Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.armaghplanet.com/pdf/Astronotes/Astronotes2006/Astronotes_Dec_2006.pdf Дата изменения: Tue Sep 20 18:48:21 2011 Дата индексирования: Tue Oct 2 01:22:41 2012 Кодировка: Поисковые слова: dark nebula

December 2006

ASTRONOTES
Incorporating FRIENDS' NEWSLETTER The Mystery of the Christmas Star Shooting the Sun at Armagh The Planetarium on Tour HAT P 1B: A Warm and Fuzzy Planet? Hubble Measures the Universe

ARMAGHPLANETARIUM


2 Astronotes December 2006

The Christmas Star Mystery
By Julie Thompson, Digital Theatre Manager Throughout the month of December, Armagh Planetarium's Digital Theatre will be presenting a very special show called `The Mystery of the Christmas Star'. Visually stunning, this full-dome presentation from Evans & Sutherland examines the theories as to what was the celestial phenomenon that guided the Wise Men to the birthplace of Jesus. Jointly written and produced by Terence Murtagh, a former director of Armagh Planetarium, the show carefully and simply explains how there are various candidate objects and occurrences which could have been the Star. Over the centuries, astronomers have proposed as possibilities from `local' events such as auroImage Credit: Evans and Sutherland

rae, meteors and lunar eclipses, to Solar System bodies such as comets and even cataclysms in deep space such as novae. There are many of these candidates and some seem very plausible. The choice is widened by the confusion over the exact year of the Nativity, a point well-explained in the show. During the show the audience is taken on a spectacular journey from Cologne Cathedral, where the Magi are said to be interred, to the Holy Land and into space. A really nice aspect of `Mystery of the Christmas Star' is how such a wide range of astronomical topics can be presented throughout it. There cannot be many planetarium shows which introduce the audience to meteors, comets, planetary motion, binary stars and much more in half an hour or so. Putting everything in context, the essential historical and cultural backgrounds to the events are presented too. The show uses the Digistar 3 projection system to great effect to present the theories in a simple style which is also appealing to the eye. A haunting soundtrack adds to the show's effect making it a memorable experience for everyone. Does the show solve the mystery? Well, after presenting and sifting through the evidence it does indeed come to a conclusion to the identity of the Christmas Star. So what was it? Why not come to Armagh this December and find out for yourself! (Show times available from www.armaghplanet. com or 028 37523689. Note that pre-booking is essential)

Moon Phases, Dec. 2006
Christmas Treat Our Digital Theatre will be running this special show until 1 January. Tue 5 Dec. Tue 12 Dec. Wed 20 Dec. Wed 27 Dec. FULL MOON Last Quarter New Moon First Quarter


December 2006 Astronotes 3

Hubble sees Red!
By Colin Johnston, Science Communicator Until the 1920s many astronomers believed that our galaxy pretty well was the entire Universe. Then Edwin Hubble, a flamboyant character of an astronomer, recognised Cepheids in the Andromeda Nebula (M31). Cepheid, stars which pulse at a rate governed by their brightness, are extremely useful `standard candles' for astronomers, who can easily tell how far away a Cepheid is just by observing how long it takes to cycle from minimum to maximum brightness. Hubble did the maths and discovered that M31 was very distant indeed (2.2 million light years away is the accepted figure today), so far in fact that it must be a galaxy in its own right. At the time this was very controversial, but Hubble was about to create an even greater stir. However first we will need to discuss light.
Image Credit: NASA and STScI

Edwin Hubble (1889-1953) Like other astronomers highlighted in this series, he has a lunar crater and an asteroid (2069 Hubble) named in his honour. NASA also named a space telescope after him. patient, we will get there eventually. Imagine you are looking at three spaceships sitting stationary beside each other in space, each has a bright green lamp attached to it. They are steadily shining a pure green light, we are using green light in this imaginary experiment as green is in the centre of the visual spectrum. At a signal, two of the ships start moving very fast while the third ship stays where it is. One ship moves directly away from you, while the other moves straight towards you. To your amazement, the colour of the lights on the moving ships changes. The one coming towards you now looks blue; the one going away from you looks red. The stationary one remains green. What is happening? Take the ship heading towards you, the waves of green light from its light are getting squeezed into smaller wavelengths as the ship moves closer to you. Shorter wavelengths are bluer, so we say the waves are `blue-shifted'. Meanwhile

"light is an electromagnetic wave"
Light travels as a wave. "A wave in what?" you may ask. "In itself" is the simplest answer, light is composed of a pair of vibrating electric and magnetic fields, they move together as an electromagnetic wave. In fact, not only is light an electromagnetic (EM) wave but so are infrared, ultraviolet, X-rays, radio and other forms of radiation. In this article we will lump these all together as `light' Now, light has a wavelength, if you imagine waves in the ocean, their wavelength is the distance between each crest. Just for a moment think about the familiar colours of the rainbow (or spectrum). At one side we start with red which has a long wavelength, next orange with slightly shorter wavelength, moving through the colours to blue and violet the wavelengths get smaller and smaller. You may be wondering what this has to do with the size of the Universe, but be


