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August 2008

ASTRONOTES
Incorporating FRIENDS' NEWSLETTER Astronaut Michael Foale's visit 2012: the End is Nigh Pluto and the Plutoids The Night Sky this Month New spacecraft exhibits

ARMAGHPLANETARIUM


2 Astronotes August 2008

Mike Foale visits Armagh
By Alyson Kerr, Education Support Officer Though I have been working at Armagh Planetarium for less than a year, I am lucky to have some favourite high points, the Halloween celebrations and 40th Birthday Conference to name a few. Now, I can add another to my list! I met a real live astronaut! Excuse me for reverting to childlike-enthusiasm but so few people have experienced the privilege of visiting and working in space that meeting someone who has is pretty impressive in my book. Dr Michael Foale (or Mike as he likes to be known) was the NASA astronaut who came to visit us on the 5th June. Mike was selected as an astronaut candidate in June 1987 on his third application after he changed the topic of his application essay from his dreams to the realities of leadership faced by NASA after the Challenger disaster. His first spaceflight came in 1992, this was a short Space Shuttle mission. By 1997 he had flown on three Shuttle missions and was accepted to spend time aboard the Russian Mir Space station. Aboard the Mir, Mike was to face one of the most challenging incidents of his career. On 25 May 1997 an unmanned Progress cargo ship crashed into the space station during an experimental docking procedure. Mike played an instrumental part in the restoration of the station's systems, possibly saving the lives of he crew. with Mir were used to counteract the station's tumble. To this day he is seen as something of a hero among the Russians. From this, his career led onto more Shuttle flights, he was appointed commander of one of these missions. He has so far logged 374 days in space, much of this aboard the ISS His visit began with a talk to 400 local schoolchildren in the Marketplace Theatre in Armagh. The response from the children was astounding, not only did they listen intently but they had a never-ending list of questions at the end. Mike has been on six missions to space, once to mend the Hubble Space Telescope, twice to spend time on the Russian Mir space station and he has been aboard the International Space Station (ISS) three times. In his space-faring career he has experienced launches in both Russian and American spacecraft. He was able to succinctly describe these,

"The crash caused Mir to spin off its axis"
The crash caused Mir to spin off its axis, turning the solar panels away from the sun and leaving the station with minimal power. By stretching his thumb out amongst the stars and watching them drift past, he was able to determine the rough direction and rate of the spin. The thrusters on a Soyuz spacecraft already docked
Image Credit: NASA

Michael Foale (born 1957) was the first Briton to perform a space walk (nearly suffering frostbite in the course of his EVA)


August 2008 Astronotes 3 much to the delight of the kids in the theatre, as he played a deafening video of one of his launches. His talk took us through the intricacies of a Shuttle flight and life on the ISS and relating the history behind his reasons for wanting to be an astronaut. Becoming an astronaut was Mike's ambition from the tender age of six years old until eventually he realised his ambition at the not so tender age of 35.

"Being around a NASA astronaut was inspirational "
By inviting a NASA astronaut to Armagh Planetarium, our intention was to help inspire children to take an interest, not only in space and astronomy, but also in Science. Mike certainly helped to inspire and we were able to see this in the questions they asked. Everything from "What does it weightlessness really feel like?" or "Do you prefer launch or landing?" to "How much do you get paid?" (much to the embarrassment of every adult in the audience!) Being around a NASA astronaut was inspirational, even to the education staff. He was asked particularly intimate questions about the fine points of personal hygiene and housekeeping. Let's just say that clean clothes are a luxury and baths are welcome when you get home! The main point that Mike tried to get across was that the children in the audience are the future of the space program and they are capable of achieving their dream if they work hard enough. By the end of the talk, there were certainly more children who were dreaming of being astronauts. During his visit, Mike also took the time to give

Mike Foale Live at the Marketplace Theatre His excellent presentations were lapped up by audiences eager for his first-hand accounts of space travel throughout the day. a talk to an audience of the Friends of Armagh Planetarium and local amateur astronomers. The venue was our very own Copernicus Hall at the Planetarium (wine and nibbles provided), and this audience was just as eager to listen to what Mike had to say. The talk covered various topics from launches to the view from the ISS, then the floor was opened for questions. I was exceptionally pleased to see an equally enthusiastic response from the audience as we had that morning at the Marketplace Theatre, and even more pleased that their questions were not as cringeworthy as the ones from the morning session. Overall, the visit was a success. We achieved our intention to inspire local schoolchildren and at the same time bring something new to our friends and colleagues. We hope that in the future there will be many more opportunities like this that we can all share.

