Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.armaghplanet.com/pdf/Astronotes/Astronotes2007/Astronotes_Dec_2007.pdf Дата изменения: Tue Sep 20 18:48:41 2011 Дата индексирования: Tue Oct 2 01:23:27 2012 Кодировка: Поисковые слова: р р р р р р р р р р р р р р р р р р р р р р р р р р р р р р р р р р р р р р

December 2007

ASTRONOTES
Incorporating FRIENDS' NEWSLETTER Polar Views Stars our Destination? Dating the Earth Comet Holmes continues to dazzle The Last Men on the Moon

ARMAGHPLANETARIUM


2 Astronotes December 2007

Season's Greetings
By Colin Johnston, Editor Welcome to this year's Christmas issue of Astronotes. This is one our occasional special extra-large editions, featuring articles by all your favourite contributors covering topics from throughout the Universe. As usual, compiling it has been a pleasure for me and I'm sure that wherever your astronomical interests lie there will be something to grab your attention over the holiday season. On behalf of everyone at Armagh Planetarium, I would like to wish you a very happy Christmas and a wonderful New Year of stargazing. See you in 2008!

Polar View
In the last issue of Astronotes I covered ESA's leading environmental satellite Envisat. In this issue I have decided to cover another satellite project called Polar View. You are probably thinking I'm obsessed with satellites, well I may be, but I've just realised how amazing they really are and just want to share their abilities with people like yourself!
Image Credit: www.photo.Antarctica.ac.uk

By Naomi Francey, Education Support Officer

"Shrinking ice shelves suggest warming sea temperatures "
There are nine different countries involved with Polar View, including the United Kingdom. It's a joint initiative devised by the European Space Agency and the European Commission with assistance from the Canadian Space Agency. Polar View's main purpose is for monitoring and forecasting services in the polar regions, but also to collect data from mid-latitude regions, for example snowfall in central Europe. Polar View uses data from orbiting satellites such as Envisat and Canada's Radarsat-1 to scan various aspects of polar landscapes which include

The Coldest Place? A British Antarctic research vessel trudging through sea ice on its way to Rothera Research Station; this is just one example of the harsh polar environment. icebergs, river and lake ice, glaciers, snow cover and ice edges. By observing locations such as these, Polar View gathers data such as ice thickness which can be monitored over the years to measure any changes that occur. It can monitor the extent of ocean coverage of ice shelves, which allows identification of retreating shelves. Shrinking ice shelves suggest warming sea temperatures. Polar View not only measures current data but also has a forecasting service which can give detailed 48 hour forecasts or less precise ten day forecasts. It can predict ice motion which includes direction and velocity, ice


December 2007 Astronotes 3 thickness, ice concentration and total ice thickness. The majority of these forecasts are used by shipping companies as the polar oceans pose a greater transport risk than other waters. These predictions allow them to plan their route safely.

"...Inuit people rely on Polar View data"
The data that is received by Polar View is used by various groups including governmental institutes, research groups and northern residents. Inuit people in the Far North rely on the data as the ice edges which they use to move from village to village are becoming unpredictable due to global warming. Polar View assists the Inuits by showing them where there are potential thin ice areas and allows them to take a safe passage. Governmental institutes can use information from Polar View to improve flood prediction and prevention methods which is extremely important, especially since flooding is becoming a more frequent occurrence. Polar View helps to develop maps of the Polar Regions and has greatly improved records; it contributes greatly to global ice data. In the past decade it has become increasingly well-known

RADARSAT-1 is the Canadian Space Agency's earth observation satellite. It has continued operate well over its planned five year life, RADARSAT-2 is due for launch this month. how important our polar landscapes are and how they must be protected. With global warming causing retreating ice shelves this is already proving to have environmental and economic implications. This fragile landscape is under threat but with satellites such as Polar View specializing in such regions it will improve data records helping us to us understand more about the unique wilderness, which in turn will help us manage it in a sustainable manner.