4 Astronotes December 2006 the green light waves from the ship moving away are `stretched' into longer wavelengths which are redder, so they are `red-shifted'. This genuinely happens (although I have greatly simplified the details; I hope all the physicists out there will forgive me). Although it sounds unlikely, it is an absolutely real phenomena and it is called the Doppler Effect after the Austrian scientist who proposed its existence in the 1840s. If an object is coming towards you its light is blueshifted, if it is receding the light is redshifted. This effect is very useful in many aspects of astronomy. For example, by studying the light from a star we can tell if it is coming in our direction (blueshift) or moving away (redshift), or we can use the Doppler Effect to measure its speed. Between 1912 and 1917, astronomer Vesto Slipher was using the Doppler Effect to measure the speed of `nebulae', including M31 in Andromeda. Remember these where the days when other galaxies were still thought to be nearby objects inside our own galaxy. To his surprise, of twenty five nebulae four were blueshifted (and therefore coming towards us) and the rest were redshifted and hence moving away from us. Hubble had heard of this and was fascinated but he was not able to begin investigating immedi-

M31 Andromeda Galaxy A Hubble Space Telescope view of the galaxy's core if a galaxy was twice as far away as another, it would appear to be travelling twice as fast. This is now called Hubble's Law, and it made his name. Soon, he was being referred to as `the world's greatest astronomer'. His fame led him to his being invited as guest of honour to the 1937 Oscar awards ceremony where he was presented to an audience of gawping Hollywood actors. As author Simon Singh has pointed out in his excellent `Big Bang', this meant that for once it was the stars that got to stare at an astronomer. This article is about measuring the size of the Universe, so we will not look deeply into why this redshift is occuring. By doing this, we are following Hubble's own approach; he was a skilful observer (with a talented staff of assistants) rather than a physicist who deliberately avoided speculation on the deeper meaning of his discoveries. In brief, we know galaxies are receding from us not because they are recoiling in disgust from the Milky Way, but as a consequence of the Universe's expansion, a subject for a whole series of articles in itself. Observers in any galaxy will see every other galaxy as redshifted, so there is nothing special about the Milky Way. However Hubble's Law opened up a new way of determining intergalactic distances. If you measure the redshift of a galaxy, you will know its velocity, and by Hubble's Law, you will automatically know its distance away. There are a few galaxies which do not fit

"galaxies are receding as a consequence of the Universe's expansion"
ately due to his military service in the First World War amongst other distractions. By the late 1920s Hubble was using the 100 inch Mount Wilson telescope, the largest in the world at the time, to look at distant galaxies. By 1929 he had catalogued 46 galaxies by their distance and speed (measured by the Doppler Effect). The conclusions were unmistakeable. Firstly most galaxies are redshifted, implying that they are receding from our galaxy, confirming Slipher's results. Secondly, the degree of redshift (and therefore the galaxy's velocity) is directly proportional to its distance away. In other words,

Image Credit: NASA / ESA & T. Lauer (NOAO / AURA /NSF)


December 2006 Astronotes 5 Hubble's Law. M31, for example, is in fact moving towards the Milky Way at 120 km/s, so it is blueshifted. Galaxies like this are said to have `peculiar velocities', these are believed to be due to interactions between galaxies and their random motions. It is also worth noting that a handful of astronomers dispute Hubble's law, some claim to have found galaxies which are interacting, in other words touching each other, yet have wildly different redshifts. This is an impossibility by Hubble's Law, and most astronomers believe these observations are mistaken. Hubble's Law is widely accepted to be our only means to measure the distances to distant galaxies and quasars in which cepheids or other standard candles cannot be seen. In the next issue I will continue this series with a look at more ways to determine the size of the Cosmos.

Scary Aliens terrorise Armagh Planetarium
Image Credit: Colin Johnston, Science Communicator

By Sharon Carroll, Science Communicator On the night of the 31st October, 2006, the scariest night of the year, Armagh Planetarium was alive with the strangest ever creatures seen on Earth, or in space for that matter. The likes of this have never been seen before at the Planetarium. It seems that it was the meeting place for all kinds of strange life forms to gather and celebrate Halloween - headless creatures from outer space, robotic space invaders, Martians, extraterrestrials, witches, imps and fairies to name a few. On this spooky night, all life forms were treated to a spine chilling show in the Digital Theatre with scary music, stories and pictures of the stars. Who would ever have thought that space was a frightening place? The night had just begun however as story teller Sheena Bleakney enticed all with a creepy tale in the Kepler room. All young and old life forms listened intently to every word told about a witch in a cave. The story teller warned all that the witch hated noise and did everything in her power to stop children, imps and fairies from disturbing her peace and quiet. Thankfully, the witch eventually learnt a valuable lesson and invited all to her cave to play games and make as much noise as possible. We have heard reports since that the robots had such a great time during the The horror! The horror! Witches and a headless entity terrify our Halloween storyteller. party that they are having one of their own now in space. Since so many aliens, witches and Martians travelled from infinity and beyond to be with us, the staff at the Planetarium decided to give a prize to the best dressed alien. This competition was won by the headless person shown in the photograph above but all life forms received a souvenir of their time spent at the Planetarium. Sadly, every good thing must come to an end and the staff said a fond farewell to their visitors, inviting them to return again in the future for more fun and games at Armagh Planetarium.


