WADHURST ASTRONOMICAL SOCIETY

OCTOBER NEWSLETTER 2006

INDEX: MEETINGS, OTHER NEWS, CONTACTS

MEETINGS

COMMITTEE MEETING

Members of the Society's Committee are respectfully reminded that there will be a meeting of the Committee on Monday October 9th 2006 at the Abergavenny Arms, Frant, beginning at 2000.

As always, any members of the Society are very welcome to come along and join us for a chat and a drink.  The meetings usually last about an hour.

SEPTEMBER MEETING

After briefly talking about our own Sun and describing it as a "G" type dwarf star, Konrad Malin-Smith compared it with a White Dwarf whose mass is rather similar to our Sun's mass but whose size is about that of the Earth.

He pointed out the position of White Dwarfs on the Hertzsprung-Russell diagram where they leave the main sequence stars because of their much higher temperature and low luminosity.  To illustrate this, Konrad projected a photograph of Sirius, the Dog Star in Canis Major.  This is the brightest star in the night sky at magnitude -1.47 although its position varies very slightly over time.  Then we were shown a highly magnified photograph of the same star and barely visible was a companion, Sirius B affectionately known as "The Pup", with a magnitude of +8.44.

Over 150 years ago a German mathematician, Frederick Bessel used the orbit of the Earth to measure the parallax of the star Cygni 61 and so was able to measure its distance.  He used his method of precise measurement in 1844 to detect the slight movement of Sirius A and this led to the discovery by Alvan Clark of Sirius B in 1862.  Later this faint companion was identified as the first White Dwarf to be discovered.

Konrad then used the white star Rigel, the foot of Orion to locate 40 Eridani, also known as Omicron Eridani.  This is a warm star with a White Dwarf orbiting about it in 248 years and at a distance similar to that of Uranus from the Sun.  In 1925, Arthur Eddington devised a method of blanking out the light from the star to actually reveal the White Dwarf.

It was Eddington who suggested that the spectrum of the white dwarf had been red-shifted by gravity. Up until now red shift had been associated only with receding stars but Albert Einstein developed a new theory.  The density of the white dwarf is calculated to be about 20 tons per cubic inch and Einstein proposed that the gravity also causes the red shift, known as the Einstein Shift. 

With the use of an overhead projector, Konrad explained that Electron Degeneracy Pressure is a force such that two electrons cannot occupy the same quantum state at the same time in the same area.  This force sets a limit to the amount of matter that can be squeezed together.  This factor is important because it prevents the White Dwarf collapsing further.

An interesting fact that Konrad mentioned is that White Dwarfs have been around from the very early stages of the Universe and none have yet died completely.

We looked at the precursor to the White Dwarf in the form of a helical nebula where hydrogen had been thrown off a massive star and looking rather like a circle of pink cloud when viewed end-on.   We see a number of such rings because of our relative position as viewed from the Earth.

At the centre of this ring of gas is a central star that has shed its outer layer of hydrogen and now has a temperature of 100,000 degrees and is producing heavy radiation.  This star will eventually become a white dwarf.

The example we looked at was in M4 close to Antares.  M4 is a cluster consisting of about 150,000 stars with 40,000 very old white dwarf stars.  Because they are in a cluster they are all at the same distance from us and thus can be compared with each other with this in mind.

One night whilst observing Cygnus, Konrad saw a bright object, which was a Nova just occurring and fortunately had his camera with him at the time.  This Nova was visible for the next 80 days.

Konrad now explained how a Nova occurs when a White Dwarf orbits a red star, sucking off the hydrogen, forming a disk before falling into the dwarf.  The example of a pair we were shown orbited each other in just 41/2 days with a distance between the pair of just a few thousand miles.  When the layer of hydrogen on the dwarf reaches about 10 miles in thickness, the layer becomes unstable and is blown off, resulting in a nuclear reaction, which results in the brightening we see as a Nova.

Finally Konrad talked of an event witnessed in the central bright area of M31, the Andromeda Galaxy in 1865 when an obvious bright spot was observed.  At first astronomers thought it was something within our own galaxy, but then it was realised that it was in fact a Super Nova taking place 2.9 million light years away!

Once again Konrad Malin-Smith had left us with plenty to think about but had presented his subject in a clear but entertaining way.  His equations can be found here and here.

OCTOBER MEETING

The next Society meeting is on Wednesday 18th October 2006 when Jerry Workman will be paying us another visit and this time talks about the latest news from Mars.

As usual, the meeting will be held in the Upper Room of the Methodist Church, the High Street, Wadhurst, opposite Uplands College. The meeting commences at 1930.

FUTURE MEETINGS

Wednesday 15th November 2006.  David Rooney, who is the Deputy Horologist at Greenwich Museum, is to give us a talk called "A Brief History of GMT".  The new Time Galleries opened last February as part of the improvements to the Museum.

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".   

This will be followed by mince pies and beverages!

