society journal - Auckland Astronomical Society

December 2011 January 2012 SOCIETY JOURNAL
Society Meeting Monday, December 12 at 8:00pm I
n “The Ever-Expanding Universe”, NOVA investigates a battery of high-tech telescopes that is joining the Hubble
Space Telescope on its quest to unlock the secrets of our Universe, a cosmos almost incomprehensible in its size, age,
and violence.
Far beyond our Solar System, we are now discovering exoplanets orbiting other suns, and beyond our galaxy, another
hundred billion galaxies, such as Andromeda, Sombrero, and Whirlpool, each harbouring hundreds of billions of stars.
We've detected supermassive black holes, spinning violently at the very centres of galaxies, including our own. We've
witnessed supernovae: exploding stars, millions of light-years away, spewing out superheated gas at 970,000 kilometres
per hour. And deep inside clouds of gas and dust, billowing trillions of kilometres high, we can glimpse new stars being
born.
Now, the latest telescopes are revealing the invisible mysteries of space that we are only just beginning to understand:
dark matter, the hidden scaffolding our entire Cosmos is built on, and dark energy, a powerful and invisible force that is
pushing our Universe apart.
This will be followed by a recent episode of Sir Patrick Moore's "The Sky at Night": "Dawn at Vesta".
The NASA spacecraft Dawn is getting up close and personal with the asteroid Vesta. Sir Patrick Moore, with Paul Abel
and Pete Lawrence, discusses the first fly-by images of this most unusual asteroid, which will tell us more about how our
Solar System formed some 4.5 billion years ago.
Solar Storm By Gavin Logan N
ovember's Film Night featured a documentary showing how
extreme solar activity could disrupt power supplies and
threaten our electricity dependent civilisation. It explained how a
solar flare sends charged particles and radiation out into space. The
Earth’s atmosphere and magnetic fields are usually adequate to protect us from these, but not completely during big events. The 1989
Montreal blackout, which was caused by solar activity, is the most
recent example covered in this film. It left 6 million people in Quebec without power for 9 hours.
The last great solar super storm was over 150 years ago. With our
very recently-adopted dependence on satellite-based technologies
and electric power, the film showed that should the 1859 event happen again, large parts of the Earth may be without power and telecommunications for months. It showed methods being developed for
predicting these events and therefore shutting down power grids so
they cannot be overloaded by excessive charged particles from extreme solar activity.
Satellites can also have their orbits affected by solar activity; perhaps the most notable one covered by the film was Skylab, which
crashed to Earth in 1979 because of the effects of solar activity.
Solar storms cause the Earth’s atmosphere to inflate and temporarily
expand into the orbit of some satellites, producing friction that can
slow their orbital speed.
Next month's film night is on Monday 19th December at 8pm at
Stardome Observatory and features the documentary film “What
happened before the Big Bang”.
After the main film, the May 2011 Sky at Night with Patrick Moore
was shown. The first part was about large raging storms in the atmospheres of the gas giant planets. Some of these storms are the size
of our planet Earth, with winds blowing at many hundreds of kilometers per hour. It also showed an interview with the Australian
amateur astronomer who discovered an impact spot on Jupiter last
year. Finally it covered the visit to Norway by the members of the
Sky at Night show team to study Aurora Borealis.
Some scientists believe that the Big Bang was not really the beginning. Our Universe may have had a life before this. This documentary explores the latest ideas about the Big Bang and what created it
or came before it. Theories about cosmic bounces, rips and multiple
universes are discussed to try to find out what happened before the
Big Bang. It is 50 minutes long and will be followed by the August
2011 Sky at Night show with Patrick Moore about Asteroids. (30
minutes).
A solar flare is on the screen for the Film Night audience.
Astronomical Society’s Submission on Auckland Plan Gets Good Hearing By Gavin Logan I
n November David Britten, Grant Christie and Gavin Logan
made a successful presentation supporting the Society's written
submission (published in last month's Journal) to the Auckland
Council on the Draft Auckland Plan. The oral presentation focused
on the growing sky glow in Auckland City coming largely from
council streetlights and private commercial lighting.
Using a PowerPoint slide show, the effects of poor quality unshielded lighting was compared with better quality, shielded lighting. They showed that shielded lighting was safer from a security
point of view, more effective for street lighting with less glare and
most importantly, it greatly reduced power consumption. Light
where it needs to be and not glowing in all directions was the theme
of the presentation.
Calgary, the Canadian city that retro-fitted all 37,000 of its old street
lights with environmentally friendly shielded lighting, was held up
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SOCIETY JOURNAL, December 2011
as an example to follow. This city of 900,000 people saved in NZ
dollars 2.1 million per year and paid for the retro-fit in about six
years with the power savings.
The Councillors were also asked to do something about non-street
level lights being needlessly left on in commercial buildings
(particularly multi-storey office buildings) when these buildings are
unoccupied and the light pollution this causes.
The Council was reminded of the old Auckland City Council and
Waitakere City guidelines for all new lighting and that these were
now not always being followed by the Super-city Council, with new
unshielded Sodium lights appearing on the newest bridge over the
South Western motorway.
The Council has now sent the matter to Urban Design for consideration and acknowledged the presenters for a good submission.
Calendar of Events December 2011 Programme
February 2012 Programme
Fri 2 7:30pm Young Astronomers with Margaret Arthur Fri 3 7:30pm Young Astronomers with Margaret Arthur Mon 5 8:00pm Practical Astronomy with Andrew Buckingham Summer Observing Night Mon 6 8:00pm Practical Astronomy with Andrew Buckingham Mon 12 8:00pm Monthly Meeting with Grant Christie The Ever‐Expanding Universe Mon 13 8:00pm Monthly Meeting Speaker/Host TBA Mon 20 8:00pm Film Night with Gavin Logan Mon 27 8:00pm Introduction to Astronomy with Bernie Brenner Mon 19 8:00pm Film Night with Gavin Logan What Happened Before the Big Bang? Please note: There are no sessions during January
MAKE STARDATE PART OF YOUR HOLIDAY PLANS!
Where: Tukituki Valley, near Havelock North, Hawkes Bay
When: 20-23 January 2012
Practical Astronomy—Summer Observing
Night, Monday 5 December 8:00pm
Our seasonal observing event.
The evening will start in the planetarium with a tour of the
summer sky and will progress to telescope viewing as it gets dark.
The EWB Zeiss Telescope will be available for viewing as well as
portable telescopes outside in the courtyard. Members will be on
hand to help people who have questions about telescopes or
your own telescope. Feel free to bring your own telescope along.
The event will be weather-independent as we will have the
planetarium available and other activities planned.
The evening is aimed to include members who are getting started
with exploring the night sky as well as the more experienced, so
come along and join in.
Film Night With Gavin Logan
Monday 19 December 8:00pm
The Phoenix Astronomical Society of NZ will be running an event
on 20-23 January 2012 in the Hawkes Bay with loads of astronomical talks and activities. Weather permitting there will be an
opportunity for using the telescopes in the evening.
This will be a great opportunity to socialise, learn more about
astronomy and it is a great fundraiser for the Society.
You don't need to be a member. If you think you might be interested, contact [email protected].
SKANZ 2012 CONFERENCE
14-16 February, 2012
Pathways to SKA Science in Australasia
AUT is again hosting the international SKANZ Conference at its
city (Wellesley) campus. The location of the SKA will be announced in 2012, so this is an opportunity to hear the latest
developments in SKA precursors, wide-field and high-resolution
science, engineering and computing.
Full details of programme and registration are on the conference
website: http://www.aut.ac.nz/skanz2012.
What happened before the Big Bang?
Some scientists believe that the Big Bang was not really the
beginning. Our Universe may have had a life before this. This
documentary explores the latest ideas about the Big Bang and
what created it or came before it. Theories about cosmic
bounces, rips and multiple universes are discussed to try to find
out
what
happened
before
the
Big
Bang.
It is 50 minutes long.
