Λίτσα Νικολάου Δέσποινα Γεωργιάδου Κατερίνα Κόρδα Δέσποινα Κωνσταντινίδου

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2 Αγλαΐα Τυπάλδου Αθηνά Τζιτζιμπάση Αλέξανδρος Μαδούρος Ανδρέας Τυπάλδος Αντωνία Σιάγκα Βάσια Κεφαλάκη Βασίλης Παπαϊωάννου Γεωργία Κονδύλη Γιάννης Παναγιώτου Γιώργος Λύκος Γιώργος Τσιβακούδης Γιώργος Χασάπας Δημήτρης Παυλόπουλος Ελίνα Τζέκα Ευαγγελία Τριανταφύλλου Έφη Φιλιπποπούλου Κατερίνα Κουτσιούμπα Λευτέρης Μοσχούτης Μάρθα Κωνσταντινίδου Μιγκέν Σεχάι Στέλλα Αντωνάκη Χρύσανθος Μποστάνης Λίτσα Νικολάου Δέσποινα Γεωργιάδου Κατερίνα Κόρδα Δέσποινα Κωνσταντινίδου Εκπαιδευτικός Αγγλικής Γλώσσας Δασκάλα Ε Τάξης Δασκάλα Δ2 Τμήματος Υπεύθυνη Δασκάλα Ολοήμερου 2

3 Περιεχόμενα The Earth Out of Control! 4 What is space? 12 The Big Bang 14 Galaxies 18 Nebulae: A stellar nursery! 22 The Stars 26 Black Holes 32 The Sun 35 The Solar System and its planets 40 Planet Earth 50 Moons (Satellites) 53 What are comets? 65 What are asteroids? 68 Constellations and asterisms 72 Are we Alone in the Universe? 75 Η Γη Εκτός Ελέγχου! 83 Τι είναι διάστημα; 91 Η Μεγάλη Έκρηξη 93 Γαλαξίες 97 Νεφελώματα: Ένα αστρικό νηπαγωγείο! 101 Άστρα (Ήλιοι) 104 Μαύρες τρύπες 110 Ο Ήλιος 113 Το Ηλιακό Σύστημα και οι πλανήτες του 117 Πλανήτης Γη 126 Φεγγάρια (Δορυφόροι) 129 Τι είναι οι κομήτες; 138 Τι είναι οι αστεροειδείς; 141 Αστερισμοί (επίσημοι και ανεπίσημοι) 144 Είμαστε Μόνοι στο Σύμπαν; 147 Βιβλιογραφία 155 3

4 The Earth Out of Control! By George Lykos, Martha Constantinides, A Andrew Typaldos, Aglaia Typaldos. ll the pieces of the puzzle lead to the conclusion that our magnetic axis has recently followed an uncommon behaviour. A chain of unexplained deaths has struck thousands of fish and crabs all over the globe since Thousands of birds were found dead on the streets of the USA, England, Sweden and Hungary. The only common ground of these massive deaths which caused the animals' disorientation could have been a number of significant and sudden disorders of magnetic field lines. On 11th January the inhabitants of Ilulissat town - on the west coast of Greenland - woke up waiting another day in the darkness; The location of their town which is three degrees north of the Arctic Circle, guarantees that each year the Sun appears for he first time on January 13th. However... this year the sun surprisingly rose was two days earlier! What caused such a change? The probability that the unexpected sunrise in Greenland, and the mass deaths of birds and fish are associated with a disorder on the magnetic field of the Earth, gets bigger as many scenarios rise preparing people for a mega-earthquake and volcanic eruptions in the U.SA. It looks as if the US admit a large change of magnetic field lines! We know that the North Magnetic Pole drifts at about 25 miles per year. But according to the Νational Geographic, the Pole is now running by miles a year! In January 2005, NASA announced that the Sumatran tsunami drifted the North Pole by about 2.5 cm and further rounded up the Earth. As a result, the planet rotated faster and the duration of the day decreased by 2.68 microseconds. Does this mean that there were successive strikes of our planet's rotational axis, which disordered its magnetic field lines? Let's go back to recent... feats of human intervention into the environment; like goblins, we "cut down the tree" that kept the Earth in place. Now the spinning toy top is rotating unpredictably, awakening the fiery Titans who slept beneath volcanoes and seismic faults. The Sun may rise earlier in the Arctic and Greenland may become green again, but the birds are not going to "die singing" any more. Let alone people... 4

5 Gravity All objects in the universe attract each other. The pulling force is called gravity. The Earth's gravitational field is the space in which each subject receives the action of the pulling power of the Earth. The force with which two bodies attract each other is determined by the first law of Newton and is proportional to the product of their masses and inverse to the square of the distance separating them. Magnetism The Earth behaves like a giant magnet. The magnetic force of the Earth was discovered by the Chinese 4,000 years ago. Magnetism has been also known in the western hemisphere since ancient times. The word magnet has its origin in the magnet stone the stone of Magnesia - named after a region of Thessaly, where this stone was discovered by the ancient Greeks. The magnetic field that surrounds the Earth, looks like the one that exists around a magnetic dipole when we drop iron filings around. The filings then repel the dynamic lines of the field. The long axis of the magnetic dipole is called the magnetic axis of the Earth and when extrapolated intersects the Earth's surface at two points, the socalled magnetic poles. The magnetic poles do not coincide with the geographic poles and have different geographic coordinates. The magnetic poles are not opposite to each other; this means that the magnetic axis does not cross the center of the Earth. The magnetic compass needle does not exactly indicate the North Pole, but forms an angle with it. This angle is called declination. The magnetic needle also angles with the horizontal plane which is tangent to the dynamic line spot. This angle is called inclination. The inclination and declination vary from place to place and this shows that the direction of the field lines and the magnetic field vary from place to place. The determination of the position of the magnetic pole at different times in Earth's history, has been based on the magnetization of rocks and is called Paleomagnetism. 5

