Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.armaghplanet.com/pdf/Astronotes/Astronotes2006/Astronotes_Oct_2006.pdf Дата изменения: Tue Sep 20 18:48:26 2011 Дата индексирования: Tue Oct 2 01:23:13 2012 Кодировка: Поисковые слова: accretion disk

October 2006

ASTRONOTES
Incorporating FRIENDS' NEWSLETTER Under Southern Skies: IPS Report Pluto Demoted: Only Eight Planets! Orion: Back to the Future for NASA? Friends Reunited A Vertical Empire: Brits in Space!

ARMAGHPLANETARIUM


2 Astronotes October 2006

Under the Southern Skies
A report on the 18th International Planetarium Society conference By Dr Tom Mason I recently attended the first ever International Planetarium Society (IPS) meeting in the southern hemisphere. It was convened in Melbourne in the state of Victoria in southeastern Australia. All participants were warned in the pre-conference literature that as it was the austral winter down under, weather in Melbourne in July could be somewhat chilly. This was reinforced on my first day in Melbourne when I noticed that all of the natives were wrapped up in scarves, gloves, woolly hats and fleeces. From a Northern Irish perspective this was overkill as the temperature was a balmy 7 to 10 degrees at night and in the high teens or low twenties during the day. We were assured that the weather would break, but it did not, and remained stable throughout our stay. If you get the chance to visit Australia, I can highly recommend Melbourne, a large city of around three million people, it is sited in relatively flat coastal terrain and has an excellent public transport system. As BAP president I was required to attend the pre-conference IPS Council meeting as an affiliate member. Council meets once a year, during which the business of the IPS is discussed by the officers and affiliates prior to the main business meeting for the IPS members which is held during the conference. The IPS conference was held in the Carlton Crest Hotel in the suburb of St Kilda, a short tram ride from the city centre. The hotel has a large conference complex capable of being configured for small meetings as well as for the larger plenary sessions. There was an extensive display area for exhibitors to show their wares, which was populated by all of the usual suspects in the planetarium business. Vendors showed all of the latest developments in what has become a very fast moving field. It was very reassuring to see that the Digistar 3 system is still evolving and provides an excellent platform for the type of work that we want to do in Armagh. I spent a lot of time examining new equipment that we would find useful in Armagh, especially new developments in portable planetariums. There were many exhibits specifically targeting portables as the vast majority of planetarium work is carried out in these relatively unsophisticated environments. I suspect that this is about to undergo a dramatic change. I will discuss these in another article in a future issue of Astronotes. An interesting panel of guest speakers and plenary session speakers included Prof David Malin who gave an excellent presentation on imaging. When I spoke to him later we reflected on the amazing advances in the amateur equipment that now allows backyard astronomers to take striking images of deep space objects that until recently were the preserve of huge research telescopes costing millions to set up and run. David was very receptive to a tentative invitation from me to come to visit us at Armagh sometime soon, to talk to local astronomy buffs about his experiences.

Scienceworks Melbourne This complex is home to Melbourne Planetarium.

