Sagittarius

The Newsletter of the Astronomy Section of La Société Guernesiaise October – December 2013

Forthcoming Inside

Events Autumn Skies: , 2 Jupiter’s return, and a Special Comet. Public Open Evening Journey to the Centre of 5 the Galaxy (note Friday)

th Abstracts from Astronomy 8 November: 6.00 pm 6 periodicals

Astronomy Section Christmas Meal

Tuesday, 3rd December: 8.00 pm (venue to be confirmed)

New format will be that Public Open Evenings will be on a Thursday evening and will comprise a talk or film show, Inserts with a clear night for observation being a bonus! chart

Section meets at the Sunset, sunrise, moonset and Observatory every Tuesday moonrise times evening at 8.00 pm

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Autumn Skies: Pegasus, Jupiter’s return, and a Special Comet.

Pegasus is one of the major the square. At the top right of the , and is regarded as a shape is the second brightest star, centrepiece of our autumn sky. The officially known as . This can be seen rising in the is a , varying in eastern part of the evening sky, brightness over an irregular period. reaching a due south position by about The top left or northeast corner has the 10 pm in mid October. bright star Alpheratz, which was previously the delta star. of Pegasus, The main part of Pegasus is easily but is now assigned to the adjoining recognizable, having a very large constellation of Andromeda, and square shape, and with a bright star having a line of well spaced bright marking each of its corners. At the top extending away northwards. right corner, two additional stars a short distance away form a regular There are several different kinds of triangle, making it even easier to objects to be seen in Pegasus. The star recognize ‘The Great Square of cluster M15 is one of the finest Pegasus’ as it rises into the sky. concentrated globular clusters seen in the autumn sky. The cluster has a brightness of magnitude 6, just visible to the naked eye, and is a good object for binoculars or telescopes, which can begin to resolve at least the outer parts of this mass of stars. It can be found to the west of and below the lower part of the Pegasus square, a short distance beyond - a yellow supergiant double star of second magnitude with a small, Figure 1: Constellation of Pegasus magnitude 9 companion star.

With its clear shape and bright stars, the constellation was known to the ancient Greeks and the Egyptians as ‘The Winged Horse’ – the Great Square representing the body of the horse. As a favourite feature of the night sky, the depiction of a winged horse was also used on coins of the classical period.

The brightest star of Pegasus is Markab, at the bottom right corner of

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Figure 3: Location of and M15

The discovery of extrasolar planets, or

Figure 2: M15 globular cluster ‘exoplanets’ has increased steadily in recent , mostly at first from this One of the more recent developments detection of the gravitational effects in modern astronomy has been the on a parent star, sometimes also discovery of evidence that planets are indicating the presence of more than in orbit around other stars, many light one planet and allowing the orbit and years away from our own solar system mass of unseen planetary companions of planets. It was in 1992 that the first to be calculated. Another increasingly evidence was found, of planets used method of detecting exoplanets is orbiting a ‘pulsar’, a rapidly rotating from transits of planets across a star, if neutron star. This was discovered as a a planetary orbit happens to be in the result of finding variations in radio line of observation, and in these cases wave pulses from the pulsar. In 1995 slight but regular variations in there was the first definite evidence of brightness can be identified. a planet in orbit around a normal star, - and this was in the constellation of In different ways, the total number of Pegasus. When the star 51 Pegasi was such planet discoveries already identified as being very similar to our exceeds many hundreds, and with the own , astronomers at the first detected atmospheres in the case University of Geneva then confirmed of transiting planets now able to be that the star had a slight and regular analysed by means of spectroscopy. wobble effect, evidently caused by the The Return of Jupiter. gravitational effect of an unseen There are usually one or more planets companion. visible in the evening sky, and this autumn has the return of Jupiter - the largest by far of the planets, being around a thousand times the size of our Earth.

