Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.armaghplanet.com/pdf/Astronotes/Astronotes2007/Astronotes_May_2007.pdf Дата изменения: Tue Sep 20 18:48:57 2011 Дата индексирования: Tue Oct 2 01:24:50 2012 Кодировка: Поисковые слова: внешние планеты

May 2007

ASTRONOTES
Incorporating FRIENDS' NEWSLETTER Kepler: Astronomy Great Risky Business Slow Lane to the Planets Giants and Dwarfs of the Cosmos Holiday with the Stars

ARMAGHPLANETARIUM


2 Astronotes May 2007

Astronomy Greats: Kepler
By Naomi Francey, Education Support Officer Visitors to the Planetarium may be curious about the names of our rooms. They are all named after great figures in the history of astronomy. So here is the start of a series of biographies of the people our rooms are named after. German mathematician, astronomer and astrologer, Johannes Kepler was born on December 27th 1571. Although he had a desire to become a minister, he accepted a job teaching mathematics and astronomy in Austria aged 23. He later moved to Austria where he was offered a position there as a teacher of mathematics and astronomy. Due to an invitation from the great Danish astronomer Tycho Brahe, he moved to an area outside Prague and worked (sometimes unpaid) as Tycho's assistant. Later, in 1601 Kepler replaced Tycho as Imperial Mathematician and these were his most productive years. Sadly they did not last. To escape growing religious tension (he had refused to convert from Protestantism to Catholicism) in Prague he took a post of Provincial Mathematician in Linz, Austria.
Image Credit: Portrait of Kepler by an unknown artist via Wikimedia

Mathematician and astronomer Kepler also dabbled in astrology- the dividing line between science and nonsense was less certain in the early 1600s. 2. Kepler's equal-area law: The line connecting a planet to the sun sweeps out equal areas in equal amounts of time. 3. Kepler's law of periods: The square of the period (the time required for a planet to orbit the sun), is proportional to its distance from the Sun cubed. The constant of proportionality is the same for all the planets. In October 1604 he observed the supernova subsequently named Kepler's Star. His work had great influence on acceptance of the Copernican system in which the Sun, rather than the Earth, is at the centre of the Solar System. Kepler does not seem to have had a happy life; he was frequently ill and short of money, and his mother was accused of being a witch and imprisoned. He died on 15 November 1630 of a fever in Regensburg, Germany. On his gravestone he had written "I measured the skies, now the shadows I measure, Sky-bound was the mind, earth-bound the body rests."

"his mother was accused of being a witch"
Why was he so important? Well, he was a key figure in the scientific revolution. Today he is best known for his laws of planetary motion. Kepler inherited from Tycho Brahe a wealth of the most accurate raw data ever collected on the positions of the planets. The difficult part was to make sense of it! He began developing the first astronomical system to use non-circular orbits. It was completed in 1606, published in 1609 and became the first and second laws of planetary motion. In simple terms, Kepler's three laws are: 1. Kepler's elliptical orbit law: The planets orbit the sun in elliptical orbits with the sun at one focus.


May 2007 Astronotes 3

Risky Business
By Tom Mason, Director In January I attended a meeting at the Royal Aeronautical Society in London where retired USMC Major-General and NASA astronaut Charles Bolden spoke to an invited audience. His lively presentation was designed to stimulate an interest in science for the young people who were there. Bolden's most memorable message to the meeting was that young people must accept risk and not fear failure. He cited his own life experience, and his relatively disadvantaged background in South Carolina, to emphasise that with application and hard work anyone who chose to do so could succeed as an engineer or scientist. His educational background is technical, and he attended the US naval academy at Annapolis, where he graduated with a BS. and joined the US Marine Corps. Bolden became a naval aviation specialist and flew many missions during the Vietnam War. He has flown many different aircraft types; both fixed wing and rotary, and eventually became a naval test pilot. He eventually was accepted into the astronaut corps, and became a Space Shuttle pilot. He acknowledged that he had risen through the ranks of the American military by his work ethic and consistent performance, but candidly confessed that his fear of failure and rejection led him to initially believe that he would not be selected for the US astronaut corps, so he did not bother applying to join.