Image Credit: Scienceworks Museum


October 2006 Astronotes 3 Other keynote speakers included NASA's Rob Landis who works at the Johnson Space Centre in Houston. He is responsible for liaising with the Russian space programme, supporting the International Space Station. He gave an insightful overview of the planned new space vehicles to be added to NASA's space fleet following the retirement of the Shuttle. I also was impressed by his easy style and asked him if he was ever stopping over to consider coming to visit Armagh and giving us a talk. For me, the most enlightening talk was by John Storey, Professor of Physics at the University of New South Wales. His work in infrared and millimetre astronomy is best carried out at what he considers to be the best observing site on Earth, the high Antarctic plateau. He made an amusing and forceful case that this environment is rather like space, as it is cold and inhospitable, but contrary to popular belief, this is a very dry, low precipitation environment, perfect for astronomy. He pointed out that most people's perception of Antarctica is of huge storms and blizzards, but these are coastal weather phenomena, and on the high plateau things are rather different. They have experience of equipment pods that can be left working on the Antarctic plateau much like a satellite, with the advantage that, unlike satellites, they can be visited for repairs. He also made the case that if you are interested in doing research work in Antarctica there are regular flights from Christchurch in New Zealand (breakfast) to McMurdo Sound in Antarctica (lunch), and thence via connecting flight to the research stations on the plateau (dinner), a far cry from the heroic era of polar exploration with dog sleds and tents. He also showed images of the huge tractor trailers that haul equipment from the coast inland, two of which could easily carry a research grade telescope. This adds fuel to the debate about the usefulness of large space based telescopes versus ground based equivalents (see www. aura-nio.noao.edu/files/antarctic-site-testing. pdf ). At the conference dinner I was expecting the post dinner speech to be dull and dry. Not so, Prof Fred Watson of Siding Spring ObservaThe World Turned Upside Down McArthur's Map of the World is a thought-provoking antidote to the northern-centric viewpoint tory gave a very funny and interesting talk about his astronomy experiences. I later found his book `Stargazer: The Life and Times of the Telescope' at a local bookstore and have ordered a copy for our shelves. Planetarium demonstration sessions were held at the Scienceworks Museum where the Melbourne Planetarium is sited. The demos were shown using Zeiss Laser projectors which have good colour saturation. At Armagh we have BARCOs as lasers are very expensive, and I would prefer to see the technology maturing and to see if there are any snags, apart from the more expensive cost of operation. When the Planetarium at Greenwich reopens next year, you will have the opportunity to see how the Digistar 3 looks with laser projectors as their Digistar laser order was announced at the conference. So much for the speakers, though I should also mention that I had a long chat with Jonathan Nally editor of Australian Sky and Telescope who not only had heard of us but is planning to come over and visit sometime. This really is the prime usefulness of such conferences. The keynote addresses, the opportunity to network with like-minded individuals, often facing similar problems, is very refreshing and a real tonic when you realise that some organisations are still struggling to obtain adequate local funding for their work. The common ground is that all are passionate about what they are doing, and this is beyond price.

Image Credit: Tom Mason, Director


4 Astronotes October 2006

Pluto Demoted
By Dr Tom Mason, Director The International Astronomical Union has voted to downgrade Pluto from its status as the ninth planet in the Solar system to a dwarf planet aka a Trans Neptunian Object (TNO), or ice dwarf. The most interesting thing about the Pluto story is the reaction of "the man in the street", asking "Who are these people of the IAU to tell us that Pluto has been downgraded?" I suppose the short answer is because that is their job. The IAU is the arbiter of planetary names, asteroid names and all of the nomenclatorial minutiae that are essential if scientific order is to be maintained. "They" represent the body of professional astronomers in the world, and are the experts in the field. They do the same job as the taxonomists who keep tabs on the names of all of the plants and animals on the planet. Having said all that I must admit that I was disappointed at their decision. I am quite schizophrenic in fact as my scientific mind knows that their decision is probably right, and that we should recognise divisions of greater and lesser objects in the skies. As our knowledge increases, it is entirely reasonable to assume that we will have to make refinements and changes. And let's face it, Pluto has been an oddball from the word go when Clyde Tombaugh first found it. Its orbit is egg-shaped; it is at a completely different angle from the other planets; sometimes it is

Pluto and Earth Compared With a volume less than 1% of Earth's, the former planet is considerably smaller than our homeworld. Neptune, may be forgotten or relegated to a sort of famous failure. It's the same feeling I have when I show classes of schoolchildren Yuri Gagarin's photograph, and then discover that the name of the first man in space is not known by the majority of them. I suspect most adults would not recognise him either which seems shocking when you consider how many can recognise the Big Brother contestants and their fleeting fifteen minutes worth of fame. So we will return to the classrooms and lecture spaces and opine upon this change. The truth is that for an educator it is a gift! It allows us to tell a fascinating story and to spice it up with all of the new discoveries out there where planets are cold icy dwarves and that they have moons that we have only discovered last year. Also some of them are twins, endlessly circling each other, with their common centre of gravity in the empty space between them. Who said astronomy was boring, you could not invent this stuff!

"Pluto has been an oddball from the word go"
closer to the Sun than Neptune and sometimes not. It has the distinct flavour of captive about it, rather than original coalescing from the new born Sun's dusty accretion disk. But my romantic side is saddened that the work of Tombaugh, who set out to look for the predicted planets beyond

Image Credit: NASA


October 2006 Astronotes 5

The (Stellar) Parallax View
Many new astronomers marvel at the vast distances separating astronomical objects, but after a while wonder how do we know for sure how big these distances are. After all we cannot send a probe to the star Altair to confirm that it is 17 light years away. So how do we measure the distances to the stars and galaxies? The most basic technique is called the Stellar Parallax method. Everyone has seen parallax in action, even if they don't know the word. Parallax is the apparent movement of an object against a background due to a change in the observer's position. Here is a little experiment to demonstrate this effect. Next time you are a passenger in a car on a straight stretch of road, look out of the side window (definitely don't try this if you're driving!) If there are trees or hills in the distance, see if you can pick out an object,
Image Credit: Wikipedia.org

