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January 2007

ASTRONOTES
Incorporating FRIENDS' NEWSLETTER Is there another Earth? 2007's Space Odysseys Time Travel in Limerick! Eric Lindsay: in memoriam The Dark Side of the Universe

ARMAGHPLANETARIUM


2 Astronotes January 2007

Is there another Earth?
By Wendy McCorry, Science Communicator The search for habitable planets will take an important turn in the next few weeks, with the launch of the COROT satellite. COROT (COnvection, ROtation and planetary Transits) is a mission led by the French Space Agency (CNES) in conjunction with the European Space Agency (ESA) and partners from other countries. The purpose of the mission is to search for Earth-like planets orbiting stars outside our Solar System. Planets existing beyond our Solar System are called exoplanets. Up until now, the only exoplanets to be discovered have been gas giants similar to Jupiter. These giant planets have been detected by ground-based telescopes, through observation of the `wobbling' effect they have on their parent star due to gravity. Smaller rocky planets do not have such a marked effect on the star they are orbiting, as they have a much weaker gravitational pull. Therefore, the detection of these rocky exoplanets is much more difficult, and can only be achieved using a space telescope, where all distorting effects of the Earth's atmosphere are removed. Using a 27cm diameter telescope and camera to monitor the brightness of stars, COROT will be able to detect the occurrence of micro-eclipses caused by a small rocky planet passing in front of its parent star. Astronomers expect to find a new class of exoplanet, several times larger than the Earth (our biggest rocky planet) but not as large as the gas giants. It is estimated that COROT will discover between 10-14 of these rocky worlds in each starfield image, and possibly dozens more of the giant gas bodies. Every 150 days, as the sun's rays begin to affect the telescope's observations, COROT will turn through 180 degrees to observe a new region.

"COROT's first target will be towards Orion"
Whilst observing a star, COROT will also be able to detect its mass, age and chemical composition using asteroseismology. Similar to the way in which seismologists can detect the composition of the Earth by monitoring earthquakes, COROT can gain information on the internal structure of stars through studying `starquakes'. These internal acoustic waves travel outwards from the centre of the star, causing ripples to spread across its surface. It is these ripples that can then be recorded. COROT is due to be launched on a Soyuz 2 rocket at Baikonur, Kazakhstan on 27th December 2006. After launch, it will be set onto a polar circular orbit around Earth. Its first target region will be towards the constellation Orion, followed 150 days later by a change in direction to point towards the centre of the Milky Way. It's possible the search will uncover other planets just like Earth ­ so watch this space.

Image Credit: CNES 2006 - D. Ducros

Earth Search An artist's view shows the COROT satellite, consisting of a 30 centimetre space telescope to be launched in late 2006. Powered by a pair of solar panels, the satellite weighs 630 kg, is 4.10 m long and is nearly 2 m in diameter.


January 2007 Astronotes 3

2007's Space Odysseys
By Colin Johnston, Science Communicator What will be the significant days in 2007 for astronomers? What exciting space adventures will take place this year? Here are some dates to note in your diary. 3 January: Our planet is at perihelion, its closest point to the Sun. The Sun will be 147 million km away. 26 January: This is the centenary of the birth of Eric Lindsay, director of Armagh Observatory. Decades of hard work by Dr Lindsay led to the founding of Armagh Planetarium, so we will certainly be celebrating this anniversary. 27 January: On this day in 1967 astronauts Gus Grissom, Edward White, and Roger Chaffee were killed by a fire in their Apollo capsule. This terrible accident delayed the Apollo project, but thirty months later Apollo 11 landed safely on the Moon. February: A single Ariane 5 booster will launch two important science missions simultaneously. Herschel is an orbiting infra red telescope and Planck Surveyor will study the cosmic microwave background. 10 February: Saturn will be at Opposition. The ringed planet will be at its closest to Earth. This could be a good time to observe Saturn and its moons. 28 February: The New Horizons probe will make a gravitational assist manoeuvre around Jupiter to change its trajectory towards Pluto. The probe will rendezvous with the dwarf planet in 2015. 3-4 March: A total eclipse of the Moon will be visible over the eastern Americas, Europe, Africa, and western Asia. 19 March: A partial Solar Eclipse will be visible in Red Moon Our satellite may be a startling sight during March's eclipse. Asia and Alaska. 29 March: The asteroid Vesta was discovered two hundred years ago today by Heinrich Olbers. 24 April: `The Sky at Night', the BBC's long running astronomy programme will celebrate the fiftieth anniversary of its first broadcast on this day. Sadly, this date is also the fortieth anniversary of a fatal space accident. Soyuz 1 was launched on this date in 1967. Tragically, the craft's pilot cosmonaut Vladimir Komarov became the first space traveller to perish during a mission when the craft's parachutes failed as it returned to Earth. Later Soyuz craft have been much more successful. Improved versions of the design are still the workhorses of the Russian space programme. 5 June: The MESSENGER spacecraft will make its second flyby of Venus en route to Mercury, finally arriving at the innermost planet in 2011. 6 June : Jupiter will be at Opposition, the giant planet will be at its closest to Earth. 20 June: The Dawn spacecraft is scheduled to be launched on a mission to asteroid Vesta (arriving 2011) and dwarf planet Ceres (arriving 2015).
Image Credit: NASA


