The Sky at Night (Patrick Moore's Practical Astronomy)

The Sky at Night

Patrick Moore

The Sky at Night



Patrick Moore Farthings 39 West Street Selsey, West Sussex PO20 9AD UK

ISBN 978-1-4419-6408-3 e-ISBN 978-1-4419-6409-0 DOI 10.1007/978-1-4419-6409-0

Springer New York Dordrecht Heidelberg London Library of Congress Control Number: 2010934379 © Springer Science+Business Media, LLC 2010 All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer Science+Business Media, LLC, 233 Spring Street, New York, NY 10013, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights. Printed on acid-free paper Springer is part of Springer Science+Business Media (www.springer.com)

Foreword

When I became the producer of the Sky at Night in 2002, I was given some friendly advice: “It’s a quiet little programme, not much happens in astronomy.” How wrong they were! It’s been a hectic and enthralling time ever since:, with missions arriving at distant planets; new discoveries in our Universe; and leaps in technology, which mean amateurs can take pictures as good as the Hubble Space Telescope. What a privilege it is to work on a programme with such a huge heritage! I am constantly amazed looking back at the flotilla of excellent programmes which have gone out over the past five decades. The Sky at Night has always been at the sharp end of science broadcasting, whether it’s showing the first view from the far side of the Moon or pictures of a new comet which has swept into our sky. Viewers can depend on Sir Patrick to tell them the latest news and explain what it means. It’s an outstanding achievement and Sir Patrick still holds the world record for being the same presenter on the longest running TV programme. Our guests love coming down to Farthings, Sir Patrick’s home. For them, meeting him is like meeting their astronomical hero. Over the past five decades, the Sky at Night has managed to talk to the space scientists and astronomers making the landmark discoveries. No matter how busy they are, they make room for Sir Patrick. We have been privileged to record astronomical history as it is made. For example, when NASA’s spacecraft hits comet Tempel 1, the Sky at Night was given exclusive access to film the astronomers using the Palomar Telescope, thanks to its Director, Professor Richard Ellis. I will never forget the night the Huygens probe landed on Saturn’s moon, Titan. Professor John Zarnecki, Principal Investigator for the surface science package on board Huygens, gave us the ‘nod’ to set up our camera in the dining room at ESA’s mission control. The world’s media was camped out next to the press room, but we trusted John and moved our camera. It paid off when the astronomers came rushing in to us for an impromptu presentation of the first images of Titan, from a distance of some 900 million miles. Filming the Sky at Night every month is always a challenge. First, there is the setting of our main interview with Sir Patrick and the guests. To make room in Sir Patrick’s study for our three cameras and lights, we have to clear much of his furniture and move his work. I always try to make sure that the Woodstock typewriter is in shot. Patrick still uses it for the programme scripts and, of course, his many books. v

vi

Foreword

Secondly, there is the programme budget. I like to remind my BBC colleagues that daytime TV programmes get more money than we do. We do not have the money to commission CGI graphics; instead, we use simpler and much cheaper props to explain complex theories. Professor Fred Watson rose to the challenge when explaining the transit of Venus with a lemon and two hoops. Dr Dave Rothery juggled coloured ping pong balls to great aplomb when discussing the formation of the Solar System. Professors Carlos Frenk and Derek Ward-Thompson resorted to dinner plates to illustrate the grand collision between our Galaxy and Andromeda. When our dear friend Dr Allan Chapman from Oxford comes on the programme, he always steals the show. He managed to cover Sir Patrick in sloppy plaster when creating craters on the Moon. When Health and Safety said he couldn’t use sulphuric acid to recreate an historic Robert Hooke experiment about understanding comets, he used vinegar instead. The bubbles may not have been as explosive, but they did the job! Another show stealer was comic and impersonator John Culshaw, who became Patrick Moore from the year 1957 for our ‘Time Lord’ programme. Seeing him adopt Patrick’s mannerisms, including the monocle, was quite unnerving. Sir Patrick, in 2007, was more than happy to admit that Patrick Moore in 1957 had got a few things wrong and told him so! There are many people I would like to thank on behalf of the programme. First and foremost are the viewers, who search the schedules for our monthly time slot and stay up late to watch us. Without their loyalty and dedication, we would not have had a programme. There are the amateur astronomers who share images and observations, with their endless enthusiasm and good humour when the clouds role in on our observing sessions; the BBC team who work behind the scenes and who love the show, and put every effort to make it the best science programme that’s all year round. I would like to thank the other man who presents the programme, Dr Chris Lintott. He has been with the programme since 2003, and reports from far flung observatories, asking the astronomers all the right probing questions, and helping me understand the complexities of the Cosmos. Finally, there is Sir Patrick himself. The past few years have been the most exciting and most enjoyable period of my career. It’s been a pleasure and honour to work with Sir Patrick. Every time I meet him, I am bowled over by the enormous breadth of knowledge, grasp of the subject and his ability to explain it simply and succinctly. He is a wonderful broadcaster. I look forward to many, many more Sky at Night programmes, with Sir Patrick at the helm presenting the show, reminding us why we should step outside and look up at the night sky. There is a whole universe out there, and Sir Patrick Moore is going to tell us all about it. Jane Fletcher Producer, the Sky at Night

Introduction

This new book, the Sky at Night series is the 13th – I hope this is not an omen! It covers an eventful period, and I hope that we have managed to cover it successfully. It is interesting to look back to the early days of the Sky at Night; after all, our programme goes back to before the start of the Space Age. There has been one important change. Chris Lintott who helped me join as copresenter, now plays a more major role than I do – which is exactly how I planned it. Unlike me, he is now a leading research astronomer. It is good to have him with me, and he will still be around long after I have faded from view. My special thanks go to Jane Fletcher (in private life Mrs Segar) for guiding the programme throughout this period, and for masterminding that never-to-be-forgotten Fiftieth Anniversary. Well, here’s to the next half-century … Patrick Moore