It will be followed by the August 2011 Sky at Night show with
Patrick Moore about Asteroids. (30 minutes). Welcome to New Members
Mark Engels (family)
The 2012 edition is available to members at the
special price of $14.00
(+$2.00 postage) per copy
when purchased from AAS.
Purchases can be made at
all AAS meetings or you
can order from Andrew
Buckingham by e-mail at
[email protected]
or by phone on 473 5877.
Glenn Urquhart (ordinary)
WWW.ASTRONOMY.ORG.NZ 3
Why Neutrinos Might Wimp Out By Davide Castelvecchi, ScientificAmerican.com P
articles that go beyond light
speed? Not so fast, many
theoretical physicists say.
In case you missed the news, a team of
physicists reported in September that the
tiny subatomic particles known as neutrinos could violate the cosmic speed limit
set by Einstein’s special theory of relativity. The researchers, working on an experiment called OPERA, beamed neutrinos through the Earth’s crust, from
CERN, the laboratory for particle physics
near Geneva, to Gran Sasso National
Laboratory in L’Aquila, Italy, an underground physics lab. According to the
scientists’ estimates, the neutrinos arrived
at their destination around 60 nanoseconds quicker than the speed of light.
Experts urged caution, especially because
an earlier measurement of neutrino velocity had indicated, to high precision
and accuracy, that neutrinos do respect
the cosmic speed limit. In a terse paper
posted online on September 29, Andrew
Cohen and Sheldon Glashow of Boston
University calculated that any neutrinos
4
travelling faster than light would lose
energy after emitting, and leaving behind, a trail of slower particles that would
be absorbed by the Earth’s crust. This
trace would be analogous to a sonic
boom left behind by a supersonic fighter
jet.
Yet the neutrinos detected at Gran Sasso
were just as energetic as when they left
Switzerland, Cohen and Glashow point
out, casting doubt on the veracity of the
speed measurements. “When all particles
have the same maximal attainable velocity, it is not possible for one particle to
lose energy by emitting another,” Cohen
explains. “But if the maximal velocities of
the particles involved are not all the
same, then it can happen.”
An effect of this type is well known in
cases where electrons have the higher
speed limit (light speed), and light itself
has the lower one because it is slowed
down by travelling in a medium, such as
water or air. Electrons, then, can move in
the medium at a speed higher than the
maximum speed of photons in the same
medium and can lose energy by emitting
SOCIETY JOURNAL, December 2011
photons. This transfer of energy between
particles with different speed limits is
called Cherenkov radiation, and it makes
the reactor pools of nuclear power stations glow with a bluish light.
In the neutrinos’ case, Cohen and
Glashow calculate that the wake would
mostly consist of electrons paired with
their antimatter twins, positrons. Crucially, the rate of production of these electron-positron pairs is such that a typical
superluminal neutrino emitted at CERN
would lose most of its energy before
reaching Gran Sasso. Then again, perhaps they were not superluminal to begin
with.
“I think this seals the case,” says Lawrence M. Krauss, a theoretical physicist at
Arizona State University. “It is a very
good paper.” So was Albert Einstein right
after all? Einstein’s relativity superseded
Isaac Newton’s physics, and physicists will
no doubt keep trying to find glitches in
Einstein’s theories, too. “We never stop
testing our ideas,” Cohen says. “Even
those that have been established well.”
NASA Probe Data Show Liquid Water Evidence on Europa From NASA P
ASADENA, Calif. — Data from a
NASA planetary mission have provided scientists evidence of what appears
to be a body of liquid water, equal in
volume to the North American Great
Lakes, beneath the icy surface of Jupiter's moon, Europa.
The data suggest there is significant exchange between Europa's icy shell and
the ocean beneath. This information
could bolster arguments that Europa's
global subsurface ocean represents a
potential habitat for life elsewhere in our
Solar System. The findings are published
in the scientific journal Nature.
"The data open up some compelling
possibilities," said Mary Voytek, director
of NASA's Astrobiology Program at
agency headquarters in Washington.
"However, scientists worldwide will want
to take a close look at this analysis and
review the data before we can fully appreciate the implication of these results."
NASA's Galileo spacecraft, launched by
the space shuttle Atlantis in 1989 to
Jupiter, produced numerous discoveries
and provided scientists decades of data
to analyze. Galileo studied Jupiter, which
is the most massive planet in our Solar
System, and some of its many moons.
One of the most significant discoveries
was the inference of a global saltwater
ocean below the surface of Europa. This
ocean is deep enough to cover the whole
surface of Europa and contains more
liquid water than all of Earth's oceans
combined. However, being far from the
Sun, the ocean surface is completely
frozen. Most scientists think this ice crust
is tens of kilometres thick.
"One opinion in the scientific community
has been if the ice shell is thick, that's
bad for biology. That might mean the
surface isn't communicating with the
underlying ocean," said Britney Schmidt,
lead author of the paper and postdoctoral fellow at the Institute for Geophysics, University of Texas at Austin. "Now,
we see evidence that it's a thick ice shell
that can mix vigorously and new evidence for giant shallow lakes. That could
make Europa and its ocean more habitable."
Schmidt and her team focused on Galileo
images of two roughly circular, bumpy
features on Europa's surface called chaos
terrains. Based on similar processes seen
on Earth — on ice shelves and under
glaciers overlying volcanoes — they de-
Europa's "Great Lake." Scientists speculate many more exist throughout the shallow
regions of the moon's icy shell. Credit: Britney Schmidt/Dead Pixel VFX/Univ. of Texas at
Austin.
veloped a four-step model to explain
how the features form. The model resolves several conflicting observations.
Some seemed to suggest the ice shell is
thick. Others suggest it is thin.
This recent analysis shows the chaos
features on Europa's surface may be
formed by mechanisms that involve significant exchange between the icy shell
and the underlying lake. This provides a
mechanism or model for transferring
nutrients and energy between the surface and the vast global ocean already
inferred to exist below the thick ice shell.
This is thought to increase the potential
for life there.
The study authors have good reason to
believe their model is correct, based on
observations of Europa from Galileo and
of Earth. Still, because the inferred lakes
are several kilometres below the surface,
the only true confirmation of their presence would come from a future spacecraft mission designed to probe the ice
shell. Such a mission was rated as the
second highest priority flagship mission
by the National Research Council's recent
Planetary Science Decadal Survey and is
being studied by NASA.
"This new understanding of processes on
Europa would not have been possible
without the foundation of the last 20
years of observations over Earth's ice
sheets and floating ice shelves," said Don
Blankenship, a co-author and senior research scientist at the Institute for Geophysics, where he leads airborne radar
studies of the planet's ice sheets.
Galileo was the first spacecraft to directly
measure Jupiter's atmosphere with a
probe and conduct long-term observations of the Jovian system. The probe
was the first to fly by an asteroid and
discover the moon of an asteroid. NASA
extended the mission three times to take
advantage of Galileo's unique science
capabilities, and the spacecraft was put
on a collision course into Jupiter's atmosphere in September 2003 to eliminate
any chance of impacting Europa.
The Galileo mission was managed by
NASA's Jet Propulsion Laboratory in
Pasadena, Calif., for the agency's Science
Mission Directorate.
WWW.ASTRONOMY.ORG.NZ 5
Dark Matter Gets Darker: New Measurements Confound Scientists From Space.com N
ew measurements of tiny galaxies
contradict scientists' best model of
dark matter, further complicating the
already mysterious picture of the stuff
that is thought to make up 98 percent of
all matter in the Universe.
Dark matter, the invisible material
thought to permeate the Universe, can
only be indirectly detected through its
gravitational pull on the normal matter
that makes up stars and planets.
Despite not knowing exactly what dark
matter is, scientists have gradually built
up a good model to describe its behaviour. The model envisions dark matter
made up of cold, slow-moving exotic
particles that clump together because of
gravity.
This "cold dark matter" model has done
remarkably well describing how dark
matter behaves in most situations. However, it breaks down when applied to
mini "dwarf galaxies," where dark matter appears more spread out than it
should be, according to the theory.
prediction about the structure of cold
dark matter in dwarf galaxies," said
study leader Matt Walker of the HarvardSmithsonian Center for Astrophysics in
Cambridge, Mass. "Unless or until theorists can modify that prediction, cold
dark matter is inconsistent with our observational data."