4 Astronotes January 2007 five years ago today when radio researcher Karl Jansky determined that some of the radio noise he was investigating originated from Sagittarius. 4 October marks the fiftieth anniversary of the start of the Space Age. The first artificial satellite Sputnik 1 was launched on this date.
Image Credit: ESA

7 October: The Gamma-ray Large Area Space Telescope (GLAST) will be launched. This satellite's task is to investigate high energy astrophysical phenomena. De la terre Þ la ISS The ATV Jules Verne approaching its destination. On board are nine tonnes of water, food and other supplies. July: ESA's first Automated Transfer Vehicle, Jules Verne, will carry a cargo to the ISS. 4 July: This is the tenth anniversary of the arrival of the Pathfinder probe on Mars. Its famous passenger was the Sojourner rover which in 83 days of operation sent 550 photographs back to Earth as it wandered through the rock-strewn landscape around Pathfinder. 3 August: This is the planned launch date for NASA's Phoenix Mars lander. This will hopefully be the first craft to land in the Red Planet's polar regions in May 2008. It will spend 90 days investigating the surrounding icecap. 20 August: This date marks the thirtieth anniversary of the launch of Voyager 2. The Voyager project was a magnificent success revealing the wonders of Jupiter, Saturn, Uranus and Neptune in unprecedented detail. 28 August: Another total eclipse of the Moon will occur. It will be visible in North America, most of South America, Australasia, the Pacific Ocean and Antarctica. 5 September: The Voyager 1 probe was launched thirty years ago today (two weeks after Voyager 2!) 11 September: Partial Solar Eclipse visible in South America and Antarctica. 16 September: Radio astronomy began seventy 18 October: On this date in 1967, Venera-4 became the first probe to directly analyse the environment of another planet as it descended through the hellish atmosphere of Venus. The harsh conditions destroyed it before it reached the surface. 11 October: The Jodrell Bank radio telescope started to scan the skies fifty years ago today. Now known as the Lovell Telescope it remains in service today 28 November: Forty years ago today, graduate student Jocelyn Bell noticed a strange "bit of scruff" in the data from the radio telescope at the Mullard Radio Astronomy Observatory. This was the first pulsar to be discovered. 14 December: On this date in 1972, the crew of Apollo 17, including Eugene Cernan and Harrison Schmitt, returned to Earth. Cernan and Schmitt are the last people to visit the Moon to date. 24 December: Mars at opposition. The red planet will be at its closest approach to Earth and its face will be fully illuminated by the Sun. This is the best time to view or photograph Mars.

Dawn of a new age Sputnik's launch began humanity's expansion beyond our planet.

Image Credit: NASA


January 2007 Astronotes 5

ERIC MERVYN LINDSAY: IN MEMORIAM
Image Credit: Armagh Observatory

by Tom Mason, Director Eric Mervyn Lindsay was born near Portadown on January 26th, 1907 as the seventh son of schoolteacher parents. He was the youngest of thirteen children. He was educated at King's Hospital School in Dublin, and later graduated with a physics BSc in 1928 and an MSc in 1929 at the Queen's University of Belfast. He travelled to Boston where he studied astrophysics under Harlow Shapley at Harvard University, earning an MA in 1931 and his doctorate in 1934. Lindsay's time working at the Harvard College Observatory in the United States significantly influenced the rest of his career, and links and friendships formed at that time shaped and directed much of his later work.