vii

About the Author

Sir Patrick Moore is one of the world’s leading popularisers of astronomy. He has written more than 100 books and presented his BBC TV programme The Sky at Night every 4 weeks since 1957, making it the world’s longest running television program of any kind. While still in school, he became a member of the British Astronomical Association (BAA) and was later appointed director of Brockhurst Observatory. He served as director of the Armagh Planetarium between 1965 and 1968. He is a fellow of the Royal Astronomical Society (and a Jackson Gwillt medallist), a member of the International Astronomical Union, a holder of the Goodacre medal, and former president and current vice president of the BAA. A minor planet (# 2602) has been named after him. He was knighted in November 2000. He was also made a Fellow of the Royal Society. As the presenter of the record-breaking The Sky at Night series, Patrick was awarded a BAFTA in 2000. The most important research Patrick has carried out has been about the Moon. He is credited with independently discovering the Mare Orientale. He did this with his “traditional” 12½-in. reflector, which still sits proudly in his front garden. His maps of the Moon were among those used by the Russians in 1959 to correlate the first Lunik 3 pictures of the far side. He was also at NASA for the lunar mapping prior to the Apollo missions. Chris Lintott, the co-star of the latest episodes of The Sky at Night, has a massive fan base that derives equally from The Sky at Night and from his paradigmshifting astronomy website Galaxy Zoo, which has some 150,000 members.

ix

Acknowledgements

My most grateful thanks to those who have joined me on the programme during this period. I give them in order of first appearance – of course many have joined me in several programmes. I hope I have not turned professors into doctors, or doctors into professors – if I have, please forgive me! Dr Chris Lintott Prof. Gerry Gilmore Prof. John Brown Mr Ninian Boyle Mr Alan Clitheroe Mr Keith Johnson Prof. Richard Ellis Dr James Bauer Prof. Iwan Williams Prof. Andrew Coates Prof. Monica Grady Dr Simon Conway-Morris Prof. Carlos Frenk Dr Robert Nicoll Prof. John Zarnecki Dr Carolyn Porco Prof. Michelle Dougherty Prof. Bernard Foing Dr Steven Squyres Dr Mark Kidger Mr Damian Peach Mr Pete Lawrence Mr Ian Sharp Mr David Tyler Prof. Richard Harrison Prof. Lucie Green Dr John Mason Dr Harriet Jones xi

xii

Prof. Michael A’Hearn Dr Andrew Adamson Dr Geoff Marcy Mr Bruce Kingsley Mr Alan Schultz Mr Tim Wright Dr Carl Murray Prof. Niall Tanvir Dr Julian Osborne Dr Helen Fraser Mr Tom Boles Prof Richard Nelson Dr David Rothery Prof Fred Taylor Dr Don Kurtz Dr Yvonne Elsworthy Dr Piers Sellers Mr John Culshaw Prof. Andrew Collier-Cameron Dr Fiona Spiritz Prof. Sir Bernard Lovell Dr Ian Morrison Dr Phil Diamond Mr Bernard Baruch Prof. Derek Ward-Thompson Mr Nik Szymanek Dr Eugene Cernan

Acknowledgements

Contents

  1  Eye on the Universe..................................................................................

1

  2  The Turbulent Sun...................................................................................

5

  3  Comet Crash.............................................................................................

9

  4  The Search for Life Elsewhere................................................................

13

  5  Mapping the Sky......................................................................................

17

  6  News from the Planets.............................................................................

19

  7  Spanish Ring.............................................................................................

25

  8  The Sizes of the Stars...............................................................................

29

  9  The Edge of the Solar System.................................................................

33

10  The Telescopes of Mauna Kea.................................................................

37

11  Turkish Delight.........................................................................................

41

12  Ringed World...........................................................................................

45

13  Matter We Cannot See.............................................................................

49

14  Gamma-Ray Bursters..............................................................................

53

15  Wandering Giants....................................................................................

57

16  The Problem of Pluto...............................................................................

61

xiii

xiv

Contents

17  Non-identical Twins.................................................................................

65

18  The Sounds of the Stars...........................................................................

69

19  Space-Man................................................................................................

73

20  Exploring Mars........................................................................................

77

21  The Lakes of Titan...................................................................................

81

22  Fiftieth Anniversary.................................................................................

87

23  SuperWASP..............................................................................................

91

24  Scorpion in the Sky..................................................................................

95

25  The August Perseids.................................................................................

99

26  Black Holes: And Black Magic............................................................... 103 27  Jodrell Bank: Fiftieth Anniversary........................................................ 107 28  The Grand Collision................................................................................ 109 29  Holmes’ Comet......................................................................................... 113 30  Cosmic Debris........................................................................................... 117 31  Nearest Star.............................................................................................. 121 32  The Flight of the Phoenix........................................................................ 125 33  Devil’s Advocate....................................................................................... 129 34  Galaxy Zoo................................................................................................ 133 35  Four Hundred Years of the Telescope.................................................... 137 36  The Merry Dancers.................................................................................. 141 37  The Fountains of Enceladus.................................................................... 145 38  The Herschel Telescope........................................................................... 149 39  Onward to the Moon................................................................................ 153

Contents

xv

40  Forty Years on.......................................................................................... 159 41  Impact!...................................................................................................... 161 42  Life?........................................................................................................... 163 Index.................................................................................................................. 167

Chapter 1

Eye on the Universe

Hubble Space Telescope (NASA)

The Hubble Space Telescope – named after the great American astronomer who proved that our Galaxy is only one of many – was launched on 24 April 1990 and was put into a near-circular path 366 miles above Earth. Ever since then, it has been orbiting the world, moving at a speed of 16,800 mph, and completing one circuit every 96.5 min. It seemed appropriate to devote a programme to it on its 15th anniversary, and I was joined by Dr. Gerry Gilmore, who has long been associated with it. The Hubble Space Telescope is now 15 years old and working almost as well as ever. I say “almost” because there are some parts which need attention, and this would have been carried out by a servicing mission, but at the moment no manned flights have been authorised, mainly because of the risks involved. The Columbia tragedy, when the returning capsule broke-up on entering the atmosphere, is still P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_1, © Springer Science+Business Media, LLC 2010

