Links to the Enews for: March 2012 February 2012
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. Royal Astronomical Society of New Zealand
. Email Newsletter Number 136, 27 April 2012
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Affiliated Societies are welcome to reproduce any item in this email
newsletter or on the RASNZ website http://www.rasnz.org.nz/
in their own newsletters provided an acknowledgement of the source is
also included.
Contents
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1. Sun Viewers for Venus Transit
2. The Solar System in May
3. RASNZ Annual General Meeting
4. Third International Starlight Conference
5. RASNZ Conference June 15-17
6. Astronomer´s Dream: Home & Astronomy Income
7. Venus Transit Photographers Sought
8. Satellite Galaxies Threaten Dark Matter
9. Find Hubble's Best Pictures
10. Yellow Supergiants Surveyed in LMC and M33
11. Solar 'Climate Change' Could Cause Rougher Space Weather
12. Earth's Minimoons
13. How to Join the RASNZ
14. Gifford-Eiby Lecture Fund
15. Kingdon-Tomlinson Fund
16. Here and There
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1. Sun Viewers for Venus Transit
--------------------------------
Solar viewers suitable for observing the transit of Venus now available.
The RASNZ has sourced a supply of viewers that will be ideal for viewing
the transit of Venus that will take place, and be visible from New Zealand
weather permitting, on 6 June 2012.
These viewers have been safety tested by one of the world's leading
authorities on solar viewing devices and provide full eye protection when
observing the Sun directly. Note that the viewer should not be used in
conjunction with any optical device such as telescope, binoculars, camera etc.
During the transit, Venus is of sufficient apparent diameter to be able to
be seen by eye through the filter. Later in the year an eclipse of the
Sun will occur and the viewer will also provide a safe and easy way to
observe this event, too. Each viewer is supplied with an information
sheet about these two events.
Order your Solar Viewers by going to:
http://www.rasnz..org.nz/Sales/SolarViewers.html
-- Glen Rowe, President RASNZ.
----------------------------------
Jennie McCormick adds:
These handy viewers have been safety tested for RASNZ by Associate
Professor Ralph Chou (School of Optometry, University of Waterloo,
Ontario, Canada) for use during the Transit of Venus on the 6th of June
and the Partial Eclipse on November 14th this year.
Your astronomical society or group may like to place an order to sell the
viewers to the local community - a perfect way to fundraise, to promote
your group, or to use during your own organised events.
There is nothing like exciting astronomical 'goings on' to stir the
public's imagination and to get everyone along to check out what your
group gets up to.
To order online see http://www.rasnz.org.nz/Sales/SolarViewers.html
Orders for 1 to 9 viewers $2.50 each
Orders for 10 to 99 viewers $2.00 each
Orders for 100 or more viewers $1.50 each
All prices include postage and packing.
As these events will take place during the working week, family, friends,
workmates and local schools might like to order a few, so please pass on
the information.
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2. The Solar System in May
--------------------------
The usual notes on the visibility of the Planets for May 2012 are on the
RASNZ web site: http://www.rasnz.org.nz/SolarSys/May_12.htm. Notes for
June 2012 will be on line in a few days.
THE PLANETS IN MAY
Jupiter is at conjunction with the Sun on May 13, so will be too close to
the Sun to observe during the month.
Venus is low in the sky to the northwest following sunset early in the
month but is much lower later in May. Mars and Saturn are easy evening
objects all month
Mercury starts May as an easy morning object but disappears later in May.
PLANETS IN THE EVENING SKY
VENUS sets about 100 minutes after the Sun in the first part of the month
so will be an obvious object, low to the northwest, after sunset. The
planet is stationary on May 16, after which it starts moving back to the
west and towards the Sun. As a result it will rapidly get lower in the
evening sky to disappear before the end of May. Inferior conjunction,
with the transit of Venus, is of course on June 6.
Venus is in Taurus throughout May, only a few degrees from El Nath, beta
Tau, at magnitude 1.7 the second brightest star in the constellation. The
star and planet are closest on May 7 when they are less than a degree
apart with Venus above El Nath. During the next few evenings, while Venus
is still moving to the east, the distance between the two increases
slightly. After being stationary, Venus will swing back again but now a
little further above the star, but they remain less than 2 degrees apart
up to the 20th. By then El Nath will be so low it will be very difficult
to see even in binoculars.