By the end of October Jupiter will be seen rising above the eastern horizon 3 during the late evening, and not far equator - similar to the main features from the twin stars of Gemini. Jupiter on Jupiter. The more distant moon will continue to be visible from Europa has a surface of cracked ice November onwards in the southeast indicating movement, and thought to and more southerly part of the evening be covering an extensive layer of sky, through and into the New . water, probably warmed also by With its size and dense cloudy Jupiter’s gravitational effect. atmosphere, Jupiter reflects a lot of sunlight, and is of interest for several Comet Ison - a Special Comet. reasons. The well known ‘Great Red A very unusual event which is being Spot’ on Jupiter is a semi-permanent anticipated this autumn is the feature of uncertain cause, but is promised appearance of a new comet, usually regarded by astronomers as a expected to become very bright as it giant storm. It varies in colour and passes closer to the Sun, much closer visibility, sometimes becoming than most other comets seen in the difficult to see or disappearing, but has past. Comets are occasional visitors to always been noted and at about the the inner part of the solar system, but a same latitude location since the early comet needs to have a large enough history of telescopic observations. nucleus developing a good tail to be seen easily. There are also two Equatorial Belts of darker material on Jupiter, at similar The new comet was discovered on distances and latitudes north and south September 21, 2012, by two Russian of the planet’s equator. The belts are astronomers making observations for often visible clearly like parallel lines, the International Scientific Optical but with one or the other sometimes Network (ISON). The comet’s early becoming less obvious or also visibility at that time - when it was completely disappearing from view. still in the outer part of the solar system and near Jupiter’s orbit was Jupiter also has its many and varied rather a surprise. A comet would not moons, with its four major moons of usually be expected to gain much of a particular interest. These can be seen warming effect on its icy materials at by using binoculars or with a such a great distance from the Sun. telescope as just points of light, changing constantly in relative For some months there seemed to be positions as they orbit the planet at little change in the appearance of the different speeds and distances. comet, with just a small tail visible, Spacecraft missions to Jupiter have but a year later and within the orbit of revealed that the moon Io has Jupiter the comet was found to be constantly active volcanoes, evidently developing in a more active way, caused by the gravitational effects of heading for the centre of the solar Jupiter, and with the most active system. Calculations of Comet Ison’s volcanoes at latitudes of around 19 track have shown that it can be degrees north and south of Io’s expected to come as close as about 4 one diameter or less away from the Our own local Society of Natural Sun’s surface. Science and Local Research, La Societe Guernesiaise, was founded in Comets of this kind have been named 1882, and it must be wondered sungrazers, and previous rare ones perhaps if any early astronomers in have been known to disappear into the Guernsey may have taken a particular Sun or break up, because of the huge interest in the new Society being gravitational or other effects. Comets formed at that time. can be unpredictable because of the Geoff Falla content of the core, and how this nucleus reacts to the solar radiation, also the effects in this case of an extremely close approach.

With a bright nucleus and with one or more tails of ionized gas and other cometary material coming away from it, the comet has already been found to be producing many tons of fine material every minute and it is hoped that Comet Ison will remain intact and visible in the morning sky before sunrise. After its predicted tight turn around the Sun at the end of November, the comet could remain visible for several weeks, also with the opportunity of perhaps seeing it in the evening sky after sunset, if the comet continues on its outward path as expected.

Of historical and perhaps local interest too, an important sungrazing comet was seen in a previous century. Tewfik’s Comet was discovered in 1882 during a total eclipse of the Sun in May of that year. It was the first time that a comet had been discovered in this way, and photographed. Very unusually, there was a ‘Great Comet’ seen during each of the years 1880, 1881 and 1882.