1

2

1  Eye on the Universe

fresh in everyone’s minds. The astronauts are all prepared to go up, and have said so, but of course the NASA authorities have the last word. Hubble did not have an auspicious beginning. I well remember sitting with the audience in 1990 and watching the telescope launched; that was a great moment, but a few weeks later it became painfully clear that something was wrong. The images were blurred. It was found that mirror had been wrongly made – not by much (less then the width of a human hair) but enough to ruin the telescope’s performance. It was a straightforward case of human error, one of the most embarrassing in the history of science, and some sections of the media made the most of it. I am delighted to say that the Sky at Night took a very different view. Hubble might be flawed, but it was still an instrument of immense value. Then came a daring repair mission. Astronauts went to the telescope, and to all intents and purposes fitted it with spectacles. The results were amazing. Hubble was not only repaired, but was also performing better than had ever been expected. Regular servicing missions have kept it in peak condition, until now. Some people do not realise that by the standards of the present day, Hubble is not a giant telescope. It has “only” a 94 in. mirror and is dwarfed by the reflectors such as the Keck twins in Hawaii and the VLT ( Very Large Telescope) in the Atacama Desert in northern Chile, which is made up of four 8-m mirrors working together. But Hubble is above the main part of our atmosphere so that there are no problems caused by the unsteadiness of the air – and it can receive all radiations from space, whereas on terra firma many wavelengths are blocked, leaving astronomers in the unenviable position of a pianist who is trying to play a concerto on an instrument that lacks everything apart from its middle octave and a few isolated notes in the treble and the bass. For many investigations, then, Hubble is supreme. There is nothing particularly unusual about its optical system, and there are no real problems in sending the images and data down to the Earth. Also, there have so far been no major hits from meteoroids and harmful interplanetary “dust”. The planners have always been worried about the possibility of a collision with a piece of debris the size of say, a teapot – which would cause serious damage and might even put Hubble out of commission permanently. After 15 years, it is starting to look as if the risk was overestimated. I remember making the comments before Yuri Gagarin became the first man in space; in 1961, pessimists were sure that he would be seared by cosmic rays and battered to pieces by meteoroids, as well as being hopelessly space-sick. None of these “Bogeys” happened. Hubble has paid attention to all branches of astronomy. Until the recent Mars rockets, the Hubble pictures of the Red Planet surpassed all others and the famous “canals” were finally laid to rest (though by 1990 I doubt if anyone still believed in Percival Lowell’s brilliant-brained Martians). Amazing views were obtained of Jupiter and Saturn, and for the first time a certain amount of surface detail was seen on Pluto. Hubble was also ready to monitor an exceptional event. When Comet Shoemaker-Levy crashed into Jupiter in 1994, leaving vast scars on the Jovian clouds, Hubble was able to obtain the best pictures, and when the Deep Impact probe was aimed at Tempel 1 in 2005, Hubble was very much a part of the observational programme. But it was in “deep space” that

1  Eye on the Universe

3

the telescope really excelled. The images of clusters, nebulae and galaxies are the best ever taken. Also, pictures sent back of the remotest galaxies within range showed that we were looking back at the very early history of the universe. In every way, the Hubble Space Telescope has been an astounding success – and remember, it has cost less then a nuclear submarine! Originally, it was planned to operate for 15 years, and this it has now done, but all the time it is sending back new data, and to lose it would be a scientific disaster. Moreover, no replacement can be sent up before 2012 at the earliest, and probably not for some years after that. The planned James Webb Space Telescope will be larger than Hubble, but will concentrate upon infra-red research. Unlike Hubble it will not orbit the Earth. It will be sent to one of the “Langrangian points”, a position near the Earth’s orbit which is stable. It will be well away from any terrestrial interference, but it will be a million miles away from us, and no servicing missions will be possible so that the designers must do their best to get everything right first time! Whatever happens, Hubble will continue to work for several years yet. It was at first planned to bring it back to Earth without damaging it. When this was deemed to be too difficult, there was a proposal to boost it into a higher orbit above all the resting part of the atmosphere, and simply leave it there until we developed techniques to make it possible to fish down. Now alas, there is a serious proposal to de-orbit it and allow it to burn away as it comes down. There are dangers here too, because it is a relatively massive structure, and it could well fall into an inhabited area. I know that all astronomers – and indeed all non astronomers, too – would be sad to see us destroying one of our very best achievements. Let us hope this does not happen. The threat seemed imminent in 2005, when our programme was transmitted, but receded when NASA changed its mind and authorised a further servicing mission. So HST is safe for the moment; it cannot remain aloft forever, but it is a vital part of scientific history, and it will never be forgotten.

Chapter 2

The Turbulent Sun

The Sun (SOHO)

It had been some time since a programme had been devoted entirely to the Sun, and it seemed that one now would be appropriate. For this, I was joined by Professor John Brown (the Astronomer Royal for Scotland), Dr Lyndsay Fletcher of Glasgow university and (from La Palma in the Canary islands) Dr Goran Scharmer, who talked to Chris Lintott. In my garden, outside my observatory dome, were Keith Johnson, Alan Clitherow, Ninian Boyle and others, suitably equipped with telescopes. As usual, the Selsey weather was kind. P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_2, © Springer Science+Business Media, LLC 2010

