WADHURST ASTRONOMICAL SOCIETY

DECEMBER NEWSLETTER 2006

INDEX: MEETINGS, OTHER NEWS, CONTACTS

MEETINGS

COMMITTEE MEETING

Committee Members are respectfully reminded that there is a meeting of the Committee on Monday the 8th of January at 2000 in the Abergaveny Arms, Frant, on the A267 just south of Tunbridge Wells.  Any member of the Society is always welcome to join us.

A NEED FOR NEW COMMITTEE MEMBERS

As mentioned at the last meeting, the Society needs one or two new members on the Committee.  We meet for about an hour four times a year and it is always convivial, but we could do with more members to bounce ideas off.

Any member interested to joining us can just turn up at the above committee meeting or talk to one of the committee members shown at the end of the Newsletter.

NOVEMBER MEETING  

Greenwich Time

Talk given by DAVID ROONEY, Curator of Timekeeping at Greenwich Royal Observatory on the 15 November 2006 to the Wadhurst Astronomy Society meeting

This was a fascinating talk covering 330 years at the Greenwich Royal Observatory, which was founded to set up and maintain the time standards. When the skies became too polluted, the astronomical work moved to Herstmonceux and Greenwich became a Museum. It is now halfway through a major re-organisation. They have created a whole suite of new Time Galleries that are already open to the public. Early next year the Astronomy Centre, complete with Planetarium will be opening.

The Museum

The new Time Galleries have trebled the number of artefacts on show, many of which have not been seen by the public previously. Much to the curator's delight, they have won the 2006 award from the Society of History of Technology.

The first section has the theme of 'Longitude and Time', a subject of great importance for navigation. They have Harrison's Time Keeper as well as many manuscripts on his work. The Astronomer Royal of that time discovered an alternative solution for finding longitude by observing Lunar Distance.

The second section is about Greenwich Mean Time and how it is referred to from all over the world.

The third section covers Time and Society - how we experience time in daily life with sundials, clocks, etc..

The last section concentrates on Time for the Navy, and is housed in the building where all chronometers for all naval ships were tested. Also in this building behind glass is the Horology Workshop where repairs are carried out.

Facts about Greenwich

The Prime Meridian, defined by diplomats in 1884, passes through Greenwich. Its most popular attraction today is as a place to pose for a photograph! Even when the Museum is closed, there is a brass strip on the ground outside which fulfils the same function.

The 6 pips for the Greenwich Time Signal on the BBC were started in 1924. In its first 2 years the BBC had tried several ways of announcing the time as kept at Westminster. This included playing the chimes on a piano, which was later replaced with a set of tubular bells tuned to Westminster. If the wind was in the right direction and the window was open, they could play along with Big Ben! In 1924 Frank Hope-Jones initiated using Greenwich Observatory Time to send a signal to the BBC to sound the pips. A Dent pendulum clock was used for the Observatory Time. It had electrical contacts to send signals along a landline to the BBC at the right moment. It was the responsibility of astronomers to make sure the clock was accurate. When the Observatory moved to Herstmonceux, the 6 pips clock moved too. Eventually, instead of a pendulum clock, quartz and then atomic clocks were used. At this stage the accuracy of the clock became the responsibility of physicists. By the time the Observatory moved again, this time to Cambridge, the BBC could provide their own signal and there were no more Greenwich pips. At the BBC, the pips machine is in the basement and controlled by a rubidium atomic clock. It checks with GPS satellites which means Greenwich time now comes from the Naval Observatory in the US.

On the roof at the Greenwich Observatory there is a Time Ball which functions at 1.00pm every day. 5 minutes before the exact time, a large Time Ball is raised halfway up a mast. At 3 minutes to go, it is hauled to the top of the mast. At exactly 1.00, the ball is released. Ships in the river could see the signal and check their chronometers.

From 1836 to 1939 the Belleville family sold 'time'. Once a week they took a pocket chronometer to the Observatory and set the time accurately. They then went around the city of London checking the time on clocks for all the important people.

