WADHURST ASTRONOMICAL SOCIETY

JANUARY NEWSLETTER 2009

INDEX: MEETINGS, OTHER NEWS, CONTACTS

A very happy New Year to everyone in the Society and to everyone interested in Astronomy.
This is the International Year of Astronomy and we look forward to clear night skies and loads of sunspots. (Providing they don’t interfere the clear skies…)

MEETINGS

COMMITTEE MEETING
            Members of the Committee are respectfully reminded that there is a meeting of the Committee at 1930 on Tuesday 13th of January in the Abergavenny Arms, in Frant on the main A267 road out of Tunbridge Wells.
            As always, any member of the Wadhurst Astronomical Society is welcome to join us.  We do need your ideas!

DECEMBER MEETING
            The meeting began with a discussion about what the Members would like to see at future meetings.  It has been suggested that we could include short five-minute talks on astronomical topics such as the use of eye-pieces and basic collimating of a telescope.  Also the idea of having a short talk about what to see in the night sky over the coming month could also be included.
            The Committee would be interested to hear what subjects Members would like to have covered in the talks.  Phil Berry has managed to find some fascinating speakers for quite some time now, but he does need some suggestions and ideas.
            It was also announced that Phil could not be at the meeting because he had broken his leg whilst on out walking, and was presently sitting with his leg raised and was in some discomfort.  Members expressed their concern and sent their best wishes.
            Then followed another excellent talk from Society member Paul Treadaway.

How Stars Work
Paul Treadaway

Members will remember Paul’s last presentation about why we are still here, despite the violent Universe.  This illustrated talk was much more reassuring and explained very well the workings inside different kinds of star.
He talked first about what we see when we look into the night sky.  Stars have dissimilar colours and different brightness.  A good example of both these is illustrated in the Orion constellation where Betelgeuse is distinctly red whilst Rigel is a blue-white star. By contrast, our own Sun is yellow.
 The apparent brightness of a star is partly due to its relative distance from the observer.
Paul described the colour as a black body being heated to temperatures high enough to give off visible colours from red though blue to white.  In 1666 Isaac Newton was the first person to look at the colour by projecting a shaft of light from the Sun through a glass prism and on to a screen.  He found that the light was split up into the individual colours of the spectrum.
This experiment led Newton to discover the wave nature of light.
In 1814 Fraunhofer passed the light from the Sun through a narrow slit and using a surveying telescope discovered a “rainbow of colours” with a great number of vertical dark lines.  What he had discovered were absorption lines.  He also found that the light from the Moon, Venus and Mars showed identical lines and correctly assumed that this was reflected light from the Sun, but the light from Sirius and some other bright stars was different.
The different absorption lines were found to indicate different elements.  The elements also emit light on the same wavelengths as their absorption lines.  For example Paul mentioned Sodium, used in many street lights.  Sodium emits strong light on two very narrow lines making it very efficient as the source for a street lamp.
Using a hydrogen-alpha filter allows only light of 656 nanometres, blocking out light pollution making it an important filter in many built up areas.
 Late in the 1800s Edward Pickering, assisted by a corps of women photographed and recorded the spectra of a huge number of stars which were catalogued.  One problem was that the spectra could only be photographed in black and white, but never-the-less one of his assistants defined the stars according to their colour (surface temperature) with the now familiar letters O, B, A, F, G, K and M.
Paul developed the history of identifying stars by referring to the Hertzsprung-Russell (H-R) diagram, which plots the Spectral Class/Temperature of the star against its Luminosity/Absolute Magnitude.
Hertzsprung found that the vast majority of the stars followed what he called the Main Sequence.
He found that some of the nearer dim stars didn’t fit the Main Sequence.  These were Dwarfs.  Other stars were rarer bright stars; Red Giants.
We were now told about the history of the understanding of energy, beginning with Helmholtz’s theory of the conservation of energy were energy could neither be destroyed nor created and he and Kelvin suggested that the Sun had to have a an enormous source of energy to produce its luminosity.  At the time only fossil fuels were known as the source of energy and they had considered gravity collapse as the possible source.
However, Eddington could not agree, realising that internal pressures in some of the larger stars in the H-R diagram would tear them apart.  He proposed the fusion of hydrogen into helium to provide the energy needed, but this would require incredibly high temperatures, not possible in or Sun.
It fell on George Gamow to introduce the idea of quantum effects that would allow the protons to interact at much lower temperatures.
Paul then explained very neatly how helium is created in three basic ways.
 The Proton-Proton reaction where two protons fuse, creating an electron and a positron that annihilate each other resulting in an enormous amount of energy and producing a helium nucleus.  This is what happens in our Sun.
Stars with temperatures up to 100 Kelvin use carbon as a catalyst.  Four protons create a helium nucleus.
In stars with core temperatures of more than 100 Kelvin a process called the Triple Alpha Process takes place where two helium nuclei fuse to result in beryllium, which then fuses with another helium nucleus to form a carbon nucleus.  This results in a large amount of gamma radiation which is absorbed by and heats up surrounding gas.
Using an image of the Eagle Nebula, Paul showed areas where Proto stars were in the course of forming from surrounding dust clouds.  When the pressures are high enough, hydrogen begins to fuse and a star is born.
Red Dwarfs are proto stars that enter the bottom of the main sequence of stars on the H-R diagram.  They are not massive enough to produce helium and it has been calculated that, given enough time, they would become black dwarfs.  It is thought that this would take longer than the age of the age of Universe, so far…
Brown Dwarfs are larger but never reach a high enough temperature to produce helium and just fade.
White Dwarfs are the dying cinders of stars unable to continue fusing within their core.  They are usually about the mass of the Sun but only about the diameter of the Earth.  They will continue to cool towards the red end of the H-R diagram.
Stars about the size of our Sun will increase in diameter and cool after billions of years, entering the upper right of the H-R diagram.
The core of stars many times the size of the Sun begin to collapse, but this generates greater temperatures and the hydrogen begins to fuse with the helium and this even fuses to carbon and oxygen.  The star swells in size to a super giant, hundreds of times that of the Sun and leaves the main sequence to join the giants at the top right of the H-R diagram.
The larger ones become neutron stars but the even bigger ones explode, leaving a black hole.
The largest stars have only a brief life time of only a few million years.  They become blue-white, and then as they run out of fuel, they become red giants with only a million years left.
Paul took us through the star’s last years.  With only 1,000 years left there is not enough helium to prevent the core collapsing.  As the carbon core depletes it contracts even more and with only 7 years left neon, oxygen and magnesium are produced.
One year to go and silicon and sulphur are produced.
A few days left and the silicon and sulphur produce iron.
Then at temperatures of about 100 billion degrees, the trapped neutrinos burst out, indicating to the observer of the impending supernova.
The star is torn apart and through a process called the Rapid Neutrino Process, heavier elements are produced.
The core now becomes either a neutron star or if massive enough, a black hole.
Reassuringly, Paul pointed out that these events take place very rarely on the human time scale, but they have been necessary to produce the elements from which we ourselves are made and even the mince pies we were about to consume!