Charles F. Bolden Jr Born in 1946, Bolden has had a distinguished career as a military officer and space explorer. He is married with two children. how boring archery would be if every arrow you loosed hit the target every time: part of the attraction is to improve enough so that you hit the target squarely a good percentage of the time. We humans are not robots, our diversity is what makes us formidable practitioners of experiment and improvement. If the early rocket pioneers had not missed a few targets would they have had the incentive to try again, and to solve the problems that had thwarted their attempts to have a successful launch? I found Bolden's common sense approach a refreshing change from the politically correct dogma that discourages people from trying something new just in case they are upset by failing to achieve their goals. I believe that this has stifled creativity and adventure in our young people. We are living in the Orwellian era of

"People must experience failure to learn from their mistakes"
Bolden emphasised that he viewed it as a prerequisite that people must experience failure to learn from their mistakes. This contrasts with our current culture which does not allow for any sort of failure, let alone "missing targets". Think

Image Credit: NASA


4 Astronotes May 2007 died in 1979, aged 84. In his lifetime we went from reliance on horse power in the flesh, to hydrocarbon fuelled motor car engines, and from travel on great passenger liners to air travel on Boeing 747s. My grandpa was fairly sceptical about the Moon landings, as he had shown me the Man in the Moon when I was very young and impressionable: he lied about it being made of green cheese. As the only cheese he ever consumed was cheddar, I guess he meant that it was blue-moulded cheddar. Maybe he was the one who planted in me the seed that led to me becoming interested in rocks and fossils, and if that was so, I owe him a great debt of gratitude. He has been dead for almost thirty years now, but I still remember what he did for me: if that is not immortality, what is?

"Bursting with ideas" Children at one of Armagh Planetarium's StarDome sessions. "deferred success" as a euphemism for a failed assignment. When we induct children into primary schools they are bursting with ideas, most of them heretical. If you ask primary school children about their complex drawings and fanciful creations, they will tell you that they rely on human powered flight and amazing antigravity machines. By the time we have corralled them into the higher educational battery farm, they all think the same: they have been shoe-horned into a boring bland uniformity. How the devil do we achieve this? I think it is very damaging to our society. When he was asked about America's reinstatement of shuttle flights, Bolden stated that he personally thought their approach had been overly cautious, and too slow. He mentioned that everyone who has given this even a tiny bit of thought realises human space flight is not easy. It is inherently perilous. He said, "It's easy to sit on the ground and worry about safety because if you don't fly, you can't have an accident. But that's not the way to run a space programme. You have to accept the risks." We are on the threshold of an amazing period in human history. We are beset with problems, but nothing has changed there. Any historian would be hard pressed to find a time in history when humanity was not overwhelmed with multitudes of supposedly insurmountable problems. Equally, it only takes a moment to list the dramatic changes that have occurred to our lifestyles in the past hundred years. When I think of how much we have progressed I remind myself of my grandfather's life. He

Image Credit: Armagh Planetarium

"My grandpa was fairly sceptical about the Moon landings"
He allowed me take many risks: the one I remember most vividly is risking life and limb with his cat. It viewed small boys as just above its prey size limit, but was quite prepared to fricassee my hands if I dared to approach too closely (infected scratches, salmonella, parasites, and mange). He let me play with his penknife (now probably an illegal weapon), and let me bash nails into pieces of wood (splinters!) with a claw hammer that could break fingers (blue bruised nail). I bled a lot in my grandfather's care. But I

"Mars is waiting" The first people to the Red Planet will have an unforgettable adventure- but not without risk. This artwork by Pat Rawlins shows future astronauts in the Noctis Labyrinthus region early on a Martian morning

Image Credit: NASA


May 2007 Astronotes 5 learned a lot also. I also discovered, just like Major-General Bolden, that people are soft and squashy things when they are challenged with whirring pieces of red hot shrapnel that scythe through soldiers' bodies as they cross battlefields. I saw the big depression on top of his head where he had been wounded, courtesy of a Turkish shell that had blown off this part of his skull when he was serving in the British Army at Gallipoli in 1915. He was 20. And I have long realised that if that shell fragment had hit his head a few centimetres either way, my computer keyboard would not have had me typing out these words, for his bones would have been nourishing the soil of the Dardanelles, and none of his children would have been born. Risky? Life is full of risk. I despair of our riskaverse society, and like Chuck Bolden would encourage all of our readers, young and old, to take the risks, learn from your mistakes, and move on. There is always something new to discover: Mars is waiting.

