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June 2007

ASTRONOTES
Incorporating FRIENDS' NEWSLETTER Observing Challenges for Summer Gliese 581c: Rorschach World David Malin visits Armagh Life in Hostile Places Missions of Gravity

ARMAGHPLANETARIUM


2 Astronotes June 2007

Summer Star Gazing Challenges
By Paul O'Neil, Education Support Officer If you enjoy a challenge and stargazing, and have access to a reasonably dark sky then here are three astronomical phenomena to keep you busy over the coming months: Mars;although those clouds are probably CO2 ice rather than water ice. Where and what should you look for? Well look towards the northern sky after sunset, as the sky becomes darker you'll have a better chance of seeing them. They appear to glow white or bluish white and often appear to resemble cirrus clouds. (Note: PMCs are not the same as aurorae; they are quite different phenomena.) Challenge Two: Meteor Trains When a dust particle enters the atmosphere at high speed it burns up producing a streak of light called a meteor (shooting star). The heat generated by friction can ionise molecules in the atmosphere resulting in a nebulous glow along part of the meteor's path which persists for some time after the meteor is gone; this is called a meteor train. They can be visible for up to 45 minutes or more, though usually it is only a few seconds.

Image Credit: NASA

Noctiiucent Clouds photographed by astronaut Ed Lu from the International Space Station (ISS) in 2003. Challenge one: Noctilucent Clouds These are also known as Polar Mesospheric Clouds (PMCs). If you live between latitudes 50°N and 60°N then June provides the best chance of seeing these elusive clouds. Little is known about them except that they form at very high altitudes (about 80km) and are made of water ice. This spring a satellite called AIM (Aeronomy of Ice in the Mesosphere) was launched by NASA to study PMCs. The mission will take two years, after which we should know more about how these clouds can form so high in the Earth's atmosphere. In recent years PMCs have become more noticeable: some scientists believe this may be due to Global Warming, though there is inconclusive evidence for this claim. Scientists studying the Martian atmosphere have also discovered very high level clouds over

"sporadic meteors can appear at any time and from any direction"
Where and when to look: sporadic meteors can appear at any time from any direction. Shower meteors are more predictable and reliable. The best meteor shower ­ the Perseids ­ is in August (on the 13th) and this year the moon will not interfere. So around the 13th, if the skies are clear, go outside (before dawn is best) and look towards the constellation of Perseus (see sky map included in every issue of Astronotes). (If you've never watched a meteor shower before then the word shower may be misleading, you'll probably only see about seven or eight meteors every hour.) Remember if you do see any meteor trains they


June 2007 Astronotes 3

Why Noctilucent clouds seem to glow The Sun is under the horizon but it can still illuminate the clouds. will probably only last a few seconds and will Sun than the Earth's. Both planets will become not have time to contort into the twisted shapes visible in the morning sky in late August. Venus shown in the NASA image below is one of the brightest objects in the sky and is usually quite easy to find. Mercury is visible to the naked eye but because it is so close to the sun it only appears low in the dawn sky a short time before sunrise (or in the evening sky after sunset); you will need a clear eastern horizon to stand a chance of seeing Mercury (I've only seen it four or five times in my life). The only close-up views we have of the planet were obtained by the NASA Mariner probe which succeeded in imaging part of the surface back in the 1970s. But a new probe ­ MESSENGER (MErcury Surface, Space ENvironment, GEochemistry and Ranging) will arrive in orbit around the planet in 2011. However, we will hopefully get glimpses of `new'parts of Mercury when MESSENGER flies past the planet in January and October 2008 and September 2009. These flypasts are a series of gravity assist manoeuvers needed to ease the vehicle into orbit about the planet. Meteor train imaged in false colour by the USAF's Starfire Optical tracking laboratory in New One of the reasons Venus is so bright is that it Mexico. is perpetually covered in thick reflective clouds. Challenge three: The inner planets This makes it impossible to see the surface of the planet using visual imaging. The NASA probe Mercury and Venus are known as the inner Magellan used radar to map the surface down to planets because their orbits are closer to the features just 100km long. The planet has many

Image Credit: Paul O'Neill, Education support Officer Image Credit: NASA


4 Astronotes June 2007 volcanoes scattered across a surface which contains large flat planes (about 65% of the total surface area) and mountainous regions.