5

6

2  The Turbulent Sun

To us, the Sun is the most splendid object in the sky; it is all-important, and without it the Earth would not have been born. True, it is only a normal star – 1 of 100,000 million in our Galaxy – but it is the only star close enough to be studied in detail; it is a mere 93 million miles away, and light from it can reach us in only 8.6 min. Light from the nearest star beyond the Sun, Proxima Centauri, takes over 4 years to reach us. Represent the Earth–Sun distance by one inch, and Proxima will be over 4 miles away. The Sun is large; its diameter is around 865,000 miles, and it could hold over a million bodies, the volume of the Earth. It is also very hot. At its surface the temperature is not less than 6,000°, and at its core a thermometer would register about 15 million degrees – assuming that a thermometer could survive there! The Sun is a gaseous throughout. It is not burning in the conventional sense; a Sun made up of coal and radiating as fiercely as the Sun actually does would turn to ashes in a million years or so. But we know that the age of the Earth is 4,600,000,000 years, and the Sun is certainly older than that. According to modern theory, it was formed from a cloud of dust and gas inside a nebula 5,000 million years ago, and it will be another 5,000 million years before anything dramatic happens to it so that by cosmological standards, it is no more than middle-aged. The core is the Sun’s power house, where its energy is being created. It contains a vast amount of hydrogen, which is the most plentiful element in the universe (atoms, of hydrogen outnumber the numbers of all other elements combined). At the core, where the temperature and pressure are so high, the nuclei of hydrogen atoms are combining to make up nuclei of another element, helium. It takes four hydrogen nuclei to form one helium nucleus; every time this happens, a little energy is set free and a little mass is lost. It is this liberated energy that makes the Sun shine, and the mass-lost amounts to four million tons per second so that the Sun now “weighs” much less than it did when you began to read this page. However, please do not be alarmed – there is plenty of hydrogen fuel left. To quote Corporal Jones, “Don’t panic!” The Sun’s bright surface is known as the photosphere. It is not as placid as it may seem; it shows granular structure, and very often there are dark patches known as sunspots. The spots are huge by terrestrial standards, but are not permanent; even large spots-groups seldom last for more than a few weeks or months. Neither is then in view continuously. The Sun is spinning on its axis, taking an average of 28 days to complete one turn so that a spot will be carried slowly across the disk until it passes over the limb. A fortnight or so later, it will reappear at the opposite limb, provided that it still exists. Spots generally appear in groups, though single spots are not uncommon; some spots are regular in shape, others irregular. A regular spot will have a dark central “Umbra”, surrounded by a lighter “Penumbra”. Many Umbrae may be contained in one penumbral mass; a typical group has two main spots, a leader and a follower. Sunspots are essentially magnetic phenomena. Lines of magnetic force run below the solar surface; when they break through the photosphere they cool it down, and a sunspot is the result. In fact a spot is not really dark; It appears so only because it is around 2,000° cooler than its surroundings. If it could be seen shining on its own,

2  The Turbulent Sun

7

its surface brightness would be greater than that of an arc-lamp. Spots are usually associated with brilliant, high attitude clouds known as faculae (Latin, torches). A word of warning here: Solar observing can be dangerous, and to look straight at the Sun through any telescope or binoculars will result in eye damage – perhaps blindness – unless careful precautions are taken. Fitting a dark filter over the telescope eyepiece is not recommended for the newcomer; filters may not give full protection and are liable to splinter without warning. Mylar filters can be used – but make sure you know exactly what you are doing. To use the telescope as a projector and send the Sun’s image on to a card held or fixed behind the eye piece is far better. In general, a refracting telescope is better than a reflector for solar work. Remember, too, that the Sun is still dangerous when it is low in the sky, veiled by haze, and looks deceptively mild and harmless. A moment’s carelessness may have tragic results, and, sadly, accidents of this kind have happened in the past. (Some small, cheap telescopes are sold together with dark “Sun caps” for direct viewing. If you have one of these caps, throw it away.) Above the photosphere comes the layer known as the chromosphere, and above the chromosphere we come to the corona, made up of very tenuous gas. Normally, the chromosphere and the corona cannot be seen with the naked eye, or with a straightforward telescope; we have to wait for a total solar eclipse when the Moon passes directly in front of the Sun and obligingly blocks out the photosphere for a brief period (never as long as eight minutes and usually much less). Unfortunately, total eclipses are rare as seen from any particular location, and generally we have to depend upon instruments based upon the principal of the spectroscope. Consider flares, for example, which occur in the chromosphere, and are immensely energetic. Very few have been observed with ordinary telescopes; the first was seen in 1859 by one of the great pioneer solar observers, Richard Carrington. I have never seen one myself. A flare begins in the lower chromosphere; it rises upwards, sending out charged particles that cross the 93,000,000-mile gap and reach the Earth, meeting the top of the atmosphere and causing the lovely aurorae or polar lights as well as causing magnetic storms and interfering with radio communication. Flares are usually (not always) associated with spot-groups, which means that they are commonest when the Sun is most active. Equipment now is less expensive than it used to be; for example, the serious solar observer will need a telescope design to cut out all light except that from, say, incandescent hydrogen. If you can afford £400, you can set up a proper solar observing station. This may sound a large sum – until you compare it with a new laptop or a couple of railway tickets between London and Glasgow! There are also phenomena such as Coronal Mass Ejections (CMEs), when huge quantities of gas are sent out, never to fall back into the Sun. There is a reasonably well-defined solar cycle with a mean period of 11 years; at maximum, many spot-groups may be on view at the same time, while at minimum the disk may be clear for several consecutive days or even a week or two. The last maximum fell in 2001 so that the next is due in 2012, but we cannot be precise, because the cycle is not perfectly regular. Moreover there have been protracted minima in the past, for reasons which are not known; for example there were few

8

2  The Turbulent Sun

spots between 1645 and 1715, and this so-called Maunder Minimum (named after E.W. Maunder, who was one of the first to draw attention to it) also marked a cold spell nicknamed the Little Ice Age. In England, during the 1680s, the Thames froze every winter, and frost fairs where held on it; in Holland, canals also froze. There have been earlier cold spells, obviously less well documented, which also seemed to be linked with solar activity, and many evidences are accumulating that shows global warming and cooling is due to the Sun and not of human activity as Politically Correct politicians claim. (En passant, similar effects apply to Mars – and there are no Martian factories as yet!) Today the Sun is under constant surveillance from Earth, and there are many solar observatories such as the Swedish station at La Palma. There are also satellites such as immensely successful Solar and Heliospheric Observatory (SOHO). New space missions and new methods of investigations are being planned, and we may hope that in the reasonably, near future we will solve some of the problems which still baffle us. There is a role here for amateur astronomers, but never forget the dangers; a cat may look at a king, but an observer must always be wary of looking directly at the Sun.