The stars our destination?
By Colin Johnston, Science Communicator Looking back, it seems that the Golden Age of Astronautics may have occurred in the era 1960-80. Satellites were orbiting the Earth and men soon followed. The Moon was reached shortly afterwards. Most space enthusiasts expected bases on the Moon and flights to Mars to be achieved in the next twenty years (sadly, decades later on these goals are still twenty years away). Looking further into the future from those days, it seemed obvious that the twentyfirst century would see the exploration and later, the settlement of the Solar System. Perhaps by the mid twenty-second century, Pluto would be the site of the Solar System's suburbs, and the inevitable `final frontier' would be the stars. The date when travelling to the stars (interstellar travel) becomes feasible has stretched into the future, but it is still a living dream. How could people travel to the stars? Space is very big indeed. Imagine the Sun is the size of the full stop at the end of this sentence. If shrunk down to this scale, Earth would be a microscopic speck 5 cm from the Sun, Mars would be a tinier still speck 7.5 cm from the Sun and Jupiter a dust mote about 28 cm from the Sun's dot. Eccentric Pluto would be on average 2 metres from the Sun. The relatively small unmanned probes of today take months to years to span these interplanetary distances. For example,

Image Credit: Canadian Space Agency


4 Astronotes December 2007 New Horizons was launched on a very fast trajectory and added speed with a gravitational assist from Jupiter, but will still take nine years to reach Pluto (keep in mind that in our scaled down Universe it takes nine years for a one-way journey of 2 m). By applying extremely advanced but plausible engine designs it does not seem impossible that people may one day make similar interplanetary journeys (see the feature on the Orion nuclear spacecraft in the December 2006 Astronotes for what could be possible). The stars however are another matter. Alpha Centauri, the nearest star system to our Solar System, is 4.3 light years from the Sun. On the Sun = Full Stop scale, Alpha Centauri would be nearly 14km from the Sun! If a 2m journey takes nine years, how long will a 14 000m journey take? The answer is 63 000 years to reach the closest star to our Sun. This is many times longer than recorded history and a significant portion of the time that the human species has existed.
Image Credit: NASA

High speed flight This fanciful view from the cockpit of a hypothetical spacecraft travelling at eight-tenths of the speed of light shows the visual distortions that would be experienced at such high speeds. There is no foreseeable technology that will allow us to achieve such speeds in reality. and Mars missions, generating power by nuclear fusion is still a couple of decades away, but it will one day be possible and later may be applied to spacecraft. What will this technological advance make possible?

"The Daedalus vehicle would be enormous, dwarfing a Saturn V"
In the 1970s, towards the end of the Golden Age, engineers drew up plans for a two-stage nuclear fusion powered interstellar probe they called Daedalus. Their report is still essential reading for anyone interested in interstellar flight and is available on CD-Rom from the British Interplanetary Society which sponsored the research. The researchers assumed that a certain amount of futuristic technology was attainable ­ but no science fictional magical technologies existed - and an enormous infrastructure in the Solar System (such as mining the planets for resources) preexisted. The Daedalus vehicle would be enormous; some 190m tall and with a mass of about 52 000 tonnes at engine ignition. In contrast the mighty Saturn 5, still the largest operational launch vehicle every constructed, stood 110 m tall and

New Horizons The fastest ever probe is shown flying past Pluto and Charon on 14 July 2015. Enormously powerful rocket engines that could reduce journey times between the stars are theoretically possible. These are not rockets burning a chemical fuel and an oxidiser as our present day launch vehicles do: for interstellar (and let us be honest, serious interplanetary) flight nuclear propulsion will be essential. Compared to theorised nuclear rockets, chemical rockets are hopelessly inefficient. Nuclear fission engines (such as NASA's 1960s NERVA concept) are better but still scarcely good enough. A reasonable interstellar rocket will have to harness the same energy source as the stars; fusing atoms into heavier elements. Rather like moon bases