"He left Harvard for a barely functioning Armagh"
After he graduated with his doctoral degree he went to South Africa where he worked as Chief Assistant at Harvard's Boyden Station. Bloemfontein nestles in a fold on the highveld, the huge elevated African plateau, where the nights are cold and clear, and the wonders of the southern skies are revealed. Lindsay worked on southern sky stars for his doctoral thesis and his fascination for this part of the heavens never waned. His contemporaries were surprised when he applied for, and was appointed to, the vacant Director's post at Armagh. He returned to Ireland as Director of Armagh Observatory in 1937. Shapley and Bart Bok at Harvard certainly thought that his move was odd, for he left what was then a very well-founded and financed Observatory at Harvard for the run down and barely functioning Armagh. When he arrived the income of the Observatory was minimal, he had no staff, and not much in the way of working

Eric Lindsay (1907-1974) He has a 32 km diameter lunar crater named in his honour. astronomical equipment. Lindsay immediately set about modernising the Observatory and with his characteristic energy he soon improved the situation. It is a matter of record that the Observatory thrived under his direction, and he was responsible for several innovative developments. The first was his ability to play with the cards he had been dealt, and he showed great skill at working the fractured politics of the time to gain support from the governments of the Republic of Ireland as well as that in Stormont. He obviously made a very persuasive case and succeeded beyond the expectations of all in his efforts to pull Armagh back to the forefront of astronomy. When he arrived in 1937 the Observatory had no other staff, and its income from the government was ¸100. At the time of his sudden death in 1974, there was a staff of four astronomers, a secretary and a technician, and an annual grant of around ¸20 000. From a planetarian's perspective, Lindsay the visionary was aware of the first modern planetarium being established in Munich in 1923. He also


6 Astronotes January 2007 was aware of the success of the new planetarium facilities that were being opened in the major cities in the USA, notably the Adler in Chicago. His experience in the United States made him aware of the American way of founding institutions that were endowed and funded by wealthy individuals who wished to return benefits and to contribute to their host or nurturing communities. Lindsay realised that the planetaria had successfully brought astronomical knowledge to a wider public, and in the middle of the Second World War he started to dream about setting up a planetarium at Armagh. He knew of the interest of people who came to the Observatory, but realised that the elegant old buildings of the Observatory were unsuitable to host large numbers of visitors. He thought that it would be best to set up a separate building, purpose-designed for its audience, and to install the latest electro-mechanical projector to show audiences the night skies on the hemispherical roof.

A Permanent Memorial This dedication plaque is mounted over Armagh Planetarium's reception desk. (later Lord Brookeborough) of the rightness of his cause, when the Fermanagh-based family was more noted for its ability to nurture famous military men, politicians and lawyers. The person who was invited to head the Planetarium project was Patrick Moore, but despite being involved in its construction, he left Armagh before the organisation started to fully function, so he was not really involved in its strategic direction following its opening in May 1968. Eric Lindsay's further great gift to the Planetarium project was his appointment of Terence Murtagh as Director in 1971. Under Murtagh's direction the Planetarium became famous for innovation and experimentation, a tradition that is being reworked today. Modern planetaria that are driven by digital projection systems, especially the Evans & Sutherland Digistar 3, owe their success to experimental work with video projection on the complex curves of the theatre dome as well as interactive seating, which also was invented at Armagh. Eric Lindsay was ahead of his time in realising that the general public were genuinely interested in things astronomical. Shortly after the Planetarium opened in Armagh the first leg of the space race was won by the Americans, when they successfully landed astronauts on the Moon. Since then the Planetarium has been busy fulfilling Lindsay's dream. In the refurbished Planetarium buildings that were re-opened to the public in July 31st 2006, we are witnessing a splendid new incarnation of the Armagh Planetarium: we are back where we belong, on the cutting edge of innovation within the planetarium industry: and already winning prizes to prove it.