6 Astronotes December 2006

Bam!...Bam!...Bam!...Bam!
By Colin Johnston, Science Communicator NASA recently announced that its next manned spacecraft will be the Orion CEV, a capsule which will be carried into space by a rocket. Weighing 25 tonnes, each Orion will carry up to six people to Earth orbit or up to four to the Moon. Accommodation on board is cosy at best, cramped at worst. Orion missions will hopefully begin in 2014. Imagine another spacecraft called Orion. As tall as a sixteen-storey skyscraper, and shaped like a giant bullet, this one weighs 4000 tons­ about 40 times as much as the Space Shuttle. It has a crew of up to a hundred and fifty people who live on aboard in privater cabins complete with home comforts. Their Orion is tough, built by a
Image Credit: NASA

"this Orion returns from Saturn. The year is 1975 "
shipyard specializing in submarines; its skin is of heavy steel plate. This giant Orion's performance makes the capabilities of NASA's Orion look puny. This imaginary Orion blasts off from the Nevada desert into space- and keeps going! A few months later it arrives at Mars and the crew begin to study the Red Planet in their spaceship's extensive scientific laboratories. A year later, the Orion is ready to leave Mars. But not to return to Earth, in fact this space odyssey is only getting started, for instead the huge space cruiser hurtles away from the Sun. The ship spends a year speeding through the darkness; as the months pass, through its giant windows the crew can see a dazzling sight growing ever larger. Saturn and its great rings lie ahead of them. The lucky crew spends another year orbiting Saturn, marvelling at the wonders they have

Flight of Fancy This is the final `small' Orion to be launched by a Saturn V (note the Apollo-style Command Module). The vital shock absorbers are the tubes towards the rear. Although designed for an Earth to Mars trip, it appears to cruising past Jupiter in this artist's impression. discovered before it is time to go home. After a five year mission, this Orion returns to its home planet, with a precious cargo of samples from Mars, Phobos, Deimos, Enceladus, Iapetus and Saturn's rings. The year is 1975. Is this preposterous science fiction? Perhaps but this Orion was very seriously proposed in 1958 by physicists Stanislaw Ulam and Cornelius Everett and studied by some of the world's smartest scientists under US government contract for several years. The project was highly secret until it ended in 1964. So how would it have worked? Why has it never been built? The answer to the first of these questions goes a long way to explaining the second. To achieve its amazing performance, the original Orion would use a very unusual form of fuel. The fuel supply consists of racks of about 1000 polyethylene capsules, each about the size of an oil drum, at the centre of each capsule, embedded in the


December 2006 Astronotes 7 plastic, is a small thermonuclear fusion device. Thermonuclear fusion device is a polite way of saying nuclear bomb. Here is how Orion would have worked: a complex feed and ejector mechanism grabs a bomb capsule from its rack and shoots it out of a chute in the rear of the spaceship. Sixty metres behind the ship, the bomb detonates, in a blast equivalent to thousands of tonnes of TNT. The bomb transforms itself and the surrounding plastic into white-hot radioactive plasma expanding outward at 100 000 m/s. Part of this wave of debris is caught by the thick steel pusher plate which forms the spacecraft's base, slamming the vehicle forward at 12 metres per second. Seconds later the next fuel capsule detonates and the ship surges forward again, another bomb is ejected and the process is repeated. Each detonation adds an extra 12 m/s to the ship's velocity and this cycle continues until Orion reaches its cruise velocity. Far above this radioactive inferno, as each bomb explodes the crew experience not a series of bone-crushing blows but a steady, tolerable thrust. Gigantic damped springs, the shock-absorbers, behind the pusher plate

Image Credit: NASA

Saturn's moon Enceladus The Orion engineers imagined chilling their martinis with ice scooped from the surface of this frigid world. heavier the Orion, the more efficient the powerplant became so a sturdy and cheap construction of steel like a sea-going vessel made perfect sense. As a result of this analysis, a submarine building company was indeed selected to construct the craft. An Orion could lift an enormous weight into space and accelerate it to fantastic speeds (8% to 10% of the speed of light would have been possible by a city-sized version) making even interstellar flights a possibility. The people working on the project were enormously enthusiastic and convinced it was a viable idea. Many of the physicists involved expected be crew members on future missions to the planets. So why was this idea not pursued? Apart from the cost of building it, there were niggling technical problems to be resolved. For example, the bomb ejection mechanism had to be made utterly foolproof as a bomb jamming in the chute would be disastrous. Probably issues such as this could have been solved, but there was a massive problem with the concept which was impossible to eliminate. The spacecraft would have left a trail of extremely unpleasant radioactive exhaust behind it. It would have flown straight up until it cleared the atmosphere to minimize radioactive contamination, but even so, British-born physicist Freeman Dyson, a true genius and a leading figure in the project, calculated that each Orion launch would lead to the death by cancer of at least ten people world-wide which was clearly unacceptable. The obvious way around this was to use ordinary