Gibraltar had a Time Ball as did many Signal stations around the world. They were connected to Greenwich by landlines to make sure the Time Ball dropped at the right moment. Actually, there was a good clock at each station which was kept regular by the landline. The clock dropped the ball. If for any reason the landline was down, the clock was good enough for several days to time the drop.

Pendulum clocks were followed by quartz clocks then atomic clocks and now the optical clock, the most accurate ever. A pendulum clock is based on the rotation of the earth. Atomic clocks, since 1955, depend on the properties of a material. They are synchronised with the rotation of the earth by adjustments of leap seconds. The USA want to break the connection between time and rotation but this is being rigorously opposed by the Royal Astronomical Society in the UK. The USA suggest introducing leap-hours. This would complicate all the many well related times, GMT, sidereal time, Universal time, etc. and leave just one standard atomic time.

An atomic clock is accurate to (1 second in 300 years. The latest invention, an optical clock, will be accurate to ( 0.5 seconds in 15 billion years!

An optical clock is being built at the National Physical Laboratory. Although it involves a large amount of equipment, at the heart of the clock is a trap, a small enclosure where a single atom is held by laser beams. This effects the atom's excitation and spin, and somehow measures time! The original trap is now on display in the museum.

Why do we need precision clocks?  We use them everyday in mobile phones, computers, transmission lines and satellite navigation. A GPS system tells you the time and where you are to within 10 metres. There are 24 satellites each with 3 atomic clocks sending time signals to earth. If you can see 4 satellites, by comparing their time signals, you can know your position. If one of the atomic clocks is out by (.001 seconds, the error in the position is 3000 kilometres - not good enough for landing on an aircraft carrier.

If you stand on the meridian line at Greenwich with a GPS, it will tell you that the meridian is 100 meters to the east! The position is marked by a litter-bin. The USA have derived this from a statistical solution of a geodetic sphere. If you can switch to 'Ordnance Survey', you will be relieved to find that the Meridian is back on the line.

Rugby Radio Station was the first ever MSF clock in the 1920s for communicating with ships. The origin of MSF may be a radio call sign or as British Telecom call it, Modulated Standard Frequency. Rugby Radio will be moving to an unmanned site in Cumbria next year.

The Museum have acquired what they now believe to be the oldest surviving quartz clock from the 1940's. It has been restored to working condition again despite a history of languishing in rubbish skips and cupboards. It is run for a few hours each week but cannot be left unattended as the heat from the valves makes it rather a fire hazard.  

TIM the Speaking Clock is still going strong, receiving more and more callers as the years go by.

From the early 17th century, very good clocks were needed for navigation and to get the star maps correct. Each place had its own Local Time determined by the sun. With the coming of the railways, it became necessary for all stations and signals along a route to use the same time. In 1840 Greenwich Mean Time was introduced as the standard time for a zone. As well as Greenwich dropping a Time Ball once a day, a signal was sent every hour to the railways.

In space ships, the relativistic effects make clocks go faster or slower depending on speed and gravity. The optical clock is so sensitive that it needs to be corrected if is lifted higher.

Finally, there is a problem with digital radio and television transmissions. The time signal always arrives later than on an analogue signal and is therefore useless. Different digital signals have different delays because they have different chips in them. The BBC says they can't do much about it except join the lobby for a common delay. Then they could send the pips early, to arrive on time. The government is planning to turn off analogue television at some future date so we might lose all reliable time signals.

Joan Grace

DECEMBER MEETING

Wednesday 13th December 2006.  Note that this will be second Wednesday of the month.  Phil Berry, a member of the Society is giving a talk he calls "The Trials and Tribulations of an Amateur Astronomer".  A subject that should be of interest to everyone either bringing back memories of past experiences or forewarning of things to come...

This is our last meeting before Christmas and following Phil's talk we are invited to enjoy mince pies and beverages provided by the Society and have chance to chat with other members of the Society.