Dwarf galaxies like Fornax and Sculptor
are especially good places to study dark
matter, because they are thought to be
almost entirely made up of the stuff.
Only one percent of matter in a dwarf
galaxy is thought to be the normal matter that makes up stars.
To determine where and how much dark
matter inhabits the dwarf galaxies, the
researchers studied the motions of 1,500
to 2,500 visible stars, which reflect the
gravitational forces acting on them from
dark matter.
Some researchers have suggested that
when dark matter interacts with normal
matter it may tend to spread out, thus
decreasing the density of dark matter in
the centres of galaxies. However, so far,
the cold dark matter model doesn't predict this.
Either normal matter affects dark matter
more than scientists thought, or it isn't
cold and slow-moving, the researchers
said.
"After completing this study, we know
less about dark matter than we did before," Walker said.
The findings will be published in an upcoming issue of The Astrophysical Journal.
In a new study, researchers calculated
the mass distribution of two dwarf galaxies using a new method that did not rely
on any dark matter theories. The scientists studied the Fornax and Sculptor
galaxies, which orbit the Milky Way.
However, their measurements still contradict cold dark matter theory, further
entrenching the problem. [Infographic
Gallery: The History and Structure of the
Universe]
According to the model, the centres of
galaxies should be packed with dense
clumps of the invisible matter. But dark
matter appears to be spread evenly
throughout Fornax and Sculptor, as well
as other dwarf galaxies whose mass distributions have been measured in other
ways.
"If a dwarf galaxy were a peach, the
standard cosmological model says we
should find a dark matter 'pit' at the
centre," researcher Jorge Peñarrubia of
England's University of Cambridge said in
a statement. "Instead, the first two
dwarf galaxies we studied are like pitless
peaches."
The measurements suggest that some
part of the theoretical model may have
to be revised.
"Our measurements contradict a basic
6
This artist's conception shows a dwarf galaxy seen from the surface of a hypothetical exoplanet. A new study finds that the dark matter in dwarf galaxies is
distributed smoothly rather than being clumped at their centres. This contradicts simulations using the standard cosmological model known as lambdaCDM. CREDIT: David A. Aguilar (CfA)
SOCIETY JOURNAL, December 2011
New Model Predicts Fallout from Big Meteorite Strike From Space.com A
major meteorite impact on Earth
could spell doomsday — or not. To
better predict what could be in store if a
giant space rock slammed into our
planet, scientists have built a new model
to simulate the seismic fallout from such
an event.
The model predicts how seismic waves
would spread through Earth after a me-
"After a meteorite impact, seismic waves
travel outward across the Earth's surface
like after a stone is thrown into water,"
research leader Matthias Meschede of
the University of Munich said in a statement. "For the Earth, these calculations
are usually made using a smooth, perfect
sphere model, but we found that the
surface features of a planet or a moon
have a huge effect on the aftershock a
2 million times more powerful than a
hydrogen bomb, is thought to have
wiped out the dinosaurs and much of
Earth's life at the time.
The new study showed that the seismic
waves resulting from the impact would
have been scattered and unfocused,
causing less severe ground displacement,
tsunamis, and seismic and volcanic activity than previously thought.
"But our results go beyond Chicxulub,"
Meschede said. "We can, in principle,
now estimate how large a meteorite
would have to have been to cause catastrophic events. Our model can be used to
estimate the magnitude and effect of
other major impacts in Earth's past."
NASA and astronomers around the world
regularly keep track of potentially hazardous asteroids. NASA announced last
month that it has found about 90 percent of the largest, most dangerous
space rocks near our planet.
Astronaut Clayton C. Anderson tweeted this picture from space, a view of Aorounga
Impact Crater, southeast of Emi Koussi volcano in Chad. CREDIT: @Astro_Clay/NASA
teorite collision. It's the first to take into
account the planet's elliptical shape,
surface features and ocean depths. In
contrast, previous models have assumed
Earth is perfectly spherical and featureless, with nothing to disrupt a meteorite's impact.
large meteorite will have, so it's extremely important to take those into
account."
The researchers used their new model to
simulate the collision that created the
Chicxulub crater in Mexico around 65
million years ago. This crash, which was
To that end, NASA is tracking a huge
space rock, the asteroid 2005 YU55,
which is the size of an aircraft carrier and
will fly close by the Earth, inside the orbit
of the moon, on Nov. 8. Though this is
considered a very close pass, the rock is
calculated to pose no risk to planet
Earth.
Meschede developed the new model
with colleagues while visiting Princeton
University through the Visiting Student
Research Collaborators program. The
researchers describe their new model in
the October issue of Geophysical Journal
International.
Society Telescopes For Hire The Society has a wide range of telescopes for hire to members. If you are looking to purchase or upgrade a telescope and are not sure what to buy, this is a very good way to evaluate some of the available equipment. See also the advertisement on the back page. To inquire about hiring or for advice on what to buy and for information about equipment, contact Ivan Vazey, curator of instruments, at [email protected] ph(09) 535‐3987 WWW.ASTRONOMY.ORG.NZ 7
The Life and History of Peter Read By Gavin Logan time from 1963 and his avuncular style
inspired New Zealanders to look at the
stars. It was the country’s longest running TV show when it was cancelled in
1974, and he was the longest serving
presenter. Peter Read was also the presenter on other science and astronomy
TV shows during the 1960s and 70s, as
well as Wellington’s nightly regional
news show “Town and Around”.
He was an accomplished artist and his
works were hung by the New Zealand
Academy of Fine Arts during the 1950s
and 60s.
He was also an excellent actor and in
1949 he started acting in NZBC radio
dramas, and he later released two comedy albums.
Peter Read.
A
t the Society's November meeting,
Gordon Hudson from the Wellington Astronomical Society and Carter
Observatory gave a presentation on Peter
Read, an amateur astronomer and TV
presenter who did much to popularise
astronomy in New Zealand.
Born in Wellington in 1923, Peter Read
was a self-taught astronomer, whose
passion for astronomy coincided with a
budding television industry and the beginning of manned spaceflight. His programme, The Night Sky, played in prime-
From 1947, Read lectured at the Carter
Observatory in Wellington, going on to
become Vice President, then President of
the Royal New Zealand Astronomical
Society, President of the Wellington
Planetarium Society and a Fellow of the
Royal Astronomical Society. He also
played a large part in getting a planetarium built at Napier. In 1971 he received
an International Visitor grant from the US
Department of State to visit Cape Canaveral and witness an Apollo launch.
Read collected historic telescopes and
other memorabilia. He also built his own
observatory in the backyard of his
Miramar home, which had a 5-inch re-
Some of Peter Read’s artwork on display at the November meeting.
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SOCIETY JOURNAL, December 2011
Gordon Hudson speaking at the November Society’s meeting.
fractor and later a 6-inch cook refractor
in it. Sadly, Peter Read died before reaching his 58th birthday in 1981.
Gordon Hudson showed two short video
interviews with his two sons, Christopher
and Adam Read and some film from his
TV shows. After the presentation, Society
members were able to examine a display
of some of Peter Read’s artworks and
telescopes. Carter Observatory in Wellington now has a permanent display of
Peter Read memorabilia.
Two of Peter Read’s Brass telescopes on display
at the November meeting.
Library Corner By Tony Reynolds New Books
The Star Guide
The Universe
Learn how to read the Night Sky Star
by Star
Leo Marriott
Robin Kerrod
“This thoroughly revised and updated edition of the international
bestselling guide to the night sky
puts the Universe at your fingertips”
Includes a planisphere
Catalogue section: QB63
Featured Section
QB980 Cosmology and Cosmogony
A picture book dedicated to HST
images (Hubble Space Telescope).
“The book starts with an examination of the history of astronomy from
earliest times. Next follows a brief
history of the HST and explains its
sensor package.”