"Even interstellar flights were a possibility"
smooth the instantaneous acceleration to levels that humans can withstand, say 1­3g. An Orion blast-off would be the most spectacular sight ever created by humans. The ship would have left a trail brighter than the Sun behind it and would be remarkably noisy (this article's title hardly does it justice). About 800 such explosions would get the ship into Earth orbit, the hardest part of any space mission. As the craft moved away from Earth, it would be visible across a whole hemisphere. By now you may be tempted to give up in disbelief, but this concept was calculated to be feasible. A coating of a special graphite-based oil would have been sprayed on the pusher plate between blasts to protect it from being vaporized by the exploding bombs. The shock absorbers were perfectly standard engineering. Mathematical analysis showed the bigger and


8 Astronotes December 2006 rockets to launch the craft so that the nuclear bomb powerplant would only be activated far from Earth. A scheme for a smaller three person Orion carried into space on a couple of Saturn V boosters was studied. This 80 tonne Orion could make a round trip to Mars in six months but was never built. An international treaty banning nuclear explosions in space finally made the whole project technically illegal and it ended. Many space enthusiasts today regret that Orion was never built and there are some who passionately decry the decision to end the project. Orions still show up often in science fiction novels by the more technically-minded authors, the best-known example is Niven and Pournelle's alien invasion epic `Footfall'. Today it is hard to see any circumstances where a nuclear Orion would be built (it may be useful in one of those `doomsday asteroid' scenarios though). It is strange to think though that if it had been built in the 1960s that people could have landed on Mars before the Viking probes or visited Saturn before the Voyagers!

Seeing our Star
By Dr Tom Mason, Director When I was a small boy my father demonstrated the power of the Sun to me using a biconvex lens to focus the Sun's rays on to a piece of paper. When he had the focus concentrated properly, the paper burst into flames. I often tell school pupils about this experiment as it graphically illustrated for me the power of the Sun and its potential to harm the foolish. We cannot emphasise enough the extreme danger of looking at the Sun with unprotected eyes, or worse using equipment with lenses which will cause even more damage: this includes cameras, binoculars and telescopes. The rest of this article refers to the fascination of observing our star using a specially manufactured telescope. As part of the Science and Skills project which is providing ancillary funding for the Planetarium's work for the next two years, we decided to enhance our solar observing abilities. Driven by our resurgent interest in all of the things that we can do with the public, we are restoring our ability to show visitors details of the surface of our closest star. For our new solar observations we are using a purpose-built telescope made by Coronado and known as the SolarMax 40. The special filters built into its optical design allow us to use the
Image Credit: Julie Thompson, Digital Theatre Manager

Our first public demonstration of the Solarmax telescope Members of the public looked through the equipment to directly observe the filtered light of the star. The filtered light shows the Sun as a reddish disk in the lens, and by looking carefully at the edge of the Sun's disk we could clearly demonstrate the prominences. telescope to view the Sun safely. We are also using a Sol Ranger sun finder attached to the main telescope that allows easier centring of the Sun's image in the optical path. We have been using standard still digital cameras attached to the telescope eyepiece lens on specially designed mounts to take some stunning images which we plan to post on the Planetarium's website later. We also have taken video images of the Sun with a web camera.


December 2006 Astronotes 9
Image Credit: Coronado Instruments

All of the statistics of the Sun are huge: its size, the violence of the solar storms, the dynamism of the surface, the fierce radiation and magnetic storms. We spend much of our time explaining these things to our visitors, and drumming into them that you must never, ever look at the Sun using lenses, whether cameras, telescopes or binoculars. A demonstration that was used in the past to graphically illustrate the Sun's energy showed that the sunlight passing through our old 16 inch telescope was powerful enough to flare a match head held in the light beam. As the light emerges from the eyepiece, a match held there will burst into flames. The unspoken message is that if this is what happens to a match, how much greater the damage will be to your sensitive, irreplaceable retinas at the back of your eye. The Sun's enormous energy output is emitted across the complete electromagnetic spectrum and is not limited to the light that we can see. Thus, ultra violet, the UV that needs blocking by sunscreens, lest we scorch our pale skins, is a well-known dangerous component of its energy. Likewise, the infra red at the other end of the vis-