On the evening of May 23 the moon will be just under 6 degrees above
Venus. The moon will be a very thin crescent only 4% lit. 15 minutes
after sunset, Venus will be to the northwest only 5 degrees above the
horizon.
MARS is highest and to the north about 8.30 pm on May 1 and 7.00 pm on the
31st. So it is best placed for observation early evening. Later in the
evening it will be to the northwest and lower. Having been stationary in
April, the planet will be moving steadily to the east through Leo. This
will take it away from Regulus, alpha Leo, their separation increasing to
nearly 15 degrees by the end of May.
The distance of the Earth from Mars increases from 141.5 million km on May
1 to 177 million km on May 31. Consequently the brightness of the planet
drops from magnitude 0.0 to 0.5 during the month. That is still
considerably brighter than the 1.4 of Regulus.
The 70% lit moon will be 7 degrees from Regulus and Mars on May 1. The
moon will be at the top of a near isosceles triangle formed by the three.
On the 29th the moon will again be above Mars and a little closer to the
planet. The moon will then be just past first quarter.
SATURN is following Mars across the evening sky. It is highest at about
11.30 pm at the beginning of May advancing to about 9.30 pm by the end of
the month. Saturn is nearly 20 degrees further south than Mars so will
transit that much higher than the red planet.
Saturn will remain in Virgo during May, moving slowly in a retrograde
sense to the west. It will be 5°; from Spica, so the two forming an
obvious pair with Saturn below Spica much of the evening. By late evening
the rotation of the sky will bring Saturn more round to the right of
Spica.
Saturn´s magnitude will drop from 0.3 to 0.5 during May, so it and Mars
will be similar in brightness. Spica is a little fainter than Saturn at
magnitude 1.1.
The moon, just short of full will be at its closest to Saturn and Spica on
the evening of May 4. At 9 pm the moon will be 5 degrees to the upper
left of Spica and just over 8 degrees from Saturn.
MORNING SKY
MERCURY is visible in the morning sky in the first part of May, the
brightest object low in the sky about 20 degrees north of east. During
May, Mercury will be getting further from the Earth. Even so it will
brighten as it moves further round the Sun and becomes more fully lit. The
planet´s altitude, as seen from Wellington 45 minutes before sunrise, will
drop from 14 degrees on the 1st to 4 degrees on the 16th. So by about the
latter date it is likely to be lost to view despite being at magnitude -0.9.
The planet is at superior conjunction on May 27 when it will be 198
million km from the Earth, 46 million km from the Sun. After conjunction
it begins to move into the evening sky.
About the middle of May, Mercury will move past the asteroid Vesta,
magnitude 8.3. The two will be moving on almost parallel paths, Mercury
considerably faster than Vesta. They are closest, 3 degrees apart, on the
12th. On the 11th the two will be at about the same level, Mercury to the
left of Vesta. A 4th magnitude star will be between them, just under 1
degree from asteroid. The following morning Mercury and Vesta will be
closest, 3 degrees apart, with Mercury a little lower than Vesta and the
star will be slightly higher. It may be possible to see Vesta in
binoculars an hour before sunrise when the Sun is 12 degrees below the
horizon.
JUPITER moves into the morning sky after conjunction with the Sun on May
13. It will be too low to see for most of the month. On the last morning
of May Jupiter will rise one hour before the Sun. Half an hour before
sunrise at the beginning of civil twilight, it will be 5 degrees up in a
direction some 30 degrees to the north of east.
***********
URANUS, magnitude 5.9, starts May in Pisces but crosses into a corner of
Cetus on the 12th. At the beginning of the month it rises about 4.20 am
and two hours earlier by the end of the month.
NEPTUNE, magnitude 7.9, rises about 1.30 am on May 1 and before midnight
by the end of the month. The planet is in Aquarius throughout May.
BRIGHTER ASTEROIDS:
Both Ceres and Vesta emerge from the Sun into the morning sky during May,
with Vesta leading by 6 to 7 degrees. At the beginning of the month Vesta
is 12 degrees from the Sun, Ceres only 6. By the 31st the elongations
will have increased to 27 degrees and 20 degrees respectively. The
magnitude of Ceres will be about 9 while Vesta is 8.4. Both will be in
Aries by the end of May.