6 The method is based on the property of magnetic minerals to be oriented parallel to the Earth's magnetic field. Each magnetic mineral has a Curie point - a temperature which magnetization is destroyed above. When cooled below the Curie point, every magnetic mineral, acquires magnetization and is oriented parallel to the Earth's magnetic field. By studying magnetic minerals found in rocks, paleomagnetists have discovered the features that the magnetic field had at the time when they cooled. By means of this method scientists found that there was a time when the magnetic poles were reversed and the position that is now the north magnetic pole was once the south. During the past 4 million years there were 9 periods of such reversals. The Earth's Movements Planet Earth rotates. Evidence for its rotation is the daily cycles of day and night, the deviation of the winds and the fact that falling bodies veer eastward from the vertical plumb line below their point of release. There are four movements that affect the Earth: the rotation around its own axis; the revolution around the Sun; The whole Solar System revolves around the center of the Milky Way galaxy. The Milky Way is also slowly moving toward the Andromeda Galaxy. Earth's rotation is the rotation of the solid Earth around its own axis. The Earth rotates towards the east. The rotational speed of the Earth depends on latitude. The rotation of the earth is completed in 23 hours, 56 minutes and 4 seconds. This motion is responsible for the occurrence of day and night, the shape of Earth as an oblate spheroid, the divergence in marine currents and winds and the tides. Τhe Earth revolves around the Sun once a year. The long axis of the Earth's orbit is called solar altitude. When the Earth's distance from the Sun is minimum, the earth is said to be in perihelion and when the distance is the maximum, the earth is said to be in aphelion. The Earth completes one orbit around the Sun in 365 days, 5 hours, 48 minutes and 18 seconds. The revolution of the Earth around the Sun is responsible for the seasons, the climate and the division of the Earth in solar climate zones. In addition to the movements of the Moon, the Earth's revolution causes the Sun eclipses, the Moon phases and the tides. Finally, revolution is responsible for the different length of day and night. 6

7 Solstices Two "magical" days are inextricably linked to the four seasons of the year due to some peculiarities of the Earth's revolution. Let's compare the ecliptic - the line that our planet seems to follow during the year - with the celestial equator which is the imaginary circle obtained when the Earth's equator is projected onto the sky. We notice they do not coincide, but intersect in two points forming a 23 angle called the obliquity of the ecliptic! This is the angle that the rotational axis of the Earth has when compared to the level on which it turns around the sun. This phenomenon is crucial for our planet. Because the Earth's rotational axis has the same direction in space throughout the year, half of the year the Earth approaches the Sun. Then the rays of the Sun directly strike the northern hemisphere where it is summer and simultaneously herald the beginning of winter in the southern hemisphere. During the rest of the year, the Earth goes away from the sun and the effect reverses; it is winter in the northern hemisphere and summer in the south. These are the two solstices and occur when the Sun has the maximum distance from the celestial equator: on June and on December When the sun reaches its northernmost or southernmost in the sky - the solstices - its motion is reversed and reset; the sun seems to stop moving northwards or southwards, which is the reason why these points were called the stop of the sun. During the Northern Summer Solstice, the Sun provides the northern hemisphere with the longest day of the year, while in the south there is the longest night. When the Northern Solstice is winter, then the Sun provides the northern hemisphere with the longest night of the year. The opposite happens when the Sun is at the Southern Solstice. 7

8 Equinoxes Two equinoxes occur at the points where the ecliptic meets the celestial equator. During the two equinoxes, the sun is over equatorial regions at noon, causing the energy to be dissipated both northwards and southwards. Then day and night are equal in both hemispheres, and the sun is above the horizon for 12 hours and beneath the horizon for another 12 hours. Precession of the Equinoxes The precession of Earth's rotational axis causes the precession of the equinoxes. With respect to the fixed stars on the celestial dome, the points of spring and autumn equinoxes move westwards along the ecliptic and contrary to orbit of the Sun. As a consequence, equinoxes change their dates. Axial Precession Planet Earth rotates like a gyroscope it is a sort of spinning toy top. So the Earth does not move either horizontally or vertically. It tilts on its axis. Why does this occur? The shape of the Earth approximates an oblate spheroid, a sphere flattened along the axis from pole to pole such that there is a bulge around the equator. The bulge is pretty considerable in terms of volume and mass. This unequal pulling effect of the sun and moon on the planetary bulge contributes to our planet's reversal; the rotational axis can not maintain the same position; it gradually shifts. This motion is called precession of Earth's axis and was discovered by Hipparchus. Precession causes a slow but steady movement of the north pole of the sky; as a consequence, polar stars historically change. In other words, precession means that the Earth's equator does not complete a circle through space; it moves in an elliptical path which scientists call nutation. 8