Image Credit: Art by Les Bossinas (Cortez III Service Corp.) via NASA


December 2007 Astronotes 5 velocity, eventually reaching seven per cent of the speed of light. At this point the craft's first stage fuel tanks would be empty so the first stage would be jettisoned, allowing the comparatively small second stage to accelerate to 0.12c (c, it should be explained, is the accepted symbol for the speed of light ­ hence 0.12c means 12 % of the speed of light). The craft could cover the six light years to Approaching Barnard After a multi-decade voyage the upper stage of the Barnard's Star ­ choDaedalus starship nears its destination. Artwork from http://www.bisbos. sen as a destination as com/rocketscience/index.html and reproduced with the kind permission of the it was believed to have artist. This website features some wonderful artwork of spacecraft and aviation a planetary system at concepts the time of the study weighed a mere 3 000 tonnes. Like modern (this is no longer certain) - in fifty years and launch vehicles, the `staging' approach would would have burned 50 000 tonnes of fuel in the be used. When the fuel in the vehicle's first stage process. Fifty years cruising through emptiness was exhausted it would be released, allowing is of course useless were the starship to have the much lighter second stage to speed ahead carried a crew but is acceptable for a robotic unhindered. vehicle. Daedalus would be controlled by a sophisticated computerised artificial intelligence with an intellect approaching (or quite possibly exceeding) human level.
Image Credit: artwork by Adrian Mann

"A Daedalus craft would be assembled in space. Its fuel would be extracted from the atmosphere of Jupiter"

A Daedalus craft would be assembled in space and its fuel tanks filled with deuterium (heavy hydrogen) and helium 3 fuel extracted from the atmosphere of Jupiter. This sounds fantastic but imagine how unbelievable today's routine off-shore oil and gas drilling would sound to our Elizabethan ancestors. The deuterium and helium would be brought together in the vessel's engine to be `ignited' to fusion by a powerful beam of electrons. Directed by a magnetic nozzle, the resulting plasma would thrust Daedalus forward, accelerating past the Sun's escape

However the final 500 tonne Daedalus probe would whizz past Barnard's Star at 36 000 km per second without stopping. The probe would scan the star and its planets with an impressive suite of instruments, including a pair of telescopes each twice the aperture of the Hubble Space Telescope. Eighteen autonomous sub-probes would be launched from the main vessel to add to the encounter's scientific bounty beamed back to Earth. The British Interplanetary Society study suggested that travelling to the stars in a long but reasonable time is not impossible. It is important to bear in mind though that it will require at minimum many decades of technical advances before we could attempt to build such a craft; we simply could not even venture to undertake this today.


6 Astronotes December 2007 or lightsails for decades. The journey time even between planets would be lengthy. Perhaps a huge array of powerful lasers could be focused on the craft and used to thrust it along faster. It is perfectly feasible but it still represents perhaps 23rd century engineering. To summarise the last couple of paragraphs, using very advanced technology it may be possible to send a craft slightly bigger than the completed ISS to a nearby star and bring it to rest. The journey would take decades and need the best part of a million tonnes of propellant. Sending a human crew in such a vehicle seems a non-starter, an even grander still vessel would be necessary to carry people to other stars. Futurists have imagined huge `space arks' or `generation ships', essentially space going cities, which cruise majestically between the stars over decades or even centuries. Eventually it is the great-grandchildren of the original crew who arrive at the destination star. Engineering a completely self-contained environment that can maintain human life for centuries may be more difficult than building the engine. Finding people prepared to spend the rest of their lives (and their children's too) in a spaceship may be harder still. Perhaps we could explore the stars by sending an advanced artificial intelligence instead. We already explore the planets this way. In the end, it may be that machines and not humans conquer the stars. Unappealing as it may be, the future may belong to bio-mechanical beings like the Cylons of `Battlestar Galactica' rather than the noble crews of `Star Trek'. Are there other, faster solutions to the problems of interstellar flight? Many have been proposed over the decades. A particularly interesting concept which might just make it possible to fly to the stars and back inside a human lifetime after all will be described in the next Astronotes. Further reading: Project Daedalus - The Final Report on the BIS Starship Study, A. Bond et al. JBIS Interstellar Studies, Supplement 1978 (available on CD-Rom from British Interplanetary Society, 27/29 South Lambeth Road, London SW8 1SZ, http://www.bis-spaceflight.com/index.htm)
Image Credit: www.projectrho.com

The Ark in Space The generation ship concept dates back to speculations by JD Bernal in 1929 and soon appeared in pulp magazines. Science fiction fans know that generation ships always meet with disaster en route. Why was Daedalus not intended to stop at its destination? To come to a halt it would need to fire its engines to decelerate, expending even more fuel in the process. That fuel would have been launched with the rest of the probe and more fuel would need to have to be used initially to do this. How much more? The mathematics of rocketry has been established for more than a century so it is easily calculated that a minimum of 740 000 tonnes of propellant would be needed at the initial launch. A bigger or faster vessel would need still more fuel. Building a starship capable of accelerating to interstellar velocities, then decelerating to a standstill means building an enormous (potentially planetoid-sized) vehicle.