No other asteroids are within reach of binoculars during May.
More details and charts for these minor planets can be found on the RASNZ
web site. Follow the link to asteroids 2012.
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3. RASNZ Annual General Meeting
-------------------------------
The 89th Annual General Meeting of the Royal Astronomical Society of New
Zealand will be held on Saturday 16 June 2012 at the Carterton Events
Centre, Carterton, beginning at the end of the conference proceedings for
the day, about 4pm. Notices of motion are invited and should reach the
Executive Secretary by 5 May 2012.
-- Rory O´Keeffe, Executive Secretary.
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4. Third International Starlight Conference
--------------------------------------------
The Starlight Conference is at Lake Tekapo, 11-13 June 2012. The website
is accepting registrations and on-line requests to give an oral or poster
paper. Visit www.starlight2012.org for full details.
It will be a multidisciplinary conference on the scientific and cultural
benefits of observing dark starlit skies. The meeting will be
of interest to RASNZ members and to many other interest groups in
education, tourism, environmental protection and to those interested in
the cultural and ethnic aspects of astronomy. As participation will be
limited, early registration is encouraged.
The Starlight Conference is jointly hosted by the University of Canterbury
and by RASNZ, and is being sponsored by the University of Canterbury, by
RASNZ, by the Royal Society of NZ, by Endeavour Capital Ltd and by the NZ
National Commission to UNESCO.
-- Abridged from a note by John Hearnshaw.
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5. RASNZ Conference June 15-17
------------------------------
Well, less than two months to go until Conference and things are coming
together nicely. And our grateful thanks to The Phoenix Astronomical
Society and the Carterton Events Centre for the work they are putting
into this.
A reminder that registrations need to be in by 15 May to avoid the late
registration fee. So if you haven't yet registered please do so as soon
as possible. Additional information re accommodation and transport is
available on the registration form. And all the information you may need
is on the Conference link on the RASNZ Webpage - www.rasnz.org.nz
Don't forget the Astronomy Outreach Workshop that will run day time
Friday. This will appeal to anyone who is involved in public and/or
educational astronomy outreach. You can register for this at the same
time you register for the main conference.
At the time I write this there is still room for a few more papers. One
thing I'd like some feedback on is whether we should include a Transit
of Venus results session (or part session) in the programme. Conference
is just over a week following the transit, and people may have some
great stories and observations to share. So thoughts please.
I think most of what needs to be covered re Conference has appeared in
recent newsletters, and of course lots of information is available on
the RASNZ Webpage. But of anyone does have any queries please contact us
- conference@rasnz.org.nz - and we will be happy to assist. This is the
main Conference for astronomers in NZ - amateur and professional. And
the content of the programme should always reflect that - hopefully.
There should be something for everyone.
As is now usual, we will be asking for feedback following Conference so
we can strive to continually improve what we can offer. If there are any
specific questions you would like us to solicit feedback from attendees
on, please let us know as soon as possible.
In the meantime, however, please register as soon as possible. If you
wish to give a paper/poster paper please submit this with some urgency,
as the final deadline is fast approaching.
Look forward to seeing everyone in Carterton.
Dennis Goodman, Chair, RASNZ Standing Conference Committee
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6. Astronomer´s Dream: Home & Astronomy Income
----------------------------------------------
New large 4 bedroom house (150 square meters - plus double garage) with
separate self-contained studio accommodation business. Private spa pool.
Observatory: 4 meter (school sized) observatory on front lawn housing 15-
inch Newtonian telescope. Parking for 3+ vehicles. Established gardens
including a banana grove at the rear of the property. 5 minutes walk to
beautiful Baylys beach in affordable sunny Northland. 2 km to golf course.
15 minutes to all the local amenities. Reluctantly selling due to a change
in family circumstances and the need to relocate due to current family
needs but would prefer not to have to dismantle the observatory and shut
down the business. I would love to find someone else who could carry on
the 'Astronomy Adventures' business. Please contact Deborah on 09 439 1856
or by e-mail for more details astronomy@igrin.co.nz .