Pluto: planet, dwarf planet or Plutoid?
By Nigel Farrell, Education Support Officer Recently a new `buzz word', "Plutoid" has entered the world of astronomy. At its meeting in Oslo on 11 June 2008, the International Astronomical Union (IAU) - the body deemed to be in charge of naming celestial objects - announced that Plutoid was to become officially

Image Credit: Armagh Planetarium


4 Astronotes August 2008

Image Credit: © BBC

The Solar System up to date (or is it?) a star, eight planets, three dwarf planets (two of them also Plutoids). The plot has thickened since this artwork was prepared, see note at the end of the article. recognised as the acceptable term to distinguish all dwarf planets lying beyond Neptune. This announcement, as you may imagine, has created quite a storm among the scientific community. As it occurs only two years after the IAU voted to remove Pluto from the official list of nine planets and demoted it to the status of "dwarf planet". This unceremonious demotion saw Pluto placed in a category of dwarf planets which included Ceres, the largest known asteroid, which is situated in orbit between Mars and Jupiter. sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape, and that have not cleared the neighbourhood around their orbit." Astronomer, Brian G Marsden, secretary of the Committee on Small Body Nomenclature (CSBN) said, "We wanted a clear name that related to Pluto, Plutoid fits the bill and I am happy enough with it, it means Pluto like." Currently there are two known and named Plutoids: Pluto and Eris, however, it is expected that many new Plutoids will be named in the future as advances are made in both science and technology which will undoubtedly lead to further new discoveries. In fact a third Plutoid may well be announced within the next few weeks. The term Plutoid, however, will not apply to all dwarf planets. For example, Ceres, will be excluded, due to its location within the asteroid belt. Ceres is believed to be the only object of its kind, it may eventually be classified in a category all of its own. Nevertheless, it seems highly unlikely that any explanation or definition will pacify those angered at Pluto's additional demotion. Alan Stern, a former space sciences chief at NASA and principal investigator on a mission to Pluto, was derisive in his denunciation of the IAU's decision, saying, "It's just some people in a smoke-filled room who dreamed it up, Plutoids or haemor-

"...scientists worried that there could be as many as fifty planets in the Solar System"
Pluto's 2006 relegation was deemed necessary as new advances in telescope technology had begun to reveal distant objects of a similar size to this small frozen world. Thus, without some formal classification scientists worried that perhaps there could soon be as many as fifty defined "planets" in the Solar System. The term Plutoid has now officially been defined by the IAU, the explanation says, "Plutoids are celestial bodies in orbit around the sun at a distance greater than that of Neptune that have


August 2008 Astronotes 5 Scientists are also set to continue the debate during a meeting between 14-16 August at Johns Hopkins University Applied Physics Laboratory. There, meeting co-organizer Hal Weaver said nobody will vote, but researchers will "address this question in terms of a scientific conference." Advocates of both sides of the "is Pluto a planet?" debate are expected to attend. One wonders, however, if any long term agreement is likely... it seems not! (Editor's note: as this issue was prepared for printing, the IAU announced that the Kuiper Belt Object 2005 FY9 also meets the criteria to be counted as a dwarf planet and Plutoid. Now named Makemake after the creator god of the people of Easter Island, this desolate world orbits between 38.5 and 53 AU from the Sun. With a diameter of between 1300-1900 km it is smaller than both Eris and Pluto.)

Makemake An artist's impression of the dwarf planet and Plutoid formerly known as 2005 FY9. rhoids, whatever they call it, this is irrelevant." But the president of the IAU was just as unwavering in her justification of the committee's decision, She said the 2006 "dwarf planet" ruling, approved at a meeting in Prague, included this clause: "An IAU process will be established to select a name for this category," meaning that it was always the IAU's intent to further define "dwarf planet" in relation to Pluto.