After that it’s just beautiful image
after beautiful image...
Catalogue section: TR
Book of Interest
From Quark to Quasar Peter Cadogan
From the invisibly small world of elementary particles to the inconceivable immensity of the most remote
astronomical objects, extremes of
size and distance are almost impossible to imagine.
From Quark to Quasar takes the
reader on a pictorial journey spanning some 42 orders of magnitude to
provide a unique insight into the
scale of our Universe.
Following an introduction to the
methods used to measure distances,
the book proceeds from familiar,
everyday objects on an outward journey in 26 steps, through our Solar
System and nearby stars, to the very
edge of the observable Universe.
Here’s where you’ll find all the answers (and inevitably more questions) about the Big Bang, the inflationary universe, space & time and all
things ‘universal’.
Titles include; ‘Bubbles, Voids and
Bumps in time: the new cosmology’,
‘The Cosmic Blueprint’, ‘Wrinkles in
Time’ and ‘The Universe: Its beginning and end’.
Each stage of the journey is ten times
larger than the preceding one, and
the pictures have been carefully selected to highlight the extraordinary
variety of exotic objects in the Universe.
The reader then returns to the human scale and the journey takes off
in the other direction. A fascinating
variety of life is portrayed, from birds
and mammals through fleas and
mites down to the smallest selfreplicating structure, the virus.
The journey concludes with a study
of modules, atoms and sub-atomic
particles before the final summary, in
which an attempt is made to view
the entire Universe.
Catalogue section: QB991
WWW.ASTRONOMY.ORG.NZ 9
ARA—Noah’s Altar By Ivan Vazey A
RA is also known as Chiron’s Altar
or Dionysius’s Altar.
Originally known as Ara Centauri, this
constellation formed a part of Chiron,
the Centaur.
Southern astronomers
know this as Centaurus. Renaming and
resizing changed many of the Southern
constellations with Carina a prime example.
Ara is a faint and seldom visited constellation even though it lies in a very star
rich area of the Milky Way, a little south
of Scorpius. The Greeks originated the
name, visualising it as the altar upon
which the Gods in Olympus swore allegiance before their battle with the Titans.
It didn’t do them too much good as the
Titans gave them a fair thrashing.
NGC 6188 and the associated star cluster
NGC 6193. Credit: Wikipedia
The main stars making up the Constellation’s Altar shape are:
Alpha Ara, a blue-white star at 242 lightyears from Earth. This is the second
brightest star in constellation Ara.
Beta Ara, an orange supergiant at 603
light-years from Earth. This is the brightest star in the constellation Ara.
Gamma Ara, a blue supergiant at 1140
light-years from Earth, with a white
dwarf optical companion at 17.9
arcseconds away.
Delta Ara, a blue-white star at 187 lightyears.
Zeta Ara, an orange giant at 574 lightyears.
Best Objects to view are:
NGC 6193, a 5th Mag. open cluster 4200
light-years away, occupying about half
the area of the full Moon.
Ara (The Altar) Credit: IAU and Sky&Telescope
Around this cluster is an irregular and
faint patch of nebulosity NGC6188.
NGC 6397 is a Mag. 6 globular cluster,
which appears like a fuzzy star and is
sometimes visible to the naked eye. It
also extends about half the diameter of
the full Moon, and is one of the closest
globular clusters to us, at a distance of
10,500 light-years.
Info courtesy of Hawaiian Astro Society,
I. Ridpath and W.Tirion.
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SOCIETY JOURNAL, December 2011
A Hubble Space Telescope (HST) image
of NGC 6397. Credit: HST / NASA / ESA
The Night Sky in December From the RASNZ Website To use the chart, hold it up to the sky. Turn the chart so the direction you are looking is at the bottom of the chart. If you are looking
to the south, then have ‘South Horizon’ at the lower edge. As the Earth turns, the sky appears to rotate clockwise around the south
celestial pole (SCP on the chart). Stars rise in the east and set in the west, just like the Sun. The sky also shows a small extra clockwise
rotation as we orbit the Sun.
Venus and Jupiter are the first ‘stars’ out after sunset. Venus is low in the west, setting two hours after the Sun. Jupiter is midway up
the north sky. It sets around 3am. Sirius, the brightest star, is due east, twinkling like a diamond. Left of it is Orion, with ‘The Pot’ at its
centre. Further left is Taurus and the Pleiades/Matariki/Seven Sisters star cluster. The Pointers and Crux, the Southern Cross, are low in
the south. The Milky Way is bright along the skyline from southwest to southeast, but fades below Orion. Right of Canopus, the second brightest star, are the Clouds of Magellan (LMC and SMC on the chart), two nearby galaxies. The Andromeda Galaxy is faint and
low in the north. The Moon is eclipsed in the morning hours of December 11.
Chart produced by Guide 8 software; www.projectpluto.com. Labels and text added by Alan Gilmore, Mt John Observatory of the
University of Canterbury.www.canterbury.ac.nz
WWW.ASTRONOMY.ORG.NZ 11
Observing Notes December 2011 By Alan Gilmore Venus and Jupiter are the 'evening
stars', appearing soon after sunset.
Brilliant Venus is low in the west. It
sets two hours after the Sun. In a
telescope it looks like a gibbous
Moon. Venus is on the far side of the
Sun from us, 200 million km away.
Jupiter is more interesting. Its disk
and four big moons are easily seen in
a telescope. Two of the moons
might be seen in binoculars. It is 650
million km away.
The brightest stars are in the east
and south. Sirius, the brightest of all
the stars, is due east at dusk, often
twinkling like a diamond. Left of it is
the bright constellation of Orion.
The line of three stars makes Orion's
belt in the classical constellation. To
southern hemisphere skywatchers
they make the bottom of 'The Pot'.
The faint line of stars above and
right of the three is the Pot's handle.
At its centre is the Orion Nebula, a
glowing gas cloud nicely seen in binoculars. Rigel, directly above the line
of three stars, is a hot blue-giant
star. Orange Betelgeuse, below the
line of three, is a cooler red-giant
star.
Left of Orion is a triangular group
making the upside down face of
Taurus the bull. Orange Aldebaran
is the brightest star in the V shape.
Aldebaran is Arabic for 'the eye of
the bull'. Still further left is the
Pleiades /Matariki/Seven Sisters/
Subaru cluster, impressive in binoculars. It is 400 light-years* away.
Canopus, the second brightest star,
is high in the southeast. Low in the
south are the Pointers, Beta and Alpha Centauri, and Crux the Southern Cross. In some Maori star lore
the bright southern Milky Way
makes the canoe of Maui with Crux
being the canoe's anchor hanging
off the side. In this picture the Scorpion's tail can be the canoe's prow
and the Clouds of Magellan are the
sails.
The Milky Way is wrapped around
the horizon. The broadest part is in
Sagittarius, low in the west at dusk.
It narrows toward Crux in the south
and becomes faint in the east below
Orion. The Milky Way is our edgewise view of the galaxy, the pancake
of billions of stars of which the Sun
is just one. The thick hub of the galaxy, 30,000 light-years away, is in
Sagittarius. The nearby outer edge is
the faint part of the Milky Way below Orion. A scan along the Milky
Way with binoculars will show many
clusters of stars and a few glowing
gas clouds.
The Clouds of Magellan, LMC and
SMC, high in the southern sky, are
two small galaxies about 160,000
and 200,000 light-years away, respectively. They are easily seen by
eye on a dark moonless night. The
larger cloud is about 1/20th the mass
of the Milky Way galaxy, the smaller
cloud 1/30th.
Very low in the north is the Andromeda Galaxy seen in binoculars in a
dark sky as a spindle of light. It is
similar in size to our Milky Way galaxy and three million light-years
away.
There is a total eclipse of the Moon
on the morning of December 11th.
The Moon begins to enter the fuzzy
edge of Earth's shadow, the penumbra, at 12:32 a.m. NZDT. It shows
an obvious darkening on the right
edge when it meets the dark inner
shadow, the umbra, at 1:45 a.m. By
3:06 it will be fully eclipsed. At 3:58
it begins to leave the inner shadow,
first brightening on the top edge. It
is fully clear of the umbra by 5:18.