For a video made in 2010 where Astronomy Adventures featured on Marcus
Lush North check out:
http://tvnz.co.nz/north/marcus-lush-goes-up-while-4009197
- episode 3 first ten minutes.
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7. Venus Transit Photographers Sought
-------------------------------------
Jeff Baldwin of California seeks the cooperation of a NZ observer in
obtaining the parallax of Venus from transit photography. Jeff writes: I
am looking for somebody who will participate in photographing the transit
at ten minute intervals as I will, after which we would exchange
photographs. I teach an astronomy class, and this is an opportunity to
measure the distance between the Earth and the Sun using the parallax
shift observed in Venus´s position in front of the Sun by two observers on
opposite sides of the Earth. I'm in California and there is a period of
time in which the transit is visible to both of us, and we are nearly as
stretched out on opposites as you can get.
For more information contact Jeff Baldwin baldjeff@comcast.net .
-- Rolf Carstens forwarded this request to the nzastronomers group.
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8. Satellite Galaxies Threaten Dark Matter
------------------------------------------
Astronomers from the University of Bonn in Germany have discovered a vast
structure of satellite galaxies and clusters of stars surrounding our
galaxy, stretching out across a million light-years. The work challenges
the existence of dark matter, part of the standard model for the evolution
of the universe.
The Milky Way consists of around three hundred thousand million stars as
well as large amounts of gas and dust arranged with arms in a flat disk
that wind out from a central bar. The diameter of the main part of the
Milky Way is about 100,000 light years. A number of smaller satellite
galaxies and globular clusters orbit at various distances from the main
Galaxy.
Conventional models for the origin and evolution of the universe are based
on the presence of 'dark matter', invisible material thought to make up
about 23% of the content of the cosmos that has never been detected
directly. In this model, the Milky Way is predicted to have far more
satellite galaxies than are actually seen.
In their effort to understand exactly what surrounds our galaxy, the Bonn
scientists used a range of sources from twentieth century photographic
plates to images from the robotic telescope of the Sloan Deep Sky Survey.
Using all this data they assembled a picture that includes bright
'classical' satellite galaxies, more recently detected fainter satellites
and the younger globular clusters.
The astronomers found that all the different objects are distributed in a
plane at right angles to the galactic disk. The newly-discovered structure
is huge, extending from as close as 33,000 light years to as far away as
one million light years from the centre of the galaxy.
As the different companions move around the Milky Way, they lose material,
stars and sometimes gas, which forms long streams along their paths. The
new results show that this lost material is aligned with the plane of
galaxies and clusters. This shows that the objects are not only situated
within this plane right now, but that they move within it. The structure
is stable.
The various dark matter models struggle to explain this arrangement. In
the standard theories, the satellite galaxies would have formed as
individual objects before being captured by the Milky Way. They would have
come from many directions. So it is next to impossible for them to end up
distributed in such a thin planar structure.
The team concluded that the satellite galaxies and clusters must have
formed together in one major event, a collision of two galaxies. Such
collisions are relatively common. They result in large chunks of galaxies
being torn out due to gravitational and tidal forces. The forces act on
the stars, gas and dust in the galaxies, forming tails that are the
birthplaces of new objects like star clusters and dwarf galaxies.
The evidence indicates that the Milky Way collided with another galaxy in
the distant past. The other galaxy lost part of its material, material
that then formed our galaxy´s satellite galaxies, the younger globular
clusters, and the bulge at the galactic centre. The companions we see
today are the debris of this 11 billion year old collision.
The team assert that their model appears to rule out the presence of dark
matter in the universe. This threatens a central pillar of current
cosmological theory. They see this as the beginning of a paradigm shift,
one that will ultimately lead us to a new understanding of the universe we inhabit.
The work appears in "The VPOS: a vast polar structure of satellite
galaxies, globular clusters and streams around the Milky Way", M. S.
Pawlowski, J. Pflamm-Altenburg, P. Kroupa, Monthly Notices of the Royal
Astronomical Society, in press. Preprint of the paper:
http://arxiv.org/abs/1204.5176
For image and movies see
http://www.astro.uni-bonn.de/~mpawlow/pr2012.html. This animation is also
available on YouTube at http://youtu.be/nUwxv-WGfHM.