Wednesday 17th January 2006  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"

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

 

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OTHER NEWS

OCTOBER NIGHT SKY

The nights are getting longer now and early on the morning of Sunday 22nd of October the clocks go back giving the astronomer a whole hour earlier to begin observing, although the only notable planet at present is Saturn, which can be seen just before sunrise.  Because of our relative positions in the Earth's and Saturn's orbits, we are now looking down onto the northern latitudes of the planet, which we haven't been able to do for some years.  The rings are now beginning to close as we view them but they don't completely close until early in 2009.

Venus, Mars and Mercury are hidden behind the Sun this month and Jupiter is now lost in the light of the evening sky.

Neptune now has a magnitude of +7.9 and is amongst the stars of Capricornus, about a degree northwest of Iota Capricornus, but will need a pair of good binoculars to see it.

Uranus is almost due south in Aquarius late evening during the month of October and is half a degree beneath Lorenzin Lambda (magnitude +3.7) at an altitude above the horizon of about 30 degrees.  Uranus has an apparent magnitude of +5.8 at present, although right at the beginning of the month, the moon passes within a degree on the 5th, which will obscure it.

I see Pluto is now officially identified as a "Dwarf Planet" along with 2003 UB313, the recently discovered "object".

Towards the end of the month, the Orionid meteor shower takes place, with a peak around the 20th to 22nd of October as we pass through the debris of the tail of one of Halley's comets.  At this time of year the Earth is moving in a direction close to the position of Betelgeuse in the constellation of Orion.  The "Radiant", or apparent origin of the meteors is just above Betelgeuse.  They are fairly bright and there can be up to 15 trails an hour at their peak.

Many years ago I charted the Orionids, placing the trails as accurately as I could on a copy of a star chart, and most of the meteors obviously radiated from the same origin close to Betelgeuse.  I observed them for two hours and had some help, but at the time I thought it was all worthwhile.

REFRACTING TELESCOPE FOR SALE

Ian Reeves' refracting telescope is for sale for 150.  Ian brought it to several Society meetings and it is certainly more than ideal for anyone starting off in astronomy particularly as the nights are drawing out now and the whole of the winter constellations will soon be there such as the winter constellation of Orion and its many interesting treasures.

The telescope is a Konus 120 mm achromatic refracting instrument with a manual equatorial mount and tripod.  Amongst the accessories are a star-diagonal and a number of eyepieces.  The Instrument comes in its own substantial travelling case.

In the past, experienced members of the Society referred to the optics as exceptionally good.

Further information can be obtained from Mavis, Ian Reeves' widow, on 01892 784255 or from Phil Berry on 01892 783544.

NASA SPACE PLACE

Snowstorm on Pluto

by Dr. Tony Phillips

There's a nip in the air. Outside it's beginning to snow, the first fall of winter.  A few delicate flakes tumble from the sky, innocently enough, but this is no mere flurry. 

Soon the air is choked with snow, falling so fast and hard it seems to pull the sky down with it. Indeed, that's what happens. Weeks later when the storm finally ends the entire atmosphere is gone.  Every molecule of air on your planet has frozen and fallen to the ground. 

That was a snowstorm - on  Pluto.

Once every year on Pluto (1 Pluto-year = 248 Earth-years), around the beginning of winter, it gets so cold that the atmosphere freezes. Air on Pluto is made mainly of nitrogen with a smattering of methane and other compounds.  When the temperature dips to about 32 K (-240 C), these molecules crystallize and the atmosphere comes down.

"The collapse can happen quite suddenly," says Alan Stern of the Southwest Research Institute. "Snow begins to fall, the surface reflects more sunlight, forcing quicker cooling, accelerating the snowfall. It can all be over in a few weeks or months."

Researchers believe this will happen sometime during the next 10 to 20 years.  Pluto is receding from the warmth of the Sun, carried outward by its 25% elliptical orbit. Winter is coming.

So is New Horizons.  Stern is lead scientist for the robotic probe, which left Earth in January bound for Pluto.  In 2015 New Horizons will become the first spacecraft to visit that distant planet (Dwarf Planet - Ed).  The question is, will it arrive before the snowstorm?

"We hope so," says Stern. The spacecraft is bristling with instruments designed to study Pluto's atmosphere and surface.  "But we can't study the atmosphere if it's not there." Furthermore, a layer of snow on the ground ("probably a few centimetres deep," estimates Stern) could hide the underlying surface from New Horizon's remote sensors.

Stern isn't too concerned: "Pluto's atmosphere was discovered in 1988 when astronomers watched the planet pass in front of a distant star-a stellar occultation."  The star, instead of vanishing abruptly at Pluto's solid edge, faded slowly.  Pluto was "fuzzy;" it had air.  "Similar occultations observed since then (most recently in 2002) reveal no sign of [impending] collapse," says Stern.  On the contrary, the atmosphere appears to be expanding, puffed up by lingering heat from Pluto's waning summer.

Nevertheless, it's a good thing New Horizons is fast, hurtling toward Pluto at 30,000 mph. Winter.  New Horizons.  Only one can be first.  The race is on....

Find out more about the New Horizons mission at http://pluto.jhuapl.edu.  Kids can learn amazing facts about Pluto at http://spaceplace.nasa.gov/en/kids/pluto.

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 November Newsletter should be with the Editor by October 28th  2006

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