Chapter 3

Comet Crash

Deep impact (Credit: NASAJPLUMDP at Rawlings)

The impact of the Deep Space probe on Comet Tempel 1 caused a great deal of interest, and we devoted two programmes to it – one before the collision, and one at the actual time. Chris Lintott was at Palomar, where the 200 in. reflector was being used; with him were Richard Ellis and James Bauer. They saw the flash and the expanding cloud of debris. Back at home, I was joined by Iwan Williams and Andrew Coates. It was a memorable event and we had a ringside view, even though we were 83,000,000 miles away. P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_3, © Springer Science+Business Media, LLC 2010

9

10

3  Comet Crash

On July 4th, 2005, one section of NASA’s Deep Impact Probe crashed into the nucleus of a periodical comet, Tempel 1. This was not the first cometary mission – as long ago as 1986, the Giotto spacecraft had flown into the heart of Halley’s Comet – but this was the first collision, and nobody knew quite what would happen. Earth– based astronomers 83 million miles away waited anxiously. The comet itself was not particularly distinguished. It had been seen on the 3rd of April 1867 by the German astronomer Ernst Wilhelm Tempel; it was then of the 9th magnitude and there was nothing special about it. (Tempel was a skilful and energetic observer; altogether, he discovered 21 comets plus 5 asteroids; a crater on the Moon is named after him.) It has a current period of 5.5 years, and its orbit lies wholly between those of Mars and Jupiter. Its nucleus is around 6 miles long by 4 miles broad, and there is seldom an appreciable tail. At its best it can easily be seen with binoculars, but it has never attained naked eye visibility. Comets are insubstantial things and have been appropriately described as “dirty ice-balls”, though “dirty snowballs” might sound better. A typical comet has a dark surface overlying a nucleus made up of ices of various kinds, naturally including water ice. When at the far part of its orbit, the comet is inert; as it moves in towards perihelion, the ice is warmed and activity begins. Jets spout out through the crust from below, and a tail or tails may develop. Most comets, unlike planets, move in paths which are markedly eccentric; Tempel’s is no exception. Really brilliant have been periods of centuries, or thousands of years; Halley’s is the only bright comet to be seen regularly (it was last at perihelion in 1986, and will be back in 2061). The Deep Impact Space craft was made of two sections; the impactor itself and the flyby. The pair began their journey on 12th of January, sent up by a Delta 2 rocket from Cape Canaveral; there were (inevitably) a few alarms, but in the end the journey to the comet was remarkably uneventful. The mean cruising speed was 64,000 mph. After 174 days in space, the probe neared its target, and the two sections were separated. The impactor used its own thrusters to put it into a collision course, and it crashed down on schedule at a relative speed of 23,000 mph. Soon afterwards the flyby swooped past the nucleus at a range of just over 300 miles, taking pictures of the chaos below. It then veered off to avoid being damaged. Obviously, the impactor was destroyed immediately it hit! The results were spectacular and recorded by observatories all over the world as well as from space telescopes such as the HST. For the Sky at Night, Chris Lintott was at Palomar, where the 200-in. Hale reflector was aimed at the comet. Precisely on schedule there was a brilliant flash and an expanding cloud of ejecta could be seen. The impactor with a mass of just over 800 pounds produced the same effects as four and a half tonnes of TNT would have done; a large crater was blasted out, though it could not be seen until the debris cloud had cleared. There were two surprises: much more dust was ejected than anyone had expected, and the crust was firmer – there had been suggestions that the impactor might plough straight through the comet, like a bullet passing through a meringue. The ices were of the expected kind, and there were complex hydrocarbons, plus silicates. The collision shed new light on cratering, particularly with the pristine material of the interior. Comets are incredibly ancient; they date back to the origin of the Solar System.

3  Comet Crash

11

Let it be stressed that there was no danger to the Earth or any other planet. Neither was there any danger to the comet; as I commented at the time, one cannot derail a speeding express train by hurling a baked bean at it. Apart from (probably) temporary shift in the positions of a few jets, the comet was completely oblivious to what had happened, and is at this moment continuing its placid journey round the Sun. It will be interesting to take some new photographs, from close range, to see whether the crater is still visible. No doubt, this will be done at a suitable time. Future comet missions are being planned in 2014; if all goes well, the Rosetta spacecraft will land upon one of these ghostly objects. When that time comes, astronomers will have every reason to be grateful for what they learned from Deep Impact.

Chapter 4

The Search for Life Elsewhere

Search for life (NASA)

All of us are anxious to know whether life exists beyond Earth – and if so, what will it be like. We periodically return to it in our programmes, and this time I was joined by Drs Monica Grady and Simon Conway-Morris. As yet, we have no ­definite ­evidence that aliens are around, but I admit that I hope there are; I would love to welcome a Martian or Europan on the Sky at night! There was a time, not so very long ago, when the Earth was thought to be the centre of the universe; everything else, Sun, Moon, stars, planets, had been created especially for our benefit. We know better now. The Earth is an ordinary planet, moving around an ordinary star in an ordinary galaxy. But what about mankind?

P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_4, © Springer Science+Business Media, LLC 2010