Friedrich Wilhelm Bessel (1784-1846) He has a crater in the Moon's Mare Serenitatis and asteroid 1552 Bessel named in his honour. navigate through the environment or perform activities like catching balls just through experience and observation. It was inevitable that this technique would be extended beyond Earth. Say we observe a star's position very accurately in January. Then we wait six months and do it again. Why six months? The Earth goes around the Sun in one year, so in six month it is in the opposite position in its orbit. As a result, we have a baseline the diameter of the Earth's orbit, roughly 300 million km. The angle the star moves through, its parallax, will be very small, a fraction of an arcsecond at best. If that sounds odd, remember that one degree of angle is divided into 60 arcminutes and each arcminute into 60 arcseconds. Hence we need to measure angles smaller than one 3600th of a degree. Up to the nineteenth century we could only guess at how far away the stars were, but once measuring instruments became precise enough it became possible to measure interstellar distance by parallax. A sort of race to be first to do this followed and the `winner' was the great German mathematician and astronomer Fredrich BesselI, despite his year long distraction by the 1835 apparition of Halley's Comet. In 1838

"Bessel determined that the star 61 Cygni was about ten light years away"
say a church, between your car and the trees or hills, and note where it is with respect to your car. Keep watching and you will see that the nearby object seems to be moving with respect to the background! Of course, it is stationary and it is you who is really moving. This principle has been understood for centuries, and surveyors still use it to determine the distance to a target object. They look at the object, walk along a known distance called the baseline and observe it again, noting the angle the target has apparently moved through by parallax. Using this angle and the baseline length, it is a matter of very simple maths to calculate how far away the target is (the longer the baseline the more accurate the result will be). When you think about it we are actually doing this all the time without thinking about it. Human beings can instinctively estimate distances well enough to


6 Astronotes October 2006 Bessel determined that the star 61 Cygni had a parallax of 0.314 arcseconds and therefore the star was about ten light years away (today the distance is more precisely measured to be 11.4 light years). In that pre-electronic age this result was an extraordinary feat, the fruit of hours of careful calculations and as many as a dozen painstaking observations in a night. Contemporary astronomers were delighted by this result. John Herschel called it "the greatest and most glorious triumph which practical astronomy has ever witnessed". Astronomers were also staggered by this value, 61 Cygni was relatively close to us but was still enormously distant. The sheer scale and emptiness of the Universe were becoming clear. The technique pioneered by Bessel is still used today and is so fundamental that a unit of distance has been designed around it. This is the parsec which professional astronomers are more likely to use than the light year. Parsec is a contraction of parallax second, and it is defined so that if something is one parsec from the Sun, then in six months it will move through one arcsecond. A parsec is about 3.26 light years (so 61 Cygni is 3.5 parsecs away). In 1989, the European Space Agency launched the Hipparcos satellite. It was designed to measure the parallaxes of nearby stars more accurately than ever before. Despite suffering the embarrassment of being accidentally placed in the wrong orbit, it was a great success. The final Hipparcos Catalogue contains 120 000 stars with parallaxes measured to within 1 milliarcseconds. Due to the difficultly of measuring very small angles (the more distant the star, the smaller its parallax), we are even today only able to measure parallax angles for stars up to about 1600 light-years away. Beyond this distance we must find other techniques to determine how far away the stars are. We'll discuss these methods in future Astronotes.

Moon Phases, Oct 2006
Sat Sat Sun Sun 7 Oct 14 Oct 22 Oct 29 Oct FULL MOON Last Quarter New MOON First Quarter

NASA's new spaceship
At the end of August NASA formally named its planned new Crew Exploration Vehicle and selected a contractor to build the craft. As predicted in the August Astronotes, the CEV, which will replace the Space Shuttle, is now the Orion spacecraft. It will be constructed by aerospace giant Lockheed Martin after a rival bid from a consortium of Northrop-Grumman and Boeing was rejected. Many consider LockheedMartin a surprising choice as this corporation has a perceived history of being awarded space vehicle development contracts which fail to deliver a successful final product. For example, in the 1990s Lockheed Martin was contracted to produce the X-33, a spaceplane which was the basis of an earlier project to replace the Space
Image Credit: NASA/John Frassanito and Associates

Orion shall rise A NASA artist's view of an Ares 1 booster sending a Orion capsule into orbit. Orion missions will be launched from the Kennedy Space Center in Florida


