WADHURST ASTRONOMICAL SOCIETY
MAY NEWSLETTER 2008
INDEX: MEETINGS, OTHER NEWS, CONTACTS
Bits and Bobs
Talk given by
Greg Smye-Rumsby at the April meeting
is a member of the Orpington Astronomical Society and also presents illustrated
talks at the Greenwich Planetarium. He
is also well known to readers of Astronomy Now as the resident technical
illustrator and many of his skills were put to use in his talk.
Greg began his
talk by saying that he liked to call his talk "Bits and Bobs" so that
he could decide at the very last moment what the subject should be.
In this case he was going to talk about the moon.
The moon is about
a quarter the size of the Earth and it would be possible to lay 29 earths in a
line between the moon and us.
To give an idea
of dimensions, Greg held a globe in his hands saying that if this was the earth
(about 20 centimetres in diameter) then the International Space Station is
orbiting inside his fingers because its orbit is so shallow.
We then looked at
drawings made by Galileo who was one of the few people to have only seen rocks
whilst others claimed to have had seen trees and creatures.
The moon is
mainly made up of craters, mountains and seas.
The seas are the results of ancient volcanic activity, with the craters
being formed by impacts over billions of years.
Greg said that virtually all lunar craters are circular suggesting that
they were the formed by vertical impacts.
experiments show that impact angles of less than 4 degrees where the only ones
to produce elongated craters and there were very few of them to be found.
Just south of
Mare Crisium in Mare Fecunditatis are two such craters called the Messier Twins.
The craters are elongated, and leading to them is a pair of long streaks
across the surface of the moon looking as though whatever struck the moon had
scraped the surface before impact.
believes that there is still some evidence of active lava flows.
imaginary large sack of Lego poured out over the floor; Greg invited us to
imagine how the pile would spread out over the floor in an attempt to simulate
the creation of the Solar System.
At the centre of
the pile, there is enough material to build a sphere (the Sun) but further out,
the pile thins and there are now not enough bricks to form more than planets.
explanation of why the inner planets are not gas planets like those further out
such as Jupiter, Saturn, Uranus and Neptune is because any gas that had
surrounded the inner planets was drawn off by the Sun's incredible gravity.
It is now thought
that, in its early stage the Earth was struck by an object about half its size,
which vaporised rock. From the
debris, the Earth reformed but now had a moon.
This moon had a plastic core with the result that there was no magnetic
field. Also, the moon never had any
After time the
moon settled and just presented one face to the Earth.
The moon's orbit
around the Earth is slightly elliptical and tilts by about 5.1 degrees from the
Earth's own orbit around the Sun. This
means that as the moon orbits the Earth, it is possible to see slightly more of
the moon's face than if the moon's orbit had been a perfect circle. This is known as the moon's libration. It means that we can actually see 59% of its surface despite
being in a synchronous orbit.
fact Greg pointed out was that over the next few months the orbit of the moon
takes it through M44, a cluster in the constellation of Cancer, creating a
number of lunar occultations. (More
of occultations at our May meeting!)
We were shown
images of the Zimbabwe solar eclipse taken in 2001 where, by adjusting the
exposure, it was possible to make out lunar surface details lit by Earth Shine.
It was also pointed out that solar eclipses were only visible through the
incredible coincidence of the angular size of both the Sun and the moon are
almost exactly the same.
We saw a slide of
the phenomenon known as Bailey's Beads caused by the Sun appearing between the
mountains on the moon just as the Sun becomes visible after total eclipse.
his talk by referring to a couple of illusions.
The apparent subjective size of the moon when close to the horizon
compared with when it is high in the night sky near the zenith where the human
eye has no earthly reference makes the brain over compensate, making the moon
appear much larger when low down.
illusion involves astronauts on the surface of the moon where there is no
atmosphere so there is no atmospheric mist.
The result is that mountains look as though they are a couple of
kilometres distant while in fact they are more likely to be at least 25
May 2008 Our own Brian Mills, who contributes the excellent Sky Notes each
month, is giving a talk about "Occultations".
For some time Brian has observed occultations and helped to take accurate
time measurements of the events. These
measurements are then coordinated at an international centre.
begins at 1930 although members are invited to arrive anytime after 1900. This is a good time to exchange ideas and discuss problems.
The venue as
always is in the Upper Room of the Methodist Church at the east end of Wadhurst
Lower High Street, opposite Uplands College.
(For those with SatNav - the
Post code is TN5 6AX)
MEETINGS & EVENTS
During June: A trip is being arranged to visit the Great Transit Circle at
Greenwich Observatory. This will be
either Friday 13th or 20th of June.
June 2008 Because this is one of the shortest nights of the year, in recent
years the Society has held a members evening when we can bring telescopes,
binoculars and other aids to amateur astronomy and chat about their use and
discuss problems. There will also
be a short video on an astronomical subject.
More information nearer our June meeting.
Wednesday 16th July 2008. There will be a talk given by James Fradgley called "Orbital Oddities - Strange Goings-on with 3 or more bodies" covering Lagrange Points, Resonances, Roche Limits, and lots of odds and ends with simulations. James is a member of the Bournemouth Natural Science Society in Dorset.
