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April 2007

ASTRONOTES
Incorporating FRIENDS' NEWSLETTER The colours of stars Hurricanes in space Armagh's other planetarium Venus: the ugly sister planet Pole Position Springs back!

ARMAGHPLANETARIUM


2 Astronotes April 2007

The Colours of Stars
By Paul O'Neill, Education Support Officer In the Northern Hemisphere the constellations associated with spring are coming into view. If you go outside and take a look at the brightest stars in two of these constellations ­ Arcturus (in BoÆtes) and Spica (in Virgo) you'll see that they are not the same colour. Arcturus has a distinct reddish tint whereas Spica is a bluish white colour. Take a look around the sky and you'll begin to notice brighter stars do have a range of colours. Fainter stars also have colours but our eyes are not sensitive to colour at low light levels and so the dimmer stars all appear to be colourless to our unaided eyes. In this article and in the next issue of Astronotes I hope to explain why stars show different colours and how astrophysicists have grouped stars into different types. I will explain how these different types of stars evolve in a later article.
Image Credit: Armagh Planetarium

The long and the short of it Blue light (top) is shorter in wavelength but carries more energy that red light (bottom). High energy photons have a short wavelength ­ our eyes see this as blue; low energy photons have a longer wavelength which to us appears red. So colour and temperature are linked. A hot star will emit lots of high energy/short wavelength photons (i.e. blue) and a cool star gives off fewer low energy red photons. The Sun is not so hot and not so cool therefore it emits lots of yellow and green photons. This brings me to the spectra of stars. Isaac Newton used a prism to split the Sun's light into a rainbow of colours ­ this is called a spectrum by scientists (the plural of spectrum is spectra). The spectrum consists of two parts: the rainbow of colours ­ called the continuum, and absorption lines. These are narrow dark lines superimposed on the continuum ­ they can be thought of as the finger prints of the chemical elements which make up the surface of the star; each element has its own unique pattern of dark lines. Spectroscopy (the study of spectra) allows astronomers to work out which elements exist on the surfaces of distant stars. Two scientists are associated with the early study of absorption lines in the spectra of the Sun and other stars ­ Joseph von Fraunhofer and Angelo Secchi. Secchi is particularly noted for classifying stars into spectral types, based on the number and strength of the absorption lines in their spectra. By the late nineteenth century this technique was well established. It was regarded as so reliable

"the Sun emits lots of yellow and green photons"
Why do stars have colours? A blue wall looks blue because the pigment in the paint reflects blue light towards your eyes. Different pigments reflect different colours. Stars are different from walls in a number of ways, but one in particular is especially important­ stars emit light (in other words they make their own light) rather than reflecting light from somewhere else. In contrast the Moon and planets do not emit any light, we see them shine because they are reflecting the Sun's light. The colour of the light emitted by a star depends on its surface temperature . Take a piece of iron and put it in a fire. After a while it will begin to glow red, as it gets hotter it glows orange then yellow...in theory it would go through all the colours of the rainbow (red, orange, yellow, green, blue, indigo and violet). Light is made up of little packets of energy called photons.


April 2007 Astronotes 3 that when a mystery line was discovered in the Sun's spectrum, scientists were confident that a new element had been found. It was named helium and twenty years later its existence was confirmed on Earth. In the next article I will tell you more about how stars are classified.

Image Credit: NASA

Stellar Spectra Stars have been classified by their spectra since the early 1800s.

The Bluffer's Guide to Venus- Earth's Ugly Sister
By Colin Johnston, Science Communicator If you are successfully posing as an astronomer, sooner or later someone will ask you a question phrased something like this: "I saw this really bright light in the sky last night, it was just hanging there so it wasn't a `plane. What could it have been?" Well, this one is a no-brainer, you can be 90% certain that what the enquirer saw was the planet Venus. This is the second closest planet to the Sun and is covered in highly reflective clouds, so it is very bright, in fact it is the brightest astronomical object in the sky after the Sun and Moon. It can occasionally be seen in daylight. This brightness is why it is sometimes reported as a UFO!
Image Credit: NASA

Veiled Venus A shroud of bland white clouds conceals a hellish surface. As the orbit of Venus lies inside that of our own planet, Venus is always in the same part of the sky as the Sun. We see it best after sunset (or before dawn, depending on where the planet is on its orbit). Sometimes the planet is the `Evening star', visible after sunset, at other times it is the `Morning star', only visible before sunrise, and for a long time people thought it was two separate objects. Galileo was first to see that Venus shows phases just as our Moon does and he cleverly used this fact (along with the planet's proximity to the Sun) to demonstrate that Venus orbited the Sun and not the Earth.