9 The precession of the Earth's axis means that Earth goes through one such complete precessional cycle in a period of approximately 26,000 years. But this motion affects the time it takes the Earth to make one complete revolution around the sun. North Precession Let's remember what is happening on our planet. The Earth is not a perfect sphere; it is an overall unstable mass of heterogeneous material made of water, stones, metals, molten rock, internal cavities, etc. This mass rotates around the Sun because it probably was once a part of it, which for unknown reasons blasted off in space. But the Sun, with its immense power of gravity, did not let the Earth go away; it pulled it back and forced it to move in a spiral path around it, which later evolved into a circular one. The same explosive force that pushed the Earth away, forced it to turn around itself much faster: it currently executes about 365 such rotations during a solar revolution. The Sun is thus responsible for the two main rotational movements of the Earth. Paradoxically, however, the spins do not fit together. Normally, they should be at the same level since they were created by the same power - as it happens with all the planets in the solar system, apart from the very distant Pluto. Yet, if we assume that revolution around the Sun forms a disk and the Earth's rotation forms another one, these discs do not coincide; they intersect at an angle of degrees. This angle is called the obliquity of the ecliptic and the reason why it occurred, is a mystery. Most scientists believe that a large comet or a huge celestial body has previously passed very close to the Earth or fell on it, disrupting its smooth course. The movements of the Earth's axis shifts are responsible for the Earth's pole shifts, which were important for the movement of continents and seas during its history. Pole shifts have also resulted in changing the position of the equator, and thus in changing the climate as it was observed in different parts of the Earth's surface in the past. Pole Shift Hypothesis The Earth's rotation does not exactly occur around the geographical poles; it usually tilts at an angle of 23.5 degrees. Since the tilt is dependent on both the Earth's shape and on "how much water there is upon the Earth's surface, the axial tilt of the planet is now higher than it was during the Ice Age. As the polar ice caps melted in the north, they turned into water which spilled in the oceans and shifted the burden towards the equator. 9

10 As a consequence, there has been an axial oscillation which is shifting the North Pole by 10 cm per year along the meridian passing through Toronto and Panama. This oscillation is growing bigger through the 'greenhouse' effect that people have caused by means of exhaust emissions and unnatural ice melting. As a result, there is an additional annual displacement of the North Pole by 2.6 inches. Moreover, scientists warn that global ocean overheat and extension will lead to even greater axial tilt! The magnetic field of sun undergoes a drastic change for every 12,000 years. As the Earth rotates like a spinning toy top, the edges of the Earth's rotational axis, gradually oscillate to form a circle. During this circular motion, the poles magnet reverse. Due to some unknown fact, the Earth is in a position of imbalance. The greenhouse effect Evidence is given by the North Magnetic Pole. Since we discovered it, in 1831, we found out that in 1904 it began "travelling" northeastwards at a speed of 15 km per year. In 1989, it started accelerating the pace and, in 2007, we made sure that it is galloping toward Siberia ατ a speed of 55 to 60 kilometers per year! But why isn't it stable? The prevailing theory, argues that the Earth's magnetic field is due to the motion of molten iron around the faster spinning "solid iron heart" of the planet. A new theory, however, emphasizes that the electrically conductive salts of the sea create an "oceanic magnetic field" that alters the one derived from the Earth's interior. If this is correct, then the melting of the πολαρ ice caps explains the frantic gallop of the magnetic pole toward Siberia... Therefore, complacency that reversal of the magnetic poles occurs every 780,000 years, and that when it happens, it happens very slowly... is no longer valid. Displacement of the Earth's Rotational Axis! All big earthquakes affect the imaginary axis around which the Earth rotates. Earthquakes of large scale can change the distribution of mass on the planet. For example, the earthquake of 9.1 magnitude in Sumatra, which caused the terrible tsunami in the Indian Ocean in 2004, shrunk the day by 6.8 microseconds and shifted the Εarth's axis by about 7 cm. The terrible earthquake of 8.8 magnitude that shook Chile in 2010, shifted the Earth s axis of about 8 cm. At the same time, it diminished the length of the day the complete rotation of the Earth around the Sun- a little more than one millionth of a second. The day must have been shrunk by 1.26 microseconds. Of special scientific 10

11 interest is the question why the tsunami triggered by the Chilean earthquake proved much lower than expected, with tidal waves eventually not exceeding two meters in height. In addition, the 8.9 magnitude earthquake that struck Japan in 2011, shifted the Earth s rotational axis by 10 cm and seems to have moved the main island of the country by 2.4 meters. The shift of the rotational axis of the Earth can cause the entire planet huge tidal waves, large and destructive earthquakes and displacement of the continents, which may result in the complete destruction of human civilization and the survival of few human beings. Einstein pointed out that in areas where the ice is two miles thick, it presses the Earth's crust. He thus worried that the massive ice might cause displacement of the Earth's crust to another equilibrium position and explained that this phenomenon would have cataclysmic results. 11

12 What is space? I By Jim Pavlopoulos, Georgia Condylis n space, no one can hear you scream. This is because there is no air in space it is a vacuum. Sound waves can not travel through a vacuum. Outer space begins about 100 km above the Earth, where the shell of air around our planet disappears. With no air to scatter sunlight and produce a blue sky, space appears as a black blanket dotted with stars. Space is usually regarded as being completely empty. But this is not true. The vast gaps between the stars and planets are filled with huge amounts of thinly spread gas and dust. Even the emptiest parts of space contain at least a few hundred atoms or molecules per cubic metre. Space is also filled with many forms of radiation that are dangerous to astronauts. Much of this radiation comes from the Sun. High energy X-rays, gamma rays and cosmic rays which travel close to the speed of light, arrive from distant star systems. The Universe Our universe is a large and unimaginable expanse of dust, gas, stars, clouds, galaxies, and life. Distant worlds are waiting to be explored by future space craft. But what is the Universe? Lets start from the beginning: The Earth revolves around the Sun. The Sun in turn revolves or circles the center of the galaxy. Our galaxy is part of a group of galaxies called the Local Group. The local group of galaxies are all part of a bigger cluster of galaxies called the Virgo Cluster. This picture shows the overall structure of our universe. This is just a small piece, but it is enough to see that matter is organized in strands, or strings. 12