13

14

4  The Search for Life Elsewhere

Are we important in the overall scheme of things? This is what we do not know. As yet, we have found no sign of life upon any world other than our own. We know that other stars have planetary systems of their own. They are of course hard to see, because they are so far away, but by now we have tracked them down in other ways – either by their gravitational effects upon their parent stars, or by a slight dimming of the star as the orbiting planet passes in transit across it. From Earth we can see transits of the inner planets, Mercury and Venus, but these two are far too small to block an appreciable amount of the Sun’s. However, our watcher on a planet in a system of another star – say Alpha Centauri – might well be able to detect the slight fade caused by a transit of Jupiter or Saturn. In our search for life we must obviously begin by considering the planets in our Solar System. Few of them are welcoming. Venus, almost the Earth’s twin in size and mass, has a surface temperature of around 1,000°F, a crushing carbon-dioxide atmosphere, and clouds rich in sulphuric acid. Mercury and the Moon are virtually airless; the four giant planets have gaseous surfaces and radiation belts, which at least in the case of Jupiter would be quick to kill any astronaut unwise enough to venture inside them. The satellites are slightly more promising. Europa, in Jupiter’s family, has an icy surface beneath which there is probably an ocean of ordinary water, kept liquid by the heat from the core; Europa is flexed by the changing pull of Jupiter. Another satellite, Callisto, may also hide an extensive ocean. In Saturn’s family there is one member, Titan, which has an atmosphere thicker than ours and is composed mainly of nitrogen, which makes up well over 70% of the air we breathe; the tiny Enceladus surprises by the fountains which shoot upward from its pole. Triton, the main satellite of Neptune, has nitrogen geysers gushing from below its crust. But can any living organisms survive there, or on the methane-drenched surface of Titan, or in the sunless sea of Europa? We have to agree that life can exist in the most unlikely places. We have found it for instance, in our Antarctic rocks, and in the hydrothermal vents of the ocean floor. Here we have a scalding hot temperature and an acidic environment which would be immediately fatal to any life forms which we encounter from day to day. Yet, these vents teem with life. There is at least a possibility that there are similar vents in the Europan oceans. This means that there could conceivably be life. And what about Titan, with its rivers of liquid methane and, chemical lakes? This is all very well, but as yet we have not yet established the existence of life anywhere except on Earth, and until we do so, we can come to no definite conclusions. Plans for drilling through the ice layer on Europa and reaching the water beneath are projects for the future; we must first practice with Lake Vostok in Antarctica – at least we know exactly where it is, and how far down it lies. But there can be no doubt that the key to the whole problem is Mars. Rovers are exploring it; there has been open water there; for a period in its history – we are not sure how long – conditions were suitable for Earth-type life. For quite a number of reasons, life cannot now be expected on the surface (radiation is one objection), but it may well survive under water. Many Mars probes are being planned, and before long, we should be able to bring back material for analysis. The results could hardly be of

4  The Search for Life Elsewhere

15

greater significance. If there are any organisms on Mars, however lowly, they will show that life will appear wherever conditions are tolerable and this will be true even if we find nothing more than extinct life – we must not be parochial; our Solar System is a tiny unit in a galaxy of 100,000,000,000 stars. We now know that many of these stars are attended by planets. Up to now, we have not found systems similar to ours, and most of the planets found seem to be giants, more like Jupiter than like the Earth, strangely close to their central stars, but it is surely premature to suggest that the Sun’s family is unusual; our techniques are not yet able to detect small, rocky, close-in planets, but our new telescopes should do so. On the other hand, we cannot tell whether intelligence will develop even upon worlds suitable for it – and the presence of life need not necessarily mean the presence of intelligent life. We may be rarer than we think! Moreover, how long will an intelligent civilisation endure? It may destroy itself – as Homo sapiens is in danger of doing that the moment. Questions of this sort will be settled only when, or if, we make contact with another race, which means looking beyond our immediate neighbourhood. There are alas, no Martians, Venusians or Jovians. (If there were, no doubt some of our present political leaders would be making preparations to drop bombs on them.) Physical contact is pure science fiction. Sending a twenty-first century type rocket to another star would take an impossibly long time. Exotic methods of travel such as spacewarps, time-warps, teleportation and thought-travel are equally beyond us; I suppose they may come along eventually, but at the moment speculation is endless and, frankly, pointless. And though we hear a great deal about flying saucers, UFOS, alien visitations and abductions, I will take such stories seriously only when a Saucer lands in my garden and a little green man calls in for a cup of tea (or, if he prefers a glass of chlorine). Fortunately, there are other courses of action which are much more promising. Radio contact is one. If there are radio operators on a planet moving around, say, Epsilon Eridani, 11 light-years away and their equipment is as good as ours, then they could pick up our signals and we could pick up their’s. If we recorded something too rhythmically and mathematical to be natural, we would know what an intelligent being had lived there 11 years ago, though our Eridanian would not receive our reply for another 11 years, and any conversation would inevitably be stilted. I wonder how people in general would react if told? Religious leaders would be nonplussed and would have to find a way to wriggle out of a delicate situation. Scaremongers would issue lurid warnings about a possible invasion, disregarding the fact that any race advanced enough to master interstellar travel would be far too sane to take part in warfare of any kind. Politicians would start plotting ways of “cashing in” and so on. Altogether, it would be fascinating. There is another possible avenue in SETI, the Search for ExtraTerrestrial Intelligence. We can make optical lasers of immense power, and so presumably can advance races elsewhere. We might watch out for a very brief but repeated signal. Optical SETI is being taken very seriously, though in my opinion at least the chances of success are slim. I have so far been discussing life of the kind we can understand. But suppose there are beings of totally different type – such as an inhabitant of, say, Polaris Q made of gold which lives on a diet of crushed rock and sulphur cocktail? BEMs (Bug Eyed

16

4  The Search for Life Elsewhere

Monsters) have been popular with SF writers ever since they were introduced by H.G. Wells in “The War of the Worlds”, and I suppose we cannot say that they are impossible, but we can say that they are very, very unlikely. If they exist, then the whole of our modern science is wrong, and the weight of evidence is overwhelmingly against anything of the sort. Right out to the depths of the universe, visible material is composed of the familiar elements, and life must be made up of these. Finally, there remains the possibility that we really are alone in the universe, and that there is absolutely no life elsewhere. I find this illogical as well as conceited, but all we can do at the moment is to keep looking, in the hope that either we will contact other beings or they will contact us. I say “hope” because of my firm belief that any race capable of communicating will be far cleverer and civilised than we are. We have not been good guardians of the Earth, and I would be the first to ­welcome an extraterrestrial who would be willing to teach us how to do it better.