"Venus is often reported as a UFO"
Venus is named for the classical goddess of love and beauty, a deity who judging from artwork appeared to spend her days frolicking in the surf, rather like a Graeco-Roman Pamela Anderson. Venus was long thought of as Earth's `sister planet'. Sadly, beneath her clouds she is a very ugly sister indeed.


4 Astronotes April 2007 inhabited by ferocious space-dinosaurs! (A bit of a leap here) Right up to the 1950s, popular astronomy books carried artist's impressions of torrid Venusian landscapes and seascapes populated with scaly behemoths and leviathans which could have lumbered straight from a Ray Harryhausen movie. The same books would also have paintings of the canals and vegetation on Mars: the Solar System was a more exciting place in those days (if you think this was silly, just check your recently published books for artist's impressions of weird sea-creatures in the hypothetical oceans under the ice of Europa). At the beginning of the Space Age, this view of Venus as a `Lost World' was already fading as new technologies such as radio astronomy were suggesting that the planet's surface was probably very hot indeed. The last hope for a planet full of exotic life was literally crushed in the 1960s when the first spacecraft visited Venus.

Venus revealed Venera 13 took this monochrome image of a barren landscape. Part of the probe can be seen at the bottom of the picture and a detached protective cover lies on a slab of rock in the foreground. Other images show the sky as a glowering orange in colour. The planet itself is almost the same size as Earth, and has about 80% of Earth's mass. It has no moons and orbits about 110 million km from the Sun (Earth is about 150 million km from the Sun). One day on Venus is 243 Earth days long and its year lasts 225 Earth days. Yes, these are the right way round, the day is longer than the year! There is still more weirdness to come: since Venus rotates from east to west, observers on Venus would see the Sun rise in the west and set in the east As its surface is hidden by clouds, Venus was regarded as a mysterious planet. Since nineteenth century astronomers could not see what was there, they could only speculate about that was lurking beneath the clouds. Perhaps surprisingly, usually they let their imaginations run riot. Their reasoning, such as it was, went like this: ·Venus is closer to the Sun than Earth so it must be hotter than Earth (so far so good); ·Venus is covered in clouds, maybe they are composed of water vapour (a reasonable guess); ·If the clouds are water vapour, the planet's surface must be wet- presumably there are huge oceans and any land must be covered in lush jungles and steamy swamps (just about possible); ·The oceans and swamps of Venus are probably

Image Credit: Don P. Mitchell

"The probe was squashed flat before it reached the surface"
The Soviet Union pioneered missions to Venus, beginning with the unsuccessful Venera 1 in 1961. It was followed by Venera 3 which was intended to land on the surface, and according to some sources was designed to be able to float just in case there really were oceans on Venus. Unfortunately it crashed there in 1966 without returning any data. In 1967 another Venera, the fifth in the series, was much more successful, returning all kinds of useful information as it descended on a parachute. Among its important revelations was that the planet's temperature was about 500°C, and that the atmosphere was much denser than expected and consisted of more than 90% carbon dioxide. So dense was the atmosphere that its pressure squashed the probe flat before it even reached the surface. Later, tougher Veneras reached the surface and returned pictures of bleak and rocky landscapes with not a space monster to be seen. Fuzzy, distorted and marred by streaks of missing data, these images made little impression at


April 2007 Astronotes 5 the time. Recently, the raw data from the probes (stored on reels of tape for decades) has been reprocessed using modern technology by computer scientist Don P Mitchell. Thanks to his work we now have crisp snapshots of the hellish desolation that is Venus. Later missions from Russia and the US have added to our knowledge of our sister planet. The latest arrival is the European Venus Express spacecraft currently exploring the planet. Here is a question all astro-bluffers ought to know the answer to: which planet has the hottest surface? The answer is not Mercury (maximum surface temperature 430°C), closest planet to the Sun, but Venus (average 470°). The very dense atmosphere of mainly carbon dioxide has promoted a `runaway' greenhouse effect. Energy from the Sun can pass through the planet's atmosphere but a very large portion of this energy is trapped there (having no atmosphere this cannot happen on Mercury). As you may have heard, we have something similar here on Earth, and if studying Venus helps us learn how to prevent global warming, that justifies every penny spent on space exploration (although the greenhouse gases of Venus probably came from volcanoes rather than powerstations).