"...the future may belong to the Cylons "
There are other ideas. Light exerts a tiny thrust on anything it falls upon. A spacecraft could be harnessed to an enormous sail of fantastically fine material and gently wafted away from the Sun. Theorists have discussed such solar sails


December 2007 Astronotes 7

The year in pictures from ENVISAT

By Wendy McCorry, Science Communicator These images were taken by ENVISAT, the European Space Agency's Earth Observation spacecraft ­ the largest of its kind ever built. Launched in 2002, ENVISAT uses ten radar and optical instruments to provide continuous observation of the Earth, allowing us to monitor human activity and environmental changes on land, sea and in the atmosphere (see last month's Astronotes for

more on this project). Clockwise from top left: ENVISAT's Medium Resolution Imaging Spectrometer (MERIS) captured this image of tropical cyclone Gamede sweeping across the Indian Ocean on 23 February 2007. The cyclone lasted for ten days and broke several world records for the amount of rainfall during a tropical cyclone.

Image Credits: ESA


8 Astronotes December 2007 The Advanced Along Track Scanning Radiometer (AATSR) sensor onboard ENVISAT took this rare image of a virtually cloudless UK during a heatwave on 18 July this year. Temperatures rose to a record high, but so too did pollution levels. MERIS also gave us this spectacular view of the autumn foliage around three of the Great Lakes (Superior, Michigan and Huron) in eastern North America on 23 September. Along with Lakes Eerie and Ontario, the five Great Lakes make up the largest area of connected fresh water on Earth. ENVISAT captured this image of the wildfires in Southern California on 22 October. Easterly desert winds can be seen blowing the smoke from the fires out over the Pacific Ocean. Eighteen fires burned over 2000 kmІ from Santa Barbara to the Mexican border. Over 1500 homes were destroyed and seven people lost their lives, with many more injured. Hot weather and strong winds were thought to be the major contributing factors to the fires, but some were caused by falling power lines and at least one was reported to have been started deliberately.

Rock of Ages
By Tom Mason, Director It is interesting to note that the most quoted work claiming a young age for planet Earth is the work of Archbishop Ussher (1581-1656). In his Annals of the World (1650) he confidently dated the Earth as having been created on the evening preceding October 23rd 4004 BC; thus when he wrote he thought that the planet was 5654 years old. While this work is often derided for its naivety, at the time when Ussher wrote it was a record of considerable scholarship.

"Archbishop Ussher's work was consistent with 17th century science"
Ussher was the Archbishop of Armagh from 1625-1656, so it is has a nice symmetry that I should be writing this article in Armagh as a direct scientific descendant of the Archbishop. His work was consistent with the understanding of science in the 17th century when he was alive. My work is consistent with the benefit of over 350 years of further study and of a body of knowledge which allows for the better scientific understanding of the Earth's age in the 21st century.

The Earth from space photographed by the crew of Apollo 17 in December 1972. Radioactive dating indicates that our planet is 4.55 billion years old. Any understanding needs to be founded on scientific observation and facts. Thus, in a stratified pile of sedimentary rock layers, the oldest are at always at the base, the youngest at the top, consistent with observations in lakes, rivers and oceans. Obviously this does not hold when the rocks have been contorted by Earth movements, folds, faults and suchlike. In such cases, other evidence is used to discern the top of the succession of rock layers. Granite is a common igneous rock which comprises an interlocked mass of crystals of quartz, mica and feldspars. The common elements which form the crystals in granite include: silicon;

Image Credit: NASA


December 2007 Astronotes 9

Image Credit: generated by www.colorado.edu radioactive decay site.