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Journey to the Centre of the Galaxy

In their classic textbook on relativity, calculate that from the viewpoint of “Gravitation” by Misner, Thorne and the people back on Earth the Wheeler, the authors pose the spacecraft will be travelling at over following question. How long would it 99% of the speed of light after just 7 take for the occupants of a rocket ship years. The spacecraft spends so much to travel the approximately 30,000 of its journey at so close to the speed light years from the Earth to the centre of light that it only takes a couple of the Galaxy? Assume they maintain more years than the 30,000 years that an acceleration of one “earth gravity” light takes for the spacecraft to reach (10 3 cm/sec 2 ) for half the trip, then the centre of the Galaxy. decelerate at one earth gravity for the remaining half. The question though was not how long the journey takes from the viewpoint Despite the title of the book, for this of observers on Earth but how long it question the authors want you to takes for the spacecraft occupants. For ignore the effects of gravity. So we this we have to take into account the assume that the rocket ship starts off relativistic effects of time dilation and close to Earth but free from Earth’s length contraction. For the occupants gravity and that it also avoids passing of the spacecraft time on Earth goes too close to any stars for their gravity slower and distances contract. As the to have any effect. In the jargon of speed builds up the effect becomes relativity we assume we are in ‘flat’ more significant and there is a spacetime. dramatic impact on the overall journey time. If my calculations are correct the Now although the authors show you time for the occupants to the half way how to work out the answer it is left as point, when the spaceship flips around an exercise and there are no answers and goes from accelerating to in the back of the book. So, bearing in decelerating, is only 9.85 years. So mind how easy it is to miss out a few their total journey time is just 19.7 factors of ten, if anyone checks my years. It is possible therefore for the answers and finds them to be wrong I spacecraft occupants to journey to the will be happy to issue a correction. centre of the Galaxy, have a quick With that caveat here are my results. look round, and be back within 40 years. The only problem is that when It is easy to imagine that with the they get back 60,000 years will have rocket ship accelerating at earth elapsed on Earth and things might gravity (incidentally providing a look a bit different. comfortable environment for the occupants) the spacecraft will soon The authors of “Gravitation” then ask achieve a speed that is an appreciable a supplementary question, which is fraction of the speed of light. In fact I what fraction of the initial mass of the

6 rocket ship can be payload for the carry to use later in the journey. The journey. They tell you to assume a result is that the amount of fuel you rocket that converts rest mass into need to carry increases exponentially radiation and ejects all the radiation as the journey time increases. I out of the back of the rocket with 100 calculate that for the journey to the per cent efficiency and perfect centre of the Galaxy the payload collimation. That is we can convert would be just a billionth of the initial mass to energy using E = mc 2 and mass of the rocket, and that’s for an assume all the energy produced is engine that is 100% efficient! used to accelerate or decelerate the Peter Langford rocket with none wasted. As with all major expeditions the problem is that [If you are further interested in this topic then most of the fuel you burn initially is type “Relativistic Rocket” into your search used to accelerate the fuel you have to engine.]

Geoff Falla’s regular roundup UK Space Agency. (Astronomy Now, of articles from popular July 2013)