Sister Planets Venus (left) compared with Earth (right). Venus is shown without its clouds, based on radar data from the Magellan spacecraft and surface colour data from Venera probes this horror the Venusian environment is quite hideous enough. It is hard to imagine people ever visiting the surface in person. The surface of Venus was pretty thoroughly mapped by radar carried on an American probe called Magellan in the early 1990s. The terrain revealed was flat plains, with two continent-sized highlands, sprinkled with a mixture of familiar and novel terrain features. There were valleys, mountains, volcanoes and meteor craters (not many of these, though, the dense atmosphere is an effective meteor shield). There are odd volcanic structures, unlike any thing on Earth, arachnoids are spidery fractures in the surface, while farra are flat pancakes of cooled lava. Most of its `geographical' features are named after famous females from history and myth. Oddly the surface is much younger than the planet itself (in case anyone asks, we can date the surface by the number of meteor craterswe know how often the planet should be hit by space debris). All the planets in the Solar System are about 4.5 billion years old, but Venus was resurfaced presumably by molten rock welling up from underground some 500 million years ago. In the distant past, Venus was probably cooler, and some scientists have suggested it was once cool enough for there to have been seas. Some daring scientists have proposed there could be still be microscopic organisms floating in the upper, more temperate, layers of atmosphere but these are probably as hypothetical as the Venusian dinosaurs were.

"The clouds are made of sulphur dioxide and sulphuric acid"
As a result of the greenhouse on Venus, the planet's surface is overwhelmingly hostile: the temperature is higher than that of molten lead and the atmospheric pressure is 90 times that on Earth's surface. All the space probes which have landed on the surface stopped working after only a few hours as they were simultaneously baked and crushed! About 40-60 km above the surface lies the unbroken blanket of thick clouds which make the planet so obvious in our skies. These consist mainly of sulphur dioxide and droplets of sulphuric acid. This uninviting composition has led many pundits to claim that visitors to the planet's surface would be corroded to death by downpours of acid rain. This is very unlikely if you compare the surface temperatures with the boiling point of sulphuric acid...but even without

Image Credit: NASA


6 Astronotes April 2007 Venus is a spectacular sight, even with the naked eye. Try looking for it in the west after sunset, at the start of this month it will be near the constellation of Aries, by the middle of April in the constellation of Taurus, so you may see the bright star Aldebaran near by it. Venus will be the Evening Star right through the summer, but in late August it will enter the morning.sky. Our Sister Planet's beauty is only skin deep but she is always worth a look!

Blowing through the Solar System
By Naomi Francey, Education Support Officer
Image Credit: NASA/Jeff Schmaltz, MODIS Land Rapid Response Team

Weather systems on our own planet are difficult to study, let alone weather systems on other planets. On Earth the weather is often unpredictable and humans are constantly inventing improved and more accurate ways of measuring it. NASA is the world's leader in developing advanced remote sensors to study all aspects of weather and climate. One of the most feared and unpredictable weather systems that occur on Earth are hurricanes, also known as tropical cyclones. 2006 was predicted to be an above average year, as 2005 experienced 27 tropical cyclones, which was a hurricane record. But it did not happen. NASA believes this was due to lower sea-surface temperatures, weak La Nina and El Nino conditions and changes in the steering flow of winds around the Bermuda High.

"2006 was predicted to be an above average year for hurricanes"
For a hurricane to develop there are certain factors that are required. Water temperatures need to be at least 26.5°C, for a source of energy strong currents of rising air must be present, low amounts of wind shear are needed and these factors must exist 5 ° N or S of the equator. When a hurricane has developed it can be identified from satellites because it has an eye, a cloudless area in the centre of the storm, and it will have circling winds surrounding the eye. You can see these features in this picture of Hurricane Katrina which destroyed New Orleans

Hurricane Katrina circling off the coast of New Orleans. in 2005. On Earth these conditions occur around June to November across the Atlantic and Pacific but in 2005 it was extended to January 2006 due to extended storm activity. But what about other planets? We have long wondered about the existence of water on other planets and it has mainly been found in the form of frost or ice. Other worlds will not have the ideal temperature for hurricanes either. The Sun provides us with heat, but the further you move away from the sun the colder the conditions are. Jupiter only receives 4% of the amount of sunlight that we obtain on Earth, but it has storms of a much


April 2007 Astronotes 7 greater severity than our own. These storms seem to be generated by an internal source of heat from the giant planet. Although wind systems do exist on other planets, they are not like anything we experience on Earth. The Great Red Spot on Jupiter is an anti-cyclonic storm with winds reaching 400 km/h and Neptune's dark spot is an anti-cyclone with winds speeds around 700 km/h. These weather systems are not like Earth's hurricanes because they are high pressure systems known as anti cyclones, hurricanes are a result of low pressure known as depressions. Storms are only classified as hurricanes when wind speeds exceed 120 km/h. The hurricane with the highest wind speeds ever recorded was Hurricane Camille in 1969 with winds over 400km/h. The wind speeds on Jupiter and Neptune are beyond our comprehension here on Earth and are literally `out of this world'.