Radioactive decay The atoms in a sample of carbon 15 decay into atoms of nitrogen 15. This graph shows the number of C15 atoms (yellow) dropping as the number of N15 atoms (purple) increases as time passes. Can you estimate the half life of carbon 15 from this diagram? potassium; oxygen; sodium; calcium; aluminium; iron and magnesium. The basic building block of all elements is the atom. Atoms have commonly been visualised (wrongly) as being like tiny Solar Systems made up of a central dense nucleus, comprising relatively heavy neutrons and protons. Together these give the atom its mass, or weight. This dense nucleus is surrounded by a cloud of fast moving electrically charged electrons, of little weight but with negative electrical charge. In stable atoms the number of electrons equals the number of protons, making an atom of neutral electrical charge. tritium isotopes greater mass than protium, the commonest form of hydrogen. Granites are defined as containing quartz, mica and feldspars, both of the latter minerals contain the light metallic element potassium (chemical symbol K). Potassium has 24 known isotopes, but for our discussion here we just need to be aware of three common ones. These are K39, K40, and K41. The commonest is K39 with just over 93% of potassium falling into this category, then there is K41 with around 6.7% and the rest (less than 0.02%) being K40. The natural isotope K40 is unstable and spontaneously changes into a more stable isotopic form (this is called radioactive decay) by losing beta particles or gaining electrons. This is a radioactive process, and is responsible for much of the background radiation which we humans experience. A long time ago, it was realised that by precisely measuring the amount of radioactive material in rock samples, we could calculate the age of the mineral, and by carefully checking that the rocks had not been altered by subsequent events, this would allow a date to be given to the sample. To understand how this works, we need to understand the concept of half life. Each radioisotope has a constant half life: irrespective of how much of it exists in a sample. Thus, if we weigh a 10 gram radioisotope sample, with a half life of 20 seconds, after 20 seconds passes, only 5 grams of the radioisotope will be left. After

"...by carefully measuring the radioactive material in rock we could calculate its age"
Elements can also exist in different physical forms known as isotopes, where the atoms of the element can have slightly different numbers of neutrons in their structure, which makes isotopes of the same element vary in weight. The simplest example is the three natural isotopes of hydrogen, Protium, Deuterium, and Tritium. These are hydrogen atoms with 1 electron and 1 proton, 1 electron, 1 proton and 1 neutron, and 1 electron, 1 proton and two neutrons respectively. These extra neutrons give the deuterium and


10 Astronotes December 2007 samples are fresh and unaltered. It works for samples from 4.6 billion years to around 100 000 years ago; this is based on the detection limits of the equipment used. All of these techniques are standard scientific methods and refute the claims of Creationists that scientists are unsure of dates, and ages of ancient events are inconsistent. Scientists are trained to include their error bars in graphs and calculations as this allows others to compare and test their own results: error bars are not mistakes, they are good science. This is actually scientific rigour in action. Advances in dating techniques include more precise methods, and of course the different methods are calibrated and compared, and their internal consistency is very good.
Image Credit: Artist unknown via wikimedia.org

James Ussher (1581­ 1656) Anglican Archbishop of Armagh and Primate of All Ireland. another 20 seconds passes the sample's weight will have halved again, and only 2.5 grams remain. This radioactive decay produces a very characteristic graph. The decay rate is constant and completely independent of all normal chemical and physical processes so it is a very predictable process. For a nice graphical demo of the 10C to 10B half life see: http://www.colorado. edu/physics/2000/isotopes/radioactive_decay3. html . To date very old rocks the potassium 40 method is used. This isotope decays to Argon 40, but its half life is 1.3 billion years, for old rocks an alternative method is to use uranium 238 which has a half life of 4.5 billion years (obviously no one has observed a complete half life of this isotope, but it has been accurately determined by observing samples undergoing decay in the laboratory) . For comparison, plutonium 239, a very dangerous man made element, is found as a by product of nuclear bombs. Its half life is 240 000 years. This makes it a permanent pollutant for humans. Single tiny particles of plutonium inhaled or ingested are fatal. This method does not work if rocks have been recrystallised by later events. So it is vital that

"There are many examples where rocks dated using fossil evidence had their dates confirmed by radiometric methods"
There are many examples in the geological literature where rocks that were initially dated using fossil evidence have had their ages confirmed by radiometric methods. Initially dated by marine microfossils (of tiny organisms called foraminifera), the best example is the 65 million year old K-T boundary extinction event whose signature has been found worldwide. Dinosaur enthusiasts among our readers will be well aware that the K-T boundary marks the point in Earth's history when the `terrible lizards' and many other species became extinct. Many glassy tektites (which are formed in meteorite impact events) found in well-defined sedimentary layers from different sites around the planet are dated at 64.5 ± 0.1 million years ago (Ma). Radiometric dating (Ar40 -Ar39) of melted rock samples from the Chicxulub crater in Yucatan where the fatal visitor from space fell provides a date of 65.07 ± 0.1 Ma (Swisher et al., 1992) which is close to two separate radiometric ages