13 Millions of galaxy clusters around the universe are strung together like a spiderweb. If you could look at the entire universe at once it would look like a giant spiderweb, made up of billions of galaxies, and trillions and trillions of stars. The areas between strands of galaxies are completely empty. You would have to travel hundreds of miles to find just one atom. The structure of the Universe 13

14 The Big Bang By Bill Papaioannou, John Panagiotou, George Tsivakoudis, George Chassapas. M ost astronomers believe the Universe began in a Big Bang about 14 billion years ago. That's how old the oldest stars are, and we think that stars began to form almost immediately after the Big Bang. At that time, the entire Universe was inside a bubble that was thousands of times smaller than a pinhead. It was hotter and denser than anything we can imagine. Then it suddenly exploded. At the moment of the big bang, the point began expanding like a balloon, versus the long-held misconception of an actual explosion. The Universe that we know was born. Time, space and matter all began with the Big Bang. In a fraction of a second, the Universe grew from smaller than a single atom to bigger than a galaxy. All the matter in the universe, as we know it today, began in a very tiny, hot and compacted point. And it kept on growing at a fantastic rate. It is still expanding today. Telescopes with the ability to measure radiation in space detect residual radiation throughout space, which indicates that something massive occurred. Nobody knows what was there before the Big Bang. Possibly there was no time before the Universe got started, so nothing happened. Another way of looking at it is to say that somehow, in the very first micro-second of the Big Bang, some space actually changed into time, so that time got started. There might have been other universes before this one, or there might be other ones at the same time as this one. As the Universe expanded and cooled, energy changed into particles of matter and antimatter. These two opposite types of particles largely destroyed each other. But some matter survived. 14

15 When the Big Bang happened, it let loose a huge amount of energy into a small Universe. The Universe immediately started to get bigger and bigger and making more space. Inside the Universe, the energy (in the form of photons (light) and bosons) went zipping around like crazy all over the place. These super-energetic photons and bosons sometimes broke up into smaller particles. The photons broke down into an electron and a positron, which is like the opposite of an electron. The bosons broke down into a proton and an anti-proton, or neutrons and anti-neutrons. Then they would lose energy and eventually glue themselves back together into protons and bosons again. But at some point, some of the positrons and anti-protons (the anti-matter) seem to have gotten lost somewhere, leaving a bunch of lonely electrons and protons with no matches. These electrons and protons got together with each other, forming the first hydrogen atoms. Over the next three minutes, the temperature dropped below 1 billion degrees Celsius. It was now cool enough for the protons and neutrons to come together, forming hydrogen and helium nuclei.once there were clouds of these hydrogen atoms floating around together and compressed by gravity, they formed nebulas, which soon developed into the first stars and galaxies. The universe contains about 200 billion galaxies. 15

16 A theory The Big Bang theory remains a theory because the evidence available are not enough. There are only traces; what we can see from our place in the universe back through time, which could be incomplete. The Big Bang theory has been the prevailing explanation of our universe's origins. But now scientists have presented alternatives to this theory, explaining the universe in different terms. The idea that time and space ultimately came from the expansion of an infinitely dense point has itself inspired a bang of discussion. Especially controversial has been the question of what caused the Big Bang, if the Big Bang caused time and space. Furthermore, how could the expansion outrun the force of gravity and, for a period of time, the speed of light? If there was no time or place before the Big Bang for a causative agency to exist, then we can attribute no physical cause to the Big Bang. Moreover, why have the specific physical laws and not some other? The Bulk Theory or String Theory The string theory points to seven hidden dimensions beyond the three we experience. Scientists expanded on string theory in They proposed that the universe was composed of "branes" (membranes). These branes are three-dimensional worlds, which exist in a higher-dimensional space. Our universe is just one 3-D brane moving through a larger 4-D background called "the bulk." If these branes can move, they can collide, unleashing a torrent of energies, similar to the Big Bang. This led to the search for cycles in the universe. A collision of branes would create the kind of universe we live in, with galaxies, planets, and stars. The space within the brane expands creating more bulk in which other brane collisions occur. This cyclical theory suggests that the universe is constantly creating and recreating itself. 16

17 Time's Arrow Theory The bulk theory fails to explain the concept of time. In 2004, a scientist explained time's one-way progression. He pointed to the concepts of entropy and equilibrium. Entropy describes a state of equilibrium (the even distribution of matter). Low entropy means far from equilibrium, while high entropy means close to equilibrium. Οur universe began with low entropy, allowing to expand to equilibrium. A universe created with high entropy couldn't expand and evolve, thus the inert environment wouldn't support the birth of new stars or life. The fact that our universe started at low entropy is why we experience time as a straight arrow. Multiverse This "time's arrow theory" suggests a multiverse concept derived from an aspect of the Big Bang called inflation. When our universe was born, it went through an accelerated period of expansion or "inflation." This inflation blew-up a small corner of another universe. Τhis process of inflation is happening continually; there is an eternal inflation. This process works in both directions, creating inverse arrows of time. Now Theory Another scientist suggests something completely different; time did not exist prior to the event. Time does not exist. It is intangible. Change creates the illusion of time. And inversely, the concept of time exists to measure change. Time is the idea of "nows." No matter how the nows are arranged, they are complete and independent of each other. In this theory, everything exists simultaneously. It is just the arrangement of our perspective on the nows that changes. 17