October 2006 Astronotes 7 Shuttle. Sadly, the company appeared to have grossly underestimated the difficulty of the project and the craft was never completed. Presumably they have now somehow regained NASA's confidence after this fiasco. The Orion development contact is to last seven years and is worth $3.9 billion, a surprisingly small amount. This is not as fatuous as it sounds, compare this sum to the $28 billion budgeted for the development of another Lockheed Martin product, the USAF's F-22 fighter jet or the 49 billion euros spent last year on subsidizing the EU's farmers. The spacecraft's very conservative basic concept has already been criticized. It is not a sleek, futuristic spaceplane. Instead each Orion will bear a strong visual resemblance to the historic three-seat Apollo spacecraft, but is considerably bigger, being about 5 m (16.5 feet) in diameter, with a mass of about 25 tonnes. In comparison, an Apollo was 3.9 m in diameter and weighed 30 tonnes- the Orion's internal volume is about 150% more than that of the Apollo capsules. An Orion will be constructed from modern Aluminium-Lithium alloy, helping Back to the Future? The Orion shows its 1960s inspiration in this artist's impression. However Apollo capsules did not have solar panels. a possible mission to Mars. For all missions, the Orion's command module will descend on parachute to a landing site in the western US, with air bags or retro-rockets cushioning the final descent. Unlike previous US capsules, it will not routinely land in the ocean, avoiding the expense of maintaining a flotilla of recovery ships and opening the possibility of reusing each craft up to ten times. The corrosive effects of seawater are so severe that reuse was never attempted with earlier capsules. NASA estimates that a flight in an Orion will be substantially safer than a Shuttle mission. An Orion's heatshield will be protected from debris until the vehicle is returning to Earth, and if an accident occurs during the mission's launch phase, an escape rocket system will carry the craft to safety. A similar device on the Russian Soyuz spacecraft has saved the lives of the crew on a couple of occasions. The hope is that the first manned Orion flight to Earth orbit will be in September 2014 at the latest, with Moon missions by 2020. This assumes that the project will continue to receive the current level of US government support for years to come which is probably unlikely, so it will be fortunate to avoid delays. This project should be welcomed by manned spaceflight enthusiasts. It may not be the USS Enterprise but it appears to be a technically sound and workable design which if successfully developed will deliver safe and reliable transport for astronauts for years to come.
Image Credit: Lockheed Martin Corp

Orion is not a sleek spaceplane
to make it lighter and tougher than the Apollo capsule, and will utilize the latest electronic and computer technology based on the systems fitted to the advanced Boeing 787 airliner. Much to the relief of crews who may have to spend days on board, the craft will be fitted with a unisex lavatory permitting a degree of privacy (in the interests of good taste, the hygene facilities onboard Apollo are best left undescribed). An Orion will be launched on an Ares 1 rocket (see the August issue of Astronotes for a description of the Ares series) and carry up to six astronauts (or cargo) to the ISS. Alternatively, an Orion with up to four crew members could rendezvous in orbit with a Lunar Surface Access Module (LSAM) and booster stage launched earlier by an Ares 5 heavy lift rocket. After linking up the combined spacecraft could take the astronauts to the Moon's surface and back again. Looking further into the future, an Orion would certainly be capable of travelling to a near Earth asteroid or may play a part in


8 Astronotes October 2006

Fly me to the Moon
By Wendy McCorry, Science Communicator Last month saw the first ever European Moon landing. Now, before you rush off to the doctor to enquire as to how you managed to neither see nor hear reports of such an event, let me explain further. Alright, so it didn't exactly involve man stepping onto the Moon, and okay, it was more of a `crash-landing', but it was a momentous occasion nonetheless. As explained in July's Astronotes, the landing in question was of SMART-1, an unmanned European Space Agency Satellite, which has spent almost 2 years orbiting the Moon. It was deliberately crashed onto the lunar surface on September 3rd to end its mission. SMART -1 (SMART stands for "Small Missions for Advanced Research in Technology") was launched on 27th September 2003, from the European Spaceport in Kourou, French Guiana. It began orbiting the Moon fourteen months later, in November 2004. The main part of the satellite's job was to test new spacecraft technologies, such as Solar Elec-