Hands on Astronomy Education in Portugal
By Rosa Doran, NUCLIO and Robert Hill, NISO Portugal has entered a new age in astronomy education. In the last week of March, with the support of the British Council and the Northern Ireland Space Office / Space Connections, the pilot education/research project: "The search for Open Clusters around O-stars" was officially launched. The project is mentored by a professional astronomer, Dr. AndrИ Moitinho (Instituto Dom LuМs/ University of Lisbon) and developed by NUCLIO (NЗcleo Interactivo de Astronomia), a non-profit professional and amateur astronomers association devoted to public outreach and education.
Image Credit: Robert Hill, NISO

"O-type are young and brilliant stars"
The objects of this study are O-type stars, a young and brilliant type of star that is believed to be embedded in a cluster of stars (see Paul's article in this issue for more about O-type stars). The aim of this program is to discover previously unknown star clusters around those stars. The

Young scientists from Cascais searching for O-type stars using FT North young scientists in Escola SecundАria da Cidadela, a high school in the Cascais area, chose their candidates from a catalogue of known O stars and observed them using the Faulkes Telescope in Hawaii. The idea of this project was born as a parallel result of an ambitious European collaboration, the European Hands On Universe program (www. euhou.net). As a partner of EU-HOU, I challenged Portugeuse, Polish and Russian teams to pilot scientific projects in schools using the Faulkes Telescopes. One goal of this project is to bring the thrill of scientific discovery into the


6 Astronotes May 2007 regular classroom environment. This was my second visit to Portugal. The first one was last year and marked the start of conversations between NUCLIO and the British Council in Portugal. During this visit we had an important meeting at the British Council where we had the opportunity to share the recent achievements regarding the inclusion of new innovative projects using ICT (information and communication technologies) into the Northern Ireland curriculum. I also met with NUCLIO scientists with the purpose to set the basis for a joint development, using the Caspian Learning Resources 3D environment, "The Thinking Worlds ". These pilot efforts are proving to be a fantastic way to share experiences. The teacher involved in this adventure reported her joy in being able to follow this path with us and the impact this experience is having on their students. We hope this project is just one of the projects NUCLIO will pilot. NUCLIO is lucky to have such an active British Council in Portugal, willing to support this unique project and to set an example that we hope will be followed by other offices around the world.

Moon Phases, May 2007
Wed 2 May Thu 10 May Wed 16 May Wed 23 May FULL MOON Last Quarter NEW MOON First Quarter

Slow lane to the planets
By Colin Johnston, Science Communicator Anyone interested in space exploration will know that travelling to the planets is a slow process. Years can pass between the spectacular launch of a rocket and a space probe's visit to the destination planet. The amazing data and images returned make it worth the wait but why do spacecraft take so long to get to other worlds? In fifty years of space travel the speeds do not seem to have improved an iota. We all know that each planet is constantly moving around the Sun in its orbit, a fixed, almost circular path with the Sun at the centre. As observed by Kepler, and explained by Newton, the Sun's gravitation means that planets in orbits closer to the Sun move faster than those further out. The distances between the worlds are enormous, so large in fact that, it is best to measure them not in kilometres but in AU (Astronomical Units, 1 AU=150 million km, roughly). Ideally, to get to, say, Mars our spacecraft would point its nose towards the planet and run its engine continuously, heading straight to its destination. Half way through the journey it would have to start to decelerate, shedding all the speed it

Between planets A 1950s spaceship concept from artist Jack Coggins. Sadly we cannot yet speed through the Solar System like this. had gained and coming to a halt at the planet. Travelling in a near straight line, this flight would be very fast, but it would not only be extremely energy inefficient, it will be impossible for the foreseeable future. There will be simply no pro-

Image Credit: www.dreamsofspace.com


May 2007 Astronotes 7 pulsion system capable of this kind of trajectory for decades to come, even the proposed Project Orion nuclear blast spacedrive (See Astronotes December 2006) could not achieve this.

