and some
details of its expansion. It is often difficult for scientists to
distinguish between a bright source far away and a dimmer one much
closer. A gravitational lens circumvents that problem by providing
multiple clues as to the distance light travels. That extra
information allows them to determine the size of the Universe, often
expressed by astrophysicists in terms of a quantity called the Hubble
constant. Scientists have known for a long time that lensing is
capable of making a physical measurement of the Hubble constant, but
gravitational lensing has never before been used in such a precise
way. The measurement is now claimed to provide as precise a
measurement of the constant as established methods such as observation
of supernovae and the cosmic microwave background. There are several
factors scientists still need to account for in determining distances
with lenses. For example, dust in the lens can skew the results.
The Hubble telescope has infra-red filters useful for reducing dust
effects. The images also contain information about the number of
galaxies lying around the line of vision; they contribute to the
lensing effect at a level that needs to be taken into account.


Bulletin compiled by Clive Down

(c) 2010 the Society for Popular Astronomy