The Night Sky in August
By Tracy McConnell, Education Support Officer Before we get started, just a quick reminder that when stargazing in the summer months, it won't get truly dark until after midnight and the darkness won't last as long as the nights are shorter. Remember to allow yourself about 15 minutes for your eyes to become accustomed to the dark. Everything I highlighted for you to see in the July sky should still be visible, and here's a quick recap. Sagittarius will be setting in the SSW by the middle of the month, but the planet Jupiter should still be visible just above and left of it. The Summer Triangle is facing South and encapsulates the three constellations of Cygnus, Aquila and Lyra. West and just to the left of Lyra is Hercules. In the east is the Great Square of Pegasus. We finished with a familiar northern facing constellation, Cassiopeia, the celestial "W". Several of the north facing constellations visible at this time of year have a related mythology. If you turn to face in a NE direction, high in the sky above you will be a small pattern that looks like a 3 or a W on its side. This pattern represents Cassiopeia, the Queen. Above her is a pattern that resembles a square with a triangle attached to its left side. This is Cepheus, the King. Below Cassiopeia, on the left is the constellation of Perseus and on the right is Andromeda. Cetus is a long constellation which rises at about 2am in an ESE direction. King Cepheus of Ethiopia, (not the Ethiopia of today but a place in modern Egypt near Jordan), was married to a beautiful woman named Cassiopeia. Queen Cassiopeia was very vain and one day proclaimed herself to be more beautiful than the Nereids, the Sea Nymphs. One of the

Image Credits: NASA, ESA and A. Feild (STScI)


6 Astronotes August 2008

Perseus and Andromeda with Cassiopeia above Nereids was named Amphitrite and was married to the God of the Sea, Poseidon. She asked her husband to punish Cassiopeia so he sent a huge sea monster called Cetus, to terrorise King Cepheus' Kingdom. An oracle told Cepheus that in order to stop the destruction, he had to sacrifice his daughter Andromeda.

"Andromeda was chained to the rocks to be devoured by the monster "
Andromeda was chained to the rocks of a cliff face and left to be devoured by the monster. The hero Perseus was passing by, on his way home after having defeated the gorgon Medusa (who could turn living things to stone with her glance), with her head still in his sack. He stopped to ask Andromeda what was going on. After telling him everything, Andromeda caught sight of the monster approaching and screamed. Perseus took Medusa's head from the sack and turned it to face Cetus. The monster turned to stone and sank to the bottom of the ocean. Perseus and Andromeda got married and had six children.

There is a beautiful natural fireworks show that appears at this time of year. It's due to the Swift-Tuttle comet. Although the comet is nowhere near Earth, its tail does intersect Earth's orbit. We glide through it every year in August. Tiny bits of comet dust hit Earth's atmosphere at approximately 212 000 km/h (132 000 mph). This spectacular display is better known as the Perseids meteor shower because they seem to emerge from the Perseus Constellation in a NE facing direction. The shower peaks around 12/13 August but they should still be visible them. until about 22 August. If you catch it on the peak nights this shower will present 2 meteors per minute and by 15 August, you should see about 10 meteors per hour. They are quite fast and will present themselves as a high number of bright meteors, which may leave persistent trails across the sky. To view the shower at its best you will need both to observe after 11 pm (BST) and a dark sky (although the Moon's light will make very dark skies difficult to find).

Image Credit: Colin Johnston (Image created with Starry night)

"A high number of bright meteors may leave persistent trails across the sky "
In the West, there is a bright orange star called Arcturus that sits at the bottom of a kite shaped constellation. This is the 4th brightest star in the night sky so it should be fairly easy to see. The constellation is called BoЖtes, the Herdsman. Finally, on 16 August, the full Moon will be close to Capricornus, the Sea-Goat, one of the twelve Zodiac signs. At this time of year Capricornus is found facing south. Watch the Moon rise this night and see if it looks odd. This is the night


August 2008 Astronotes 7 ened region may look an omnious dark red. It will be visible from South America, Europe, Africa, Asia and Australia. The eclipse begins at 8.35 pm and ends at 11.44 pm (BST). At maximum about 10.10 pm just under one quarter of the Moon will be eclipsed. Enjoy your stargazing! (Thanks to David Asher of Armagh Observatory for details on the Perseid meteor shower.)

Image Credit: artist unknown

The Great Meteor Shower of 1833 That year's Leonids was the most spectacular meteor shower ever seen. Sadly this year's Perseids are unlikely to match it. of a partial lunar eclipse and part of the Earth's shadow will fall on the Moon's surface. The dark-

Moon Phases, Aug 2008
Fri 1 Aug Fri 8 Aug Sat 16 Aug Sat 23 Aug NEW MOON First Quarter FULL MOON Last Quarter