"in the middle of WW2 he dreamed about starting a Planetarium in Armagh"
It took twenty five years of hard work, including much footslogging in the United States seeking funding and advice from colleagues in the astronomy world, but he eventually raised sufficient funding from the local community and both governments in Ireland, and Armagh Planetarium was opened in 1968. In his dealings with the Northern Ireland government he also carefully sought assistance from Eamon de Valera in Dublin, who of course had founded his own brainchild, the Dublin Institute of Advanced Studies (DIAS) in 1940. At Lindsay's prompting De Valera expanded the original DIAS concept to include a school of cosmic physics that brought Dunsink Observatory under DIAS wing. At the same time the Armagh Dunsink Harvard Observatory was set up in South Africa, again due to Lindsay's personal contacts and judicious lobbying. De Valera was a mathematician, so this support was in character, but even more remarkable was Lindsay's ability to convince Sir Basil Brooke

Image Credit: Colin Johnston, Science Communicator


January 2007 Astronotes 7 The purpose of this short article was to remember Dr Eric Mervyn Lindsay, and it is fitting that at a ceremony held at the Planetarium on December 7th 2006, Archbishop Robin Eames, in his last official function as Chairman of the Board of Governors and the Management Committee, unveiled a plaque in the main entrance area to commemorate the event and which dedicated the entire Planetarium building to Eric Lindsay's memory, we hope that this will be seen as a fitting tribute to his vision. Reach high, for stars lie hidden in your soul. Dream deep for every dream precedes the goal. Pamela Vaull Starr

Moon Phases, Jan 2007
Wed 3 Jan Thurs 11 Jan Fri 19 Jan Thurs 25 Jan FULL MOON Last Quarter NEW MOON First Quarter

The Size of Space
By Colin Johnston, Science Communicator As visitors to the Planetarium admire the images in our Celestial Cathedral, they often ask variations on the question "How do we know how far away these things in space are?" In recent Astronotes I have tried to answer this by showing how astronomers have, over the past couple of centuries, carefully developed techniques to measure the Universe. As pioneered by Bessel, the distance to relatively nearby stars can be determined through their parallax, their apparent movement in the sky as the Earth's orbital movement alters our vantage point. For more distant stars we must use other techniques. Fortunately nature has provided us with a very useful standard candle. Leavitt showed that the yellow variable stars called cepheids pulse at a steady beat proportionate to their brightness. By watching the pulse rate of a cepheid proportional to the galaxies' distances. This was later called Hubble's Law. Here then is another method to gauge the size of the Universe and there are yet more. Novae are enormous nuclear explosions which occur when a white dwarf star in a binary system accumulates a critical mass of hydrogen leeched from its companion star. When there is enough hydrogen crushed into a small enough volume at high enough temperature a nuclear fusion reaction sweeps across the white dwarf's surface and eventually we will see a spectacularly bright new star (hence nova) in our skies. The white dwarf itself is left more or less intact

we can tell how bright it is and work out how far away it is. Hence if we see a distant galaxy and can pick out any cepheids lying within it, we can calculate its distance. Later Hubble discovered than the light from distant galaxies was `stretched out' or redshifted by amounts

A section of the Hubble Ultra Deep Field The light from these galaxies was emitted as ultra-violet. They are so far away that the Hubble red shift has transformed ultra-violet to visible.

Image Credit: NASA

"the star is blasted apart, briefly becoming the brightest star in the galaxy"