Average Distances from the Sun in AU
Mercury Venus Earth Mars Ceres Jupiter Saturn Uranus Neptune Pluto Eris 0.4 0.7 1.0 (by definition!) 1.5 2.8 5.2 9.5 19.6 30.0 39.5 67.7
Image Credit: Rlandmann via Wikimedia

Instead, after being hefted into space by a launch vehicle (i.e. a rocket) such as an Ariane 5, Atlas V or Soyuz-Fregat, most spacecraft run their onboard rocket motors long enough to build up sufficient speed to insert themselves into a very elliptical orbit around the Sun. This orbit is carefully chosen to pass nearby their target planet. The vehicle spends months to years coasting through space in a lazy arc towards its target. The path is slow but steady and it is sure to get there in the end. Such trajectories are called Hohmann transfer orbits after the German engineer Walter Hohmann (1880-1945) who discovered the concept in 1916 (and who later refused on principle to work on the Nazi rocket projects, a noble act which saw sadly few imitators). Hohmann orbits are the easiest way to reach other worlds.

Hohmann transfer orbit A spacecraft leaves an inner planet (orbit 1) and travels along a transfer orbit (2) to an outer planet (orbit 3). Note that unless it brakes at its destination the craft will keep on going until it returns to its starting point. land on the surface according to the plans of the people who sent it. As you can see, apart from occasional course corrections during the cruise phase, the probe's motors only fire at the beginning and end of the journey. If you feel like planning a space mission, here are the travel times from Earth to the planets and dwarf planets. Note that the transit time from Earth to Mercury is less than the transit time to Venus despite being a longer distance - remember orbital speeds are greater closer to the Sun!

"To arrive at empty space would be an embarrassment"
In practice, spacecraft never complete a whole Hohmann orbit as it would take them sailing past the planet only to loop back and return to the original starting point. Instead, as the spacecraft nears its destination, a push from its rocket motor slows it down enough for it to be caught by the gravity of its target planet. From then on it may achieve a stable orbit around the planet or

Typical Hohmann orbit journey times (departing from Earth)
Mercury Venus Mars Ceres Jupiter Saturn Uranus Neptune Pluto Eris 3.5 months 4.8 months 8.5 months 1 year 3.5 months 2 years 8.8 months 6 years 1 month 16 years 1 month 31 years 4 months 46 years 100 years!


8 Astronotes May 2007 There is of course a slight additional complication. Nothing in space is standing still. The planets are continually moving in their orbits. This means that the timing of the launch must be extremely precise so that when the spacecraft reaches the other side of the Hohmann transfer orbit the target planet is there to meet it. To make an arduous journey through millions of kilometres only to arrive at empty space would be an embarrassment! In practice there are only certain periods when it is feasible to launch from Earth to reach another planet by transfer orbit. It is possible to calculate tables of possible departure times for each planet. For example, opportunities to fly to Mars occur only every 780 days. These periods are called launch windows, and they form a kind of timetable for launching missions to other planets. A launch window lasts only a comparatively short time and if you miss it you may have a long wait! In fifty years of spaceflight, engineers have become accomplished at planning missions to elegantly send craft from world to world with minimum expenditure of energy. Hohmann transfer orbits are the sure and steady roads to the planets. However they are a very slow way to reach the most distant worlds. A Hohmann tra-

Launch windows (for departure from Earth) occur every
Mercury Venus Mars Ceres Jupiter Saturn Uranus Neptune Pluto Eris 116 584 780 467 399 378 370 368 367 365 days days days days days days days days days days

jectory from Earth to Mars would take about nine months, but from Earth to Saturn would take more than six years. The equivalent time to Pluto is more than forty-five years, more than half a typical human life span. So how is NASA's New Horizons probe (launched 2006) going to reach Pluto on schedule in 2015? The key to shorter space journey times is to exploit the gravity of the planets for a free extra boost. We will take a look at this very clever application of Isaac Newton's Laws in the next Astronotes.

A Universe of Dwarfs and Giants
By Paul O'Neill, Education Support Officer A star is basically a big ball of very hot hydrogen, with some helium and small amounts of a few other things. We know this from studying their spectra (see last issue of Astronotes). However, although they are made of basically the same stuff they are not all the same. Scientists love to classify things and one way to classify stars is by their different spectral types. The first attempt to do this was by Angelo Secchi in the 1860s; he divided stars into five different groups. This system was modified, refined, reworked etc.. several times; eventually ending up with the system we use today. One consequence of this

Orion the Hunter This constellation contains several giant and super giant stars.