Will the world end in 2012?
by Orla O'Donnell, Education Support Officer 2012 is a big year for many reasons: the Olympics will be held in London, Poland will adopt the euro, the asteroid Eros, the second largest near space object, is due to pass by Earth and one more thing... the world is going to end! According to some interpretations of the ancient Mayan calendar the world is due to end on 2 December 2012. One needs only to type the numbers 2012 into an internet search engine to find a litter of web sites all counting down to the predicted last day. So in this article I'm going to investigate the claim that we are all doomed in four short years. The Mayans were an advanced civilisation who existed around 250-900 AD with an empire stretching across Mexico, Guatemala, Belize, El Salvador and western Honduras. The Maya built vast cities such as Palenque centred around majestic places of religious worship and some of these stepped temples are still standing today. The Mayans had developed advanced skills in written communication and were also keen mathematicians and astronomers; they built observatories and mapped out phases of the moon and the cycle of phases of Venus. Their joint interest in both mathematics and astronomy lead to the invention of many calendars. These calendars were often very short. One of their more crude calendars called the `Haab' charted only a solar year of 365 days. The combination of the `Haab'' and another calendar the `Tzolk'in' resulted in the `Calendar Round' which ran in 52 year cycles (the average life span of a Mayan). The `Long Count' calendar is the longest Mayan calendar and is the calendar that is causing all the concern about the end of the world. The


8 Astronotes August 2008 calendar was developed to measure dates over longer periods of time and to mark historic events. The Long Count is the most advanced Mayan Calendar and resembles the modern Gregorian calendar that we use, both have a year consisting of 365 days. The Long Count begins on 11 August 3114 BC and lasts for a run of about 5126 years. All calendars work off a base number; the Gregorian uses the number 10 while the Long Count uses a base of 20 (this is called the vigesimal system where 20 is the base number, we currently use the decimal numeral system where ten is the base). The Long Count calendar is set to complete its 5126 year cycle on 21st of December 2012 and some are predicting that the end of this fascinating ancient culture's calendar signals the end of the world. This is silly; at the end of the count the calendar would have been reset to zero and started again. Worrying about it reaching the end is like fretting that the world will end at midnight on 31 December when our calendar `ends'. In fact, experts in the ancient Mayan's culture such as archaeologists and mythologists, believe that the Mayans actually predicted an age of enlightenment when the Long Count ends. in 2012. We have all heard predictions made by many groups, both religious and others that the world is going to end on such and such a date and we have survived them all including the forecasted chaos of the New Millennium. There are still those who are certain that we are all doomed; a French laboratory worker Patrick Geryl, has quit his job to enable him to focus full time on preparing for the end of the world.

"An end of the world theory points to Planet X as the cause of our demise"
An end of the world prediction would be nothing without forecasts of a horrific natural event: claims include the possible eruption of a massive volcano, NASA forecasts of increases in solar storms and the melting of the Earth's ice caps. Another end of world theory points to the mysterious Planet X as the cause of our predicted demise. Nineteenth century astronomers noticed that the orbit of Neptune seemed to be disturbed by perhaps the gravitational pull of another planet; this led to a search which eventually found Pluto in 1930. However Pluto was too small to have caused this perturbation so scientists predicted that a potential Planet X may exist. Nowadays this looks unlikely as the observations of anomalies in Neptune's orbit were in error. Yet Planet X has been adopted by Doomsday predictors who forecast that this Kuiper Belt object is due to hit the Earth in 2012 and create widespread havoc. These scaremongers have reforecast that this hypothetical planet Planet X is on a long-period comet-like orbit and is due to collide with the Earth when it passes back into the inner Solar System in 2012 (note that these people are not scientists and that this not taken seriously by astronomers). One would think that an event of this magnitude may be a governmental concern. Conspiracy theorists have suggested that there is a massive international cover up in place with government bodies like NASA hiding the awful truth. This sounds like an `X-Files' plot and indeed that show did predict Very Bad Things to happen in 2012. So will the world end into 2012? I don't think so but we will have to wait and find out.

Image Credit: Axcordion via Wikimedia.org

City on the Edge of Forever: North Acropolis, Tikal, Guatemala, an example of Mayan architecture. The end of this calendar's life span may have gone completely unnoticed by the greater public if it was not for the release of some well timed publications, with names like `2012: the return of the Quetzalcoatl' and `Apocalypse 2012: a scientific investigation'. The predictions even have the backing of the hip hop community with influential American Rapper Lili Wayen said to be a keen supporter of the predicted apocalypse


August 2008 Astronotes 9

Three space explorers go on display at Armagh
By Colin Johnston, Science Communicator
Image Credit: nigel Farell, Education support Officer

Thanks to the generosity of the European Space Agency, and with the assistance of the Northern Ireland Space Office, Armagh Planetarium is now displaying ј-scale models of three important yet often over-looked unmanned science spacecraft. Allow me to introduce our latest exhibits. SMART (Small Missions for Advanced Research in Technology) was the first European mission to reach the Moon and in fact was placed in orbit around our natural satellite. It travelled to the Moon using solar-electric (or ion) propulsion rather than a conventional rocket motor. Rather than burning explosive fuels this method of propulsion uses an electric field to eject atoms of xenon from the spacecraft providing a gentle but steady thrust that can be maintained for long periods. This was only the second time that ion propulsion has been used as a spacecraft's main propulsion system (the first was NASA's Deep Space 1 probe launched in 1998).