Chapter 5

Mapping the Sky

Samuel Oschin Telescope (Credit: Caltech) P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_5, © Springer Science+Business Media, LLC 2010

17

18

5  Mapping the Sky

Celestial mapping methods have been revolutionised in recent years, and for this programme, I was joined by three of the astronomers most deeply involved, Carlos Frenk, Bob Nichol, and (from Palomar, with Chris Lintott) Richard Ellis. The first really useful star maps date back to the second century ad. Around the year 150, Ptolemy, last of the great astronomers of Classical times, produced charts which were the basis of others for many years, and which gave us the constellations which we still in use today. All 88 of Ptolemy’s constellations are still there, admittedly with altered outlines. In pre-telescopic times with the maps drawn by the Danish astronomer Tycho Brahe, between 1576 and 1596 were much the best and were amazingly good. Even so, they could not rival maps by telescopic observers and this was why Greenwich observatory was founded, by express order of King Charles II, so that British seamen could use them in navigation. The RGO survived as the headquarters of British astronomy until the end of the twentieth century, when it was wantonly destroyed by the Labour Government. Meanwhile in 1881, David Gill, in South Africa, had realised that the best way to map the stars was to use photographic methods. At the time this was certainly true. A major project was undertaken during the second half of the twentieth century at the Palomar Observatory in California. Of course, Palomar is best known because of its two great reflectors, the Hooker 100-in. and the Hale 200-in., each of which was supreme in its day, but today there are also various other large instruments there – one is the 60-in. reflector, which was brought into action in 1970 to relieve the 200-in. of some of its routine work. I was once at Palomar on a night when the 60-in. was “between programmes” and was not being used. To the amusement of the ­resident astronomers, we inserted an eyepiece and observed Saturn and Uranus. I am prepared to bet that the telescope has not since been used visually! There is also the 48  in. Schmidt, now christened the Samuel Oschin Telescope, and it was this which was used for the Palomar Sky survey; it has a 72-in. mirror and a 49.75-in. Schmidt corrector plate. The first survey extended from 1948 into 1958. In the end the survey, with a slightly more southerly extension, included 937 high-quality plate pairs. Now, of course, photography has given way to electronics, and so far as the survey is concerned the Oschin has completed its task. However, it has been given a new and valuable role searching for supernovae in external galaxies and monitoring near-Earth asteroids and also Kuiper Belt Objects in our own Solar System. It has already shown that it is ideally suited to work of this kind; for instance, it has been responsible for discovering two particularly interesting trans-Neptunians – Eris, which is larger than Pluto and is officially classed as a dwarf planet, and Sedna, which has a period of around 10,000 years and travels a long way out towards the Oort Cloud. It is in action every clear night.

Chapter 6

News from the Planets

Enceladus from Cassini (Credit: NASA)

P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_6, © Springer Science+Business Media, LLC 2010

19

20

6  News from the Planets

In October 2005, a major international planetary conference was held at Cambridge. Sadly, I was not mobile enough to attend, but Chris Lintott did and reported on all the latest news from the Solar System. Among those, he interviewed were John Zarnecki, Carolyn Porco, Michelle Dougherty, Bernard Foing and Steven Squyres. Dr Squyres was in a gleeful mood; the Spirit rover on Mars had been handicapped by dust accumulating on top of it; just as things were becoming really critical, a gust of wind swept down and cleaned the panels as efficiently as any hoover could have done. Mars can sometimes be unexpectedly helpful! It sometimes seems strange to realise that the Space Age began only in October 1957, with the ascent of Russia’s Sputnik 1 – an event which was by no means universally popular in the USA. Remember, this was the time of the Cold War; the USSR was a super power, and the American space programme was in trouble. The Sky at Night had started earlier and it is worth looking back at some of the ideas then current. This applies particularly to the bodies of the Solar System. Venus could be a welcoming world, with a reasonably temperate climate and broad, possibly life-bearing oceans; Mars had extensive vegetation tracts, and through the canal-building Martian engineers had vanished, the canals themselves had a basis of reality; the lunar seas might be deep, treacherous dust-drifts, much too soft to support the weight of a spacecraft; Pluto was a true planet, at least comparable with the Earth in size; satellites such as Io and Europa were mere chunks of barren rock, and so on. We had no idea that the Sun’s family would turn out to be as exciting as it actually is. The rate of progress is not steady; it is accelerating as quickly as the universe itself. Even with our nearest neighbour, the Moon, we are learning. SMART-1, the first ion-powered lunar probe, has provided new data about the make up of the rock, and at the end of its career was successfully crashed into a southern lava-plain, the Lacus Excellentiae, not too far from the great walled formation Schickard. At almost the last moment it was realised that instead of plumping down in the plane, it would strike the wall of a well-formed crater, Clausias. This was not what NASA wanted, and so the space-craft was given a last burst of power with the final scrap of xenon “fuel”, lifting it over the wall and the crater-floor. A cloud of dust was thrown up, and well seen (though almost all observers in Britain were clouded out). NASA hoped to see traces of water ice. They did not, and I for one am utterly convinced that there has never been any water on the Moon. It is simply not that kind of world. Mars remains very much a focal point of attention. The Rovers, Spirit and Opportunity, go on and on; they are still operating excellently, far beyond their expected life times. Initially, Opportunity was the “glamour probe”; it landed in a small crater with interesting rock structures, while Spirit came down in a crater, Gusev, believed to be an ancient lake. By now Spirit is proving equally valuable. After 156 Martian days, it has reached the Columbia Hills and has sent back amazing panoramic views – even though the Columbia Hills are hardly Himalayan in attitude! One expected hazard was cleared by courtesy of Mars itself. The Red Planet has a decidedly dusty atmosphere, and dust was expected to accumulate on Spirit, putting the instruments out of action. The dust fell, but before it could do any real harm an