-- From a Royal Astronomical Society [UK] press release forwarded by Karen Pollard.
---------------
For a view on dark matter's effect on the Milky Way see "Scientific
American" October 2011, p.24.
===============================================================
9. Find Hubble's Best Pictures
-------------------------------
Since 1990, the Hubble Space Telescope has made more than a million
observations. Many of these are featured on spacetelescope.org, and the
most stunning are in our Top 100 gallery at
<http://www.spacetelescope.org/images/archive/top100/> and iPad app.
But there are thousands of pictures in Hubble´s science archive that have
only been seen by a few scientists. We call these images Hubble´s hidden
treasures - stunning images of astronomical phenomena that have never been
seen and enjoyed by the public. Every week, we search the archive for
hidden treasures, process the scientific data
<http://www.spacetelescope.org/projects/hiddentreasures/imageprocessing/>
into attractive images and publish them as the Hubble Picture of the Week
<http://www.spacetelescope.org/images/potw/> . But the archive is so vast
that nobody really knows the full extent of what Hubble has observed.
This is where you come in. Searching Hubble´s archive for hidden treasures
is a lot of fun, and it's pretty straightforward, even if you don't have
advanced knowledge. So we're inviting you to come and help us find iconic
Hubble images that have never before been shown to the public. See
<http://www.spacetelescope.org/projects/hiddentreasures/>
-- Thanks to Joan Gladwyn for passing this request along.
===============================================================
10. Yellow Supergiants Surveyed in LMC and M33
----------------------------------------------
Stars live for a long time, with even the most massive stars having
lifetimes measured in millions of years. But, for a mere few thousand
years towards the end of their lives, some massive stars go through what
astronomers call the yellow supergiant phase. This is remarkably short in
astronomical terms, and, as a result, stars in this phase are incredibly
rare. In a recent study, astronomers from Lowell Observatory have
identified hundreds of these rare yellow supergiants, and their more long-
lived descendants, the red supergiants in two neighbouring galaxies.
The Lowell astronomers use these newly identified populations to provide a
stringent observational test for the theoretical models which describe how
these stars change from blue, to yellow and then to red. These constraints
are vital because the behaviour of the models in this phase can influence
many theoretical predictions, including something as basic as what types
of stars explode as supernovae.
Nearby red supergiant stars include such well-known stars as Betelgeuse,
Antares, and Mu Cephei, and yellow supergiant stars include names like
Canopus and Rho Cassiopeiae, although these stars were not included in the study.
Using telescopes in Chile and Arizona the astronomers have observed a
relatively complete set of red and yellow supergiants in the Large
Magellanic Cloud (LMC) and M33. They compared their observations with
computer models of stars derived by a group at Geneva Observatory,
Switzerland. They found excellent agreement between their observed sample
and theory in predicting the stellar lifetimes and general stellar
properties during a critical period near the end of the stars' lifetimes.
This is in contrast to studies from three years ago by the same teams that
showed large discrepancies between yellow supergiant populations and a
previous version of the Geneva evolutionary models.
These two studies were led by two young researchers at Lowell Observatory,
Kathryn Neugent (lead for the LMC study) and Maria Drout (lead for the M33
study). Both involve an international collaboration with Dr. Georges
Meynet (Geneva Observatory), one of the world¹s experts in stellar
evolution theory.
To astronomers, the Hertzsprung-Russell (HR) diagram -- a plot of the
intrinsic luminosity versus temperature of all stars -- is key to
understanding the evolution of stars. For most of their lives stars are
fueled by hydrogen in their cores. During this time they are constant in
brightness and temperature. This is called the main sequence phase. It is
well understood.
However, there have been problems with understanding how the temperature
and luminosity of a star rapidly changes as the core of the star is
exhausted at the end of the stellar life. Understanding the late stages of
stellar evolution is important for other questions, too. Yellow
supergiants may be the progenitors of core-collapse supernovae, and
understanding supernovae completely has important implications for
cosmology.
Interpreting the HR diagram depends on mathematical models of a star's
interior, which indicate how stars of different masses change with age.