Astronomy and Space Secrets of the Brightest Objects in Journals the Universe. Quasars, Quasi-stellar radio sources, were noted during the A Century of Discovery. A summary previous century as being at extreme of the key developments during the distances but unexpectedly bright past century of astronomy, from sources of light. These centres of Einstein’s Special Relativity theory to active galaxies are now better Hubble’s discovery of ‘island understood, as being activated black universes’ - galaxies; the expansion of holes, and with 3C 273 - the nearest the cosmos, the development of the one, being of particular importance. ‘big bang’ theory, radio astronomy, (Astronomy, July 2013) the discovery of pulsars, the age of space missions, and the discovery that Remembering the astronomer Carl other stars also have planets. Sagan . The famous astronomer Carl (Astronomy Now, July 2013) Sagan is remembered, in particular for UK Astronaut for Space Station his epic television series ‘Cosmos’- a mission. The first official UK Personal Voyage, and seen by more astronaut for twenty years, since than 500 million people worldwide. It Helen Sharman’s visit to Russia’s Mir was acclaimed as an outstanding Space Station, Major Tim Peake, a presentation of astronomy and the former military test pilot, is due to exploration of our solar system. travel to the International Space (Astronomy, July 2013) Station in 2015. Astronomy Now editor Keith Cooper’s interview with Great Astronomical Discoveries. To Major Peake about his training for the celebrate the 40th anniversary of the mission, his work, and his role for the best-selling magazine ‘Astronomy’, a 7 selection of 40 greatest discoveries, planets as there are stars. (Sky & not in a considered order of Telescope, August 2013) importance - which would be different for cosmologists and planetary The Women who created Modern specialists - but in order of distance, Astronomy. The part played by from solar system discoveries to stars several women at Harvard College and galaxies, observations and Observatory, examining photographic cosmological breakthroughs. plates in detail, with spectroscopic (Astronomy, August 2013) observations of stars, and establishing a classification of stars into an Mysteries of the Universe. accepted system of seven basic types Knowledge about the universe has according to their mass and been expanding continuously, with temperatures. (Sky and Telescope, surprises along the way. It is now August 2013) understood that the expansion of the universe is speeding up, that the The Milky Way. All of the stars observable has a limit, but that there which we see in the sky are part of our must be more beyond that horizon. A own Milky Way galaxy. A guide to summary of the many questions observing the Milky Way’s main band relating to the universe, with most of of stars, star clusters and nebulae, the answers as presently understood - which can be seen extending overhead but with many mysteries still to be through the constellations of Cygnus explained. and Aquila, and southwards to (Astronomy, August 2013) Sagittarius and Scorpius. (Astronomy Now, August 2013) A matter of Cosmic Principle. Recent observations confirm that there Solar Storm Warning. The solar are features in the universe which defy cycle of sunspot activity is broadly explanation, according to the predictable, but the behaviour of the conventional view that the universe is Sun - particularly at times of the same in all directions, and that this maximum activity, is unpredictable. may require rewriting the fundamental Solar flares and coronal mass ejections principles as presently understood. of material from the Sun’s surface (Astronomy, August 2013) release energy, which can interact strongly with Earth’s magnetic field. Exoplanets Everywhere. Since the This can produce disruption of discovery almost twenty years ago that communications and power supply, planets are in orbit around other stars and could be a danger during the apart from our own Sun, the pace of present peak of solar activity. discovery has been accelerating, in (Astronomy, September 2013) particular with the launch of the Kepler space telescope. It is now Comet Ison. A report on what estimated from the most recent promises to become, perhaps, the evidence that there are as many brightest comet for many years. 8

Comet Ison was discovered in September 2012. By September this year the comet was inside the orbit of Jupiter, and is due to be visible not far from Mars and passing close to the star Regulus, in the eastern sky before dawn during October. The comet is Astronomy Section Officers expected to be at its brightest towards the end of November. (Astronomy, Secretary Frank Dowding 255215 September 2013) Hon Treasurer Peter Langford 239575 Editor Colin Spicer 721997 Facilities Geoff Falla 724101 Curiosity’s Year on Mars. It is a George De Carteret year since the largest Mars Rover Public Relations David Le Conte 264847 vehicle Curiosity landed on the red Library Geoff Falla 724101 planet. An account of the NASA Research Colin Gaudion Light Pollution Vacant mission’s achievement and progress at Curiosity’s location of Gale Crater, close to interesting geological Observatory formations of the nearby Mount Rue du Lorier, St Peters, Sharp, where organic materials may Guernsey exist, and due to be investigated Tel: 264252 during the coming year. (Astronomy Now, September 2013) Web page www.astronomy.org.gg Material for, and enquiries about Sagittarius should be sent to the Editor

Colin Spicer 60 Mount Durand, St Peter Port Guernsey GY1 1DX Tel: 01481 721997 [email protected]

Articles in Sagittarius are copyright the authors. Views expressed are those of the authors and are not necessarily endorsed by the Astronomy Section or La Société Guernesiaise.

Copy deadline for next issue is 3rd Jan uary 2014

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