WADHURST ASTRONOMICAL SOCIETY

AUGUST NEWSLETTER 2008

INDEX: MEETINGS, OTHER NEWS, CONTACTS

MEETINGS

JULY MEETING

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 the Newsletter.

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.

He then introduced this month's talk.

Strange 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.

James Fradgely 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.

The French 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.

From a 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 seemed react...)

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 later.

Klemperer 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.

Everything fell 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 radiation.

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 follow.

Our Chairman, John Vale-Taylor thanked James Fradgely who now had to start his journey back to far off Dorset.

CHAIRMAN REDUCES PAIN IN THE NECK

John 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.

The 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.

John 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.

THE ASTRO-BARBECUE

Saturday 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.

This weekend is the weekend of the late August Bank Holiday and all members are welcome.

In 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.

Barbecue facilities are provided and we need to take just our own food and drink.

Michael suggests that members aim to arrive around 7.00 pm.

Greenman Farm, Wadhurst, is on the south side of the B2099 immediately to the west of the railway over-bridge.

The entrance to the farm is through two huge gates and there is plenty of room inside for parking.

FUTURE MEETINGS & EVENTS

Wednesday 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".

It 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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  OTHER NEWS  

THE ANGUS GROUP

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 astronomical observing.

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 solving them.

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 drive.

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 any vibration.

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 CCD camera.

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.

SKY NOTES FOR AUGUST

Planets

Mercury is not suitably placed for observation this month.

Venus at 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.

Mars is not suitably placed for observation this month as it is lost in twilight.

Jupiter at 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.

Saturn is not suitably placed for observation this month.

Eclipses

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.

Lunar Occultations

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

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!

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 more details.

Phases of the Moon for August

Meteors

The Perseid 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.

ISS

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:

www.heavens-above.com

Times are all BST.

Brian Mills

NASA SPACE PLACE

Death of a Supergiant

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."

And that's 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 marvels.

"GALEX has 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.

With these advantages, GALEX is uniquely equipped to catch a supernova before it explodes. "Just when we like to see it," Schawinski says.

For more information, visit: www.galex.caltech.edu

"Ultraviolet Gives View Inside Real 'Death Star'." Kids can check out how to make a mobile of glittering galaxies at: spaceplace.nasa.gov/en/kids/galex_make1.shtml

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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CONTACTS

Chairman   John Vale-Taylor 

Phil Berry  01892 783544

Treasurer  Mike Wyles  01892 542863

Publicity & Website  Michael Harte  01892 783292

Newsletter Editor  Geoff Rathbone  01959 524727

Any material for inclusion in the September 2008 Newsletter should be with the Editor by August 28th  2008

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