18 Galaxies By Alex Madouros, Athena Tzitzibassis, Chryssanthos Bostanis, Catherine Koutsioubas. W e cannot see anything that happened during the first 300, 000 years of the Universe. Scientists try to work it out from their knowledge of atomic particles and from computer models. The only direct evidence of the Big Bang itself is a faint glow in space. Spacecrafts and telescopes on balloons see this as a patchy pattern of slightly warmer and cooler gas all around us. These ripples also show where the hydrogen clouds were slightly denser. As millions of years passed, the dense areas pulled in material because they had more gravity. Finally, about 100 million years after the Big Bang, the gas became hot and dense enough for the first stars to form. Andromeda Galaxy New stars were being born at a rate 10 times higher than in the present-day Universe. Large clusters of stars soon became the first galaxies. Telescopes are now beginning to find galaxies that were created about one billion years after the Big Bang. These small galaxies were much closer together than galaxies are today. Collisions were common. Like two flames moving towards each other, they merged into bigger galaxies. Our Milky Way galaxy came together in this way. Nearly all stars belong to gigantic groups known as galaxies. The Sun is one of at least 100 billion stars in our galaxy, the Milky Way. And there are billions of galaxies in the Universe. Everywhere we look in the sky there are galaxies of different shapes and sizes. Some are spirals, with curved arms wrapped around a bright central core. Most galaxies are moving apart at high speed, except in galaxy clusters where they dance around each other. 18

19 The largest galaxies look like squashed balls. They contain up to 10 million million stars, but they have very little gas or dust. Nearly all galaxies have a supermassive black hole at the centre. There are three kinds of Galaxies; Spiral, Elliptical, and Irregular. The only difference between the three is what shape they are. Spiral Galaxies The most beautiful type of galaxies are spiral galaxies. Their long twisting arms are areas where stars are being formed. Where do the spirals come from? Like ripples in a pond, the spiral arms seen in this kind of galaxy are circling waves. These waves cause new stars to form. That's right, they are like star farmers, planting star seeds where ever they go. What causes the waves to glow? Some of the new stars created in the wave are very large. Because of their size these large stars glow brighter than their smaller cousins, causing the nearby dust clouds to glow brightly. Thus any area near one of these waves glows like a fluorescent light. colliding spiral galaxies In other words you can't actually see the waves, the spirals that we see are the glowing clouds illuminated by large, hot stars. As the waves move on the clouds behind them dim down, no longer glowing until another wave passes through. Why doesn't the whole galaxy shine brightly? The large bright stars created in the waves don't live very long. Their large size makes them burn all their fuel quickly. Usually they die before they ever leave the wave. Only the smaller stars which do not glow brightly survive to leave the waves they formed in. Elliptical Galaxies The stars found in elliptical galaxies are often very old. This is because elliptical galaxies don't actively create new stars. The only stars found in them were created a long time ago. 19

20 Although they are usually smaller, this type of galaxy can be large. Most have only a few thousand stars, but some can have billions of stars. The stars in an elliptical galaxy are often very close together making the center look like one giant star. If the Earth were inside an elliptical galaxy it would be bright both day and night. Irregular Galaxies Irregular galaxies are simply all the galaxies which are not spiral or elliptical. They can look like anything and have many different characteristics. Many irregular galaxies probably used to be spiral, or elliptical until they had some kind of accident which changed them such as crashing with another galaxy. Many other irregular galaxies probably were never spiral or elliptical; they simply didn't evolve that way. The Local Group There are billions of galaxies in our Universe. Most of these are clumped together in small groups. Our own galaxy which is called The Milky Way Galaxy lies within a group of galaxies that we call "The Local Group". The Local Group consists of about 30 galaxies. The three largest are The Andromeda Galaxy, The Milky Way Galaxy, and Triangulum. The Milky Way We live in one of the arms of a large spiral galaxy called the Milky Way. The Sun and its planets lie in this quiet part of the galaxy, about half way out from the centre. The Milky Way is shaped like a huge whirlpool that rotates once every 200 million years. It is made up of at least 100 billion stars, as well as dust and gas. It is so big that light takes 100,000 years to cross from one side to the other. 20

21 The Milky Way The centre of the Galaxy is very hard to see because clouds of gas and dust block our view. Scientists think that it contains a supermassive black hole that swallows anything passing too close. Outside the main spiral are about 200 ball-shaped clusters of stars. Each globular cluster is very old and contains up to one million stars. Apart from the Andromeda Galaxy and Triangulum, the other galaxies are much smaller. They include two galaxies that can be seen with the naked eye from countries south of the equator. The galaxies are called the Magellanic Clouds, after the Portuguese explorer Ferdinand Magellan. 21