SMART-1 model hanging in front of the fantastic new windows in our Celestial Cathedral. to allow spacecraft to navigate themselves, and miniaturised scientific instruments to examine the surface of other worlds in visible, infra-red and X-ray wavelengths. As well as testing new technology, SMART-1 looked for water (in the form of ice) on the Moon and did the first comprehensive search for key chemical elements in the lunar surface. It also investigated the theory that the Moon was formed following the violent collision of a smaller planet with Earth, 4.5 billion years ago. The spacecraft studied the Moon's craters to better understand the ancient impacts that created them. Launched in September 2003 by an Ariane 5 rocket, SMART-1 arrived in lunar orbit in November 2004. This long journey time was due to the low thrust from the solar-electric propulsion system. After having finished lunar orbit science operations, its mission was ended when it was deliberately crashed into the lunar surface on 3 September 2006. (SMART-1's mission and demise have been covered in more detail previous issues of Astronotes, notably `Fly me to the Moon' in the October 2006 issue.) Our other two new spacecraft models depict

Image Credit: ESA

From the Earth to the Moon SMART-1 climbs out of our planet's gravity well in this artist's impression. In reality the reflected sunlight from the spacecraft and the Moon would wash out the stars. Proving new technology was the mission's primary aim. It tested future deep-space communication techniques for spacecraft, techniques


10 Astronotes August 2008 explorers of exotic phenomena through wavelengths far beyond human senses. One model represents the X-ray Multi-Mirror Mission or XMM-Newton, European Space Agency's (ESA's) unique X-ray space observatory satellite. When launched it was the biggest scientific satellite ever built in Europe and its telescope and cameras are amongst the most powerful ever developed in the world, so it has seen much more of the Universe in X-rays than any previous satellite. Why is XMM-Newton based in space rather than at an observatory on Earth? Surprisingly, X-rays are easily blocked by the gases of our atmosphere, this means that (unfortunately for Superman!) X-ray vision would have a range of only a few metres. X-rays which have travelled thousands of light years through space are absorbed by our planet's atmosphere, fading out a few hundred kilometres above our heads. On the Earth's surface, we are blind to the wonders of the Universe in X-rays. To appreciate them we must rise out of the atmosphere. XMM-Newton on Earth would be blind, but beyond our planet's atmospheric cloak it can gaze into the depths of space.

XMM-Newton orbits Earth in this artist's impression. In reality the Earth would appear considerably smaller from the satellite's vantage point and the stars would be much less prominent. of instruments is completed by a fourth telescope which observes ultra-violet and ordinary visible light. XMM-Newton has detected more X-ray sources than any previous satellite. It is giving scientists insights into intriguing cosmic questions, from the behaviour of black holes to the formation of the galaxies in the distant past of the Universe. The XMM-Newton spacecraft was launched by an Ariane 5 launch vehicle in December 1999. It has long exceeded its two year planned life and will continue to let us study the most violent events in the universe until at least 2010. XMM-Newton is not alone in witnessing dramatic cosmic events at the extreme end of the EM-spectrum. It is partnered by INTEGRAL, represented by the Planetarium's third new model. The most sensitive gamma-ray observatory ever launched, ESA's INTEGRAL is used to
Image Credit: nigel Farell, Education support Officer

"..unfortunately for Superman, X-ray vision would have a range of a few metres"
The satellite was placed in an unusual orbit. Every two days XMM-Newton soars almost a third of the way to the Moon before swooping to within 7000 km (4350 miles) of Earth and out again. This is not only to allow XMM-Newton long, uninterrupted views of distant objects but also to keep it beyond the Earth's natural belts of radiation most of the time. This radiation could otherwise confuse its sensitive instruments. The real spacecraft is not a tiny satellite. XMMNewton is 10 m (32.8 m) long and its solar arrays are 16 m (52.5 m) in span and it weighs a hefty 3800 kg (3.7 tons). It uses three Italian-made X-ray telescopes to focus X-rays onto sensitive cameras and spectrometers. We also have a sample of one of its mirrors on display. Its suite

XMM-Newton model suspended above our Galileo Hall.