FUTURE MEETINGS

Wednesday 17th January 2007  The talk is given by Bob Seaney, one of our Society members and the title of his talk is "The Astronomical Art of Chesley Bonestell - Destination Moon (1953) Highlights".  Chesley Bonestell is regarded as the father of modern space art.

This will be followed by the Society's Annual General Meeting, which takes place in January for the first time.

Wednesday 21st February 2007  Ian King presents a talk he calls "The GranTeCan" which might have something to do with a trip he took recently.

Wednesday 21st March 2007  Our guest speaker will be Dr. Stephen Serjeant and his talk is called "The Big Questions in Cosmology".

Wednesday 18th April 2007 Jerry Workman will return to update the Society with the progress of Mars Express.

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OTHER NEWS

SUBSCRIPTIONS

Subscriptions become due on the 1st of January 2007 for the coming year.  Subscriptions remain the same as previous years at 15 per member and 20 for two members within the same family.

DECEMBER NIGHT SKY  

The Geminids meteor shower reaches its peak at 0500 on the morning of December the 14th.   At previously there have been up to seven or eight meteors per hour at the peak.

The December night sky is dominated by the constellation of Orion the Hunter with Lepus the rabbit beneath his feet and followed from the east by Canis Major the dog.

Orion is probably the best-known constellation in the northern hemisphere because of its easily recognisable shape and its position in the darkest skies of the winter.

The most recognisable feature is made up of the three hot white stars that make up Orion's belt.  From the left is Alnitak, at 800 light years, Alnilam, 1,400 light years away and Mintaka, at 900 light years, all with apparent magnitudes of about +2 which indicates just much more powerful Alnilam is, although these three stars point left to Sirius, the brightest star in the night sky which appears in the dog collar of Canis Major and therefore often called the Dog Star.

Sirius has an apparent magnitude of -1.44 and yet is 1020 light years away.

The red star in the top left of Orion (is right shoulder) is the red giant Betelgeuse that is so massive that if it were where our Sun is, the orbit of Mars would be well inside it!  Betelgeuse is 427 light years away.

The top right star in Orion is Bellatrix and to bottom left is Saiph representing Orion's right foot.

The bright star bottom right is Rigel with an apparent magnitude of +1.8, at a distance of 772 light years.  Rigel is a white super giant and shines 40,000 times the luminance of our Sun.  Rigel is a triple star. The main star is orbited by a binary system, Rigel B and C, which orbit one another closely at 28 AU (Astronomical Unit: the distance between the Earth and the Sun) and in turn orbit around Rigel as a unit, at a distance of about 2000 AU.

Below Alnitak is the naked eye nebula M42, often referred to as the jewel in Orion's sword and is the nearest birth place of stars to the Earth at 1,500 light years away.  It is estimated to be about 30 light years across.  The red glow is the result of ionised hydrogen, but the slight green glow is now thought to be the result of a low-probability electron transition in doubly-ionized Oxygen, a so-called "forbidden transition" not easily reproducible in an Earth based laboratory.

The angular distance between the stars in Orion's belt is about one and a half degrees.  One of the hardest challenges for the amateur astronomer is the Horsehead nebula, to be found about half a degree beneath the left hand star, Alnitak.  It and is a dark nebula, seen against the background of ionised hydrogen and certainly lives up to its name.  I have only ever seen it once through my 11-inch reflecting telescope but it was a very satisfying occasion.

Just a note in passing, during the day in the middle of December, the Sun is in line with centre of our galaxy as viewed from Earth but the most recent estimate of its distance from the Solar System is about 26,000 light years.  Just as well if, as suggested, the centre harbours a hungry black hole!

AN UNUSUAL EVENT IN CASSIOPEIA

The editor has received the following note from the British Astronomical Association:

Did you photograph the "W" of Cassiopeia in October?