The Moon sets before it is fully clear
of the penumbra at 6:32.
The Geminid meteor shower peaks
in the morning hours of December
15. The meteors appear to come
from the constellation of Gemini,
low in the northeast at midnight,
moving to the north by dawn. Light
from the gibbous Moon will hide the
fainter meteors.
Mars and Saturn rise in the morning
hours. Mercury appears low in the
dawn later in the month. Mars rises
after midnight mid-month, easily
recognised by its orange-red colour.
It is brightening as we catch up on it.
Mars is 180 million km away midmonth. Saturn makes a close pair
with Spica, the brightest star in
Virgo. Saturn is the brighter of the
two and lower. Saturn is 1,500 million km away. Mercury moves up
into the dawn in the second half of
December. It is 120 million km away
mid-month, moving to the far side of
the Sun. At mid-month the three
planets are equally spaced in line and
similar in brightness.
*A light-year (l.y.) is the distance
that light travels in one year: nearly
10 million million km or 1013 km.
Sunlight takes eight minutes to get
here; moonlight about one second.
Sunlight reaches Neptune, the outermost major planet, in four hours. It
takes four years to reach the nearest
star, Alpha Centauri.
Notes by Alan Gilmore, University of Canterbury's Mt John Observatory, P.O. Box 56, Lake Tekapo 7945, New Zealand. www.canterbury.ac.nz 12
SOCIETY JOURNAL, December 2011
Diary of Solar System Events for December 2011 From the RASNZ Website December 1 40% lit Moon 6.5° below Neptune, magnitude 7.9, evening sky. December 2 Moon at first quarter at 10.52 pm NZDT (09:52 UT). December 4 69% lit Moon 7.5deg; to lower right of Uranus, magnitude 5.8, evening sky. December 4 Mercury at inferior conjunction. December 6 Moon at apogee, its greatest distance from the Earth for the Lunar month, 405415 km. December 6 85% lit Moon 7° to lower left Jupiter, evening sky. December 9 99% lit Moon 9° left of Aldebaran, α Tauri magnitude 1.0, evening sky. December 10 Full Moon mid‐way between Aldebaran, α Tau mag 1.0, and El Nath, β Tau, best seen late evening sky. December 11 New Full Moon at 3.36 am NZDT (Dec 10, 14:36 UT). Total eclipse of the Moon visible from Zealand. Moon furthest north, so lowest southern hemisphere transit for the month. December 11 Uranus stationary, forward motion commences. December 14 Mercury stationary. December 17 65% lit Moon 8.3° to upper right of Regulus α Leo magnitude 1.4 and 11° to upper left of Mars, magnitude 0.5, early dawn sky. December 18 54% lit Moon 8.5° to upper right of Mars, magnitude 0.5, early dawn sky. December 18 Moon at last quarter 1.48 pm NZDT (00:48 UT). December 21 21% lit Moon 8° to right of Saturn, magnitude 0.7. Spica, α Virginis magnitude 1.1, 5.5° above Saturn and 9.7° from Moon. December 22 Moon at perigee, its closest to the Earth for the lunar month, 364803 km. December 22 Southern summer solstice. Sun furthest south at 6.31 pm NZDT (05:31 UT). December 24 Moon furthest south, so highest southern hemisphere transit for the month. December 25 New Moon at 7.07 am NZDT (Dec 24, 18:07 UT). December 26 Jupiter stationary. December 27 8% lit Moon 7° to lower right of Venus, dusk sky. December 28 15% lit Moon 15° to right of Venus and 9° to lower left of Neptune, early evening sky. December 29 Pluto at conjunction with Sun. December 31 42% lit Moon 6.7deg; below Uranus, magnitude 5.8, evening sky. Lunar Eclipse Visible In December
There will be a Total Lunar Eclipse visible in from New Zealand in the early morning of December 11th. Although the Moon will be
low in the sky, it should be easily visible. The best place to view will be where you have a clear view in the north / northwest direction.
Totality will be 51 minutes long, during which the Moon will turn a deep copper / red colour
Partial (Umbral) Eclipse starts at:
Total Eclipse begins at:
Maximum Eclipse is at:
Total Eclipse ends at:
Partial (Umbral) Eclipse ends at:
1:46am
3:06am
3:32am
3:57am
5:18am
Stay up late or get up early to enjoy this fantastic sight.
More details can be found on the NASA Eclipse website at http://eclipse.gsfc.nasa.gov/eclipse.html or on wikipedia at
http://en.wikipedia.org/wiki/December_2011_lunar_eclipse.
WWW.ASTRONOMY.ORG.NZ 13
NASA Telescopes Help Solve Ancient Supernova Mystery From NASA A
mystery that began nearly 2,000
years ago, when Chinese astronomers witnessed what would turn out to
be an exploding star in the sky, has been
solved. New infrared observations from
NASA's Spitzer Space Telescope and
Wide-field Infrared Survey Explorer, or
WISE, reveal how the first supernova
ever recorded occurred and how its shattered remains ultimately spread out to
great distances.
The findings show that the stellar explosion took place in a hollowed-out cavity,
allowing material expelled by the star to
travel much faster and farther than it
would have otherwise.
"This supernova remnant got really big,
really fast," said Brian J. Williams, an
astronomer at North Carolina State University in Raleigh. Williams is lead author
of a new study detailing the findings
online in the Astrophysical Journal. "It's
two to three times bigger than we
would expect for a supernova that was
witnessed exploding nearly 2,000 years
ago. Now, we've been able to finally
pinpoint the cause."
In 185 A.D., Chinese astronomers noted
a "guest star" that mysteriously appeared in the sky and stayed for about 8
months. By the 1960s, scientists had
determined that the mysterious object
was the first documented supernova.
Later, they pinpointed RCW 86 as a supernova remnant located about 8,000
light-years away. But a puzzle persisted.
The star's spherical remains are larger
than expected. If they could be seen in
the sky today in infrared light, they'd
take up more space than our full Moon.
point to a low-density environment for
much of the life of the remnant, essentially a cavity.
The solution arrived through new infrared observations made with Spitzer and
WISE, and previous data from NASA's
Chandra X-ray Observatory and the
European Space Agency's XMM-Newton
Observatory.
Scientists initially suspected that RCW 86
was the result of a core-collapse supernova, the most powerful type of stellar
blast. They had seen hints of a cavity
around the remnant, and, at that time,
such cavities were only associated with
core-collapse supernovae. In those
events, massive stars blow material away
from them before they blow up, carving
out holes around them.
The findings reveal that the event is a
"Type Ia" supernova, created by the
relatively peaceful death of a star like
our Sun, which then shrank into a dense
star called a white dwarf. The white
dwarf is thought to have later blown up
in a supernova after siphoning matter, or
fuel, from a nearby star.
"A white dwarf is like a smoking cinder
from a burnt-out fire," Williams said. "If
you pour gasoline on it, it will explode."
The observations also show for the first
time that a white dwarf can create a
cavity around it before blowing up in a
Type Ia event. A cavity would explain
why the remains of RCW 86 are so big.
When the explosion occurred, the
ejected material would have travelled
unimpeded by gas and dust and spread
out quickly.
Spitzer and WISE allowed the team to
measure the temperature of the dust
making up the RCW 86 remnant at
about minus 200 degrees Celsius. They
then calculated how much gas must be
present within the remnant to heat the
dust to those temperatures. The results
But other evidence argued against a core
-collapse supernova. X-ray data from
Chandra and XMM-Newton indicated
that the object consisted of high
amounts of iron, a telltale sign of a Type
Ia blast. Together with the infrared observations, a picture of a Type Ia explosion into a cavity emerged.
"Modern astronomers unveiled one secret of a two-millennia-old cosmic mystery only to reveal another," said Bill
Danchi, Spitzer and WISE program scientist at NASA Headquarters in Washington. "Now, with multiple observatories
extending our senses in space, we can
fully appreciate the remarkable physics
behind this star's death throes, yet still
be as in awe of the cosmos as the ancient astronomers."