December 2007 Astronotes 11 for the K-T boundary from the continental US: 65.00 ± 0.04 Ma and 65.4 ± 0.1 Ma (Gradstein et al., 1995: Obradovich, 1993). These are just examples. Independent researchers' results agree that the Earth is many times older than Archbishop Ussher's calculations. Although he would no doubt be greatly surprised by the correct value, as a man who delighted in truth and scholarship, the Archbishop would readily accept this new knowledge and envy us for our marvellous scientific tools. References FM Gradstein et al., 1995 Soc.Econ.Paleontol. Mineral.Spec.Publ. 54, 95. Obradovich, JD, 1993, A Cretaceous time scale, in Caldwell, WGE, and Kauffman, EG, eds., Evolution of the Western Interior basin: Geological Association of Canada. Swisher, CC et al., 1992 Coeval 40Ar/39Ar Ages of 65.0 Million Years Ago from Chicxulub Crater Melt Rock and Cretaceous-Tertiary Boundary Tektites. Science,

Stars and Spooks
storyteller, Sheena. Some boys were even brave enough to taste her magic potion of worms and eyeballs, or as some people call them, spaghetti and cherry tomatoes! If all that wasn't enough, the little ghosts and goblins still had enough energy left to play party games afterwards. The deserving winner of our fancy dress competition was a very original Doctor Who, who was awarded a kitchen chemistry set from our Astrosales shop, to wreak even more havoc in his own home!
Image Credit: Armagh Planetarium

Scary creatures Inventive costumes on display at the Planetarium. By Wendy McCorry, Science Communicator On Halloween night the Planetarium invited visitors to come along in fancy dress for our special evening of Stars and Spooks. Costumes ranged from the traditional (witches) to the original (a corpse bride), and parents had obviously been very busy in the days and hours beforehand with the face paint and black bin liners! Children made their own terrifying aliens to take home, before battling through the skeletons and cobwebs to take a seat upstairs in the Digital Theatre. The audience trembled as they watched a special Halloween version of our live show Pole Position, and younger monsters were then treated to the spooky tale of a novice witch from our

After Rose and Martha? A newly regenerated Doctor and his latest companion step out of the TARDIS at our Halloween event.

Image Credit: Armagh Planetarium


12 Astronotes December 2007

Visitors from deep space
by Paul O'Neill, Education Support Officer If you had a space ship and were able to travel to the outer solar system you would eventually reach the Kuiper Belt and eventually the Oort Cloud. Out here the sun appears as just another star against the blackness of space; it produces little light and no heat, but you are still inside the Solar System. This part of space is not entirely empty. Objects made of ice and rock dust drift about. Occasionally as a result of some force one of these blocks of dusty ice starts to fall towards the inner Solar System. As the object moves closer to the Sun it accelerates and eventually the radiation from the Sun begins to warm parts of the ice. Of course if you heat up ice it will eventually begin to melt. In space there is no air pressure, the space between the planets is a vacuum, therefore as the ice melts it doesn't turn to liquid but instead it immediately becomes a gas. The ice block has now acquired a kind of atmosphere. The gas is often blown away from the chunk of ice by the solar wind (a stream of charged particles and radiation emanating from the Sun). The dirty ice ball has developed a tail (or two). This tail contains ionised gas and dust. We call this a comet.
Image Credit: NASA

Comet close-up This image shows the view from the Deep Impact mission of comet 9P/Tempel 1's nucleus. The nucleus is about 14km long and 4 km wide. few years to a human lifetime or more. One such comet is called Comet Holmes; comets are usually named after their discoverers. On the night of November 6 1892 Mr. E. Holmes of London happened to point his telescope to a part of the sky near the Andromeda Galaxy and found an object that had a bright nucleus surrounded by a fuzzy cloud. This new comet was shown to have a period of around seven years. Comet Holmes was lost after the 1906 apparition. It was again picked up in 1964, it had a magnitude of about 19 (this is extremely faint and would require a powerful telescope to see). Comet Holmes has been observed at every return since 1964. The comet was due to return this year. In early October it was very faint ­ as expected. But then on the 24th October it suddenly brightened by a factor of over half a million. Exactly why the comet should brighten by so much is unknown. One possible explanation is that a layer of ice was exposed and as this melted the comet emitted large amounts of gas and dust. The gas and dust reflects sunlight back towards us ­ meaning the comet, as seen from the Earth,