Image Credit: ESA


August 2008 Astronotes 11 between the Earth and Moon. It is here, in deep space, that it makes its scientific observations. As INTEGRAL is a powerful instrument for studying the Universe in gamma-rays, through it we are learning about the most violent and exotic objects in the Universe, such as supernovae and their remnants, such as black holes and neutron stars, and the processes in the centres of active galaxies. INTEGRAL is also helping us understand gamma-ray bursts, the most energetic phenomena in the Universe whose origin is still a mystery. INTEGRAL in orbit Yevgeny Zamyatin's SF novel `We' (1921) featured a spacecraft called Integral. Coincidence or an in-joke by an early 20th century Russian dystopian literature fan in ESA's management? Once again the prominence of Earth and the stars are exaggerated for visual impact in this artist's impression. detect some of the most energetic radiation that comes from space. A co-operative mission between ESA, Russia, the Czech Republic, Poland and the United States, INTEGRAL is short for INTErnational Gamma-Ray Astrophysics Laboratory. Like X-rays, gamma rays are blocked by our atmosphere, so must be observed from space. INTEGRAL is a sort of younger brother to XMMNewton. To save development money, INTE-

Image Credit: ESA

"Integral at its furthest is close to half way between the Earth and Moon "
INTEGRAL was launched in October 2002 by a Russian Proton rocket. It too has gone beyond a planned life of two years and is expected to continue operating until at least 2012. Sadly, in July 2008, the UK's Science and Technology Facilities Council decided to reduce British support for INTEGRAL in its next three year funding package.

"XMM-Newton has long exceeded its two year planned life"
GRAL's service module or body is identical to the older satellite's. INTEGRAL sees the Universe through a gamma ray telescope of 3.7m (146 in) aperture. Beneath this, at the satellite's heart are four instruments, heavily shielded against background radiation. These are a gamma ray camera and spectrometer, backed up by an X-ray monitor and an optical camera used to identify the gamma-ray sources under observation. Once again this satellite was placed in an orbit which is far from circular: INTEGRAL takes three days to go around the Earth and at its closest to Earth is about 10 000 km (6200 miles) above us but for most of its time INTEGRAL is much further away. At its furthest distance it is 153 000 km (95 000 miles) from Earth, close to halfway

INTEGRAL model now suspended outside our Kepler Room. These three marvels of human ingenuity are far beyond our planet, one lies smashed on the lunar regolith, while the others continue to observe the extremes of radiation. Through our displays visitors to Armagh Planetarium can start to appreciate what amazing achievements they are.

Image Credit: Nigel Farell, Education support Officer


12 Astronotes August 2008

Summer Blast off success
by Alyson Kerr, Education Support Officer This summer got off to a great start with our Summer Blast Off event on 28-29 June. This was a weekend packed full of activities and entertainment for all the family, not to mention the launch of our new shows. Children were able to enjoy an activity booklet that was packed full of crosswords, word searches and our Alien Hunt activity. We placed planetarium-made aliens all around the Astropark. This gave families an opportunity to explore the grounds and have some fun trying to pronounce our Alien names.
Image Credit: Armagh Planetarium

"The Knights of the Empire gave out prizes to rocket competition winners"
To make the day extra special, we were joined by the Knights of the Empire, a Star Wars costuming club. They appeared fully dressed in the garb of the Empire and made a spectacular impression on young and old. We had Imperial Stormtroopers, Sandtroopers, Princess Padme and a really cool blue alien called Aayla Secura (she's a Twi'lek and one of the Jedi). The Knights were in full character as well as costume and

A New Hope The Stormtroopers apprehended the brave rebels including our own Alyson, Orla, Neil and Nigel. Luckily the Emperor's minions had forgotten that the Astropark is swarming with Ewoks at this time of year... many a child was laughing gleefully while being `arrested'. It was quite amazing how readily those in the queue to the show had their tickets ready with a bit of encouragement from a Stormtrooper! The Knights of the Empire also gave out prizes for the winners of our rocket launching competitions throughout the day. We held three sessions per day and gave out prizes for the top three in each group. There were some remarkable rockets, some even rivalled the `Black Deceptor', which was made by our very own Nigel in a very boy-toy fashion (he spent hours perfecting it!). The standard was very high and all the prizes well deserved!

Image Credit: Armagh Planetarium

"Highlight of the day was the audience response to the new shows"
The highlight of everyone's day had to be the audience response to the new shows. Zula Patrol proved to be a real hit with all the kids and

The Empire Strikes Us Imperial Stormtroopers (boo!) marched into the Planetarium to apply the smack of firm government to the rebels.