8 Astronotes January 2007 after this ordeal. As this cataclysm always occurs at a particular threshold, the magnitude of the explosion tends to be always the same. In other words all novae are, more or less, equally bright. Therefore they are another standard candle. Novae have been observed in nearby galaxies and their brightness has been used to compute their distances. The results are good matches to the distances obtained through cepheid variable stars. This, however, is not the only catastrophe that can befall such a white dwarf star. Some experience a much worse fate. If enough material falls fast enough on to the dwarf, the additional mass can cause the star to collapse in on itself, abruptly compressing the matter in the star. Now white dwarfs are rich in carbon, and in these unusual circumstances, nuclear fusion occurs in this carbon. This releases so much energy so quickly that the star is blasted apart, briefly becoming the brightest star in the galaxy. This dramatic utter destruction of a star is called a Type 1a supernova (the `1a' is to distinguish it from stars which have exploded through other mechanisms). A supernova can remain extraordinarily luminous for a long time: in the early 1600s Kepler's supernova was visible for 366 days. From observations we know that the bigger and brighter the 1a supernovae, the longer it takes to fade. So we have yet another standard candle, some 1a supernovae have been seen in other very distant galaxies, too far away for us to resolve cepheids, allowing astronomers to determine their distances, and helping verify Hubble's Law. Spiral galaxies rotate extremely slowly, taking hundreds of millions of years to make a rotation. It may seem surprising but we can measure their speeds of rotation. Once again, the technique uses the Doppler effect, the phenomenon where light waves from an approaching source are squeezed towards the blue end of the spectrum and light waves from a receding source are stretched into red. In a nutshell, by observing the red shift of the side of the galaxy which is turning away from us and the blue shift of the side turning towards us we determine the galaxy's rotation speed. Why is this relevant to the size of the Universe? Analysis shows that there is a relationship between the rotational speed of a galaxy and its brightness. This is called the Tully-Fisher relation. So if the rotational velocity of a spiral galaxy can be measured, the luminosity can be determined. Combine this with how bright it looks and we get the galaxy's distance. Astronomers have developed a range of methods to measure the size of the Universe to a great deal of confidence. At present, the deepest image of the universe ever taken in visible light is the celebrated Hubble Ultra Deep Field. This astonishing picture from the space telescope includes about ten thousand galaxies like scattered grains of sand. Some of the smaller, reddish galaxies are the most distant galaxies we have ever seen, existing when the universe was just 800 million years old. These are the furthest away things in the observable Universe (not necessarily in the entire Universe) and they are some 13 billion light years away. Bessel, Leavitt and Hubble's discoveries were the foundations on which our knowledge of the scale of the Universe is built. They would be astonished and awed by what has been revealed.

Time Travel in Limerick
By Robert Hill, Northern Ireland Space Office On November 14th 2006, and as part of the National Science Week in Ireland, the Armagh Planetarium, Northern Ireland Space Office and Space Connections, in collaboration with the University of Limerick, gave four presentations entitled `Time Travel with the Hubble Space Telescope'. All four lectures, given by Robert Hill, were completely booked out by teachers and pupils from local primary and secondary schools. The last show of the day was held at the University of Limerick Concert Hall in front of nine hundred and fifty schoolchildren and teachers. The feed-


January 2007 Astronotes 9 back from the event has been tremendous with teachers asking for more events of this kind to be hosted by the University. The Shannonside Astronomy Society prepared an exhibition in the Atrium area at the university's Foundation Building to coincide with the talks. This was an opportunity for children to get their hands on some real telescopes and enhance their understanding of our Universe. The Faulkes Telescope project was also represented at the Shannonside stand with many leaflets and flyers going home with students and teachers. Many thanks go to Lars Lindberg Christensen at ESA Hubble for providing the imagery for the talks, Bernie Quilligan at the University for organizing and hosting the event and the folks at the Shannonside Astronomical Society for dealing with the huge crowds so splendidly! ESA/Hubble, NISO and Space Connections are
Image Credit: Robert Hill, NISO

The Roar of the Crowd Robert's final lecture was to almost a thousand people. now collaborating on a permanent exhibit at the Armagh Planetarium and on creating 3D stereographic shows about the NASA/ESA Hubble Space Telescope to be shown at various venues and events across Ireland. It is hoped that these will be available for viewing at the Planetarium early next summer.