"Venus is one of the brightest objects in the sky"
When Venus appears in the morning sky it is often called the morning star (and the evening star in the evening sky). It looks beautiful and it's the closest planet to the Earth but it's probably one of the last planets humans would ever want to visit ­ the heavy poisonous atmosphere (mainly CO2) produces crushing pressures and traps so much heat that surface temperatures are hot enough to melt lead.

Mercury revealed A map based on Mariner probe images. note the smooth blank areas which were not imaged by the spacecraft.

The Rorschach World
by Colin Johnston, Science Communicator If you go outside at about 11.30 pm in the middle of June and look towards the South you will see some interesting things in the sky. Lying almost due South will be the giant planet Jupiter, a brilliant sight. Just below and to the right of it will be reddish Antares. Almost directly in the South-West will be the bright and bluish Spica. Between these stars lies the faint constellation of Libra, looking more like a flowerpot than a set of scales. If your observing conditions are good, try finding Beta Librae (also called Zubenelschamili) the brightest star in the constellation. If you can see Beta Librae you are looking towards another star, the M-class red dwarf Gliese 581, which suddenly became very famous in April 2007. Sadly you won't be able to see it, it is just too faint. So why did Gliese 581, a dim and obscure star, gain so much attention? The media reported that this star has a `habitable' planet. The planet may receive just enough heat from its sun so that it is neither too warm nor too cold for liquid water to exist there. All the other exoplanets (extra-solar planets) discovered so far are either too hot (because they are too close to their stars) or too cold (because they orbit too far out) for water to remain a liquid, which is essential for the existence of life as we know it. Artists' impressions of its surface depicted landscapes with dark oceans, jagged spires of rock and the neighbouring Gliesian planets looming in crimson skies. Just possibly, life could have arisen there. Perhaps we have neighbours just 20.4 light years (6.3 parsecs) from us. Should we send them a friendly greeting or prepare for visitors here on Earth? Or is this planet just science fiction?

"Just possibly, life could have arisen on Gliese 581c"
Research carried out by a team led by StИphane Udry of the Geneva Observatory, suggests that there are three planets orbiting Gliese 581. We cannot see the planets directly; it will be dec-

Image Credit: NASA


June 2007 Astronotes 5
Image Credit: ESO

Gliese 581c Although we can see the red dwarf, this fanciful artist's impression suggests a second, whiter star is also illuminating the planet. ades before we have telescopes which can make images of such faint and tiny objects. Instead we infer their existence from observable `wobbles' in the star. Presumably the gravitational pulls from orbiting worlds are enough to tug the star out of position. The Gliese 581 system is very different from our Solar System. The innermost planet, Gliese 581b, is as big as Neptune. Meanwhile, the outermost planet, Gliese 581d, is eight times as big as the Earth and orbits closer to its star than Mercury does to the Sun. This is fascinating, but it is the planet between them that grabbed the public's attention. This is Gliese 581c. There are no protocols for naming exoplanets, so Gliese 581c is all the designation the planet may ever have. Unfortunately it is a clumsy, unfriendly name, so for the rest of this article I am going to refer to Gliese 581c as `Rorschach'. Please do not think I am trying to name it, this is just to make this article easier to read. Why this name? Well, you will see why it is appropriate by the end of the article. Like all red dwarf stars, Gliese 581 is much smaller and cooler than the Sun. It is only about a third the size of our star and about 3000° C cooler. As a result it is much dimmer (only 1% as bright as the Sun). The lower temperature means that it is redder that the Sun. Beings native to Rorschach would have eyes adapted to this so they would see yellow, orange, red and infra-red light, but blue and violet would be as invisible to them as ultra-violet is to us. If the observations by Udry and colleagues

are correct, Gliese 581 is accompanied by a planet five times as massive as Earth and about 1.5 times as wide. This is Rorschach, Gliese 581c. The planet orbits 0.073 AU from the star (1AU=150 million km, the earth orbits 1AU from the Sun). Assuming these statistics are correct we can begin to make predictions about its environment. For example, its surface gravity is 2.2 times that on Earth's surface, so a 70 kg person standing on Rorschach would weigh 155 kg. We know how bright the star is so we can calculate how much solar energy the planet receives. We have seen how Gliese 581 is very small and dim compared to the Sun, but Rorschach is much closer to it than Earth is to the Sun. If you stood on the surface of Rorschach and could see Gliese 581 it would appear as a distinctly reddish glowing disc five times as wide as the Sun appears from Earth. This proximity means that in fact, the planet receives more than twice as much solar energy per square metre than the Earth. Straight away, here is an enormous difference between our planet and the new discovery. If the Earth suddenly started to receive as much heat from the Sun as Rorschach does from its star it would be a disaster. Trapped by the greenhouse effect, the heat would soon bake the life from the Earth's surface. This does not necessarily mean the same thing has happened on Rorschach; perhaps it is covered pole to pole with a layer of reflective clouds at the top of its atmosphere. Solar radiation would bounce off this curtailing a runaway greenhouse effect there.