August 2008 Astronotes 13 back about this show. Another hit of the day was our in-house show, Pole Position. As a live show, narrated by one of the staff, it has a lot of character. Tracy and Orla were both chuffed to bits to receive rapturous applause from the audience at the end of the show. They took the audiences on a tour of the summer night sky, pointing out interesting constellations and other celestial objects and as always it proved a great success.

Image Credit: Armagh Planetarium

Rocket Scientists Alyson with Megan and Taylor, (a couple of regular visitors to the Planetarium) and their rockets. parents, especially because there were worksheets to do after the show. The Zula Patrol are a crew of zany alien space explorers who must stop the evil but bumbling villain Dark Truder (and Trixie, his talking wig) before he steals weather systems from the planets. If Truder gets away with this, he will have the key to finding the magic ruby which will make him ruler of Planet Zula. Everyone coming out of the shows was humming the catchy songs and the names of the characters were mentioned throughout the day. I saw lots of kids heading home with their very own Gorga toy at the end of the day. Seven Wonders was just as popular with the adult audience. This show took us through the Seven Wonders of the Ancient World and Seven Wonders of the Universe. Many of the audience commented on the fantastic images that were shown and we received a lot of positive feedImage Credit: Armagh Planetarium

Rocket Racers and spectators watch the competition. All the staff cannot wait for our next family event. On the 23 and 24 August we will be hosting the `Last Blast' to mark the end of summer and the return to school. We will have lots of the same activities including alien hunts and rocket competitions but this time you can come in fancy dress and we will see who has the best outfit of the day! We hope to see you there!

Solar System speed limits
By Colin Johnston, Science Communicator To the best of our knowledge the Solar System we see today formed from a vast cloud of dust and gas in the distant past. All the major objects orbiting the Sun (Mercury to Neptune and main belt asteroids) are at present roughly where they were when they condensed from this Solar Nebula and travelling at the same speeds as they were when they were formed. Why are they moving at all? Well, if they weren't moving, they would not be there today. Most of the material in the Solar System today had very little momentum with respect to the forming Sun, that is, most of the gas and dust was stationary and was pulled straight down into the Sun, adding to its mass. However,


14 Astronotes August 2008 by collisions and gravitational interactions over the aeons. For example, it has been calculated that near Earth asteroids only survive in their orbits for 10 million to 100 million years before eventually being eliminated either by collisions with the inner planets, or by being ejected from the inner Solar System by near misses with planets. Since there still are near Earth asteroids, there must be a steady supply of `new' ones (these could be dead comet nuclei or asteroids perturbed from the main belt). Thanks to the great renaissance-era astronomer Johannes Kepler we know bodies closer to the Sun move round it faster than those further out -- in fact this is Kepler's Third Law. If you want to go around the Sun in a particular orbit, at every point in it, you must be going at an appointed speed with no exceptions. So Mercury is whizzing round the Sun at about 48 km/s (30 mile/s), Earth is moving at an average speed of about 30 km/s (18.6 mile/s) while Neptune plods along at a steady 5.5 km/s (although equivalent to nearly 20 000 km/h, an outrageous speed in terrestrial terms, note that the ISS is going round the Earth faster than this- at about 8 km/s). Immensely further out still the comet nuclei in the Oort Cloud are moving, as Carl Sagan pointed out, scarcely faster than a little propeller plane buzzes along. This dropping off of speed with distance from the Sun is a consequence of the Sun's gravitational attraction reducing with distance from its centre.

The 1708 Solar System illustration from the Harmonia Macrocosmica of Andreas Cellarius. material that was moving `across' the forming Solar System was pulled into curved paths. Those paths, or orbits, never intersected the Sun but survived to form the various worlds and debris we see today. Why were these clumps and lumps moving at all? The best guess is that whatever kicked off the formation of the Solar System, a shock wave from a nearby supernova possibly, imparted some motion to the gas and dust cloud.