SMART-1 took a one-way trip to the moon A tiny part of the Moon will be forever Europe. spectroscopy was also used to investigate the Moon's chemical composition, leading to an announcement by ESA in 2005 that calcium was detected on the Moon. Having completed an 18 month-long thorough investigation of the Moon (initially planned to last only 6 months), and yielding a huge wealth of data, SMART-1 was finally brought down at 05.42 on 3rd September 2006. Moving at approximately 4473 mph, the satellite hurtled onto the lunar surface in the Lake of Excellence region, close to the line which separates day and night. This simulated a meteor impact visible through telescopes on Earth, and also exposed surface materials with the potential for analysis. Unfortunately for us, the Moon was not visible in Europe at the time of impact, but it could be seen in North and South America. ESA have hailed the project as an enormous scientific and technological success, leading the way for future missions to the moon and beyond. So as poor SMART-1 lies shattered upon the surface of our own satellite, perhaps the tiny craft only 1m across can take heart from the words of Professor Southwood, ESA's Director of Science, "It seems that right now everyone in the world is planning on going to the Moon. Future scientific missions will greatly benefit from the technological and operational experience gained thanks to this small spacecraft."

"SMART hurtled into the Lake of Excellence"
tric Primary Propulsion, which uses solar-powered thrusters to propel the craft. It also experimented with the use of miniaturized scientific instruments, which are thought to produce enhanced efficiency. SMART-1's secondary objective was to gather more information about the Moon, thus providing clues as to how it was created. Using X-ray and Infrared imaging, SMART-1 took pictures of the lunar surface from several different angles. This has allowed scientists to create updated 3D images of the Moon's morphology, including the Peaks of Eternal Light (PELs) - mountaintops permanently bathed in sunlight, surrounded by deep valleys in permanent darkness. X-ray

Image Credit: ESA


October 2006 Astronotes 9

Stuck on the Launch Pad
A Vertical Empire by CN Hill reviewed by Colin Johnston In the early 1950s, the wonderful `Dan Dare' comic strip showed a generation of British schoolboys how the future would be. In the early 21st Century, explorers from Earth would venture into space. Naturally, Britons piloting spaceships clearly descended from Spitfires and Lancaster bombers would be at the forefront of the conquest of the planets. Even to adults this did not seem unlikely. Britain was still one of the three great world powers while British technicians had led the way in developing radar and jet engines. Another new age of progress seemed around the corner. Yet now in 2006, Europe's Arianespace make huge profits launching commercial payloads into orbit, and even India and Israel can launch their own satellites- but the UK has neither the ability nor interest. Why did things turn out this way? Space was never really of interest to Britain's ruling classes. True, rocketry was investigated for military purposes to some extent until cheaper options were developed. As for space exploration, the cabinet ministers, and more importantly, it seems, the civil servants with responsibilities in that area saw their task as limiting British involvement in the new field; they didn't want to build "a vertical empire". Their motives were mainly to save money, combined with a certain lack of imagination. As the certainties of the immediate post war period were replaced by the more ambivalent and cynical 1960s, increasingly there was an attitude that "rocketeering" wasn't something Britain should be concerned with. That attitude has lasted to the present day and shows no signs of changing. However it should be emphasised that British engineers proved themselves every bit as competent as their colleagues in other nations. In fact, based on the lukewarm support for and appreciation of their endeavours from their superiors, they deserve a great deal of credit for
Image Credit: Amazon.co.uk

No Ministry of Space Hill's book brilliantly chronicles how rockets never appealed to the UK's politcal establishment their perseverance. `A Vertical Empire' charts the largely dismal history of the management of Britain's rocket and space projects between 1950 and 1971. The author's style is witty and clear, although he does rely on the reader having a certain degree of knowledge of Britain's post-war politics, defence policy and of the technicalities of rocketry, so it is not a book for those new to the field. It is highly recommended to anyone who wants to know more about this neglected part of the UK's history. The book does get to describe one triumph: Black Arrow was a very low-key rocket development program, but on 28 October 1971 the third and final Black Arrow placed the UK's Prospero satellite into orbit and it still circles our planet today. However, the project had actually been cancelled mere months before Prospero flew and the team who built the Black Arrow rocket were out of a job the day after the launch. Somehow, this is a very British story. Imperial College Press, 2001, ISBN: 1860942687, 260 pages