"Wind speeds on Jupiter and Neptune are beyond comprehension"
There has only been one planet where a hurricane type weather system has been found and that is on Saturn. It can be seen in the image on this page taken by the Cassini probe. In this image the characteristics of a hurricane can be seen. It has an eye in the centre which is slightly smaller than Earth. It has rings of cloud circling in a clockwise direction, which are rising to a great height. Though the problem is that hurricanes are powered by water vapour and there

Hurricane-type weather system on Saturn imaged on 11 November 2006. are no water oceans on Saturn, as far as we know! Scientists got excited by this image as it's a system that has never been seen before on another planet. Hurricanes hoover up material from the ground surface so it would be interesting to find out what lurks beneath Saturn's gaseous atmosphere. Although it looks like a hurricane, this system did not act like one. It did not move like hurricanes on Earth, but stayed at the south pole of Saturn. It was also 8,000km across whereas on Earth they would average about 500km in width. But it's the closest thing on other planets that resemble our own weather phenomena. We will just have to wait to see if Cassini can bring back more images of weather systems similar to those we experience on Earth.

NISO goes to ESTEC
By Robert Hill, Northern Ireland Space Office February was another busy month for NISO, I attended many conferences and gave presentations on topics such as remote sensing, Astronomy and Earth Observation. I was especially honoured to be asked to be a member of the International Advisory Committee for the 2nd Space and Society Conference, Space Options for the 21st Century, which was held at ESTEC, Noordwijk, The Netherlands. The conference, which ran from 27th February to 1st March, was organised under the auspices of the European Space Agency, the International Academy of Astronautics and the Canadian Aeronautics and Space Institute. Its purpose was to cover space solutions to global challenges.

Image Credit: NASA/JPL/SSI


8 Astronotes April 2007 The conference explored some of the many important and critical issues which are having an impact on society such as global warming and climate change, natural disasters, energy needs and resources, water management and security with a view to emphasising how space systems, technologies and applications are helping to provide viable solutions to terrestrial problems. Details of the conference and outcomes can be found on ESA's Conference Web site: http:// www.congrex.nl/06a12/. NISO would like to thank Dr David Raitt from the ESA Technology Transfer Program for the invitation and congratulate all speakers for giving a variety of very varied and thought provoking presentations over the period of the conference. NISO hopes to host conferences of this kind at Armagh Planetarium in the near future to encourage debate of these themes with stakeholders in our own region. We want to expose ESA and its partners to the experience and talent of local acImage Credit: ESA

Also at ESTEC Jules Verne, ESA's first Automated Transfer Vehicle, is under test for its flight to the ISS later this year. tors involved in the Astronomy and Space sector. Watch this space for updates over the coming months!

Armagh's Other Planetarium
By Wendy McCorry, Science Communicator For any readers who have visited the Planetarium since its reopening, you may have been lucky enough to see The Armagh Story, a short fulldome show by Julie Thompson, Digital Theatre Manager. The six minute piece relates the history of the Armagh Planetarium from its foundation by Dr Eric Lindsay, through to the present day. The Armagh Story begins with a stark picture of the Planetarium's main building, having clearly fallen into disrepair. The caption reads, `In 2000, Armagh Planetarium was forced to close'. Although these must have been dark days indeed for the staff, we learn that the one beacon of hope which kept the name, and reputation, of the Planetarium alive was its educational outreach programme ­ the StarDome. The StarDome provides a unique learning experience for all ages. Holding up to thirty children or 25 adults at a time, the StarDome takes the audience on a voyage around the most fascinating objects in the night sky. As the lights go down inside the dome, the inner wall becomes a starry backdrop, looking almost exactly like the real sky at night - only this sky is totally devoid of clouds and light pollution. The more familiar constellations are pointed out to the audience with the aid of a laser pointer, as their nomenclature and history are explained. Other interesting objects like nebulae or very bright stars are also highlighted. Just as everyone is beginning to get their bearings and feeling that, yes, they can make out the shape of Taurus the Bull, the audience is wowed by the appearance of line drawings of the characters over each of their constellations. All at once, the inside of the StarDome seems to have been turned into a