N
Image Credit: Karen Wehrstein via Daily Kos

Gliese 581c Seascape Artist Karen Wehrstein's impression of a scene on the planet is more accurate than most. Note that this is not a sunset; the star is fixed in this position in the sky.


6 Astronotes May 2007 It is very likely that Rorschach is tidally locked to its star. The powerful torque applied by the very close star's gravity over the aeons will have forced Rorschach to take as long to rotate around its own axis as it does to revolve around its sun. A year on Rorschach lasts 13 of Earth's days and almost certainly a day on Rorschach lasts equally long, so the planet will not rotate with respect to its star. One side always faces the star in eternal daytime sunshine, the other side always faces the dark in eternal night. This immediately means Rorschach is again very different from Earth. If you are on the dayside of Rorschach, the sun will never set, hanging ominously in the sky. This may seem odd but tolerable, however imagine what could happen to a planet with an atmosphere and oceans which suddenly started to rotate like this. The dayside would warm up, with no cool of night, temperatures would soon become intolerable. Meanwhile the darkside cools, and the oceans become icebound. Wind circulation will act to distribute the heat, but on the darkside the gases in the atmosphere begin to liquefy, then freeze. In the icy darkness, the atmospheric pressure drops, sucking more and more air from the dayside. Soon the surface on the darkside is an icy, airless wasteland, probably resembling the surface of Ganymede or Callisto. In contrast, the dayside is a hot, almost airless desert, like Mars baked in an oven. To avoid this fate, Rorschach must have a relatively thick atmosphere to `even out' the temperature, but not so dense as to lead to a runaway greenhouse. Discovering a comparatively tiny world around another star is an amazing achievement, but we cannot pin down any other significant facts. All the information we have about Rorschach can be listed in a couple of sentences. We know its size, mass and distance from its star. As to what the planet is really like, we can only speculate. Here are just a few possibilities as to what Rorschach could be, all are equally likely based on the limited information we have at present: ·A huge airless ball of barren rock, a sort of super-Mercury ·A giant version of Venus, rendered hellish by the combination of abundant solar heat and a greenhouse effect ·An almost airless desert on one side, a dark, frozen steppe on the other ·A world where the continuous cloud cover means the dayside enjoys a temperate climate with oceans of water and conditions suitable for terrestrial life. ·A world covered with oceans almost at boiling point with a steamy atmosphere of carbon dioxide ·A warm `mini-Neptune' with a hydrogen and helium atmosphere swamping a huge rocky core Psychologists used to show their patients cards featuring coloured blobs and asked them to describe the picture they could see. This was the celebrated Rorschach Test and was designed to give the psychologist insights into the patient's personality. Gliese 581c is a kind of cosmic Rorschach test. Look at the data; what kind of world do you see?

ISO goes to ESTEC First in Ireland!
By Naomi Francey, Education Support Officer Armagh Planetarium is proud to present a new interactive exhibition, which is the first in the whole of Ireland! This new exhibition has only been in operation for two weeks but is already proving very popular with the children that come to visit. Not forgetting the adults and OAPs, who also can't resist trying it out and I also have to admit the staff are also partial to this new exhibition! It's an interactive floor which once you step on you can walk over the lunar surface and see

"Mummy, what are those scary creatures?" "Don't worry dear, they work here." Naomi leads the Planetarium staff on just another bug hunt.

Image Credit: Armagh Planetarium


May 2007 Astronotes 7 your footprints that you have left behind. You can get your feet nibbled by angry crabs, squish alien bugs by stomping on them, discover the names of various galaxies in the Universe and leave trails of stars over the Moon. The opportunities are endless! It is a programme created by OM interactive and consists of a 3D interactive projection system, which projects 3D images unto a vinyl mat allowing people to interact by simply moving over the surface. I couldn't help but notice on Sunday one group of kids were on the mat most of the afternoon walking, jumping and rolling over it! Another excellent addition to our ever growing exhibition area! Ill encourage you to come along and check it out, although you may have to drag me off it, just to get your turn!