This image combines data from four
different space telescopes to create a
multi-wavelength view of all that remains of the oldest documented example of a supernova, called RCW 86. The
Chinese witnessed the event in 185
A.D., documenting a mysterious "guest
star" that remained in the sky for eight
months. X-ray images from the European Space Agency's XMM-Newton
Observatory and NASA's Chandra X-ray
Observatory are combined to form the
blue and green colours in the image. The
X-rays show the interstellar gas that has
been heated to millions of degrees by
the passage of the shock wave from the
supernova.
Infrared data from NASA's Spitzer Space
Telescope, as well as NASA's Wide-Field
Infrared Survey Explorer (WISE) are
shown in yellow and red, and reveal dust
radiating at a temperature of several
hundred degrees below zero, warm by
comparison to normal dust in our Milky
Way galaxy.
14
SOCIETY JOURNAL, December 2011
"Blue Stragglers" Rejuvenate by Stealing From Sky&Telescope M
ost stars that get a second lease
on life do so through thievery —
or so say two astronomers who think
they’ve finally settled a question that’s
been around for more than half a century.
“Blue stragglers” have been a mystery
since Allan Sandage discovered them in
1953. These are stars that appear deceptively young; they’re hot, bright, and
blue compared to the other members of
an aged population of which they’re a
part. Long after all the other hot, massive stars in a cluster have aged into redgianthood, blue stragglers continue to
burn with the brilliance of extended
youth.
Astronomers have proposed three scenarios for how these pretenders could
reclaim their youthful glow long after
entering middle age. All involve a radical
addition of mass, resetting the star’s
evolutionary clock back as if to a new
birth. Two stars could collide and become one. A binary pair could somehow
lose orbital energy, spiral together, and
merge. Or one member of a close binary
could siphon off most of the mass of a
close companion star.
In the October 20th issue of Nature,
Aaron Geller (Northwestern University)
and Robert Mathieu (University of Wisconsin, Madison) suggest that, for blue
stragglers in star clusters, siphoning is
surprisingly far more to blame than collisions or spiral-togethers are.
“We've had individual systems that we
knew quite a bit about, in quite a number of clusters, but this is the first time
we have learned something about essentially all the blue stragglers in a cluster,”
says Alison Sills of McMaster University
in Ontario, who was not involved in the
research.
they are white dwarfs — cinders left
over from dead stars that lost their outer
layers.
If the blue stragglers had come from
collisions, this average mass would be
nearly doubled. In a collision scenario at
least three stars are involved, Geller says.
That’s because a binary system is a much
bigger target for an interloper star to
swing at; one-on-one direct collisions are
scant at best, especially in a sparse cluster like NGC 188. But three or more
stars can “come together and do a
longer type of dance with each other,”
he says. “As they’re exchanging partners
and flying back out and coming back in
and doing all sorts of crazy things, sometimes two stars get close enough together that they collide.”
In this case, any leftover companion
tends to be on the massive side, because
a smaller star is more easily flung out of
the system.
That’s not the case with mass transfers.
A blue straggler born via siphoning starts
out as the less massive star in a binary.
“Basically, in a mass-transfer scenario,
the reason the one star ends up as a
blue straggler is that its companion
dumps mass on it,” says Christian
Knigge (Southampton University, England), who was not involved with the
study but is working with Geller and
Mathieu to follow up on their results.
The more massive star burns faster, ages
faster, and swells toward red-gianthood
first. Being in a close binary, as it swells
it spills over its Roche lobe, the region
around it where it can gravitationally
hold onto its outer layers. “At that point
the companion is basically a white dwarf
with a big envelope, and it's the envelope that gets dumped onto the aboutto-be blue straggler. The end result of
the process is a blue straggler with a
white-dwarf companion.”
White dwarfs, unlike the main-sequence
partners predicted by the collision scenario, fall nicely in the half-a-solar-mass
range. The interesting thing about Geller
and Mathieu’s result is that the range of
average companion masses predicted in
NGC 188 is so small: 0.57 to 0.59 times
that of the Sun. Knigge says that’s because a white dwarf’s mass depends on
its progenitor’s original mass, which in
turn corresponds with what type of star
is currently reaching old age in the cluster. “Since we know the age of the cluster, we know the mass of those stars
and hence can predict the mass of those
white dwarfs,” he says. “This also explains why the mass distribution is so
narrow.”
Blue stragglers that formed by the third
scenario, binary spiral-togethers, can
have additional companions looking on,
but these would have a wide range of
masses. Most would be main-sequence
stars, Geller says.
Since Geller and Mathieu weren’t able to
see any of the companion stars directly,
they couldn’t confirm that they are really
white dwarfs. “We don’t see them in
the optical because they’re very faint,
and especially faint compared to the
blue stragglers,” Geller says. But white
dwarfs should show up quite well in
ultraviolet. The team plans to use the
Hubble Space Telescope in late 2012 to
look for ultraviolet signals from the companions.
Blue stragglers can exist solo, but they
may also have companions. In this case,
the companion’s mass is a red flag on
the stellar evolutionary trail, because
each origin scenario predicts different
ranges for the consorts’ masses. So
Geller and Mathieu peered into the open
cluster NGC 188 to study 16 bluestraggler binaries and see exactly what
kind of buddies the stragglers have.
Although the companions were unseen
in visible light, the astronomers detected
them and their likely masses from Doppler shifts in the stragglers’ spectra as
the stars swung around the hidden objects. The solution that fits the data best
put each of the unseen partners at just
over half a solar mass, suggesting that
Deceptively youthful stars called blue stragglers are circled in this image of part of the
open star cluster NGC 188. Blue stragglers may most often get their new lease on life
by stealing mass from a companion star. K. Garmany & F. Haase / NOAO / AURA
WWW.ASTRONOMY.ORG.NZ 15
2012: Killer Solar Flares Are a Physical Impossibility, Experts Say From Science Daily G
iven a legitimate need to protect
Earth from the most intense forms
of space weather — great bursts of electromagnetic energy and particles that can
sometimes stream from the Sun — some
people worry that a gigantic "killer solar
flare" could hurl enough energy to destroy the Earth. Citing the accurate fact
that solar activity is currently ramping up
in its standard 11-year cycle, there are
those who believe that 2012 could be
coincident with such a flare.
But this same solar cycle has occurred
over millennia. Anyone over the age of
11 has already lived through such a solar
maximum with no harm. In addition, the
next solar maximum is predicted to occur
in late 2013 or early 2014, not 2012.
Most importantly, however, there simply
isn't enough energy in the Sun to send a
killer fireball 93 million miles to destroy
the Earth.
This is not to say that space weather
can't affect our planet. The explosive
heat of a solar flare can't make it all the
way to our globe, but electromagnetic
radiation and energetic particles certainly
can. Solar flares can temporarily alter the
upper atmosphere, creating disruptions
with signal transmission from, say, a GPS
satellite to Earth causing it to be off by
many yards. Another phenomenon pro-
disrupt its systems.
In an increasingly technological world,
where almost everyone relies on cell
phones and GPS controls, not just your
in-car map system, but also airplane navigation and the extremely accurate clocks
that govern financial transactions, space
weather is a serious matter.
The Solar and Heliospheric Observatory
(SOHO) spacecraft captured this image
of a solar flare as it erupted from the
Sun early on Tuesday, October 28, 2003.
This was the most powerful flare measured with modern methods. (Credit:
NASA/SOHO)
duced by the Sun could be even more
disruptive. Known as coronal mass ejections (CME), these solar explosions propel
bursts of particles and electromagnetic
fluctuations into the Earth's atmosphere.
Those fluctuations could induce electric
fluctuations at ground level that could
blow out transformers in power grids.
