31 Eye on the Universe 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. 5 P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_2, © Springer Science+Business Media, LLC 2010 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. Chapter 2 The Turbulent Sun The Sun (SOHO) 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, 72 The Turbulent Sun 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 photo- sphere 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 tele- scopes; 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. 9 P. Moore, The Sky at Night, DOI 10.1007/978-1-4419-6409-0_3, © Springer Science+Business Media, LLC 2010 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. Chapter 3 Comet Crash Deep impact (Credit: NASAJPLUMDP at Rawlings) 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. 113 Comet Crash 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. [...]... 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. .. 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... 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... 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. .. 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... LLC 20 10 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... 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,... 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... 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. .. 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 . to the origin of the Solar System. 113 Comet Crash 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. 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. 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