Life in Hostile Places
by Tom Mason, Director When I was still working as a Geology professor in Africa, I spent a lot of time in Namibia researching ancient river and lake deposits, and finding fossil evidence of life in the Namib Desert when it was a more pleasant place to live, being much wetter than today. The Namibian rocks contain some dramatic evidence of the sudden climatic shifts that humankind may be about to face now, as the Earth's overall temperature rises. The ancient Namibian lake beds had fossil plants and animals around their margins that would not survive there today as, apart from sporadic showers every seven years or so, the only moisture to be had is from the dense sea fogs that roll inland from the South Atlantic. The fogs are created by the cold water of the Benguela Current meeting very much warmer air from the African continent. This means that the air over the Namib is unusually humid and fogs are extremely common. The desert outcrops show that there were a number of wetter climatic cycles at various times during the past 65 million years. The evidence is found in Etosha Pan near the Angolan border, and at various sites in the Namib ranging in age from mid-Tertiary to Pleistocene. There is evidence that during wet seasons the rivers periodically flooded, and there is ample evidence that large animals that must drink daily to survive once lived there, as well as hosts of smaller creatures that have rather more specialist life-styles. What strikes people most forcefully when they enter the Namib Desert for the first time is that
Image Credit: Ute Schmiedel University of Hamburg, Botany Department

Window algae This shows the under surface of a white quartz pebble, normally protected by the pebble and in the desert soil. The greenish coating is made by algae living under the quartz. Conditions of light penetration through the pebble, temperature and a supply of condensed moisture from fog are sufficient for the algae to thrive. Such microhabitats in the extreme climate of Earth's deserts provide clues as to where we should look for signs of life on Mars.

while it is very hot and dry, there is often quite a lot of life, clinging on to existence in odd places. In almost all cases this means that there is a water source somewhere nearby, either metres deep underfoot or close by as a seep or spring from the rock strata. The water is often very brackish and foul tasting, but plants do not seem to mind. As a rule of thumb, if you can irrigate, then things will grow. For some dramatic examples, see the Libyan Desert on satellite images showing irrigation circles at http://earthobservatory.nasa.gov/Newsroom/NewImages/Images/


8 Astronotes May 2007 ISS010-E-5266_lrg.jpg Southern hemisphere night skies are spectacularly bright and full of interesting sights. But you will discover for yourself the richness of night time desert life as you must be careful not to find a sand dune and lie down without looking as small poisonous snakes and scorpions are active at night. During the day they lie low, many of them underground. And if you excavate a tunnel in the sand sea during the day, digging deeper into the sandy soil, you will detect coolness and even a hint of dampness. Zebra and elephant often dig down to the water table in the dry river beds, for even though there is no water flowing in the river, there is a constant underground flow. This shows up as green lines of deep rooted vegetation that can exploit this hidden supply. Namib plants are adapted to minimise moisture loss by transpiration, and in some extreme cases, like the Nara melon, a sort of squash, the plant has no leaves at all, but photosynthesises using its stems and the long thorns that festoon them. The desert surface can be gravelly, sandy or rocky: the gravelly desert surfaces often include translucent quartz pebbles, sculpted into weird shapes by the sand blasting effect of the wind. As the fogs roll inland and condense on the pebbles, liquid water runs down the side of the pebble and into the soil beneath. The critical combination of soil, water and sunlight allows lichens and algae to grow. Lichens are a symbiotic collaboration between an alga and a fungus. The two can survive together where they would perish on their own. Lichens can take many forms, but the most beautiful are those that are