6  News from the Planets

21

obligingly wind blew it away. No doubt mechanical or electronic ­breakdown will eventually end Spirit’s active career, but during 2005 everything went according to plan. Opportunity, in Meridiani Terra on the opposite side of Mars, had problems of its own, and spent some time a treacherous dune before managing to extricate itself, but it looked forward to an extended programme during the next Martian season. It is just as well that the instruments on Spirit and Opportunity were so reliable, because few of them were backed up – partly because of weight constraints, and partly for financial reasons. The same is true for the various orbiters, of which the latest are Odyssey, Mars Express and MRO. The NASA designers have reasons to congratulate themselves. Further, the Cassini probe at Saturn has also been tremendous success. The ring system is amazingly complicated; the tiny embedded moonlets cause “waves” in the ring outlines. Perhaps the most startling results have come from the satellites. The soft landing on Titan by the Huygens space-craft must rank as one of NASA’s greatest achievements to date. Released from Cassini, the Lander plunged down through the satellite’s thick atmosphere and touched down upon a surface, which seemed to have about the consistency of wet sand. The landscape showed what were obvious drainage channels – but of liquid methane rather than water. Later analyses taken together with the results from fly-by encounters indicate that there is almost constant “methane drizzle”, and there are chemical lakes. Life? It seems unlikely, but we cannot be sure, though any Titanian organisms would be quite unlike ours. Yet, the results from two of the smaller satellites have been even more surprising. Iapetus, the outermost of the eight fairly large satellites known before the Space Age, is over 800 miles in diameter, and takes 79 days to complete one orbit. At its best, when west of Saturn, it is a very easy telescopic object, but when the eastern elongation it fades to below the 11th magnitude-Giovanni Cassini, the Italian astronomer who discovered it in 1671 (and after whom the present space-craft is named) believed, wrongly, than it disappeared completely for 7 days in each revolution. The reason is that one part of the surface is as bright as snow, while another part is blacker than a blackboard. Like all the major satellites apart from Hyperion, Iapetus has captured or synchronous rotation, so that it keeps the same face turned towards Saturn all the time, just as our Moon behaves with respect to Earth. At western elongation the bright hemisphere is turned towards us, while at eastern elongation we see the dark area. We already knew that both bright and dark regions were hilly and cratered; appropriately, the dark area was named Cassini Regio. But was Iapetus a dark world with an icy coating, or an icy world with a dark stain? I remember referring to this as the “zebra problem”. When it became clear that the overall density of the globe is low, the second of these alternatives had to be right, but we had no idea of the composition of the dark material, or its depth. In fact we still have not, though the material is generally believed to be organic. The Cassini results indicated that the material had not been “sprayed on”. There have been suggestions that it had been knocked off the more distant satellite Phoebe, which is a full 8,000,000 miles from Saturn and is dark; it has retrograde motion, and is undoubtedly a captured body, either an ex-asteroid or else an escapee from the Kuiper Belt. But the colours do not match, and at present the puzzle is still unsolved.

22

6  News from the Planets

This is not at all. Cassini showed that a high mountain ridge runs for a long distance round Iapetus, making it look rather like a table-tennis ball which has been broken in half and then unskilfully glued together. The ridge is high, rising to a maximum of 8 miles above the surrounding terrain, running for 800 miles almost among the geographical (should it be the Iapetographic?) equator. It is unlike anything else known in the Solar System, so how was it formed? Could it be that it is due to icy material which welled up from below and then solidified? Could it be that, as suggested by Paulo Frerie of Arecibo observatory, Iapetus once grazed the outer edges of the ring system, and later retreated to its present distance? It has even been suggested that Iapetus itself may have had a ring – a ringed satellite orbiting a ringed planet. Less plausibly, some UFO enthusiasts have claimed that Iapetus itself is artificial, put together by the usual nebulous aliens from afar. Certainly, it may be a popular sight for future interplanetary tourists because its orbit is inclined to the plane of Saturn’s equator by almost 16°, and travellers will see the rings well displayed – while the inner satellites, including Titan, orbit almost in the equatorial plane so that seen from them the ring system will always be edgewise-on. Perhaps, the greatest surprise of all came from Enceladus, discovered in 1787 by William Herschel. It is a mere 310  miles across (about the distance between London and Penzance) and was expected to be icy and inert. This is certainly true of the even smaller Mimas, discovered by Herschel at the same time; incidentally, these were the first of the few important results coming from Hershel’s largest telescope, the 40-foot focus reflector with its 49-in. mirror. Mimas is dark with one vast crater, which had led to its being compared with Darth Vader’s “Death Star”. Enceladus has the highest albedo of any Solar System body; there are no large craters and wide areas where there are no craters at all. This must mean that these areas are young, and have been resurfaced in comparatively recent times. When Cassini flew past Enceladus on 17th of February 2005, at a range of 725 miles, it detected a tenuous but appreciable atmosphere – totally unexpected for a world with so weak a gravitational pull; In fact no atmosphere could be retained for long, and so there must be continual replenishment from below. Next came the discovery of ice geysers spouting from the south polar region; the jets rise to hundreds of miles above the ground. At NASA, they caused great excitement. To quote Carolyn Porco, head of the Cassini imaging team: “I think this is important enough to see a redirection in the planetary exploration programme. We’ve just brought Enceladus to the forefront as a major target of astrobiological interest.” The readings from Enceladus’ geyser plumes indicate that all of the prerequisites for life as we know it could exist below Enceladus’ surface. “Living organisms require liquid water and organic materials, and we know we have both on Enceladus now”. A few tens below the surface the temperature and pressure may be sufficient to keep water in a liquid state. Further evidence comes from the so-called “tiger stripes”, which indicate cracks. The ice here is a more amorphous and virtually crater-free, so that it must have welled up comparatively recently. The geysers rise upward for several 100 miles, so that they are violent – and violence was the last thing to be expected on a world as small as Enceladus. Most of the ice crystals fall back as snow, but some break and free altogether to become part of the wide, thin

6  News from the Planets

23

E-ring. It is not yet clear whether the venting and the geyser activities confined to the South Pole region. If so, this must be the hottest part of the whole globe. Can there be hydrothermal vents below? At any rate, Enceladus is one of the only two bodies active enough for its heat to be detected by remote-sensing instruments – the other is Jupiter’s satellite Io, but Io and Enceladus are very different worlds. Certainly, the past few months have been of immense interest. So many new phenomena have been seen. Which is the most intriguing? Make up your own mind – but I have to say that my personal vote must go to the fountains of Enceladus.

Chapter 7

Spanish Ring

Spanish ring eclipse team (Credit: Pete Lawrence)

On 3 October 2005, there was annular eclipse of the Sun. The track of the annularity began in the Atlantic and crossed Spain, which was convenient enough. I have to admit that my travelling days are over, but the Sky at Night team led by Chris Lintott was well represented in Madrid, and was rewarded with a perfect view. I had to stay at home and make do with my very small partial… An annular eclipse occurs when the Earth, Sun and Moon line up, with the Moon in mid position – but with the Moon in the further part of its orbit, so that its disk is not quite big enough to cover the Sun completely. The Sun’s mean angular diameter is

P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_7, © Springer Science+Business Media, LLC 2010

25

26

7  Spanish Ring

32 min 1 s of arc; the apparent diameter of the Moon ranges between 33 min 21 s and