A star (GSC 3656-1328 at RA 00 09 22 Dec +54 39 44 (2000)) recently brightened from approx. magnitude 11.5 to as bright as magnitude 7.5 on Halloween night!  (This is in the western end of the "W" of Cassiopeia)

Since its discovery in late October the star has been intensely studied by amateurs, professionals and observing time of orbiting telescopes has even been allocated to observe this object!  We have very little coverage of this object before discovery, so any image taken of this field in October can tell us a great deal about how this star behaved before the start of intense coverage.

If you photographed this field at any time of the month of October, your image has scientific value.  It can be an image taken with film, digital SLR, CCD... anything.  Even a wide field shot taken with a short focal length lens can reach deep enough to show the presence or absence of a star of the brightness we're talking about.

Why all the fuss about one star?  It appears to be a very unusual event: possibly a gravitational microlensing event.  (Spectra of the star don't show the typical signs of an exploding/outbursting star, and the light curve from late October to mid-November appear to fit what one would expect for a microlensing event.  But more data is needed to provide the best possible analysis and conclusion about this event)

If by any chance any member is lucky enough to have such an image, please let the Editor know.

NASA SPACE PLACE

Staggering Distance

By Dr. Tony Phillips

Tonight, when the sun sets and the twilight fades to black, go outside and look southwest.  There's mighty Jupiter, gleaming brightly.  It looks so nearby, yet Jupiter is 830 million km away.  Light from the sun takes 43 minutes to reach the giant planet, and for Earth's fastest spaceship, New Horizons, it's a trip of 13 months.

That's nothing.

Not far to the left of Jupiter is Pluto.  Oh, you won't be able to see it.  Tiny Pluto is almost 5 billion km away.  Sunlight takes more than 4 hours to get there, and New Horizons 9 years.  From Pluto, the sun is merely the brightest star in a cold, jet-black sky.

That's nothing.

A smidgen to the right of Pluto, among the stars of the constellation Ophiuchus, is Voyager 1.  Launched from Florida 29 years ago, the spacecraft is a staggering 15 billion km away. It has travelled beyond all the known planets, beyond the warmth of the sun, almost beyond the edge of the solar system itself.   

Now that's something.

"On August 15, 2006, Voyager 1 reached the 100 AU mark-in other words, it is 100 times farther from the Sun than Earth," says Ed Stone, Voyager project scientist and the former director of NASA's Jet Propulsion Laboratory.  "This is an important milestone in our exploration of the Solar System.  No other spacecraft has gone so far."

At 100 AU (astronomical units), Voyager 1 is in a strange realm called "the heliosheath." 

As Stone explains, our entire solar system-planets and all-sits inside a giant bubble of gas called the heliosphere.  The sun is responsible; it blows the bubble by means of the solar wind.  Voyager 1 has travelled all the way from the bubble's heart to its outer edge, a gassy membrane dividing the solar system from interstellar space.  This "membrane" is the heliosheath.

Before Voyager 1 reached its present location, researchers had calculated what the heliosheath might be like.  "Many of our predictions were wrong," says Stone.  In situ, Voyager 1 has encountered unexpected magnetic anomalies and a surprising increase in low-energy cosmic rays, among other things. It's all very strange-"and we're not even out of the Solar System yet."

To report new developments, Voyager radios Earth almost every day.  At the speed of light, the messages take 14 hours to arrive.  Says Stone, "it's worth the wait."

Keep up with the Voyager mission at voyager.jpl.nasa.gov.  To learn the language of Voyager's messages, kids (of all ages) can check out

 spaceplace.nasa.gov/en/kids/vgr_fact1.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   Tim Bance  01732 832745 timbance@hotmail.com

Phil Berry  01892 783544 phil.berry@tiscali.co.uk

Treasurer  Mike Wyles  01892 542863 mikewyles@globalnet.co.uk

Publicity & Website  Michael Harte  01892 783292 michael@greenman.demon.co.uk

Newsletter Editor  Geoff Rathbone  01959 524727 Geoff@rathbone007.fsnet.co.uk

Any material for inclusion in the January Newsletter should be with the Editor by December 28th  2006

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