The CME's particles can also collide with
crucial electronics onboard a satellite and
But it is a problem the same way hurricanes are a problem. One can protect
oneself with advance information and
proper precautions. During a hurricane
watch, a homeowner can stay put . . . or
he can seal up the house, turn off the
electronics and get out of the way. Similarly, scientists at NASA and NOAA give
warnings to electric companies, spacecraft operators, and airline pilots before a
CME comes to Earth so that these
groups can take proper precautions.
Improving these predictive abilities, the
same way weather prediction has improved over the last few decades is one
of the reasons NASA studies the Sun and
space weather. We can't ignore space
weather, but we can take appropriate
measures to protect ourselves.
And, even at their worst, the sun's flares
are not physically capable of destroying
the Earth.
Endless Void or Big Crunch: How Will the Universe End? From Space.com N
ot only are scientists unsure how
the Universe will end, they aren't
even sure it will end at all.
Several possibilities for the fate of our
universe have been bandied about. They
tend to have names such as Big Crunch,
Big Rip and Big Freeze that belie their
essential bleakness. Ultimately, space
could collapse back in on itself, destroying all stars and galaxies in existence, or
it could expand into essentially an endless void.
"The truth is that it's still an open scenario," said astrophysicists.
On the brighter side, any eventuality will
take billions or even trillions of years to
occur, long after our great-great-great-
16
great-great-great-grandchildren should
be past caring. If humans are still in existence at that point, however, they may
have a tough time of it.
Dark energy's role
The fate of our Universe largely depends
on a mysterious entity dubbed dark energy. This is the name for the unexplained force that is counteracting gravity, pulling the Universe apart at the
seams.
Dark energy was originally discovered
when scientists set out to find out how
much the expansion of the Universe was
slowing down, due to gravity pulling it
back inward. They found, instead, that
this expansion is actually accelerating.
SOCIETY JOURNAL, December 2011
This shocking discovery earned three
astrophysicists the 2011 Nobel Prize.
If dark energy continues to exert the
same force on the Universe in the future,
then space will continue to expand, the
distance between galaxies stretching
wider and wider and at a faster and
faster pace. Eventually, we won't be able
to see anything beyond the Milky Way
because everything will be so far away.
"Today we look up in the sky and we
see just fantastic things; galaxies, clusters
of galaxies stretching out all over the
sky," Allen told SPACE.com. "But if the
expansion is going to get faster and
faster, eventually those galaxies will get
pulled too far away for us to see. Space
becomes an ever less beautiful and rich
place. The Universe becomes a relatively
lonely place."
This scenario is sometimes called the Big
Freeze, because the Universe will end up
largely cold, dark and empty.
Placing bets
This vision is the most likely future for
our Universe, scientists say, because the
best observations of the young, distant
universe to date suggest that the
strength of dark energy has remained
steady throughout time.
nitely dense. However, most physicists
think this theory is incomplete and cannot fully describe the quantum and
gravitational forces going on at that
time.
the Universe will stop accelerating and
eventually slow down. [7 Surprising
Things About the Universe]
If dark energy became weak enough,
gravity might ultimately win the tug of
war and pull the Universe back in on
itself. The result would be the Big
Crunch.
Thus, if the Universe did crunch back in
on itself, it's unclear whether it would
stop once it got down to its smallest,
densest state, or if some kind of repellent force would kick in, forcing space
back outward and beginning the cycle all
over again.
"The collapse initially would just be very
harmless; the density of the Universe
would increase, but very slowly," Bo-
Unravelling the mystery
This is in fitting with a theory that dark
energy is what Einstein called the cosmological constant, a term he added to his
general theory of relativity.
If scientists have any hope of solving the
mystery of the Universe's fate, they must
get a better handle on dark energy.
"Today, to the best of my knowledge, all
the best data we have are consistent
with a cosmological constant, consistent
with dark energy being constant over
time," Allen said. "If people had to bet
on anything, they would bet on that."
"Our biggest question is, what is the
dark energy?" said astrophysicist Alexey
Vikhlinin of the Harvard-Smithsonian
Center for Astrophysics in Cambridge,
Mass. "All these answers sensitively depend on the physical nature of dark energy."
Big Rip
It's a question on which researchers do
have hope of making headway, as they
continue to look farther and farther
away, taking more and more precise
measurements of the expansion rate of
the Universe over time. In the next decade or so, scientists expect to be able to
say with significantly more confidence
whether dark energy has been constant
or has changed over the 14 billion years
since the Big Bang.
But a Big Freeze isn't inevitable. If dark
energy isn't a constant and instead increases over time, we could be facing
what scientists call a Big Rip.
The current strength of dark energy is
not thought to be enough to overcome
gravity on small, local scales. However, if
dark energy gets stronger, it may be
enough to counteract even that, expanding not just the space between galaxies
but the space within them.
"At some point galaxies themselves
could be ripped apart," said Martin Bojowald, a physicist at Pennsylvania State
University. "The Milky Way would be
ripped apart. The question is whether it
goes down even to the Solar System."
Snapshot from a computer simulation of
the formation of large-scale structures in
the Universe, showing a patch of 100
million light-years and the resulting coherent motions of galaxies flowing toward the highest mass concentration in
the centre. CREDIT: ESO
Big Crunch
jowald said. "But at some time the collapse would lead to densities of the
same size as the Big Bang."
Another, equally dire possibility is that
the strength of dark energy diminishes
over time. In that case, the expansion of
According to general relativity, at the
moment of the Big Bang the Universe
was as small as a single point, and infi-
Grant Christie (021) 024‐04992 Vice President David Britten (09) 846‐3657 Treasurer & Membership Andrew Buckingham (09) 473‐5877 Secretary Kleo Zois (022) 6912‐055 Curator of Instruments Ivan Vazey (09) 535‐3987 Librarian Tony Reynolds (09) 480‐8607 Clive Bolt Journal Editors "The Universe is kind of humbling when
you look at it and start to appreciate its
scale," Allen said. "It feels like a privilege
to be able to ask these questions."
Society Contacts
The 2011 Council
President It's a challenge scientists relish.
Auckland Astronomical Society Inc, P O Box 24‐187, Royal Oak, Auckland 1345, New Zealand Email [email protected] Journal [email protected] (09) 534‐2946 Website www.astronomy.org.nz (09) 480‐5648 Membership inquiries contact Andrew Buckingham at [email protected] or by phone on (09)‐473‐5877 or by mobile on 027‐246‐
2446 Shaun Fletcher Milina Ristić (029) 912‐4748 Webmaster Nick Moore (09) 268‐9910 Council Gavin Logan (09) 820‐6001 Council Bernie Brenner (09) 445‐3293 WWW.ASTRONOMY.ORG.NZ 17
Giant Planet Ejected from the Solar System? From Science Daily J
ust as an expert chess player sacrifices a piece to protect the queen,
the Solar System may have given up a
giant planet and spared Earth, according
to an article recently published in The
Astrophysical Journal Letters.
"We have all sorts of clues about the
early evolution of the Solar System,"
says author Dr. David Nesvorny of the
Southwest Research Institute. "They
come from the analysis of the transNeptunian population of small bodies
known as the Kuiper Belt, and from the
lunar cratering record."
These clues suggest that the orbits of
giant planets were affected by a dynamical instability when the Solar System was only about 600 million years
old. As a result, the giant planets and
smaller bodies scattered away from each
other.
Some small bodies moved into the Kuiper Belt and others travelled inward,
producing impacts on the terrestrial
planets and the Moon. The giant planets
moved as well. Jupiter, for example,
scattered most small bodies outward
and moved inward.
This scenario presents a problem, however. Slow changes in Jupiter's orbit,
such as the ones expected from interaction with small bodies, would have con-
veyed too much momentum to the orbits of the terrestrial planets. Stirring up
or disrupting the inner Solar System and
possibly causing the Earth to collide with
Mars or Venus.
One planet was ejected from the Solar
System by Jupiter, leaving four giant
planets behind, and Jupiter jumped,
leaving the terrestrial planets undisturbed.
"Colleagues suggested a clever way
around this problem," says Nesvorny.