These models, based on knowledge of the physics of nuclear reaction rates,
predict how a star of a given mass will change in temperature and
luminosity over its lifetime. The models require careful comparison with
actual observations.
Suppose curious aliens visited Earth and, from a quick schoolyard survey,
noted that human weight and height increase with age. The
aliens might propose a model for human growth in which weight and height
increase smoothly with age, but this model would not allow for adolescent
growth spurts or middle age. If they compared their model with further
measurements of fast sprouting teenagers, they would be puzzled. This is
akin to the problem astronomers have faced in understanding the red and
yellow supergiants. Previous evolutional models predicted far too many
yellow supergiants. Theoretical yellow supergiants seem to live much
longer than the real stars in nature. This may resonate with those
familiar with star names: it's easy to come up with examples of red
supergiants like Betelgeuse. It is more difficult to think of examples of
yellow supergiants. That's because yellow supergiant lifetimes are
measured in only a few tens of thousands of years.
The Lowell group studied the supergiants in nearby galaxies, rather than
our own Milky Way, to avoid the problems of identifying and characterizing
stars at different distances. First, they selected stars based on their
colours and angular motion across the sky. Then they looked at their
spectra. The spectra show a star's radial velocity: motion towards or away
from us. This is key to deciding which stars are actually foreground red
and yellow stars in our own Milky Way galaxy masquerading as red
supergiants in these other galaxies.
Published version of the LMC paper: ttp://lanl.arxiv.org/abs/1202.4225
Preprint of the M33 paper accepted for publication:
http://lanl.arxiv.org/abs/1203.0247
Text & Images: http://www.noao.edu/news/2012/pr1201.php
-- from a National Optical Astronomy Observatory press release forwarded
by Karen Pollard.
===============================================================
11. Solar 'Climate Change' Could Cause Rougher Space Weather
------------------------------------------------------------
Recent research shows that the space age has coincided with a period of
unusually high solar activity, called a grand maximum. Isotopes in ice
sheets and tree rings tell us that this grand solar maximum is one of 24
during the last 9,300 years and suggest the high levels of solar magnetic
field seen over the space age will reduce in future. This decline will
cause a reduction in sunspot numbers and explosive solar events, but those
events that do take place could be more damaging. Graduate student Luke
Barnard of the University of Reading will present new results on 'solar
climate change' in his paper at the National Astronomy Meeting in Manchester.
The level of radiation in the space environment is of great interest to
scientists and engineers as it poses various threats to man-made systems
including damage to electronics on satellites. It can also be a health
hazard to astronauts and to a lesser extent the crew of high-altitude aircraft.
The main sources of radiation are galactic cosmic rays (GCRs), which are a
continuous flow of highly energetic particles from outside our solar
system and solar energetic particles (SEPs), which are accelerated to high
energies in short bursts by explosive events on the Sun. The amount of
radiation in the near-Earth environment from these two sources is partly
controlled in a complicated way by the strength of the Sun's magnetic field.
There are theoretical predictions supported by observational evidence that
a decline in the average strength of the Sun's magnetic field would lead
to an increase in the amount of GCRs reaching near-Earth space.
Furthermore there are predictions that, although a decline in solar
activity would mean less frequent bursts of SEPs, the bursts that do occur
would be larger and more harmful.
Currently spacecraft and aircraft are only designed and operated to offer
suitable protection from the levels of radiation that have been observed
over the course of the space age. A decline in solar activity would result
in increased amounts of radiation in near-Earth space and therefore
increased risk of harm to spacecraft and aircraft and the astronauts and
aircraft crews that operate them.
By comparing this grand maximum with 24 previous examples, Mr. Barnard
predicts that there is an 8% chance that solar activity will fall to the
very low levels seen in the so-called 'Maunder minimum', a period during
the seventeenth century when very few sunspots were seen. In this
instance, the flux of GCRs would probably increase by a factor of 2.5 from
present day values and the probability of observing a large SEP event will
fall from the presently seen 5 down to 2 events per century.
However, the more probable scenario is that solar activity will decline to
approximately half its current value in the next 40 years, in which case
the flux of GCRs will increase by a factor of 1.5 and the probability of
large SEP events to increase from the current value to 8 events per
century. As a result the near-Earth space radiation environment will
probably become more hazardous in the next 40 years.