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Observatory Greenwich has not yet confirmed the June date for our visit.
Almost certainly it will be Friday 20th of June, although the 13th still
remains our back-up date. We hope
to know by our May meeting.
At present the 16
members who have shown an interest in going are:
Douglas Hall Michael Harte Geoff Lezemore Mrs. Lezemore
Angus Macdonald Brian Mills Gavin Mills Larry Mowat
Geoff Rathbone John Vale-Taylor Michael Wyles
Any other member
interested in adding their name should contact Phil Berry or Geoff Rathbone.
The event is free
apart from the planetarium although members need to make their own travel
List" on a clipboard is available at each meeting and is for members to use
when asking for help or information. This
is a useful way of introducing problems being experienced and queries by
SAG AS NOTE
There is to be a
SAGAS Summer Meeting on Saturday 19th June 2008 and it is being hosted by the
Basingstoke Astronomical Society.
It is a long way
and the cost is £10 but there are talks and trade stands.
The event is open
from 1300 until 1900 and members of the Wadhurst Astronomical Society are
welcome although there is limited space.
is available through the link to be found on the SAGAS website at:
NOTES FOR MAY
at its most favourable this month as far as evening observing is concerned;
however early risers in October will see the best morning apparition. By mid May
Mercury will set two hours after the sun at around 22.50 BST and can be found
low down near the west-north-west horizon at magnitude +0.4. If you intend to
sweep for it with binoculars, make sure that the sun has set before you do so.
too close to the sun for observation this month.
magnitude +1.3 by the middle of the month is still fading in brightness as the
distance between us increases. The red planet crosses the border between Gemini
(the twins) and Cancer (the crab) as it moves steadily eastwards.
magnitude -2.4 in the constellation of Sagittarius (the archer) will be low in
the sky for the entire year. It is a morning object rising around 01.00 BST in
the middle of the month but only manages a maximum 17° above the horizon when
lies in the constellation of Leo, close to Regulus (a Leonis) the bright star at
the bottom of the asterism that looks like the mirror image of a question mark.
On May 3rd it is stationary before beginning its eastward motion once more. At
magnitude +0.6 it is still a prominent evening object but by the middle of May
it will set just before 03.00 BST.
Occultation of Mars
|New||First Quarter||Full||Last Quarter|
Below are details
of the most favourable passes of the ISS this month that occur before midnight
as seen from Wadhurst. 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: - www.heavens-above.com
|Date in May||Magnitude||Time||Altitude||Azimuth|
Compass for Space Explorers
by Patrick L.
In space, there's
no up or down, north or south, east or west. So how can robotic spacecraft know
which way they're facing when they fire their thrusters, or when they try to
beam scientific data back to Earth?
familiar compass points of Earth's magnetic poles, spacecraft use stars and
gyros to know their orientation. Thanks to a recently completed test flight,
future spacecraft will be able to do so using only an ultra-low-power camera and
three silicon wafers as small as your pinky fingernail.
are actually very tiny gyros," explains Artur Chmielewski, project manager
at JPL for Space Technology 6 (ST6), a part of NASA's New Millennium Program.
use spinning wheels to detect changes in pitch, yaw, and roll-the three axes of
rotation. For ST6's Inertial Stellar Compass, the three gyros instead consist of
silicon wafers that resemble microchips. Rotating the wafers distorts
microscopic structures on the surfaces of these wafers in a way that generates
electric signals. The compass uses these signals-along with images of star
positions taken by the camera-to measure rotation.
Inertial Stellar Compass (ISC) is based on this new, radically different
technology, NASA needed to flight-test it before using it in important missions.
That test flight reached completion in December 2007 after about a year in orbit
aboard the Air Force's TacSat-2 satellite.
performed beautifully," Chmielewski says. "The data checked out really
well." The engineers had hoped that ISC would measure the spacecraft's
rotation with an accuracy of 0.1 degrees. In the flight tests, ISC surpassed
this goal, measuring rotation to within about 0.05 degrees.
paves the way for using ISC to reduce the cost of future science missions. When
launching probes into space, weight equals money. "If you're paying a
million dollars per kilogram to send your spacecraft to Mars, you care a lot
about weight," Chmielewski says. At less than 3 kilograms, ISC weighs about
one-fifth as much as traditional stellar compasses. It also uses about one-tenth
as much power, so a spacecraft would be able to use smaller, lighter solar
Draper Laboratory, the Cambridge, Massachusetts, company that built the ISC, are
already at work on a next-generation design that will improve the compass's
accuracy ten-fold, Chmielewski says. So ISC and its successors could soon help
costs-and spacecraft-stay on target.
Find out more
about the ISC at nmp.nasa.gov/st6. Kids
can do a fun project and get an introduction to navigating by the stars at:
was provided by the Jet Propulsion Laboratory, California Institute of
Technology, under a contract with the National Aeronautics and Space
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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 June 2008 Newsletter should be with the Editor by May 28th 2008
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