JANUARY  MEETING
            Wednesday 21st January 2009: This is the Annual General Meeting.  That should not take too long and then Phil Berry gives a fascinating talk, bringing us up to date with the impressive progress he has achieved with his observatory following on from his previous talk earlier in 2008.  This time Phil calls his talk “The Further Trials and Tribulations of an Amateur Astronomer”.
            The meeting begins at 1930 although members are invited to arrive anytime after 1900 as 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 the entrance to Uplands College.  (For those with SatNav – the post code is TN5  6AT)

FUTURE MEETINGS
            Wednesday 18th February 2009 is the date of the February meeting.
            Wednesday 18th March 2009 is the date of the March meeting.

OTHER NEWS AND INFORMATION

MEETING OF THE ANGUS GROUP
            Tuesday 3rd February  There will be a meeting of the Angus Group this evening.  Further details will be provided nearer the time, but it will probably be at Phil Berry’s house and begin about 1900.
            The Angus Group is open to any member of the Society who is interested in the practical side of telescope making.  You do not need to have any particular skills, but it provides the opportunity to see what the group is doing and to discuss any interests or problems.

INTERESTING WEBSITE ON EVOLUTION
            A rather interesting website worth a visit has been suggested by Angus Macdonald which illustrates the evolution timeline for the Universe but ending at our time.  It can be found at: http://www.johnkyrk.com/evolution.html
            It takes the visitor right from the Big Bang through the development of the Universe in ever increasing detail to end with Homer Simpson on our televisions.

SKY NOTES FOR JANUARY

Planets
Mercury is an evening object at the start of the month reaching its most easterly point, with respect to the Sun, on the 4th. For around the first two weeks of January the planet will be visible low down in the south west at magnitude -0.7 although it fades very rapidly. On January 9th Mercury sets almost an hour and a half after the Sun. By the January 20th it is in conjunction with the Sun before becoming a morning object once more. The best times to see Mercury this year will be during the evening in April/May and in the early morning in September/October.

Venus is a brilliant object in the south west at magnitude -4.4. It also reaches its most easterly point this month (on the 14th) and around this time it sets four hours after the Sun. Venus exhibits phases very similar to the Moon, and at the moment is around 50% illuminated. In the next couple of months its phase will decrease while at the same time its apparent size and magnitude will increase. This is due to the distance between us closing.

Mars is not suitably placed for observation this month.

Jupiter is poorly placed for observation this month and will be in conjunction with the Sun on the 21st.

Saturn at magnitude 1.0 lies in the constellation of Leo, rising before 22.00 by the middle of the month.

Lunar Occultations
            You will notice that they are many more occultations than usual this month. This is because on the night of January 7th the Moon passes in front of the Pleiades star cluster in Taurus. There are actually far more occultations than are shown but these are of fainter stars.
            As usual in the table I’ve only included events for stars down to around magnitude 7.5 that occur before midnight. DD = disappearance at the dark limb and RD = re-appearance at the dark limb. Times are all GMT.

