WADHURST ASTRONOMICAL SOCIETY
AUGUST NEWSLETTER 2008
INDEX: MEETINGS, OTHER NEWS, CONTACTS
The meeting was
introduced by Phil Berry who reminded members that there is to be a partial
eclipse of the Sun on the morning of Friday 1st of August.
There are fuller details in Brian Mills's Sky Notes for August later in
Phil also invited
members to join the "Angus Group" on Wednesday 23rd July to see what
he has managed to achieve with his observatory so far.
introduced this month's talk.
Goings-on with 3 bodies or more
Talk given to
the July Meeting by James Fradgely from Wessex Astronomical Society
Our speaker had
come all the way from Wimborne in Dorset to give his talk this evening. Wessex is one of the participating members of the Southern
Area Group of Astronomical Societies - SAGAS, and we were delighted to welcome a
fellow society member.
began his illustrated talk by introducing the meeting to the Lagrange Points.
He described the
points as positions in space, which exhibited stable conditions of gravity
around bodies as they orbit around each other.
astronomer Lagrange wrote a paper in 1772 that eventually became known as "Lagrangian
Mechanics" in which he described three points, L1, L2 and L3 as being
points of stable orbits with respect to Earth in its orbit around the Sun.
L1 is a point at
which the Earth's gravitational pull equals that of the Sun and is at 1.5
million kilometres from Earth in line with the Sun.
As the Earth orbits the Sun this point remains in direct line with the
Sun and is a point orbiting at a rate faster than a satellite would normally
orbit in this position.
In fact this is
the position that is home to SOHO the Solar and Heliospheric Observatory placed
in orbit by NASA to monitor the Sun.
By contrast, L2
is on a point in line with the Sun, like L1 but is on the other side of Earth in
a similar orbit.
NASA proposes to
launch a telescope called the James Webb Space Telescope that will orbit 1.5
kilometres from Earth at L2 to gather information about the earliest galaxies.
L3 is exactly
opposite the Sun but in the Earth's orbit.
James said that if there was anything there, we would not know about its
existence. Science fiction writers
suggest this is where aliens, considering an attack on Earth, would gather!
James now turned
to Roche Limits, named after a French astronomer, Eduard Roche who wrote a paper
in the nineteenth century in which he showed that this limit was the distance
within which a body would break up due to the tidal force of another body.
It was explained
that this applied to a body that was loosely held together by its own gravity
rather than a solid body.
mathematical formula for an average comet, the Roche limit would be 34,700 km
for Earth. For Jupiter, it would be 242,000 km and for Saturn it would
be 164,000 km.
We then looked at
the effect on any ring system around a planet.
The rings would have to be in a very flat plane and in the same plane as
the planet's rotation. It is also
suggested that Saturn's rings will last for about another 100 million years
before they are eventually ripped apart.
There are well
known gaps in the rings and James explained how they were created by some of
Saturn's moons. He showed Mimas,
one of the smallest moons with a very distinctive crater named after Herschel. (In fact he first showed the Death Star from "Star
Wars" which also has a similar dimple and quickly moved on, but no one
Mimas acts rather
like a Hoover, bringing material in the rings into some kind of order, leaving
gaps such as the Cassini and Encke gaps.
As the moon
passes, material speeds up or slows down and thus takes up a position on a
slightly different orbit.
We were also
shown the interesting orbits of Epimetheus and Janus, which are co-orbital.
As they orbit Saturn in almost the same orbit, every four years, their
gravity interacts and they change places, only to repeat the event four years
Rosettes refer to many moons forming a circle around a planet, with all moons
having the same period. They
balance each other out and are locked in synchronous orbits.
It works for an even number of moons but will not for an odd number. James illustrated this with a computer simulation that ran
until the orbits became unstable and the moons flew off in different directions.
Still looking at
Resonances, James mentioned that Bode's Law suggests there is a mathematical
relationship between the radii of the planets in the solar system.
The predictions fell very closely to the actual orbits of the planets
with one gap being in the position of the asteroid belt which Bode suggested
cold be the debris of an object.
apart on the discovery of Uranus, which contradicted all that Bode had
predicted, and the law was discredited.
Finally we looked
at Roche Lobes. This is the region
around a star in a binary system of gravitational equilibrium inside which,
material is bound to the star. It
is in the form of a teardrop shape around each star where the points of the
teardrop come together between the two stars at Lagrange point L1.
James used this
to help explain how material from a more massive star gives up material through
the L1 point to a white dwarf; first forming an accretion disk before the
material finally falls into the white dwarf itself giving off recognisable
During his talk
James used many PowerPoint features to great advantage to achieve some very
clear descriptions of what might have otherwise been a very difficult subject to
Our Chairman, John Vale-Taylor thanked James Fradgely who now had to start his journey back to far off Dorset.