"They proposed that Jupiter's orbit
quickly changed when Jupiter scattered
off Uranus or Neptune during the dynamical instability in the outer Solar
System." The "jumping-Jupiter" theory,
as it is known, is less harmful to the
inner Solar System, because the orbital
coupling between the terrestrial planets
and Jupiter is weak if Jupiter jumps.
"The possibility that the Solar System
had more than four giant planets initially, and ejected some, appears to be
conceivable in view of the recent discovery of a large number of free-floating
planets in interstellar space, indicating
the planet ejection process could be a
common occurrence," says Nesvorny.
This research was funded by the National Lunar Science Institute and the
National Science Foundation.
Nesvorny conducted thousands of computer simulations of the early Solar System to test the jumping-Jupiter theory.
He found that, as hoped for, Jupiter did
in fact jump by scattering from Uranus
or Neptune. When it jumped, however,
Uranus or Neptune was knocked out of
the Solar System. "Something was
clearly wrong," he says.
Motivated by these results, Nesvorny
wondered whether the early Solar System could have had five giant planets
instead of four. By running the simulations with an additional giant planet
with mass similar to that of Uranus or
Neptune, things suddenly fell in place.
Artist's impression of a planet ejected
from the early Solar System. (Credit:
Image courtesy of Southwest Research
Institute)
The Oddly Magnetic Moon From Sky&Telescope T
here’s a problem with the Moon.
Rocks from Earth’s natural satellite
show evidence of magnetic fields existing
too recently in lunar history to fit the
theory of how the Moon’s magnetic field
was created. Now, two papers in Nature
offer different mechanisms for how a
lunar dynamo could have been maintained long after it should have been
dead.
“These are extremely important papers,
because we suspected that there were
relatively late magnetic fields on the
Moon for a long time,” says Benjamin
Weiss (Massachusetts Institute of Technology), who wasn’t involved with either
study. “These provide a mechanism for
doing it.”
The Earth creates its global magnetic
field through the convection of its metal-
18
lic liquid core, “lava-lamp style,” explains
Weiss. The convection is basically driven
by the planet’s gradual cooling over
time. Liquid metal (like solid metal) conducts electricity, and when an electrical
conductor moves in the presence of a
weak field, electric current is generated
inside the conductor — which creates
more magnetic field, in a runaway process like the one used in an artificial, selfsustaining dynamo. But for small bodies
like the Moon, cool-off should have
come pretty fast — so fast that convection would soon stop and a core dynamo
would cease to exist. For the Moon the
cut-off date was around 4.2 billion years
ago, according to models of the Moon’s
evolution. In fact, Weiss and his collaborators confirmed that there was a field
on the Moon 4.2 billion years ago from
studies of a lunar rock.
SOCIETY JOURNAL, December 2011
Yet magnetic hints pop up in lunar rocks
that are hundreds of millions of years
younger than that. Rocks encode magnetic fields that prevailed at the time
they solidified. Certain atoms align with
a background field like little bar magnets
when they are free to move, as they are
in lava. As the rock solidifies these minimagnets become locked in place, preserving a record of the ancient field.
A magnetic field doesn’t have to come
from a core dynamo. Impact-created
plasmas could create local, short-lived
fields lasting about a day. Work is ongoing to determine how many lunar samples gained their magnetization by a
long-lived dynamo as opposed to more
transient processes like impacts, says
Weiss. But there are so many magnetized
lunar rocks of various ages, he adds, that
“it’d be hard to believe that they’re all
from an impact.”
The two papers suggest different ways
that a dead dynamo could have restarted
inside the Moon to create a late, longlasting field.
In the first, a difference between the spin
axes of the core and mantle is the culprit.
In this model, the core’s spin axis once
pointed perpendicularly to the ecliptic
plane, while the mantle’s axis was
slightly off from that and precessing
around the core’s axis. In the case of
Earth, the core and mantle are locked
together, so this process can’t work. But
in the Moon this precession — driven by
Earth as the Moon circled farther and
farther out in its orbit over time — created a stirring mechanism.
“It’s sort of analogous to a laundry machine,” Weiss explains. If the chamber
precesses as it spins, the water inside is
stirred even though there’s no propeller
in the water moving it around.
Once the Moon receded far enough
from Earth, about 48 Earth radii —
which would have happened 2.7 billion
years ago, Christina Dwyer (University of
California, Santa Cruz) and her colleagues predict in the paper — the dynamo would have shut off from insufficient power.
The second theory stirs the core by moving the mantle in a totally different way:
by smacking it with a huge impact big
enough to jerk the Moon out of synchro-
The Moon's mare show up nicely in this
color mosaic of images taken by the Galileo spacecraft. Researchers studying
three of the basins shown here, Serenitatis, Humboldtianum, and Crisium (middle
left, centre, and centre bottom respectively) suggest that the large impacts that
created these basins could have jumpstarted the Moon's magnetic dynamo.
NASA / JPL / USGS
nous rotation. A team of French and
Belgian researchers looked at six lunar
craters that contain magnetic anomalies,
places where magnetic fields are preserved in the crust from bygone days.
The researchers suggest that the melt
rocks in these basins, all from around 4
billion years ago, probably formed their
anomalies as they cooled in the presence
of a magnetic field.
“The large impacts that we need in our
model to make a dynamo were present
around 4 billion years ago, which is exactly the time when the Moon’s dynamo
is expected,” explains co-author Michael
Le Bars (IRPHE, CNRS and Aix-Marseille
Université, France). The hits came all
within about 100 million years of each
other, he notes, and each could have
created a temporary dynamo lasting
2,000 to 8,000 years. If the hit caused
longitudinal oscillations in the Moon, the
effect could last a bit longer, maybe
10,000 years.
“The problem with the lunar magnetic
record is that it is very confusing,” Garrick-Bethell explains. “The patterns of
magnetism you see in the Moon's crust
are nothing like what you see on the
Earth. The magnetism in its rocks may
have been magnetized by exotic shock
processes that don't operate on the
Earth.”
For now, the mystery stands, albeit less
darkly.
The studies affect more than our understanding of the Moon’s magnetization.
The question of whether the Moon even
has a core, instead of being a “pile of
primordial space dust” like an asteroid,
as Weiss puts it, has recently been clarified. That both theories depend on the
Moon having a liquid-metal core is “one
of the major reasons for caring about
this,” Weiss says. “If the Moon generated a magnetic field in a core, by definition it has a core.”
“That’s really, really short,” Weiss says.
“I mean, the Moon’s billions of years
old.”
Still, the theory is a good one. “This is an
elegant and carefully thought-out idea
that creates a dynamo just long enough
to magnetize cooling, molten rocks that
formed in the very same crater event,”
says Ian Garrick-Bethell (University of
California, Santa Cruz), who worked on
the 2009 study.
Both theories predict surface magnetic
fields of around 1 microtesla, matching
previous predictions. The Earth’s field at
its surface is about 50 times greater.
Distinguishing between these theories
will depend in part on figuring out which
rocks were magnetized when. Big bull’seyes happened pretty rarely in lunar history. If an impact created a dynamo, any
molten surface rock around the time of
the crash —such as lava created by the
hit itself — would record the magnetic
field created. But lava that erupted on
the surface between these infrequent
events wouldn’t. If most lunar rocks
everywhere were magnetized during a
particular time period, including rocks
not made by impacts, that would sway
the balance toward the precession argument, Weiss says. If impact melts are
always associated with a magnetic field,
the balance swings the other way.
The Humboldtianum Basin, shown here
in false color based on altimeter data
from the Lunar Reconnaissance Orbiter,
spans 650 kilometres and sinks 4.5 km
deep. The impact that created the basin
may have jolted the Moon out of synchronous rotation with Earth, one study
suggests. Credit: NASA / GSFC
And because the Moon is a half-step
between planet and asteroid, the models
might explain how asteroids could have
magnetic fields. “This is interesting from
the perspective of understanding the
Moon,” Weiss says. “It’s also interesting
from the perspective of just understanding the physics of how magnetic fields
are generated by planets.”
But the mechanisms aren’t exclusive,
either. Both could have happened at
different times in the Moon’s history, or
together.
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