The Universe's Dark Side
by Paul O'Neill, Education Support Officer What is Cosmology? It is the study of the universe in its totality including its past and predicted future forms. During the latter half of the 19th and early part of the 20th centuries Physics underwent a revolution with the introduction of Einstein's theories and Quantum physics. At present cosmology may be undergoing an equally radical change. The ideas of Dark Matter and Dark Energy are certainly revolutionary. But as yet they are far from being understood. A conversation between a cosmologist and a noncosmologist might go something like this: Non-cosmologist: Cosmologist: What is the universe made of? Dark Energy = 70% Dark Matter = 25% Free H and He = 4% Stars = 0.5% Neutrinos = 0.3% Heavy elements = 0.03% What is Dark Matter? Cosmologist: Non-cosmologist: Cosmologist: We aren't sure. What is Dark Energy? We have no idea. So if we have little or no idea what these `dark' things are how can we say they exist? The answer begins with galaxies. To weigh a galaxy we can look at its distance, size and luminosity (how much electromagnetic radiation is emitted by the galaxy). From this we can estimate the mass of the galaxy. Or we can study the spectra of stars in different parts of the galaxy and from this estimate their velocities (the stars in a galaxy are rotating around the galaxy's centre of gravity). From these velocities we can estimate the galaxy's mass. The problem is when we use these two methods we get two very different results. Also, we expect the stars in the outer parts of a galaxy to have lower rotational velocities than the stars in the inner parts but this is not what we actually see. There are two ways we can interpret this: 1. Our observations are wrong or our interpreta-

Non-cosmologist:


10 Astronotes January 2007 Where does the Dark Energy come in? When we study the spectra of distant galaxies we see they are red shifted ­ we interpret this as the expansion of the universe ­ a consequence of the Big Bang. The problem is this expansion is accelerating...where does the energy to cause this acceleration come from? Dark Energy? In this case the adjective dark suggests something unknown rather than something which doesn't emit radiation. How does Dark Energy fit into the evolution of the universe? · The Big Bang ­ Universe expands rapidly · Ordinary matter appears ­ stars etc. · The mutual gravitational attraction between this matter slows the rate of expansion · Once the universe is beyond a certain size Dark Energy, which is a repulsive force, forces galaxies apart. In other words it accelerates the expansion of the universe. One possible alternative is Modified Newtonian Dynamics (MOND), this idea attempts to explain the observational data by making gravity stronger at great distances or in weak fields. The theory however has problems: it's difficult to construct a relativistic MOND. One or two recent attempts are looking promising, for example, the Nonsymmetric Gravitational Theory proposed by J.W. Moffatt. These ideas and another called Tensor-Vector-Scalar (TeVeS) may be able to match observational data without the need for exotic (i.e. nonbaryonic) dark matter. So there are two camps ­ on one side are the cosmologists who favour Dark Matter and Dark Energy (the Dark Side?) versus those who are searching for an alternative theory for gravity ­ eliminating the need for exotic unknown forces and matter.
Image Credit: NASA

Einstein Ring A gravitational lens created by a galaxy cluster believed to reveal the presence of Dark Matter. tions of the observations are wrong. 2. The galaxies are much more massive than expected and consist of matter we can detect and something else we can't see i.e. Dark Matter. So what might this Dark Matter be? Many cosmologists believe that it may consist of nonbaryonic particles. Baryonic matter is the family of subatomic particles which are made of three quarks, such as the familiar proton and neutron. Other possible candidates include ordinary and heavy neutrinos, dwarf stars and planets and clouds of gas. Whatever it is this matter must be considerably more common than `ordinary' matter, in fact we are made of some of the most exotic material in the universe i.e. heavy elements such as carbon and iron.

Bluffer's Guide to Orion
by Colin Johnston, Science Communicator Orion the Hunter is the easiest identifiable constellation in the skies of the Northern Hemisphere. Big, and full of bright stars and interesting objects, Orion is a favourite amongst stargazers. Best of all, Orion is one of the tiny minority of constellations that actually looks like what is supposed to represent! Take your audience outside about 10.00pm on an evening in the middle of the month and look south. You cannot miss Orion, a broad-shouldered, narrow-waisted figure with raised arms. Straight away the three stars in his belt will grab your attention, followed by the glittering white star Rigel in his left foot and the bright orangish star Betelgeuse in his right shoulder (assuming