REDUCES PAIN IN THE NECK
Vale-Taylor showed a device he had built which had a built-in flat
surface-silvered tilting mirror on a rigid stand.
This stand incorporated a mount to hold binoculars.
binoculars look down onto the mirror, which reveals the night sky without all
that neck aching! The device will
sit conveniently on a table in the garden and prevents all that falling asleep,
whilst reclining on a sun lounger during observations.
did warn of something that had to be taken into account, and that was that the
sky would be vertically reversed, but a number of computer star programmes
include a facility that presents the star map inverted.
The instrument was beautifully built in John's workshop and very well finished. It produced a lot of interest and it is hoped it will be at the Astro-Barbecue on the 23rd of August.
23rd August 2008 There is no
Society meeting in August but Michael Harte and his wife Claire have very kindly
invited the Society to an Astro-Barbecue at Greenman Farm.
weekend is the weekend of the late August Bank Holiday and all members are
the past is has been a very enjoyable event and we usually take the occasional
telescope and binoculars. There is
often the appearance of the latest gadget and members take great delight in
trying them out.
facilities are provided and we need to take just our own food and drink.
suggests that members aim to arrive around 7.00 pm.
Farm, Wadhurst, is on the south side of the B2099 immediately to the west of the
entrance to the farm is through two huge gates and there is plenty of room
inside for parking.
MEETINGS & EVENTS
17th September 2008 At this meeting
there will be a talk by John Punnett, a member of the Orpington astronomical
Society. He calls his talk "An
Enthusiastic Amateur's Journey in Astrophotography".
is worth looking at John's website if
you get a chance.
Members interested in learning a bit about imaging with affordable equipment are encouraged to attend.
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It has been
decided to call the "Hands Group" the Angus Group since it was Angus
Macdonald who suggested starting a group of members interested in meeting
occasionally to discus problems and experiences in building devices to aid
On Wednesday the
23rd of July, a total of ten members met at Phil Berry's home to see what he has
achieved so far with building an observatory in his garden.
We were met by
Phil's wife, Nicky who welcomed everybody with tea and biscuits before Phil
described a few of the problems he had been having with the dome and how he was
Rotating the dome
remotely is what Phil would finally like to achieve and at our previous meeting,
Angus had suggested adapting a car windscreen wiper motor.
Using a bicycle
style chain travelling in a channel made from what looked like curtain track
bent to the right shape and fitted round the inside of the dome.
The chain looped round an appropriate cog on the end of the wiper motor,
Phil demonstrated the rotation of the dome.
Then to achieve
remote, or semi automatic control he had built a timing device with power relays
to drive the motor to achieve the drive.
At present the
dome rotation works perfectly but Phil is still working on a more sophisticated
We were then
shown round the observatory itself. What
Phil has achieved in what seems a very short time shows an enormous amount of
ingenuity and care.
He uses a Vixen
GPD equatorial mount built on a huge piece of concrete beneath the centre of the
floor of the observatory but totally unconnected with the structure to prevent
On the mount he
has two Williams Optic scopes, one is an 80 mm refractor, which uses a rotating
filter wheel and a CCD camera. This
telescope achieves focus using RoboFocus.
Phil uses a high
quality 66 mm William optic scope with a colour SMVX - C high-resolution colour
There are two
guide telescopes to complete the array, one with an illuminated pulsed red
reticule, adjustable to make visibility easier.
The mount is
driven to achieve an error of less than half a pixel.
Phil hopes to be
ready to start imaging this coming winter.
not suitably placed for observation this month.
magnitude -3.9 is moving away from the sun and is becoming an evening object
although it is extremely low in the west after sunset.
not suitably placed for observation this month as it is lost in twilight.
magnitude -2.6 lies in the constellation of Sagittarius (the archer) but is low
in the southeast and sadly will not attain any great altitude this year.
not suitably placed for observation this month.
There are 2
eclipses this month, both partial as seen from the UK - one of the sun and one
of the moon.
Solar Eclipse of
August 1st. All times are BST.
The partial phase
as seen from our area begins at 09.33 and ends at 11.05 with maximum obscuration
(21%) occurring at 10.18. Please remember that you should NEVER look directly at
the sun with ANY type of optical aid unless it is fitted with a good quality
solar filter. Even looking at the sun with the naked eye for extended periods
can cause damage to the eye. The safest method is of course projection where the
image of the sun is allowed to fall onto a piece of card held a short distance
behind the eyepiece. If you cut a hole in another piece of card and fit it over
the front of the telescope it will cast a shadow and allow the image to be seen
much more clearly.
This is actually
a total eclipse as seen from other parts of the world although it is only of
relatively short duration. The track starts in Canada and runs through
Greenland, Russia, Mongolia and China.
Lunar Eclipse of
August 16th. All times are BST.