22 Nebulae: A stellar nursery! E By Alex Madouros, Athena Tzitzibassis, Chryssanthos Bostanis, Catherine Koutsioubas. ver wondered where stars are made? Well, now you are about to find out! Just where these hot balls of gas start their lives, begins what astronomers call a nebula and they are basically the nurseries of the Universe. Horsehead Nebula Well, whatever you remember from the nursery that you went to, stellar nurseries are quite different! For one, a nebula is a gigantic cloud of dust and gas; mainly of hydrogen and helium gases, a nebula can be light years across - that s trillions of miles. Imagine how many nurseries you can fit into one of these enormous star factories! Secondly, nebulae look quite fuzzy in appearance - pretty much like fluffy clouds or cotton wool in the sky. Imagine having to go nursery in a massive splattering of cotton wool? Nebulae come in not just a variety of sizes, they also come in a range of shapes with some of them looking very much like anything from horses (the Horsehead Nebula) to crabs (the Crab Nebula). The massive question is though, how do they form or have they always been there? Astronomers believe that nebulae are made from the huge collapse of gas which they call the Interstellar Medium - the gas, dust and cosmic rays that can be found between planets and stars in galaxies. As the material falls in on itself under its own weight, large stars are made in the centre. When this happens, ultraviolet radiation shoots out like a laser beam and the nebula is lit up - just like a Christmas tree! Astronomers have a name for these types of nebulae. Crab Nebula M16 Herschel Nebula 22

23 Emission Nebulae There are many famous emission nebulae, one of them is probably one that you have heard of and is easily one of the most well known; astronomers call this the Orion Nebula because you can find it in the constellation of Orion. This type of nebula is very, very hot because of the hot, newborn stars that zap their surroundings with sizzling rays of hot particles with lots of energy - much like how the Sun throws out hot beams on our planet but only so much hotter! Orion Nebula Emission nebulae are usually found to glow red or pink in colour - this is because they are filled with lots and lots of hydrogen gas. If pink or red is not your favourite colour though, then you might prefer the next type of nebulae that we are going to look at next. Reflection Nebulae M45 Reflection Nebula Sometimes, stars do not have enough pent-up energy to zap their surroundings with high energy particles. So they happily sit in clouds of dust and these clouds reflect their 23

24 light. You might be able to see little pieces of dust floating around in the air right now. Do you know why you can see them? Because there s light (either from a lamp or the Sun) illuminating them. This light is reflected and that s pretty much what happens in a reflection nebula. Reflection nebulae appear blue due to the same reason why the sky is blue and this is due to scattering. But how does scattering work? The light that is thrown out from a star, or our Sun, is reflected. Light that comes from the Sun and most newborn stars is called white light and it is made of many different colours, very similar to a rainbow. Cats-eye Nebula When this light travels passed particles of dust, the blue light is scattered; bouncing off every dust particle that it encounters before reaching our eyes - very much like how balls on a pool table are thrown in all directions as the white ball hits them and they start to bounce off of each other if they come into contact. The remaining light gets to travel through without being touched and that s why we don t really get to see other colours in the sky above us or in reflection nebulae. Where there s a reflection nebula, you can usually guarantee that an emission nebula is not too far away. Astronomers call them diffuse nebulae when they are found together. If you asked an astronomer to give you an example of one of these nebulae, then they are more than likely going to answer with the Witch Head reflection nebula which is also found in the constellation of Orion. Witch Head Nebula 24

25 Planetary Nebulae That s not the end of our tour of nebulae - there s more! Last but not least there s planetary nebulae - but do not be fooled - these shells of gas have absolutely nothing to do with planets! This type of nebula earns its name because some astronomers of the 18th Century believed that they looked like giant worlds through the eyepiece of small telescopes. Planetary nebulae are made when a star runs out of fuel to burn. What happens next is amazing. What do you expect to happen when a star runs out of fuel? It s not quite the same as when your car runs out of gas, where it stops moving - what happens to a star is quite a bit different; it blows off its outer layers of gas in the shape of a ring or bubble. When stars do this, astronomers say that a star is dying. But it s not a sad ending for the star, it s a beautiful colourful one! n6720 Planetary Nebulae What we mean in terms of a dying star, at least when it comes to stars just like our Sun, is that it s changing into a red giant star. A red giant is a huge star that can swell to a size that swallows up everything in its path. After spending millions of years as a heavy weight giant, it shrinks again, pushing off the outer layers that we mentioned earlier. Planetary nebulae are usually visible for around 50,000 years before starting to mix with the space that surrounds them; so there s plenty of time to get out your telescope to have a look. Planetary Nebula Bok Globule The nebulae that we have been learning about are not the only places where star birth can be found - there s the Bok globules which are really thick dark clouds of cosmic dust and gas. Because they are so dense, they block out light behind them, so astronomers can find them quite easily! 25 Bok Nebula

26 The Stars By Alex Madouros, Athena Tzitzibassis, Chryssanthos Bostanis, Catherine Koutsioubas. Star birth L ike people, stars are born, they grow old and they die. Their birth places are huge, cold clouds of gas and dust, known as 'nebulae'. The most famous of these is the Orion nebula, which is just visible with the unaided eye. Rosetta Nebula These clouds start to shrink under their own gravity. As the cloud gets smaller, it breaks into clumps. Each clump eventually becomes so hot and dense that nuclear reactions begin. When the temperature reaches 10 million degrees Celsius, the clump becomes a new star. After their birth, most young stars lie at the centre of a flat disc of gas and dust. Most of this material is eventually blown away by the star s radiation. Before this happens, planets may form around the central star. Infrared observatories are able to detect heat coming from invisible stars that are forming inside such clouds. Star death Most stars take millions of years to die. When a star like the Sun has burned all of its hydrogen fuel, it expands to become a red giant. This may be millions of kilometres across - big enough to swallow the planets Mercury and Venus. After puffing off its outer layers, the star collapses to form a very dense white dwarf. One teaspoon of material from a white dwarf would weigh up to 100 tonnes. Over billions of years, the white dwarf cools and becomes invisible. 26