SolarMax 40 A nicely-designed and easy to use instrument to directly observe the solar disc. affect conditions on Earth, from the amazing displays of the aurorae at the Earth's poles to interference with our satellites and the energy transmission systems on the earth's surface. The Sun's disk appears to be granulated as the convection cells that transfer energy from the depths of the star reach the surface. Through our Solarmax telescope we can observe sunspots, which are regions on the Sun's surface that are characterised by being at a lower temperature than the rest of the surface. The Sun is also a place of intense magnetic activity, which inhibits the smooth operation of the convection cells, forming areas of low surface temperature. This makes the cooler sunspot regions appear as darker spots on the Sun's disk. Although they actually are extremely bright and exhibit temperatures of around 4000 - 4500 C, the contrast with their surrounds at about 6000 C differentiates them as darker spots. We have been observing prominences (also known as filaments) at the edge of the solar disk. They are gassy outbursts from the Sun that extend into space. To see them we are using a hydrogen alpha filter that only allows light from a specific wavelength to pass through the optical path. Prominences can last for a few weeks or months. We were also able to see faculae. These are smaller than sunspots and are brighter than the rest of the Sun's surface. They also are associated with areas of strong magnetic fields, just like sunspots, but they are not well understood.

"infra red is a further danger to our eyes"
ible spectrum is a further danger to our eyes. You can check out images of the Sun made using different parts of the spectrum at the following website - http://umbra.nascom.nasa.gov/ The complex physics of the Sun's outer layers is difficult to see, as observation is obscured by the brightness of our star's disc. This is one reason why eclipses are so vital for observers, as the Moon blocks the solar disc, allowing us to see details of the atmosphere or corona, which is dramatically hotter at 1 to 3 million °C than the Sun's surface which is around 6000 °C. The corona is very active, and vast flares and prominences can be observed under favourable circumstances. Each of them is larger than our planet, and represents enormous quantities of energy. These outbursts from the Sun directly


10 Astronotes December 2006

A Warm and Fuzzy Planet?
By Colin Johnston, Science Communicator
Image Credit: David A. Aguilar (CfA)

in Arizona and Hawaii. In the constellation Lacerta, 450 light years (138 parsecs) from Earth lies a Sun-like star designated ADS 16402 B. Around this star circles the newly discovered planet HATP-1b. This world orbits only about 0.55 AU from the star's surface, with a `year' lasting a mere 4.46 days. It must be a hot and desolate place. The planet is unusual not only because it is so close to its star. The planet is huge, nearly 200 000 km across, it is about 1.36 times as wide as Jupiter. Stranger still is its mass. It is unusually light, with only about 60% of Jupiter's mass, so on average a 1m `cube' of HAT-P-1b would weigh less than 290 kg. This is about the same weight as a block of cork the same size, so this imaginary lump of planet is light enough to float (of course the planet as a whole would also float if you managed to find a bathtub big enough). In contrast, a 1 m cube of Jupiter would weigh more than a tonne, about 1300 kg, heavier still would be a chunk of our own Earth which weighs 5.5 tonnes per cubic metre. By the way, these values are averages over the entire planets, which tend get denser the deeper you go into them. For example, near the Earth's surface the soil's density is roughly 1500 kg/cu m, but if you were to sink into the interior the surrounding material would get ever heavier. When you reached the inner core you would find the molten nickeliron around you to weigh 15 tonnes per cubic metre, ten times as dense as near the surface. This new planet's abnormally low density was a real surprise to its discoverers. Compared to the planets in our own Solar System, HAT-P-1b is a big and fluffy lightweight. Why this should be is unknown. One suggestion is that a heat source inside has bloated the planet. It would not be a nice place to visit; although the gravity would be only a comfy 80% of Earth's, the planet's searingly hot atmosphere will be even less pleasant than that of Venus. HAT-P-1b is probably composed of primarily hydrogen and helium and was formed far from

The newly discovered world HAT-P-1b (shown here in an artist's rendering) has baffled astronomers, since it is puffed up much larger than theory predicts. HAT-P-1 has a radius about 1.38 times Jupiter's but contains only half Jupiter's mass. Astronomers continue to discover exo-planets. Most fall into the category of `hot Jupiters', these are giant planets orbiting very close to their parent star. A typical such world is just 0.05 Astronomical Units from its Sun, in contrast Earth is 1 AU from the Sun and tiny, scorched Mercury orbits 0.3 AU from the Sun. Note that we have discovered so many hot Jupiters because they are the easiest type of planet to find, they are not necessarily particularly common in the galaxy. No one expected such strange planets to exist until we found the first one ten years ago, but

"The planet would float if you managed to find a bathtub big enough"
now they are taken for granted. However a really strange exo-planet has recently been discovered by scientists using telescopes


December 2006 Astronotes 11 its parent star before migrating sunward. The strange orbits of most exo-planets have led astronomers to the surprising conclusion that planets, once believed to be firmly fixed in place by gravity, actually can wander across solar systems. HAT-P-1b was detected when it transited across the face of its parent star. As the planet passed in front the star (as seen from Earth), it blocked out a tiny portion (just 0.6% ) of the star's light. This was enough to reveal its existence. Already several similar hot and fuzzy worlds have been discovered the same way, proving this that planet is not a one-off oddball. The inhabitants of the exo-planet `zoo' are proving to be much stranger beasts than anyone expected.