Image Credit: NASA


May 2007 Astronotes 9

Hertz-Russell diagram This shows the relationship between star's brightness and surface temperature. It is named for Ejnar Hertzsprung and Henry Norris Russell who independently originated the concept, process is the apparently random letters used for the names of the groups: OBAFGKM There are various mnemonics to help remember this list, for example: Oh Be A Fine Girl Kiss Me. My favourite variation on this is: Only Boring Astronomers Find Gratification Knowing Mnemonics When we gather together lots of information on stars and plot a graph of spectral type against intrinsic brightness (i.e. how bright a star really is) we get the diagram at the top of the page. This is called the Hertzsprung-Russell diagram (or HR diagram). It is a very important tool in Astrophysics. You can see that the diagram is divided into several groups. The most important one being the `main sequence' which runs from the top left to the bottom right. Our Sun is a G type main sequence star. Only about 8% of all stars are G type so our Sun is actually quite exotic. The most common group by far is the M type stars (about 78% of the main sequence stars are M type). Most of these are small red dwarf stars. In contrast O-type stars are very big and very luminous though not always very bright ­ at least not in visible light; because they are so hot they shine mainly in UV light. Since they are so hot it is believed that planets cannot form around them (the planets would evaporate!). An easily spotted O-type star is Alnitak, the lowest

"Brown dwarfs can be thought of as failed stars"
star in Orion's Belt. We will take another look at the HR diagram and stellar evolution i.e. what happens to a star from its creation to its death in next month's Astronotes. I want to finish off this article by taking a look at some of the more exotic spectral types. W or WR stars: They are also called Wolf-Rayet stars. These have extremely high surface temperatures (up to 70,000 °), eleven or twelve times

Image Credit: Paul O'Neill, Armagh Planetarium


10 Astronotes May 2007 Some of them are so small that they are not even classed as proper stars. A star must produce its own light. These objects are either very dim or even black when looked at in visible light. The little they radiate is mainly infra-red light. Brown dwarfs can be thought of as failed stars; much bigger than a planet but just not big enough to make it as a star. Tiny trio A small red dwarf star compared to a brown dwarf and Jupiter. the surface temperature of the sun. Their spectra have very strong helium lines. It is believed that they are the dying remnants of super giant stars; the outer layer of the star has been blown off into space revealing a hot helium-rich layer beneath. L and T type stars: at the smaller cooler end of things are the tiny red and brown dwarf stars. D type stars: These are also dwarf stars but this time white rather than red. They are believed to be the cores of dying stars. All that's left after the outer layers have been blown away. White dwarf stars no longer produce light by nuclear fusion, they continue to glow like a dying ember until they have slowly cooled and become cold black balls of dense matter not much bigger than a planet. Our sun will one day end up as one of these cold dead black dwarfs.

Image Credit: Paul O'Neill, Education Support Officer

Holiday with the Stars
By Wendy McCorry, Science Communicator Tired of going to the same old holiday destinations? Fancy going somewhere a bit different? Got a few thousand pounds to spare? Then perhaps you might like to book a trip to space on Richard Branson's Virgin Galactic spaceline. At a cost of $200,000 (about ё105 000) per ticket, Virgin Galactic are offering a three day package including hotel accommodation (with meals and champagne thrown in); pre-flight training; transport to and from the Spaceport America launch site in New Mexico, as well as the 2.5 hour space flight. Of these 2.5 hours, only around seven minutes are actually spent in space, with approximately four minutes of zero-gravity, where passengers can release their seatbelts and float around the cabin. The spaceship will be fitted with numerous windows, offering views of thousands of kilometres in every direction, and allowing passengers to marvel at the sight of our Earth viewed from space. You might think all this sounds like a far-off dream, but Branson hopes to begin his unusual

SpaceShip 2 Virgin Galactic's craft for space tourism looks like a science fiction toy but is a practical vehicle. package holidays as soon as 2009. He has teamed up with aerospace designer Burt Rutan to create The Spaceship Company, whose aim