April 2007 Astronotes 9 prehistoric cave, with intricate illustrations covering its walls. From this point onwards, the audience sit back and relax as they learn about the astronomy behind the Zodiac, and how each of our starsigns is allocated. All are spellbound as they listen to the incredible and often terrifying myths and legends whose characters are depicted in the stars. All too soon it is time for the lights to come back up and, as the stars and pictures gradually fade, eyes are rubbed as if waking from sleep. Soon everyone goes away content, because tonight they will be able to relive the whole experience again - simply by looking up at the sky from their own back garden. At the end of The Armagh Story we see the Planetarium as it is today - refurbished and updated, open to the public once again. Does this mean there is no longer a need for the outreach programme? On the contrary, the StarDome is more in demand than ever, with repeat and new bookings flooding in on a daily basis. This month the Dome has travelled as far south

Wendy and friends More pupils ready to enjoy learning in the StarDome as Wexford, and has toured around Primary and special needs schools in the West of the Province. In April the StarDome will visit special needs Schools in Londonderry and Belfast and Primary Schools in the Newtownabbey area. The StarDome is available to hire Mon-Fri, evenings and weekends. If you would like further information about the programme, please ring the Outreach Officer on 028 3751 2936.

Pole Position Springs back!
By Julie Thompson, Digital Theatre Manager April will see the premiere of the latest version of `Pole Position', our show where the audience is led through a fascinating tour through the current night sky by a live presenter. In this thirty minute show, the Digistar 3 projection system will be put through all its paces to generate the stunning visuals. The presenter will show how even complete beginners to astronomy can use easy-to-find star patterns to locate some fascinating celestial objects. I don't want to reveal too much about what's in the show here. Suffice to say, not only will the audience learn how to find their way through the Spring sky, but they will discover the stories behind some of the brightest stars and famous constellations in the Spring sky. They will find out about a discovery made with the world's biggest telescope - which in those days was in

New kids at the console Education Support Officers Naomi and Paul. Ireland! There are stories from mythology of heroes, battles and beasts and there is the tale of how an astronomer used his knowledge to save an innocent man from execution. We will also

Image Credit: Armagh Planetarium


10 Astronotes April 2007 harness the power of Digistar 3 to investigate just how big some stars can grow. The Pole Position series has proved a fantastic success and I hope this latest show will prove just as popular. I would also like to welcome two new additions to the theatre presentation team, Paul O'Neill and Naomi Francey. I hope they'll see you in the Digital Theatre soon. (Pole Position: Spring Skies opens on 7 April. Check www. armaghplanet.com for more details or call 028 3752 3689)

Space Exploration 2007
Review by Colin Johnston As a book,`Space Exploration 2007' is an interesting experiment. Edited by Brian Harvey, it is hoped to be the first in a series of annual publications featuring news, views and commentary on space exploration. This first edition contains fourteen features on various up to date topics, all are well-written and informative. The book includes welcome coverage on some under-reported topics such as the planned Indian and Chinese lunar missions and the project to launch Russian Soyuz rockets from the ESA facility in French Guyana. As well as the serious content, each article is preceded by a full-page colour cartoon starring `Bunny the Cat'! I have one minor quibble with the book though; there is a very useful `annual review' covering the year's space exploration highlights and featuring a log of all the year's space launches. However this is a very fast-moving field, and the article covers only the year 2005, it would have been nice if it could have been extended even
Image Credit: Amazon.co.uk

Retro-look book The publisher says the book's layout was inspired by the `annuals' popular with children in the UK . to cover the first half of 2006 to give it a more contemporary feel. This is a very useful volume and hopefully it will prove successful enough to become a regular publication. Space Exploration 2007 edited by Brian Harvey, Springer-Verlag New York Inc, ISBN-10: 0387333304, ISBN-13: 9780387333304, 178 pages

Are you an astronomer?
By Colin Johnston, Science Communicator Amateur Astronomy is a fascinating and rewarding hobby, enjoyed by people from all walks of life and all ages. It is so fashionable at the moment that many of the coolest celebrities want to get in on the act. For example, Johnny Depp, Madonna, Angelina Jolie and Will Smith are all very keen observers, well-known for spending nights in their back gardens dressed up in anoraks and scarves, fighting off the cold with sips from flasks of cuppa-soup as they carefully sketch craters along the Moon's terminator or plot light curves of variable stars. If you believed that, then I have a genuine piece