Graze Occultation
            During the Moon’s passage “through” the Pleiades on the 7th its dark limb passes extremely close to the bright star Alcyone (magnitude 2.8) as seen from Wadhurst at around 17.52. If anyone is interested I would like to organise a trip that evening to a location further west, possibly between Horsham and Hazlemere, where we will see the star “graze” the moon’s limb. If we are successful we should see the star disappear and reappear through the lunar mountains and valleys. Accurate timings of these events are extremely valuable for calculating the exact profile of the limb. Please let me know if you would like to take part – a telescope and a stop watch would be a minimum of equipment required although members who simply wanted to watch the event would also be most welcome. I know the Society has telescopes that would be more than adequate for a star as bright as this. The only negative point to be made is that the Moon will be gibbous (between half and full) so there will be quite a lot of glare.

Phases of the Moon for January

Meteors
            The Quadrantid shower is active from January 1st to the 6th with maximum occurring on the 3rd when there are suggestions that the ZHR (zenithal hourly rate) could reach 90 or 100. In the evening the radiant (in the constellation of Boötes (the herdsman) will be low on the north eastern horizon and also the moon will be just before 1st quarter. In previous years observers have reported seeing meteors with a distinct blue, green or yellow hue.

Comets
            There are reports that comet C/2007 N3 (Lulin) is brightening faster than originally expected and by mid January could be of 5th magnitude. At this time it will lie in the constellation of Libra which will mean it will rise at around 03.00. However, if current predictions prove correct, by the end of February it will have brightened to magnitude 3.9 and its westward motion, just north of the ecliptic, will have taken it into the constellation of Virgo which means it will rise at around 21.00.

ISS
            Many of the ISS passes this month as seen from Wadhurst are low in the sky or occur in the early hours of the morning. I have only included those that are the brightest, attain reasonable altitude and occur before midnight. The information given is for when the ISS is at maximum altitude, so it is best to look some minutes before this time. Full details of all passes can be found at:
 www.heavens-above.com
Times are all GMT.

Iridium Flares
            The flares that I’ve listed are only the brightest, there are many more that are fainter and occur at lower altitudes. If you wish to see a complete list, go to:
www.heavens-above.com

Brian Mills

NASA SPACE PLACE

Superstar Hide and Seek
by Dr. Tony Phillips

            It sounds like an impossible task: Take a star a hundred times larger in diameter and millions of times more luminous than the Sun and hide it in our own galaxy where the most powerful optical telescopes on Earth cannot find it.
            But it is not impossible. In fact, there could be dozens to hundreds of such stars hiding in the Milky Way right now. Furiously burning their inner stores of hydrogen, these hidden superstars are like ticking bombs poised to ‘go supernova’ at any moment, possibly unleashing powerful gamma-ray bursts. No wonder astronomers are hunting for them.
            Earlier this year, they found one.
            “It’s called the Peony nebula star,” says Lidia Oskinova of Potsdam University in Germany. “It shines like 3.2 million suns and weighs in at about 90 solar masses.”
            The star lies behind a dense veil of dust near the centre of the Milky Way galaxy.  Starlight travelling through the dust is attenuated so much that the Peony star, at first glance, looks rather dim and ordinary.  Oskinova’s team set the record straight using NASA’s Spitzer Space Telescope. Clouds of dust can hide a star from visible-light telescopes, but Spitzer is an infrared telescope able to penetrate the dusty gloom.
            “Using data from Spitzer, along with infrared observations from the ESO’s New Technology Telescope in Chile, we calculated the Peony star’s true luminosity,” she explains. “In the Milky Way galaxy, it is second only to another known superstar, Eta Carina, which shines like 4.7 million suns.”
            Oskinova believes this is just the tip of the iceberg.  Theoretical models of star formation suggest that one Peony-type star is born in our galaxy every 10,000 years.  Given that the lifetime of such a star is about one million years, there should be 100 of them in the Milky Way at any given moment.
            Could that be a hundred deadly gamma-ray bursts waiting to happen?  Oskinova is not worried.
            “There’s no threat to Earth,” she believes. “Gamma-ray bursts produce tightly focused jets of radiation and we would be extremely unlucky to be in the way of one.  Furthermore, there don’t appear to be any super massive stars within a thousand light years of our planet.”
            Nevertheless, the hunt continues. Mapping and studying super massive stars will help researchers understand the inner workings of extreme star formation and, moreover, identify stars on the brink of supernova.  One day, astronomers monitoring a Peony-type star could witness with their own eyes one of the biggest explosions since the Big Bang itself.
            Now that might be hard to hide.
            Find out the latest news on discoveries using the Spitzer at www.spitzer.caltech.edu. Kids (of all ages) can read about “Lucy’s Planet Hunt” using the Spitzer Space Telescope at: spaceplace.nasa.gov/en/kids/spitzer/lucy.
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 

Talks   Phil Berry  01892 783544

Treasurer  Mike Wyles  01892 542863

Sky Notes   Brian Mills   01732 832691

Newsletter Editor  Geoff Rathbone  01959 524727

Any material for inclusion in the February 2008 Newsletter should be with the Editor by January 28th  2008

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