27 Stars heavier than eight times the mass of the Sun end their lives very suddenly. When they run out of fuel, they swell into red supergiants. They try to keep alive by burning different fuels, but this only works for a few million years. Then they blow themselves apart in a huge supernova explosion. For a week or so, the supernova outshines all of the other stars in its galaxy. Then it quickly fades. All that is left is a tiny, dense object a neutron star or a black hole surrounded by an expanding cloud of very hot gas.the elements made inside the supergiant (such as oxygen, carbon and iron) are scattered through space. This stardust eventually makes other stars and planets. There are several different kinds of stars in the sky. Some are very big. A couple of stars have been found that are 100 to 200 times larger than the sun. Some very old stars are smaller than the Earth. Scientists study stars and place them in groups based on how they are alike and how they are different. Red Dwarf stars Red Dwarf stars are smaller than our Sun. And since they are smaller, they also have less mass. Because of their small size, these stars burn their fuel very slowly, which allows them to live a very long time. This also causes these stars to not shine as brightly as others. Some red dwarf stars will live trillions of years before they run out of fuel. Why are red dwarf stars red? Because red dwarf stars only burn a little bit of fuel at a time, they are not very hot compared to other stars. Think of a fire. The coolest part of the fire is at the top of the flame where it glows red, the hotter part in the middle glows yellow, and the hottest part near the fuel glows blue. Stars work the same way. Their temperature determines what colour they are. Thus, we can determine how hot a star is just by its colour. Red dwarf stars are by far the most common type of star in outer space. However, very few stars that you see in the sky are red dwarfs. This is because they are so small and make very little light. 27

28 Yellow Stars Like the Sun, these medium-sized stars are yellow because they have a medium temperature.their higher temperature causes them to burn their fuel faster. This means they will not live as long, only about 10 billion years or so. Near the end of their lives these medium-sized stars swell up, becoming very large. When this happens to the Sun, it will grow large enough to engulf even the Earth. Eventually they shrink again, leaving behind most of their gas. This gas forms a beautiful cloud around the star called a Planetary Nebula. When will the Sun expand into a giant, and then shrink leaving behind a planetary nebula? Don't worry, the sun is only about 5 billion years old. It still has another 5 billion years or so before it will expand and turn into a planetary nebula. The Sun is so hot that when it dies, it will take a long time to cool off. The Sun will die in about 5 billion years, but it will still glow for many billions The Sun of years after that. As it cools, it will be what is called a white dwarf star. Eventually, after billions, maybe even trillions of years, it will stop glowing. At that point it will be what we call a black dwarf star. Because the process for a star to become a black dwarf takes such a long time, it is believed there are still no black dwarf stars in the universe. Giant Stars Remember when we talked about sun-sized stars? We said that at the end of their lives these stars expand, taking up much more space than before. This is exactly what a Giant Star is. As a sun-sized star gets old, it starts to run out of its hydrogen fuel. When the process of burning hydrogen in the star's core begins to slow down, the core gets more compact and dense. This means all the stuff in the middle of the star gets really close together. As the center gets smaller and smaller, it starts to heat up again. When it gets hot enough, it will start to burn a new fuel called helium. 28

29 Once ignited, helium burns much hotter than hydrogen. The additional heat pushes the outer layer of the star out much further than it used to be, making the star much larger. As the giant star gets hotter, its outside stretches out further and further. When our own Sun begins to stretch into a giant star, it will engulf Mercury, Venus, Earth and Mars. Many of the stars you see at night are giant stars. This is because like a lighthouse, giant stars glow very brightly. When the Sun becomes a giant star, it's light will shine much further into space than it does right now. Super Giant Stars A super giant star is the exact same thing as a giant star only much bigger. Remember that as a star gets older, it begins to run out of fuel. As the star runs out of fuel, it will start to burn out. The only difference between Giant Stars and Super Giant Stars is their size. Super Giant Stars are much bigger. If the Sun were replaced by a super giant star, it would extend from the center of our Solar System almost all the way out to Uranus. Dead super giant stars/blue giant stars often turn into black holes. A black hole is a very compact object. How does this happen? As the star dies, it explodes in a huge explosion called a supernova. The supernova blasts away most of the star. Anything left behind begins to fall into the middle of the star. It gets more and more compact, and smaller and smaller. If there is enough of the star left after the explosion, the star will be heavy enough to squash it down to the size of an atom, or even smaller. Blue Giants Blue stars are large and compact, this causes them to burn their fuel quickly which in turn makes their temperature very hot. These stars often run out of fuel in only 10, ,000 years. Just like the sun-sized stars, blue giant stars also begin to burn helium.as they do, these stars get much hotter. This extra heat makes the outside of an old blue giant star stretch out further. A blue giant is extremely bright. Like a lighthouse, they shine across a great 29