April 2007 Astronotes 11 of the Roswell UFO you might want to buy! As far as I know none these people are amateur astronomers, however there are some celebrities who are genuinely into astronomy. They tend not to be major Hollywood celebs though. The list includes (and pretty well consists entirely of) guitarist Brian May, xylophonist Patrick Moore, fantasy author Terry Pratchett, pianist/popstar/ presenter Mylene Klass and high school principal and cartoon character Seymour Skinner. Amateur astronomers do seem to have an image problem. So do you ever worry that you may be astronomically-inclined? Try my fun quiz to find out! (Score 1 for every time you answer (a), 0 every time you answer (b), 2 for every (c) and 10 for every (d)) 1. a. b. c. How many telescopes do you own? One Telly-whats? You're not sure, so you'll have to count them.

"What shall I observe tonight?" A typical astronomer arranging observing sessions around his busy social calendar. 6. What is your opinion of Alt-Azimuth? a. His sci-fi novels about robots were great, and his popular science books are still worth checking out. Oops! No, that's Isaac Asimov! b. Er...I don't know, can you repeat the question? c. Alt-Azimuth mounts are great for small scopes, but for astrophotography you really need an equatorial mount. 7. What are the Helix? a. Nebulas! b. Er...are they c. Nebulae, but Barnard 33 and Rosette, The Horsehead and the

2. What are you normally doing at 1 am in the morning? a. Sleeping in a nice cosy bed. b. Partying! c. Obtaining a CCD image of M42 through a hydrogen-alpha filter. 3. It's a lovely sunny day. What should you do? a. Spend the afternoon in the garden, but taking care not to receive a nasty dose of sunburn. b. Spend the day at the beach working on your tan. c. Get out the solarscope to count the number of sunspots and see if any prominences are visible. 4. Which of these publications do you read regularly? a. `Battlestar Galactica Magazine'. b. `The Daily Star'. c.`Sky and Telescope'. d. `Astronotes'. 5. Which of these DVDs do you own? a. `Apollo 13'. b. `Star Wars Episode 3: Rise of the Sith' c.`Ian Littlewood's guide to equatorial mounted telescopes'. d.You never watch DVDs as you're always outside observing.

pubs? to me they'll always be M27, NGC 7293

Scores 0-5 Congratulations! You are either too cool or too lazy be mistaken for an astronomer! 6-10 Oh dear! You may be teetering on the brink of astronomy. Do not give in to the Dork Side! Come back to the light before its too late! 11 or more. You spend all the hours of darkness outdoors and are obsessed with the phases of the Moon. You are either an astronomer or a werewolf!

Moon Phases, Apr 2007
Mon 2 Tue 10 Tue 17 Tue 24 April April April April FULL MOON Last Quarter NEW MOON First Quarter

Image Credit: Still from `Metropolis' (1927)


12 Astronotes April 2007

Image of the Month
Image Credit: NASA, JPL-Caltech, Kate Su (Steward Obs, U. Arizona) et al.

Here is a radical new view of an astronomical favorite. This startling `eye in the sky' is the Helix Nebula (NGC 7293) in Aquarius as seen by NASA's Spitzer infra-red space telescope. This a classic example of a planetary nebula with a white dwarf star at its centre. About two light years across, the nebula is a shroud of gas and dust ejected in stages by the central star after it left the main sequence. This could be a preview of the future of our own Sun which will evolve in the same way. But this familiar object still has surprises for astronomers. Data from the Spitzer telescope indicates that the central white dwarf is encircled by a disc of dusty material, softy glowing with infra red. Far two small to be seen in the image above, this debris circles around the star at a distance of about 35 to 150 AU (an AU is an astronomical unit equal to the distance between the Sun and Earth,

which is 150 million kilometres). If it was superimposed on our Solar System, Pluto would only just touch the inner part this band of dust, while fellow ice dwarf Eris would be deep inside it. This newly-discovered material is probably unrelated to the actual nebula. Rather than having been thrown off as the star died, this is debris which has survived since its creation. Packed with comets and possibly ice dwarf worlds, it is a bumper-sized version of the Kuiper Belt and Oort Cloud which surround our own star. Occasionally some of this debris falls on the white dwarf and is annihilated in a flash of X-rays. Why X-rays were being emitted from this star has been a mystery until recently but the new discovery has solved it. Perhaps astronomers will look on our own Sun some five billion years hence and see a similar spectacle. (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