Planetarium on Tour
Image Credit: Julie Thompson, Digital Theatre Manager

By Wendy McCorry, Science Communicator What do a library, a pub and a chapel have in common? Well, these are all venues which have been visited by the planetarium's Stardome in the past few weeks! Readers peered quizzically over the tops of their books in Deansgrange library, Dun Laoghaire at the beginning of the month, when the large blue igloo (as it has been described by numerous schoolchildren) materialised in the middle of the Adult Fiction section. The following week, Lennard's Arms in Clones, Co. Monaghan hosted the dome on their

"thousands of children have come to join the fun"
dancefloor, usually reserved for the local twentysomethings wanting to execute some slick dance moves on a Saturday night. This week the stars were not the only heavenly bodies to be seen, as the dome set up home in the chapel at Waterford Institute of Technology. Sixty children at a time arrived with their teachers to be wowed and amazed by the stars and the wonders of science. These events are all part of Science Week Ireland, an annual programme of innovative and interactive workshops which take place in venues throughout Ireland. This year marks the tenth year of Science Week, which should by rights be referred to as `Science Month', as events are taking place throughout the whole month of November. The aim of the initiative is to promote science as

Prepare to meet thy Dome Armagh Planetarium's Stardome has been in all kinds of venues. an accessible and enjoyable subject to young people, students and their parents. Entrance is free to most of the 350 events, which are so widespread that there is something going on in just about every corner of the country. So far, thousands of children of all ages have come along to join the fun - either as part of a school group or with their family. Next stop for the Stardome is Galway Education Centre, followed by some further school visits in the West of Ireland. Christmas should provide a welcome rest for the well-travelled Stardome, which must be about to reach retirement age any day now. In the new year we are planning to review our Stardome operation, so watch this space for the latest news. In the meantime, I think I hear another 60 schoolkids approaching...


12 Astronotes December 2006

Bluffing your way in Astronomy: Taurus
By Colin Johnston, Science Communicator It is Autumn, and there are plenty of easily visible and interesting things in the sky, so it is time to move your bluffery into top gear. Memorise this article, wait for a clear night in the middle of December and lead your audience outside about eight o'clock or so. Look south east, and find a rather pretty little tight group of stars, a bit below them and to their left and there should a very bright orange star. Continue looking and you will see that there are other stars around them in a vaguely V-shaped constellation. When you are sure you have found them, announce to your audience that this is Taurus the Bull.
Image Credit: Colin Johnston, Science Communicator

Taurus the Bull In this diagram the Pleiades are at the tip of the right horn, the Hyades and Aldebaran are in the `chin'. Image created with Starry Night software. they will reveal over two hundred. The faint haze around the stars appears as a beautiful blue mist in photographs. Older astronomy books say this is a wispy remnant of the molecular cloud in which they were born. However astronomers now think the stars in the Pleiades are at least 100 million years old, old enough to have blown away any such residue, so we are actually seeing part of a cloud of interstellar dust and gas, called the Taurus Dark Cloud, which by coincidence lies between us and the cluster. The Pleiades are about 380 light years from Earth. Most of the stars in the Pleiades are spectral classes A and B (big, bright white stars), recently both brown dwarf (tiny and dark stars) which are visible only at infrared wavelengths and, surprisingly, white dwarfs (very small and faint dead stars) have been discovered amongst them. These white dwarfs must be the remains of massive stars that went through their life very rapidly and have already ejected their outer layers. The stars in the Pleiades are only associated temporarily by cosmic standards; they are not locked together in orbits and will gradually drift apart until they resemble the Hyades. The cluster

"the Aztecs and Mayans had gruesome human sacrifices when the Pleiades were highest in the sky"
Taurus is one of the ancient constellations and is of course one of the signs of the Zodiac. It contains the nicest-looking open star cluster in the sky, the Pleiades, a rather less-impressive open cluster, the Hyades, and the bright star Aldebaran. Open clusters are groups of stars which were born in the same molecular cloud and are still loosely associated and held together by gravity. The Pleiades, alias the Seven Sisters, are just part of an open cluster of 400-500 young stars. They are called the Seven Sisters, but it is virtually impossible to see more than six, proving that real astronomers do a bit of bluffing too. Allegedly, sharp-eyed observers with clear skies can see about ten stars, but if you use binoculars