"Comet Holmes was lost between 1906 and 1964"
It is impossible to predict when a new comet might come from the Oort Cloud but some comets as they enter into the inner solar system are perturbed by the gravitational pull of Jupiter and get themselves into periodic orbits. This means the comet after passing close to the Sun doesn't fly off again to the outer reaches of the Solar System, never to return, but instead returns after a certain period. If we can calculate the orbit of such a comet we can then predict where and when it might appear in the sky. The orbital period for such comets can vary from a


December 2007 Astronotes 13 suddenly brightened. I first saw the comet on Oct. 25th it was easily visible to the naked eye but at that time it didn't look like any comet I'd ever seen before; it looked like a bright new star had suddenly appeared in the constellation of Perseus ­ more like a nova than a comet. By early November the comet was beginning to look more like a comet, i.e. it appeared fuzzy and extended but still had no tail. Unfortunately because of the position of the Earth and the comet we can't really get a good view of any tail that does develop. By the evening of November 8 the comet was still visible to the naked eye but now appeared as a faint extended fuzzy disc of light. (See our Image of the Month for more on this extraordinary comet)

Tails of the comets Many comets display both a gas and a dust tail.

The last men on the Moon
by Alyson Kerr, Education Support Officer On 14th December 1972, the Apollo 17 crew finished 22 hours of rock and dust sampling and started the journey home. As they left the surface, the mission commander uttered these words, `As I take man's last step from the surface, back home for some time to come - but we believe not too long into the future - I'd just like to say what I believe history will record- that America's challenge of today has forged man's destiny of tomorrow. And, as we leave the Moon at TaurusLittrow, we leave as we came and, God willing, as we shall return, with peace and hope for all mankind.' The famed Apollo lunar missions had finally ended. The program was created in a tense political environment between the USA and USSR. President John F Kennedy announced in 1961 that it was the country's intention to have a Man on the Moon by the end of the decade. The USA had been plagued by the USSR's continuing success in obtaining the World's Space `firsts',
Image Credit: NASA

Apollo 17 crew Eugene A. Cernan, Ronald E. Evans and Harrison Schmitt pictured before the flight the Russians had put the first object into space in the form of Sputnik, the first animal, Laika the dog and more importantly, the first man in space, Yuri Gagarin. America was lagging behind so they set their sights even higher by proposing a lunar landing. Public support was overwhelming as the country realised the need to show the Russians that they were technologically equal if not more advanced. By 1969 they achieved their goal when Neil Armstrong stepped onto the Moon. Their success was helped by the fact

Image Credit: NASA


14 Astronotes December 2007 that the Russian chief designer, Sergei Korolev, had died in 1966 leaving a gap in their development programme. Several more lunar landings were planned to study the surface and there were hopes that one day a permanent base may be established. By 1972 after six successful lunar missions, (Apollo 13 met with near-disaster and never reached the Fra Mauro highlands), the program ground to a halt. The crew of Apollo 17 knew that they would be the last to set foot on the Moon's surface for many years. Further planned missions to the Moon had been cancelled and no more were planned.

"The Apollo program has ended but the idea has not died"
But why would NASA cancel a successful program like Apollo? The main reason was financial. The expense of putting a man on the moon was astronomical. By 1965, NASA's budget was 0.8% of the country's Gross Domestic Product and by the time it finished had cost over $25 billion, this equates to $135 billion in today's money. The program was born out of necessity and was rushed. If it had not been for the tense relations with USSR, the program may have taken longer to develop. Research into cost-efficient technology would have been the norm and the program would have developed at a stable pace. This was not to be and it was the main reason that the program ended, it could not be financially sustained. Politicians had difficulty in justifying the expense to the public. Support for the program had waivered in the years since achieving