Unnamed crater in the Centauri Montes Region This is a mosaic of several Mars Global Surveyor images, colourised using Mars Reconnaissance Orbiter camera colour data and overlaid on part of a Mars Odyssey Thermal Emission Imaging System image From what we know of Martian surface conditions there is water in abundance under the surface. The Viking spacecraft of the 1970s scraped the surface to look for evidence of biological activity. With the benefit of hindsight this was a mistake, as the surface is likely to be sterilised by the fierce solar radiation, even at the distance Mars is from the Sun, its thin atmosphere provides no shield against the radiation that we are spared on Earth because of the absorption in our thick atmosphere. But if there is water, there may be life. It is true that on Earth we are now discovering life in places where we would not have looked in the past because conditions were so extreme. But the extremophiles, as they are now known, can be found in places that we would find uncomfortable at best, and at worst fatal. ESA's Mars Express spacecraft has used its MARSIS radar probes to penetrate up to 5 km under Mars' surface , and to demonstrate major deposits of frozen underground water. Another recent discovery (released December 2006) showed that liquid water may have flowed on Mars during the past seven years. Two images of the same part of a crater margin in the Centauri Montes region, taken by one of NASA's Mars Global Surveyor cameras, shows that liquid water has formed a brighter gully deposit, similar to

"There is water in abundance under the surface of Mars"
brightly coloured: vivid scarlets, sulphur yellows and various hues of green. The contrast with the crustose lichens could not be more striking, as these tend to be rather dull dark browns and blacks. The lichens' main ability is to survive where all else dies. It is long-lived and slowgrowing, and the comparison with Mars is worth making.

Image Credit: NASA/JPL/Malin Space Science Systems


May 2007 Astronotes 9

Crater wall in close-up, as it appeared in August 1999, and later in September 2005. No light-toneddeposit was present in August 1999, but it had appeared by February 2004. those that occur in arid regions on Earth. While this work is tantalising, it is still inconclusive, as we do not know what mobilised/thawed the frozen water. It shows that we need to carefully examine old and new images to seek changes that have occurred over a short time span. This would be akin to astronomers using photographic plates in blink comparators to seek out asteroids and other phenomena moving in star fields. Viking's experiments looking for signs of biological activity in the Martian soils were equivocal and they raised more questions than they answered. If we could safely transport humans to Mars with a mission of sufficient length that they could explore a large area, we will find out much more than by using robots. The physical dangers to the astronauts may be reduced by new ideas involving magnetic field generators which could be used to make strong magnetic fields that could shield astronauts in their relatively flimsy craft from damaging radiation during their three year round trip. This may go some way towards solving what is a huge risk, which is the danger of excessive radiation exposure on such a long trip to Mars and back. The Earth's magnetic field protects us, so maybe an artificially generated field within the space craft could do the same for Martian explorers. Of course the Martian water, liquid or frozen, is a raw material that will allow exploitation of the hydrogen for fuel and the oxygen for life support, using simple electrochemical separation. For now, the research that is being carried out on the desert environments on Earth may hold the keys to unlocking the secrets of Mars.

Moon Phases, June 2007
Fri 8 June Fri 15 June Fri 22 June Sat 30 June Last Quarter NEW MOON First Quarter FULL MOON

Image Credit: NASA/JPL/Malin Space Science Systems


10 Astronotes June 2007

"The Man who Colours Stars" visits Armagh
Schmidt Telescope, he created colour images of the cosmos which are now regarded as classics of astrophotography. Photographs created by David Malin can be found in many popular astronomy books and magazines, and are displayed in museums and planetaria throughout the world. David Malin visited Armagh Planetarium on 11 and 12 May. In special presentations to school audiences, Friends of the Planetarium, the public and the Irish Astronomical Association he displayed some of his most spectacular views of the Universe and gave us a fascinating insight into his career and how he created these amazing images. Professor Malin's talks at this unique event were superb examples of science exposition at its best, being accessible to all the members of the audience and stimulating the vital sense of wonder that is so much a part of astronomy. The Planetarium has been visited by other notable guests recently. On 18 May Dr. Lachezar Matev, Bulgarian ambassador to the UK and Councillor William Irwin, Mayor of Armagh called in to the Planetarium to sample our Digital Theatre. Judging from the questions and comments from their party they found it an unforgetable experience!
Image Credit: Armagh Planetarium

David Malin (pale blue shirt) with Planetarium staff members Colin, Julie, Robert and Tom. By Colin Johnston, Science Communicator Armagh Planetarium was recently privileged to play host to renowned astronomer and photographer David Malin. Based in Sydney Australia, David Malin began working for the Anglo-Australian Observatory (AAO) in 1975. This was a dramatic career change as before then Professor Malin had worked as a chemist, specialising in optical and electron microscopy. During his time with the AAO, he developed new photographic processing techniques, notably unsharp masking, to reveal the faintest details in astronomical images. Once he was employed to explore the very small, but at the AAO he specialised in imaging the unimaginably vast. These new processes were invented to enhance the scientific return from astronomical photography, giving us new insights into the processes inside nebulae and the evolution of galaxies, but there was another benefit. David Malin was able to produce stunning colour images of the most beautiful objects in deep space. Using the 4m Anglo-Australian Telescope and the 1.2m UK

Mr and Mrs Matev and the Mayor meeting outside the Planetarium.