In presenting his results, Mr. Barnard comments: "Radiation in space can
be a serious issue for both people and the delicate electronic systems
that society depends on. Our research shows that this problem is likely to
get worse over the coming decades -- and that engineers will need to work
even harder to mitigate its impact."
For text and images see
http://www.jodrellbank.manchester.ac.uk/meetings/nam2012/pressreleases/nam12.html
-- from a Royal Astronomical Society [UK] press release forwarded by Karen Pollard.
===============================================================
12. Earth's Minimoons
---------------------
Earth usually has more than one moon, according to a team of astronomers
from the University of Helsinki, the Paris Observatory and the University
of Hawaii at Manoa.
Our 3000 km-diameter Moon has been orbiting Earth for over 4 billion
years. Its much smaller cousins, dubbed 'minimoons' are thought to be only
a few feet across and to usually orbit our planet for less than a year
before resuming their previous lives as asteroids orbiting the Sun.
The team calculated the probability that at any given time Earth has more
than one moon. They used a supercomputer to simulate the passage of 10
million asteroids past Earth. They then tracked the trajectories of the
18,000 objects that were captured by Earth's gravity.
They concluded that at any given time there should be at least one
asteroid with a diameter of at least one meter orbiting Earth. Of course,
there may also be many smaller objects orbiting Earth, too.
According to the simulation, most asteroids that are captured by Earth's
gravity would not orbit Earth in neat circles. Instead, they would follow
complicated, twisting paths. This is because a minimoon would not be
tightly held by Earth's gravity, so it would be tugged into a crazy path
by the combined gravity of Earth, the Moon and the Sun. A minimoon would
remain captured by Earth until one of those tugs breaks the pull of
Earth's gravity, and the Sun once again takes control of the object¹s
trajectory. While the typical minimoon would orbit Earth for about nine
months, some of them could orbit our planet for decades.
In 2006, the University of Arizona's Catalina Sky Survey discovered a
minimoon about the size of a car. Designated 2006 RH120, it orbited Earth
for less than a year after its discovery, then resumed orbiting the Sun.
The team's paper, "The population of natural Earth satellites" appears in
the March issue of the journal Icarus.
-- From a University of Hawaii Institute of Astronomy press release
forwarded by Karen Pollard.
===============================================================
13. How to Join the RASNZ
-------------------------
A membership application form and details can be found on the RASNZ
website http://www.rasnz.org.nz/InfoForm/membform.htm.
Please note that the weblink to membership forms is case sensitive.
Alternatively please send an email to the membership secretary
members@rasnz.org.nz for further information.
The annual subscription rate is $75. For overseas rates please check with
the membership secretary, member@rasnz.org.nz.
================================================================
14. Gifford-Eiby Lecture Fund
-----------------------------
The RASNZ administers the Gifford-Eiby Memorial Lectureship Fund to
assist Affiliated Societies with travel costs of getting a lecturer
or instructor to their meetings. Details are in RASNZ By-Laws Section H.
For an application form contact the Executive Secretary, secretary@rasnz.org.nz,
R O'Keeffe, 662 Onewhero-Tuakau Bridge Rd, RD 2, TUAKAU 2697
=========================================================
15. Kingdon-Tomlinson Fund
--------------------------
The RASNZ is responsible for recommending to the trustees of the Kingdon
Tomlinson Fund that grants be made for astronomical projects. The grants
may be to any person or persons, or organisations, requiring funding for
any projects or ventures that promote the progress of astronomy in New
Zealand. Full details are set down in the RASNZ By-Laws, Section J.
For an application form contact the RASNZ Executive Secretary, secretary@rasnz.org.nz
R O'Keeffe, 662 Onewhero-Tuakau Bridge Rd, RD 2, TUAKAU 2697
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16. Here and There
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MOST UNUSUAL
The geology around Svalbard and Spitzbergen is most unusual. It has
fossil evidence of trees that lived 300,000 million years ago. -- Exodus
Travels, advertising brochure, 2011 April, p. 11.
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Alan Gilmore Phone: 03 680 6000
P.O. Box 57 alan.gilmore@canterbury.ac.nz
Lake Tekapo 7945
New Zealand
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