December 2006 Astronotes 13 will to all intents and purposes be gone in 250 million years. The name Pleiades comes from Plione, the mythical mother of seven daughters by the giant Atlas. The seven brightest stars in the group are named for these daughters (their names were Alcyone, Asterope, Electra, Maia, Merope, Taygeta and Celaeno, if you really want to show off you should learn these names) and there are stars in the cluster named for Atlas and Plione too. The Pleiades' beauty has been celebrated by cultures all over the world. They are mentioned in the Book of Job, Homer's `Odyssey' and Tennyson's poem `Locksley Hall' (this is in danger of turning into a bluffer's guide to literature!) Remember to use a suitably scary voice when you tell your audience how the Aztec and Maya peoples timed gruesome rites of human sacrifice for when the Pleiades were highest in the sky. The best cultural reference to the Pleiades though is in the logo of the Subaru car company, the six stars in it represent the Pleiades. The big name star in Taurus is Aldebaran. This name comes from the Arabic for `the Follower' as the ancient Muslim astronomers saw it as trailing behind the Pleiades across the sky. By the way, be very careful not to get to get Aldebaran confused with `Alderaan'. If you do, you will immediately lose all credibility as an astronomer and reveal yourself to be a sad Star

The Pleiades A glorious sight in the Autumn sky for naked eye and binocular observers our Sun's surface with one square metre of Aldebaran, the bit of Sun would be a blindingly-bright yellow, while the bit of Aldebaran would be a noticeably dimmer orange. However since Aldebaran has a surface area about 1600 the size of the Sun's, there is a lot more of it to shine light into space, so it still ends up brighter than the Sun. It's a old star too, being much further through its lifecycle than the Sun, having exhausted its supply of hydrogen it is now generating energy by fusing atoms of helium into carbon. In other words, it isn't too well and is on the stellar equivalent of life support. Aldebaran is orbited by a dim red dwarf star which is much too faint to see and there may also be a large planet out there too but that is not confirmed yet. There is smattering of stars around Aldebaran, these are the Hyades. The Hyades are another open cluster. In Greek mythology, the Hyades were the five daughters of Atlas and half-sisters to the Pleiades. They are definitely not as impressive as their sisters and it can take a minute or two to pick out the Hyades. It does look as though Aldebaran is the biggest star in the Hyades, but this is misleading. At 150 light years, the Hyades are more than twice as far away, so they are actually behind the giant star. Hopefully after you have shown your audience the wonders of Taurus they will be impressed and ready for more. Luckily, right beside Taurus is the very spectacular constellation of Orion. We'll show you how to bluff your way around Orion in the next Astronotes.

"Aldebaran-not to be confused with Alderaan"
Wars fan rather than a serious Scientist. Aldebaran is supposed to be the bull's eye and it is 65 light years from Earth. It is a very big star indeed, about forty times as wide as the Sun. Real astronomers call it a K class (the K means it is cooler than the Sun by about 2000єC) red giant star and about it is 350 times as bright as our Sun. It actually does appear reddish-orange in our sky. Now here is a potentially tricky bit: if Aldebaran isn't as hot as the Sun, how can it be brighter? Someone may ask you this, so it is as well to be prepared. The reason is because its size. If you compared one square metre of

Image Credit: NASA


14 Astronotes December 2006

The Leonid Meteors, 2006
by Paul O'Neill, Education Support Officer Meteors (or shooting stars) are the result of debris, essentially tiny dust particles entering the Earth's atmosphere and burning up. The debris is left behind by comets as they enter the inner solar system and cross the Earth's orbit; the Leonid meteor stream was left behind by the comet Swift Tuttle. It is possible to predict when meteors are visible by knowing when the Earth passes through a meteor stream. One such stream is known as the Leonids (because the meteors appear to come from the constellation of Leo). This year the Earth was predicted to pass through or close to a part of the Leonid meteor stream at around 4.45am on the morning of Sunday, November 19th. Twenty years ago I probably would have stayed up all night to observe as many meteors as possible but this year I watched the sky for around one hour each side of the predicted maximum. I saw about ten Leonids and eight sporadic meteors (these meteors can appear from any part of the sky at any time). I estimated the average magnitude of the sporadic meteors at around 3. The Leonids were fainter around magnitude 4, (as a guide the magnitude of Polaris is around 2 so the Leonid meteors were quite faint).
Image Credit: Sherry Buttnor

An example of a Leonid Meteor The trail is a result of the white hot meteor vaporising about 100km above the ground. If you would like to try meteor watching it is quite easy and requires no special equipment. You can see sporadic meteors at any time of the night. If you'd like to try observing a meteor shower the next reliable one will be the Geminids (from the constellation of Gemini (see star map) on the night of December 13/14. These meteors may be quite bright and you may be able to see some different colours, i.e. blue, yellow or orange. Good luck. (Editor's note: Paul's name will be new to you. Paul is one of three new members of the team at Armagh. In the past month we have been pleased to welcome not only Paul, but also new colleagues Neil Cullen and Naomi Francey. No doubt you will be hearing a lot more about them in future issues of Astronotes!)