Geologist and astronaut Harrison `Jack' Schmitt poses with the US flag. He was the first scientist to carry out research on another world. their main aim. The novelty had worn off and the public were left to look at an enormous bill for their pride. Sensing this, politicians began to take the focus away from Space and onto issues in their own country. The Apollo program may have ended but the idea has not died with it. There are NASA plans for further lunar landings starting about 2020, but the missions which follow these may be internationally funded. Many countries, including America, Russia and European countries, are working together on project such as the International Space Station and this amicable relationship will be developed to incorporate missions the Moon. The benefits of international cooperation are obvious. Not only will the cost be shared but the technology will be advanced from the many sources available. In the meantime, scientists are still analysing and compiling data on the samples brought back from the Apollo missions and hope to supplement their research in the years to come. When we mark the anniversary of Apollo 17 this month we can appreciate its legacy for the future and it will always be remembered for it

The December sky
by Paul O'Neill, Education Support Officer Three planets are currently visible to the naked eye. Venus starts the month as a morning object in the constellation of Virgo. Mars has become an evening object in the constellation of Gemini (being brighter than the stars of Gemini and a distinctive orange colour makes Mars an easy object to find with the naked eye).

Image Credit: NASA


December 2007 Astronotes 15 Saturn is visible by late evening; it's best seen in the SE before dawn (in the constellation of Leo). Jupiter moves behind the Sun from the Earth's point of view and so is not visible this month.

The Winter sky is rich in prominent constellations. In early evening the stars of the Summer Triangle are setting in the west. The Pleiades and Taurus are well up in the south east sky and Gemini and Orion are rising in the east. Orion is probably one of the most recognisable constellations in the night sky. If you've never seen it go outside on the next clear evening and take a look for Orion's distinctive belt of three stars in a line. The Geminids ­ one of the most reliable meteor showers of the year ­ reaches its maximum on the 14th December at around 5pm. The waxing crescent moon sets in the early evening, meaning that for those who are patient enough to stand outside in the cold, you should be rewarded with several bright meteors. (Provided the sky is clear of course.)

Orion the Hunter The constellation as depicted in Johann Bayer's Uranometria published in 1603. Unusually the hero is shown looking west rather than east

Stop Press!
By Tom Mason, Director Robert Hill has recently been officially confirmed as a member of the International Astronomical Union Executive Committee Working Group for the International Year of Astronomy 2009 (IYA09)! As a member of the International Astronomical Union Executive Committee Working Group, Robert will be working closely with Prof. Mike Redfern, Head of the Astronomy Centre of the National University of Ireland, Galway and Prof. Ian Robson who heads the UK Astronomy Technology Centre in Edinburgh. These two individuals are designated as the Single Points of Contact for their respective countries and are planning the events that will take place during the International Year of Astronomy 2009. Not only is this quite a feather in Robert's cap, but is also recognition of his tireless work in astronomical education Robert is currently on secondment to the UKbased Space Connections and he represents the Northern Ireland Space Office (NISO) at Armagh Planetarium. This is a pilot project for European Space Agency funded regional centres of excellence for space education. Congratulations Robert, and very well done!

Moon Phases, Dec. 2007
Sat 1 Dec. Sun 9 Dec. Mon 17 Dec. Mon 24 Dec. Mon 31 Dec. Last Quarter NEW MOON First Quarter FULL MOON Last Quarter

Image Credit: courtesy of the United States Naval Observatory Library


16 Astronotes December 2007

Image of the Month
Image Credit: Dr. Apostolos Christou

Comet Holmes continues to dazzle and amaze observers throughout the world. The comet's nucleus of ice and rock is belived to be only about 3.6 km ( 2.2 miles) in diameter but has produced his amazing eruption of dust and gas. By 9 November the comet's coma had grown to a diameter of over 1.4 million kilometres, even bigger than the Sun, making it the largest object in the Solar System. The wispy gas and dust are of course much less dense than our star. As the comet has expands it has begun to appear fainter, and is harder to see from light polluted locations or when moonlight is present. Speculations that the outburst is a result of the

nucleus fragmenting, possibly after a collision with another object appear to be unfounded. When Holmes discovered it in 1892 the comet was behaving just it is today. Presumably it has some topographical quirk which occasionally causes material to break through its surface and escape. Holmes has lost about 1% of its material in the current outburst. This image of Holmes was taken by Dr. Apostolos Christou of Armagh Observatory on 22 November 2007 using a 15 cm Newtonian telescope and was processed by Dr. David Asher (also of Armagh). (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