"near Earth asteroids only survive in their orbits for 10 -100 million years"
Obviously this is grossly simplified and the processes that led to the formation of the Sun's family of worlds are very poorly understood. Also observations of newly discovered solar systems suggest that some of them experience a sort of orbital migration where planets form in the outer solar system and move inwards. This may have happened in our Solar System as well So nowadays the major planets and main belt asteroids are moving in good approximations to circular orbits. They have stayed in these orbits because they are nice, stable and are never going to lead to embarrassing collisions as their orbits won't ever intersect with that of another world. If they did, they could actually catastrophically collide but a more likely alternative to this is a gravitational interaction where the smaller of the two bodies is `slingshot' into a radically new orbit. Hence the number of objects in more eccentric elliptical orbits has been winnowed down

Image Credit: via wikimedia.org

Part of the 2008 Solar System a very schematic illustration depicts the Sun, planets, main belt asteroids and Pluto. Missing are the other dwarf planets, KBOs and Oort Cloud

Image Credit: NASA


August 2008 Astronotes 15
Image Credit: D. Roddy, USGS

Any comet or asteroid moving in an orbit through the inner solar system - between Mercury and Mars - will have a speed roughly in the range 20 - 50 km/s. An object (asteroid, comet or whatever) in an elliptical orbit moves slower at its furthest from the Sun -- a jet plane-like 1125 km/h (700mph) perhaps for some comets -- and fastest at its closest. As an extreme case sungrazer comets have been clocked at 1.6 million km/h (1 million mph) at perihelion. This is a fantastic speed: if we could attain it we could leap from the Earth to the Moon in less than fifteen minutes! So what speed could an asteroid or comet strike the Earth at?

"...at 70 km/s every tonne of asteroid would be equivalent to 600 kg of TNT"
Some sources quote Earth-impacting asteroids and comets as having speeds in the range 11 to 74 km/s (6.8 ­ 46 mile/s). How did they arrive at these figures? The lowest value is straight forward, it's assuming the asteroid is not moving laterally with respect to the Earth and is just freely falling from the depths of space under the Earth's gravitational attraction (an unbelievably improbable occurrence). Approaching like this, the maximum speed it can attain is about 11 km/s (this is the same as the Earth's escape velocity- in fact it's exactly the same. Escape velocity will be discussed in a future Astronotes). Historical pseudoscience In the 1950s psychologist Immanuel Veliovsky wrote a series of books claiming mythological events could be explained by wandering planets passing by the Earth. We still get questions about this silly theory.

Meteor Crater in Arizona. It is about 1 200 m (4,000 ft) in diameter and some 170 m (570 ft) deep. The impactor was a nickel-iron meteorite about 50 metres (164 ft across) which fell 50 000 years ago. The crater was only proven to be of extraterrestrial rather than volcanic origin in 1960. Alternatively, the greatest speed that a natural object could have as it crosses Earth's orbit is just over 40 km/s (24.9 miles/s), which is solar escape velocity at the Earth's orbit - note this another fantastically unlikely situation as the asteroid would essentially be falling past the Sun. The Earth is moving along at about 30 km/s, so the two speeds combine. So there are two extreme scenarios for collision: either a `stationary' asteroid just falls on the Earth and is going at 11 km/s as it hits the ground, or the asteroid is going at 40km/s in the opposite direction to the Earth and they slam into each other with a combined velocity of (30+40=) 70 km/s (plus an extra few km/s caused by the Earth's gravity accelerating the asteroid towards it. It is fortunate that this is so unlikely; at 70 km/s every tonne of asteroid would have a kinetic energy equivalent to about 600 kg of TNTenough to spoil the whole day of anyone unlucky enough to be underneath it when it comes down. Any comet or asteroid which does hit the Earth will probably be moving between these limits, and probably at the lower end. As a presumably typical example, the object that formed the famous Meteor Crater in Arizona is estimated to have hit the Earth at about 12.8 km/s (about 8 miles per second). Our vast Solar System is full of these high speed projectiles- and more than one of these cosmic bullets has our planet's name written on it!

Image Credit: Amazon.com


16 Astronotes August 2008

Image of the Month
Image Credit: Gemini Observatory/Association of Universities for Research in Astronomy

Almost identical twins, these spiral galaxies were imaged appropriately enough by the Gemini Observatory. As noted in the caption to last month's image, interactions between galaxies are not as rare as one might think. In densely populated galaxy clusters they are common. Collectively known as Arp 271, NGC 5427 (left) and NGC 5426 (right) are 90 million light years (27.5 megaparsecs) from Earth and are slowly brushing past each other. NGC 5426 is currently the closer of the two galaxies, but millions of years hence NGC5427 will be in front. The two galaxies

are exchanging gas and dust with each other across the 60 000 light years (18.4 kiloparsecs) divide separating them. We must remember that is view is not current. Thanks to the finite speed of light we are looking back in time at events that happened in the heyday of the dinosaurs. To be precise this cosmic gavotte has already taken place and today the two galaxies must already be moving apart and separated by a huge distance. (Caption by Colin Johnston, Science Communicator)

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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 Assistant Editor: Alyson Kerr ©2008 Armagh Planetarium All rights reserved