This is only a
partial eclipse but at maximum 81% of the moon will be immersed in the umbral
shadow and given clear skies we ought to see it turn a red/brown colour. The
moon rises at 20.11 and first contact follows soon after at 20.36 although
sunset is not until 20.21 that evening. Maximum eclipse occurs at 22.11 and the
event finally ends at 23.44. It is rather unfortunate that throughout this
eclipse the moon is fairly low in the sky - around 15 to 20 degrees.
As usual I've only included events for stars down to around magnitude 7.5 that occur before midnight BST. DD = disappearance at the dark limb whilst RD = reappearance at the dark limb. Times are all BST
|August||Time||Star||Magnitude||Phase||Position angle degrees|
Interestingly, there are 16 lunar occultations on the night of the WAS bar-b-q as the moon passes through the Pleiades star cluster. Perhaps a little disappointingly they are all re-appearances, with the first occurring just after 22.15. There are several events of note (listed below) due to the magnitude of the stars involved, the brightest being Alcyone or Eta Tauri.
The others are in the range of magnitudes 6 to 10. The bad news is that the moon only rises at 22.09 - nine minutes before the first event!
|August||Time||Star||Magnitude||Phase||Position angle degrees|
Still on the
subject of occultations there are four events that occur during the lunar
eclipse on August 16th. Unfortunately the stars (that both suffer a
disappearance and a re-appearance) are of magnitudes 9.4 and 9.9 so require a
reasonable sized telescope to see them. Please let me know if you would like
Phases of the Moon for August
|New||First Quarter||Full||Last Quarter|
meteor shower is one of the best to observe because there are a reasonable
number of meteors around maximum (August 12th) and also because usually there is
no need to wrap up warmly. Sadly the moon will interfere this year being full a
few days after maximum although the shower is active from July 23rd until August
20th.In 1992 there was a return of the parent comet (109P/Swift-Tuttle) when
increased activity was observed although the ZHR has now returned the norm of
about 90. The ZHR is the showers Zenithal Hourly Rate and refers to the number
of meteors that could theoretically be seen if the radiant (the point where
meteors appear to emanate from) where at the zenith or overhead point. This is
very rarely the case, so if the radiant is low in the sky the number of meteors
that will actually be seen will be reduced by sky-glow and extinction due to the
amount of atmosphere that we are observing through.
As you can see
there are very few favourable passes of the ISS this month as seen from
Wadhurst. There are others, but they either occur after midnight or attain only
limited altitude. The information given is for when it is at maximum altitude,
so it is best to look a few minutes before this time. Full details of visibility
can be found at:
Times are all BST.
Death of a
By all outward
appearances, the red super giant appeared normal. But below the surface, hidden
from probing eyes, its core had already collapsed into an ultra-dense neutron
star, sending a shock wave racing outward from the star's centre at around 50
million kilometres per hour.
The shock wave
superheated the plasma in its path to almost a million degrees Kelvin, causing
the star to emit high-energy ultraviolet (UV) radiation. About six hours later,
the shock wave reached the star's surface, causing it to explode in a Type IIP
supernova named SNLS-04D2dc
Long before the
explosion's visible light was detected by telescopes on Earth, NASA's Galaxy
Evolution Explorer (GALEX) space telescope captured the earlier pulse of UV
light - scientists' first glimpse of a star entering its death throes.
"This UV light has travelled through the star at the moment of its
death but before it was blown apart," explains Kevin Schawinski, the
University of Oxford astrophysicist who led the observation. "So this light
encodes some information about the state of the star the moment it died."
exactly why astronomers are so excited. Observing the beautiful nebula left
behind by a supernova doesn't reveal much about what the star was like before it
exploded; most of the evidence has been obliterated. Information encoded in
these UV "pre-flashes" could offer scientists an unprecedented window
into the innards of stars on the verge of exploding.
In this case,
Schawinski and his colleagues calculated that just before its death, the star
was 500 to 1000 times larger in diameter than our sun, confirming that the star
was in fact a red super giant. "We've been able to tell you the size of a
star that died in a galaxy several billion light-years away," Schawinski
played a very important role in actually seeing this for a few reasons,"
Schawinski says. First, GALEX is a space telescope, so it can see far-UV light
that's blocked by Earth's atmosphere.
Also, GALEX is
designed to take a broad view of the sky. Its relatively small 20-inch primary
mirror gives it a wide, 1.2-degree field of view, making it more likely to catch
the UV flash preceding a supernova.
advantages, GALEX is uniquely equipped to catch a supernova before it explodes.
"Just when we like to see it," Schawinski says.
Gives View Inside Real 'Death Star'." Kids can check out how to make a
mobile of glittering galaxies at:
This article was provided by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.
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Chairman John Vale-Taylor
Phil Berry 01892 783544
Mike Wyles 01892 542863
Website Michael Harte 01892 783292
Newsletter Editor Geoff Rathbone
Any material for inclusion in the September 2008 Newsletter should be with the Editor by August 28th 2008
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