Image Credit: Armagh Planetarium


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Armagh Planetarium to Showcase Malin Images
By Julie Thompson, Digital Theatre Manager David Malin is currently digitally remastering his classic astronomical images, so that a whole new generation can appreciate them. Audiences in Armagh Planetarium will be the first to see them as we have been lucky enough to be granted a licence to use initially twenty of them in our shows. It is much more difficult to obtain suitable images for full-dome use than you might think. There is a wealth of pictures from spacecraft and telescopes but most of them are not high enough resolution to look good on an 11 metre dome. Then some high quality images cover a fairly small field of view, for example the famous HST `Pillars of Creation' image is only a tiny part of the whole Eagle Nebula. So audiences will find the David Malin images we have permission to use a rare treat, covering as they do a much wider field in higher resolution than most full-dome images. They are also astonishingly beautiful. During his visit, I was able to give David a preview of how they will look in our Digital Theatre and he was very pleased with the results. At the moment, I am creating the first show that will showcase some of these marvellous images and I intend to seek permission to use more of them as they are remastered. I am pleased to say that Armagh Planetarium will be the first facility in the world to present visitors
Image Credit: Armagh Planetarium

David Malin and Theatre Manager Julie Thompson at our 16 inch telescope. with this new visual treat. On a personal note I was delighted to meet David. As a very amateur astrophotographer myself I can appreciate the skill involved in taking these images. Whether you admire David's pictures for the wealth of scientific data they reveal or purely from an artistic perspective I'm sure you will find his images enthralling. (If you would like further information on David Malin's digitally remastered images, please contact Armagh Planetarium and we will be delighted to pass your details on to David.)

Astronomy Greats: Galileo
By Naomi Francey, Education Support Officer In last months' edition of Astronotes I was explaining how all our rooms at Armagh Planetarium are named after famous Astronomers. Our main exhibition hall is called `Galileo Hall', named after Galileo Galilei who lived in the 16th and 17th Centuries.


12 Astronotes June 2007

The Life of a Star
By Paul O'Neill, Education Support Officer In the northern hemisphere the winter sky is dominated by the constellation Orion. Below Orion's belt you might just be able to see a small fuzzy patch ­ the Orion Nebula. This is part of a huge region of star formation. Some of these giant clouds of gas and dust may begin to condense (perhaps triggered by the shock waves from supernova explosions). As more and more gas comes together the tem-

Image Credit: Portrait of Galileo Galilei by Justus Sustermans ca. 1639 (via Wikimedia)

Galileo made many discoveries throughout his life and most are due to his ability to improve the telescope to observe the Solar System. It is a common misapprehension that Galileo invented the telescope; however he was one of the first to use it to look beyond the Earth. He was the first to discover the mountains and craters on the moon surface, the first to discover the phases of Venus and the rings of Saturn. Galileo discovered Jupiter's satellites Io, Europa and Callisto (in a single evening), followed by Ganymede four nights later. He was the first European scholar to recognise sunspots. In 1624 he created the first known example of the microscope. He also located Neptune but did not recognise it as a planet, seeing it as a dim star. He had three children, two daughters and a son. His eldest daughter inherited her father's sharp mind and was Galileo's favourite child.

"Just a poor boy, from a poor family" according to the noted scholar Freddie Mercury. Gallileo was also the man who dropped balls of various masses off the leaning tower of Pisa to prove time of descent was independent of their mass Galileo was a very talented astronomer and experimental physicist. Born in Pisa, Italy as one of seven children, he accomplished a great deal during his lifetime. He was educated from an early age and was the most talented one of his siblings. His tertiary education began at the University of Pisa, but was cut short due to financial difficulties. He was later offered a job there teaching mathematics. He soon moved on to the University of Padua where he taught geometry, mechanics and astronomy, focusing more on science, and this is when he made most of his scientific discoveries.