30 distance. Even though blue giant stars are rare, they make up many of the stars we see at night because they shine so brightly. Blue giant stars die in a spectacular way. They grow larger just like the sun-sized stars, but then instead of shrinking and forming a planetary nebula, they explode in what is called a supernova. Supernova explosions can be brighter than an entire galaxy, and can be seen from very far away. Because blue giant stars only live a short time, scientists use them to find places in outer space where new stars are forming. Supernovas Every now and again our Milky Way galaxy is lit up by a huge explosion. Known as a supernova, this violent event marks the death of a supergiant a heavyweight star which is many times bigger than the Sun. One of the last supernovas in the Milky Way took place about 340 years ago in the constellation of Cassiopeia, so it is known as Cassiopeia A (Cas A). Cassiopeia A Cas A is located ten thousand light-years from Earth. The images show a shredded ring of material that is moving rapidly away from the site of the explosion. Some of the material is moving at about 50 million km per hour (fast enough to travel from Earth to the Moon in 30 seconds!). The huge swirls of debris are glowing because they have been heated by the shock wave from the supernova as it passed by. There are several types of supernova explosions. Cas A blew up when a small star, known as a white dwarf, pulled a lot of material from a nearby star. As the gas built up, the white dwarf became so hot and active that it exploded. Other supernovas occur when massive stars run out of nuclear fuel in their cores. Unable to give out any more energy, the core collapses, destroying the star. Supernovas are important because they spread star material across the galaxy. Almost everything on Earth (including us!) is made of elements (such as carbon and iron) that came from this stardust. 30

31 Quasars Quasars are extremely distant objects in our known universe. They are the furthest objects away from our galaxy that can be seen. Quasars are extremely bright masses of energy and light. The name quasar is actually short for quasi-stellar radio source or quasi-stellar object. Quasars are the brightest objects in our universe, although to see one through a telescope they do not look that bright at all. This is because quasars are so far away. They emit radio waves, x-rays and light waves. Quasars appear as faint red stars to us here on Earth. A quasar is believed to be a supermassive black hole surrounded by an accretion disk. An accretion disk is a flat, disk-like structure of gas that rapidly spirals around a larger object, like a black hole, a new star, a white dwarf, etc. A quasar gradually attracts this gas and sometimes other stars or or even small galaxies with their superstrong gravity. These objects get sucked into the black hole. When a galaxy, star or gas is absorbed into a quasar in such a way, the result is a massive collision of matter that causes a gigantic explosive output of radiation energy and light. This great burst of energy results in a flare, which is a distinct characteristic of quasars. The light, radiation and radio waves from these galaxies and stars being absorbed into a black hole travel billions of light years through space. When we look at quasars which are billion light years away, we are looking billion years into the past. Pretty amazing, right? 31

32 Black holes W By Lefteris Moschoutis, Miguen Sechae hat are black holes? Have you ever had to vacuum your bedroom? When you do, watch closely because you will see the dirt and crumbs start to move towards the vacuum cleaner. A black hole is similar to a vacuum cleaner, cleaning up debris left behind in outer space. However, it is not suction power that makes things fall into a black hole. Suction would not be strong enough. Instead, a black hole uses the power of gravity to pull things towards it. How do black holes form? When a large star runs out of fuel it can no longer support its heavy weight. The pressure from the star's massive layers of hydrogen press down forcing the star to get smaller and smaller and smaller. Eventually the star will get even smaller than an atom. Imagine that for a moment, an entire star squashed up into less space than a tiny atom. How can something get smaller but retain the same amount of mass, or stuff? It is really quite simple. If you take a sponge the size of a soda can, you can easily squish it in your hands until it is completely covered. But here is the interesting part! If you make something smaller by squishing it, its gravity becomes much stronger. 32

33 A black hole's gravity becomes so powerful that anything, including light that gets too close, gets pulled in. That's right, not even light can escape the grasp of a black hole. Anatomy of a Black Hole Black holes are made up of 3 main parts. The very outer layer of a black hole is called the Outer Event Horizon. Within the Outer Event Horizon you would still be able to escape from a black hole's gravity because the gravity is not as strong here. The middle layer of a black hole is called the Inner Event Horizon. If you didn't escape the black hole's gravity before you entered the Inner Event Horizon, then you have missed your chance to escape. The gravity in this layer is much stronger and does not let go of objects it captures. At this point you would begin to fall towards the center of the black hole. The center of a black hole is called the Singularity. This is simply a big word that means squashed up star. The Singularity is where the black hole's gravity is the strongest. How can you fall into a black hole? Think of the Earth. When you are in outer space you can float around. If you get too close to the Earth you will be pulled in by its gravity. On the Earth, you could leave again in a rocket ship. However, if you fall into a black hole, there would be no way to get out because the gravity is so powerful. What types of black holes are there? Black holes often look very different from each other. But this is because of variety in what happens in their surroundings. The black holes themselves are all identical, except for three characteristic properties: the mass of the black hole (how much stuff it is made of), its spin (whether and how fast it rotates around an axis), and its electric charge. Astronomers can measure the mass of black holes by studying the material that orbits around them. So far, we have found two types of black holes: stellar-mass (just a few times heavier than our Sun) or supermassive (about as heavy as a small galaxy). Recent observations suggest there may be black holes with masses between stellar-mass and supermassive black holes. Black holes can spin around an axis, although the rotation speed cannot exceed some limit. Some astronomers think that many black holes in the Universe probably do spin, because the objects from which black holes form (stars for example) generally rotate as well. Observations are starting to shed some light on this issue, but no consensus has so far Binary black holes 33