Is it RIP for MGS?
By Colin Johnston, Science Communicator Scientists and engineers at NASA's Jet Propulsion Laboratory are fearing the worst after they lost contact with the Mars Global Surveyor (MGS) probe currently orbiting the Red Planet. MGS was last heard from on 5th November, shortly after informing ground controllers that it had problems with one of its solar panels. Weeks of attempting to restore contact with the Mars orbiter have been met with silence from the probe, which is the oldest of the five NASA spacecraft currently active on or around Mars. MGS was launched in November 1996 and was expected to last for two years. For the past decade the probe has returned superb imagery. Its loss is unfortunate but not a tragedy as it has already triumphantly surpassed its objectives.


December 2006 Astronotes 15

A Message from the Director
When I last wrote to you at the beginning of the Christmas season last year, we were eagerly awaiting returning to our main building and starting the job of revival that had started three years earlier when the money to refit the Planetarium was agreed. What a year we have had! We are very pleased with the reaction and feedback we have had from our visitors. From the day of re-opening on July 31st this year, we have had a steady stream of guests coming to see what all the fuss was about. This year we have had our busiest August ever, with almost 17 000 people coming to Armagh to see our shows. This momentum has continued into September and October with over 6000 more visitors during that time. And at Limerick in November we have had a record 1566 children on one day attending astronomy talks run by the Planetarium as part of the annual Irish Science week. We also have a very new team working with the visitors: six new staff have been employed during the past six months. Audience reaction to the new Digistar 3 is as we anticipated; all spoke of it as a unique experience, and we really are extremely pleased with its performance, and its versatility a teaching aid. It is worth remembering at this point that our primary purpose is Education. We exist to spread the word about astronomy, and to describe and explain the stunning things that are found in the Universe. Our prime function is to light the fires of curiosity in the minds of our young visitors so that they will also want to know more about the workings of the heavens. We are spoiled for choice, and every time we embark upon an explanation to any audience, the hardest bit is knowing what we should leave out. It is also worth remembering that our audiences comprise people of all ages who come to Armagh Planetarium to discover something of the nature of their world, or our star, or the Solar System or other bits of the cosmos. Luckily for us this story is one that is still being told, and the unravelling of the mysteries of the cosmos provides us with a steady stream of stories to tell. For that is the message I want to leave with you: at the start of this 2006 Christmas season we are unveiling our new show, The Mystery of the Christmas Star. It tells an ageless story of the Messiah that is of huge importance to every human on the planet. It represents the hope of rebirth, tells of salvation and presages an end to the darkness of winter. It is a great story, and that is our basic job, all of us on the staff at Armagh Planetarium are story tellers par excellence. We are continuing the long tradition of oral history that is still enshrined in more primitive, pre-literate societies, where no-one can write or record history. The story of the tribe, of its triumphs and disasters, of its religion and great deeds are remembered by the story tellers. We are carrying on this tradition. I would like to take this opportunity to thank all of you for your support in the past. I also would like to thank all of my colleagues at the Planetarium for their hard work and their continued commitment to all that we stand for: they are the bedrock on which the Planetarium is founded. We look forward to building on our excellent start this year, and going from strength to strength. And lastly I would like to wish all of you a very peaceful and happy Christmas season, and that the New Year brings you all prosperity and happiness. Tom Mason


16 Astronotes December 2006

Image of the Month
Image Credit: NASA/JPL-Caltech/T. Megeath (University of Toledo) & M. Robberto (STScI)

M42, the nebula in Orion's `sword' must be the most well-known of all the nebulae in our sky. Located 1500 light years (460 parsec) from our Solar System, it is clearly visible to the naked eye on winter evenings as a patch of fuzz under the three stars of Orion's belt. The Orion Nebula is only part of a much larger giant molecular cloud (which is over 100 light years across) which is invisible in the visual spectrum but can be detected in infra red wavelengths and by radio telescopes. We see the portion we know as M42 because the radiation from hot young stars is illuminating it. This nebula is indeed a stellar birthplace. Shock

waves from young stars are crashing into the surrounding cloud, creating knots of higher density material. Some of these concentrations will themselves become protostars which will eventually light up more of the nebula. Infrared, ultraviolet and visible-light images from NASA's Spitzer and Hubble Space Telescopes were combined to create this stunning picture which reveals all this frenzied activity in the nebula. Swirls of hydrogen and sulphur (depicted as green) and even carbon-rich organic molecules (shown as red and orange) have been detected in the nebula. Eventually the ultraviolet radiation will remove the surrounding gas and the nebula will become an open star cluster like the Hyades.

www.armaghplanet.com
Astronotes, Incorporating Friends' Newsletter is published monthly by Armagh Planetarium, College Hill, Armagh, Co. Armagh BT61 9DB Tel.: 02837 523689 Email: cj@armaghplanet.com Editor: Colin Johnston ©2006 Armagh Planetarium All rights reserved