January 2007 Astronotes 11 Orion is standing facing us and not with his back to us). Then as your eyes become accustomed to the dark you will discern the fuzzy star of his sword (except it's not a star as we shall see later). Rigel is well-named, as the name is a mangled version of the Arabic for `the left foot of the Central One'. The star is a B-class supergiant, according to the Hipparchos satellite it is 773 light years away and is about 40 000 times as bright as the Sun, making it the brightest star in our galactic neighbourhood. Betelgeuse is an M-class red supergiant, one of the largest stars known. If it were at the centre of our Solar System, its outer surface would possibly extend to the orbit of Jupiter, but thankfully Betelgeuse is really about 430 light years away. Betelgeuse is a highly variable star, sometimes it is actually brighter than Rigel. The star in the opposite shoulder from Betelgeuse is called Bellatrix and is the third brightest in the constellation. Orion's sword hangs from his belt (the stars in the belt are called Alnitak, Alnilam and Mintaka) and looks like a diffuse star. It is in fact a nebula catalogued as M42. M42 is about 1500 light years away and thirty light years across, and is the closest region of star formation to Earth. A lot of what proper astronomers know about how stars and planetary systems are formed from collapsing clouds of gas and dust has come from observing the Orion Nebula. As well as finding about seven hundred stars in various stages of formation, astronomers have discovered protoplanetary discs, brown dwarf stars and chaotic flows of hot gases in the nebula, these are all thing you would expect to find in stellar nurseries. As well as being interesting, the nebula looks really cool too (see Image of the Month in the December 2006 Astronotes). Also in M42 (although you will need a telescope to pick it out) is the Trapezium, a tight open cluster of stars which have formed out of the nebula. So who was Orion and what is he doing in the sky? Well, everyone knows he was a hunter but that is about it. The problem is that, unlike most constellations, the myths about Orion are rather rambling and contradictory, for example there are two totally different versions of his death. In short, Orion was a big, loud giant of a man and
Image Credit: Colin Johnston, Science Communicator

The Mighty Hunter Orion stands proudly in the sky. Sirius is the prominent star in the lower left, and part of Taurus can be seen at upper right. Diagram created with Starry Night software. indeed a mighty hunter, he also inherited some aquatic superpowers from his father who was the sea god Neptune. He also had a pet dog. When Orion met Diana, goddess of hunting, which they shared as a common interest, they got on famously, and soon wedding bells were in the air. Unfortunately for the couple, her brother Apollo didn't approve of the union and set out to get rid of his future brother-in-law-permanently! One version is that Apollo sent a scorpion to sting Orion to death. The other story goes that in one of those underhand tricks Greek gods were good at, one day when Orion was out for a swim; Apollo bet his sister that she could not hit a distant speck far out at sea with her bow. To prove him wrong, she fired an arrow which scored a direct hit; only when Orion's body washed ashore did Diana discover that her target had been her boyfriend. Whichever way he was killed, after a good cry, Diana put Orion up among the stars along with his favourite belt, sword, lion's skin and club. Sirius, his dog, was put up beside him. Orion's Belt is a handy guide to find other interesting objects. Following the line it makes upwards takes you to Aldebaran. Go the other way and you'll get to Sirius, the brightest star in the sky. The next bluffer's guide will fill you in with the details of Orion's other celestial neighbours.


12 Astronotes January 2007

Image of the Month
Image Credit: NASA/Mars Reconnaissance Orbiter/HiRISE Operations Centre/University of Arizona.

This breathtaking photo is a close-up of Meridiani Planum, a region located close to the equator of Mars. Taken at the local Mars time of 3.28pm, it shows the 800m diameter Victoria Crater illuminated from the west. The sun is shining on the crater from 33.8 degrees above the horizon, which beautifully highlights the crater wall. As the sun hits the crater, the scalloped cliff edges can be clearly seen casting shadows over the top. These jagged cliff edges are a result of erosion since the impact that gave birth to the Victoria Crater, and the downward movement of sediment is clearly visible from the streaks that descend to its centre. This

residue from erosion has gathered at the bottom to form a cluster of sand dunes, which add a beautiful, rippling visual to this image. This stunning picture was captured using the High Resolution Imaging Science Experiment (HiRISE) camera, onboard the Mars Reconnaissance Orbiter Spacecraft. This overhead view of the crater will assist the Mars Exploration Rover Opportunity to explore the Victoria Crater by greatly increasing the capability of sustained exploration through the combined efforts of orbiters and Landers. (Caption by Naomi Francey, Education Support Officer)

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