10 Astronotes October 2006

Friends Reunited
By Sharon Carroll, Science Communicator Thursday 24th August was a special night in the eyes of all the staff at Armagh Planetarium. It was a night to remember indeed, but not because of some spectacular vision in the sky or even a cloudless sky that allowed us to get out our telescopes. It was an evening where we were able to welcome new and old friends to see our sparkling new Planetarium. We welcomed the chance to spoil the Friends' Society members, who have faithfully supported us throughout the years. This invitation allowed us to show off our new facilities, introduce the new team and share a few stories about the whole refurbishment. The Director, Tom Mason invited all the members to visit the new Digital Theatre for their own private viewing. He thanked his guests for their commitment to the Planetarium, introduced the new Science Communicators to all and expressed how proud he was of the success and achievements to date of all staff. The Digital Theatre Manager, Julie Thompson, treated the audience to a spectacular journey through space to demonstrate the remarkable Digistar 3 technology and new surround sound system. Julie also took the members on a trip back in time to 1943 showing the `Armagh Story'- her own personal view of the highlights and lowlights of our famous Planetarium. Robert Hill (Business Development Manager) invited the members to take a tour of the exciting new exhibition area. The feedback from all our guests was very positive indeed. Many wished us all continued success in the future and were looking forward to returning with their families to see the public shows. We know however that secretly they can't wait to come back to take part in our space art activities and build their very own rocket.
Image Credits: Armagh Planetarium

Nice to see you Friends were greeted with wine or soft drinks and a buffet meal

Fly me to the moon Director Tom Mason sings!

Private viewing Enthusiastic Friends get access to our exhibits


October 2006 Astronotes 11

Spaced Out on the Ards Peninsula!
By Robert Hill, Business Development Manager In August, and as part of the Ards Peninsula summer activities program, Armagh Planetarium and the National Trust hosted the `Spaced Out' event at the beautiful Mountstewart Gardens, Newtownards. This was the second `Spaced Out' event organised by Armagh Planetarium. Throughout the day, adults and children had a chance to design and launch their own rockets and make their own astronaut mission patches. Face painters turned little faces into terrifying aliens and there was an array of telescopes on view courtesy of the Irish Astronomical Association. The fine weather allowed for safe viewing of the Sun with many members of the public having their first glance of our star through a telescope. Many members of the IAA assisted in making the event such a success. Newtownabbey-based Ballyduff Silver Band played an integral part of the space themed day. Under the baton of Mr William Hill, the band performed versions of various astronautical themed music including the theme tunes of `Thunderbirds', `Superman' and `2001' also got an airing during the proceedings.

Image Credit: Robert Hill, Business Development Manager

Open air workshop The ever popular rocket building activity at Mountstewart. The main goal of the event was to raise awareness of the link between science, nature and the arts. Our friends at Mountstewart have informed us that over 1,500 members of the public attended the event- much higher than expected. Arrangements are already under way for next year's `Spaced Out' day with even more on offer than this year.

Astronews
· Space Shuttle Atlantis was launched on 9 September for a mission to the ISS. The six person crew successfully installed a new set of solar arrays and their associated support structures and batteries on the station before returning safely to the Kennedy Space Center on 21 September. · As predicted in the September Astronotes, Armagh Planetarium had its busiest August ever this year with the largest ever total number of visitors in the month. A number of people equivalent to more than 1% of the population of Northern Ireland came to visit us during the month. We are proud and delighted by this amazing support from the public. · A new NASA study has found that temperatures on Earth are approaching their highest in more than 12 000 years. Global temperatures have been going up approximately 0.2° Celsius per decade for the past 30 years. In fact, global temperatures are now within one degree Celsius of the hottest temperatures measured in the last million years.


12 Astronotes October 2006

Image of the Month
Image Credit: Eliot Young (SwRI) et al., NASA

This is the dwarf planet Pluto (134340 Pluto) depicted in its true colours. Until last month Pluto was the smallest planet. Now it is the secondlargest dwarf planet (after Eris, the former UB313). Between 1985 and 1990, Pluto and Charon underwent a series of transits, eclipses, and occultations. This map was created by tracking Pluto's brightness changes when it was being partially eclipsed by its largest moon Charon. The distribution of bright and dark features of Pluto's surface can be plotted from these events with high precision; for example, when a bright spot on Pluto is eclipsed the total brightness change is greater than if a greyish spot had been eclipsed. Created using computer processing, the final map has a

resolution as fine as 200 km in some areas, far surpassing current direct observation techniques. The map shows the hemisphere of Pluto that directly faces Charon which maintains a constant position in Pluto's sky (the moon is in the local equivalent of a geostationary orbit). This map reveals a prominent bright feature that may be due to ice condensing around a geyser or in a crater. The origin of Pluto's pinkish brown colour is thought to be frozen methane deposits metamorphosed into some other organic compound by the Sun's faint light. This lies over a substrate of frozen nitrogen and carbon monoxide. Pluto probably broadly resembles Neptune's moon Triton.

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