"he located Neptune but did not recognise it as a planet"
Galileo published his final book in 1638 when he was almost blind. He died on 8 January 1642. He is currently buried beside his eldest daughter in Basilica di Santa Croce di Firenze in Florence, Italy. He had a great life of unique discoveries and we owe a lot to this giant of astronomy. NASA named one of their probes after Galileo and, like Galileo, it made many original discoveries. On its way to Jupiter to explore the Galilean moons, it was the first probe to fly past an asteroid and the first to discover a moon of an asteroid!


June 2007 Astronotes 13 on Earth will not survive. The oceans and the atmosphere will be blown off into space: our blue green planet will become a scorched lifeless ball of rock. Of course the new fuel (helium) will not last forever either and the core will go through a series of collapses; each resulting in the creation of new heavier elements and new thermonuclear reactions; the carbon in your DNA and the iron in your blood were all created in a star that is now dead. The outer layers will expand into thin shells of gas which move away form the sun out into interstellar space. The sun will now have become a planetary nebula.
Image Credit: NASA, WIYN, NOAO, ESA, Hubble Helix Nebula Team, M. Meixner (STScI), & T. A. Rector (NRAO)

Image Credit: NASA / ESA

M42, the Orion Nebula This star forming region is 1500 light years from the Sun. perature inside the proto-star rises, eventually reaching a critical level allowing thermonuclear reactions to begin. The gas cloud has become a new star. Gravity continues to try to collapse the star in on itself while at the same time energy created by the thermonuclear reactions tries to blow the star apart. Once a dynamic equilibrium is reached the proto-star has joined the Main Sequence. How long it remains on the Main Sequence depends on how fast it burns up its supply of hydrogen fuel in the core. Very hot, bright stars like the giant O-type stars have a

The Helix Nebula This planetary nebula is 450 light years from the Sun. The tiny white dwarf star at the centre of the planetary nebula will slowly cool and fade becoming a cold black dwarf. This description of the Sun's fate is true for all stars up to 1.5 solar masses. Heavier stars (between 1.5 and 3 solar masses) have a different fate.

"giant stars have a kind of rock and roll life-style"
kind of live fast die young ­ rock and roll life style while small cool M-type stars live a quiet life, never really attracting attention to themselves and living to a ripe old age. Our Sun is a middle aged Main Sequence star. But of course it won't last for ever. What will happen to the Sun as the fuel runs out? Well fortunately none of us will be around to experience this. As the hydrogen runs out the core will collapse increasing the density and temperature enough to allow helium fusion reactions to occur; meanwhile the outer layers will cool and expand. The Sun will have become a red giant, swallowing up Mercury and possibly Venus in the process. Any life that does exist

"the red giant tears itself apart in a supernova explosion"
Rather than becoming a red giant they become a red super giant. After this stage things become more violent. Instead of gentle billowing gas shells being ejected into space (a planetary nebula) the red super giant tears itself apart in an unbelievably violent explosion called a supernova. As the radiation and debris clear, a neutron star emerges. This tiny object, about 20 km in diameter, is all that's left of the massive super gi-


14 Astronotes June 2007

Unto their manifold dooms Stars can end their lives in several ways depending on their mass. ant. It is so dense that a teaspoon of its material would weigh one hundred million tonnes. Stars larger than three solar masses also explode in a supernova, but the remaining material collapses in on itself so much it becomes a black hole.

Missions of Gravity
By Colin Johnston, Science Communicator In the last issue of Astronotes I described how interplanetary spacecraft travel in slow but energy-efficient transfer orbits to their destinations. The `classic' trajectory of this type is the Hohmann orbit and I gave journey times for the planets of the Solar System for spacecraft following Hohmann orbits. I think that I should clarify one point, Hohmann orbits are those which allow you to reach a planet using the lowest possible energy to accelerate the craft, but there are an infinite number of possible transfer orbits. If you are willing to spend more energy by burning more fuel, it is possible to use a transfer orbit which allows a shorter journey time and a wider choice of launch windows. For example, in 1969, thanks to their high-enery trajectories, Mariner 6 and 7 reached Mars in five months rather than the nine months you would expect if they had used a Hohmann orbit. Reaching the outer planets is always a slow process, but early in the Space Age we learned to exploit Nature to shave years off the journeys. This is the principle of gravitational assists (sometimes called slingshot manoeuvres). Here is a good, recent example of a gravitational assist in action. The probe New Horizons was launched in 2006 and, thanks to a mighty Atlas V launch vehicle,