Image Credit: Virgin Galactic


May 2007 Astronotes 11

White Knight I Virgin Galactic intends that an enlarged version of this aircraft, White Knight II, will carry a SpaceShipTwo into the stratosphere for launch. Effectively it is the first stage of a two-stage space launcher . is to manufacture an entire fleet of commercial spaceships and launch aircraft. In June 2004, Rutan and his team flew the first privately funded human space flight on SpaceShipOne. In the same year they won the Ansari X Prize, a $10 million reward offered to the first non-government organization launching a reusable manned spacecraft into space twice in two weeks. In 2005, with funding from Branson, work began on constructing SpaceShipTwo (a scaled-up version of SpaceShipOne), of which 5 will be built for commercial use by Virgin Galactic.

climb, with the aid of rockets, to a height of 110 km (360 000 feet). Virgin Galactic claim that this method of launching is not only much safer than a ground launch, but is also kinder to the environment, as less fuel is required to launch the craft. Branson is planning to make one of the first flights himself, along with his parents and his children, in a bold effort to allay fears about safety. Numerous well-known figures have also reportedly booked their tickets. These include astrophysicist Stephen Hawking, Star Trek actor William Shatner and Hollywood director Bryan Singer. But before you race out to buy your ё105 000 ticket, it may be more prudent to wait, as Virgin executives have forecast that, once the industry is underway, the price of seats is set to tumble. If you would prefer to stay in space a little longer than a few minutes, Virgin Galactic also have plans to create a space hotel with which future spaceships will be able to dock. Watch this space...

"Branson is planning to make one of the first flights himself"
Unlike the Space Shuttle, SpaceShipTwo will be launched from the air rather than the ground. A launch aircraft named White Knight II will carry the spaceship, containing six passengers and two pilots, to a height of 15 km (50 000 feet). The spaceship will then detach and begin its

An irony of history
By Colin Johnston, Science Communicator On 28 January 1986 the Space Shuttle Challenger exploded shortly after launch. All seven crew members were killed. The tragedy was recognised world-wide and letters of sympathy flooded in to NASA and the White House. Historian Dwayne Day recently located a letter from a well-wisher among the papers of the late President Reagan. In light of recent history its sender's name may surprise you. It reads in part: "I have learned with profound sorrow the news of the explosion and crash of the Challenger. While viewing the accident as a great scientific loss, may I express my deepest condolences...to the American people and especially to the families of the victims of this accident. I pray that God will grant all of them fortitude. Saddam Hussein, President of the Republic of Iraq"

Image Credit: Wikimedia.org


12 Astronotes May 2007

Image of the Month
Image Credit: NASA, ESA, Hubble Heritage Team (STScI / AURA) Hubble Heritage (STScI/AURA)

Here is possibly the only joke in all of astronomy. Two spiral galaxies walk into a pub. The first one goes up to the bar and asks for two drinks, one for him and one for his friend. The barman looks suspiciously at the second spiral galaxy and says "I'm sorry but I can't serve your friend, he'll have to go." The first spiral galaxy complains, "Why can't you serve him?" The barman replies, "He's barred." Get it? He's a barred spiral galaxy! Many spiral galaxies have bars of stars, gas and dust running across their centres. We have even discovered that our own Milky Way has a modest central bar. However the bar in NGC 1672, shown in the spectacular Hubble Space Telescope image above, is a much more prominent feature. Galaxies are islands of stars and dust in a Universe otherwise empty of `ordinary' matter. A galaxy can contain between a million and a trillion stars. Galaxies like the Milky Way and NGC 1672 are classed as spirals

(although of differing sub-type). The spiral arms are made of stars and gas pressed together in `density waves' where their average speed is less than the galaxy's rotational speed. Bars are believed to be temporary structures caused by a density wave radiating from the galaxy's centre. Apart from the bar, the image shows all the familiar galactic elements. There is a bright nucleus that is likely to contain a supermassive black hole, concealed by the orange glow of the old Population II stars gathered in the core. We can also see dark wispy dust lanes, scattered nebulae glowing in the distinctive red of hydrogen and clusters of bright blue new stars. NGC 1672, is about 75 000 light years (23 kpc) across, somewhat smaller than the Milky Way. It is 60 million light years (18 Mpc) from us in the Southern Hemisphere constellation Dorado (the Swordfish). (Caption by Colin Johnston, Science Communicator)

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 ©2007 Armagh Planetarium All rights reserved