Image Credit: Paul O'Neill


June 2007 Astronotes 15 giant planet and the spacecraft, so Jupiter was slowed by about a million trillionth of a millimetre per second. Such gravity assist manoeuvres are common place now, there are several scheduled this year. Apart from New Horizons at Jupiter, ESA's Rosetta flew by Mars on 25 February to send it towards comet 67P/Churyumov-Gerasimenko and MESSENGER will fly past Venus on 6 June. MESSENGER's gravity assists are interesting as they are necessary to give the probe enough velocity to enter orbit around Mercury. Fly-by photo 1 Gravity assist manoeuvers are a great opportunity to take spectacular images. New horizons took this evocative shot of Europa rising over Jupiter. was the fastest moving spacecraft to leave Earth yet. When its rocket motor shut down, New Horizons was travelling at 16.21 km/s (58 000km/h or 36 000mph). Thanks to this impressive speed, it passed the orbit of the Moon in nine hours. However the probe did not travel directly to its final destination- Pluto and its family of moons. Instead New Horizons arced across the Solar System towards Jupiter. As it neared the giant planet, New Horizons began to speed up as Jupiter's gravitational influence increased, at the same time its course began to change as Jupiter pulled the probe towards it. Seen from above, the probe's path would have developed a distinct kink, as Jupiter eased it into a new trajectory. On 28 February this year, the tiny probe made its closest approach, about 2 million kilometres from Jupiter. It then continued on its way, travelling 4 km/s faster than before, at a stroke taking four years off its journey time to Pluto. This sounds outrageous. Where did this increase in speed come from? The mathematics of the encounter show that energy and momentum were conserved throughout. The probe's gain in speed was essentially stolen from Jupiter. As a result of the encounter New Horizons sped up by a significant amount, but Jupiter was slowed down in its orbit around the Sun by a small amount. Thanks to New Horizons, the length of Jupiter's year has slightly increased, but not by much. The scale of Jupiter's speed loss is in proportion to the size difference between the
Image Credit: NASA

Fly-by photo 2 lander took this est approach at Mars. A portion solar arrays are

The camera on Rosetta's Philae image just 4 minutes before closa distance of some 1000 km from of the spacecraft and one of its visible in nice detail.

The classic (and most fortuitous) use of gravity assists was probably when Voyager 2 used three gravity assists (at Jupiter, Saturn and Uranus) to facilitate its epic tour of the outer planets. It was fortuitous as the planets are rarely neatly lined up to permit this. It is worth noting that the Voyager project was a cut-down version of a much more ambitious scheme, Project Grand Tour, which was rejected for financial reasons when NASA's bugdet was cut in the early 1970s. The Grand Tour project would have used a series of gravity assists, thanks to a once in 176 years planetary alignment, to send a probe to Jupiter, Saturn, Uranus, Neptune and Pluto!

Image Credit: CIVA / Philae / ESA Rosetta


16 Astronotes June 2007

Image of the Month
Image Credit: NASA,

This could be a scene from the fulldome show "Astronaut", but it is actually a self-portrait of astronaut Steve Robinson taken as he repaired Space Shuttle Discovery's heatshield on 3 August 2005. Robinson removed a pair of protruding gap fillers from the Shuttle's scorched underside which can be seen reflected in his helmet's visor. A Shuttle Orbiter is protected during re-entry to Earth's atmosphere (when its skin temperature can exceed 1250° C) by typically 21 801heat-resistant tiles and 1977 thermal blankets. Each tile is unique and identified by number. Carried under the Shuttle by the International Space Station's robot arm, Robinson successfully removed the gap fillers which were sticking out

between tiles on the Orbiter's heat shield.The gap fillers had apparently been loosened by the vibration of take-off. The decision to remove them was made as a safety precaution. The inner clear section of an EVA suit's helmet is made of polycarbonate material which is lighter, less fragile and more scratch proof than glass. The helmet also has an adjustable visor to filter direct solar glare and dangerous UV rays. This is kept lowered almost continuously, so you can rarely see the faces of astronauts in photos. The lamps on the sides of the helmet were added to aid work in the variable light conditions outside the ISS. (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