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href="../827/cosmology.html">Cosmology</a></label></li><li class=""><label style="padding-left: 0px"><i class="fa fa-fw"></i><a href="../834/age-of-the-universe.html">Age of the universe</a></label></li><li class=""><label style="padding-left: 0px"><i class="fa fa-fw"></i><a href="../1153/ahl-stellar-processes.html">AHL Stellar processes</a></label></li><li class=""><label style="padding-left: 0px"><i class="fa fa-fw"></i><a href="../1154/ahl-further-cosmology.html">AHL Further cosmology</a></label></li></ul></div> <div class="hidden-xs hidden-sm"> <button class="btn btn-default btn-block text-xs-center" data-toggle="modal" data-target="#modal-feedback" style="margin-bottom: 10px"><i class="fa fa-send"></i> Feedback</button> </div> </div> <div class="col-md-9" id="main-column"> <h1 class="page_title"> Objects in the universe <a href="#" class="mark-page-favorite pull-right" data-pid="830" title="Mark as favorite" onclick="return false;"><i class="fa fa-star-o"></i></a> </h1> <ol class="breadcrumb"> <li><a href="../../../physics.html"><i class="fa fa-home"></i></a><i class="fa fa-fw fa-chevron-right divider"></i></li><li><a href="../823/astrophysics.html">Astrophysics</a><i class="fa fa-fw fa-chevron-right divider"></i></li><li><span class="gray">Objects in the universe</span></li> <span class="pull-right" style="color: #555" title="Suggested study time: 10 minutes"><i class="fa fa-clock-o"></i> 10'</span> </ol> <article id="main-article"> <p><img alt="" src="../../astro/hubble-deep-field-1.jpg" style="float: left; width: 172px; height: 150px;">The universe is the complete region of space in which things exist. The best-known theory to date is that the universe commenced with a 'hot Big Bang' of energy and matter and that it continues to expand.</p> <p>This image shows the Hubble telescope 'deep field'. The blotches of light might look like stars observed by the eye in the night sky, but in fact are entire galaxies. The redder the galaxy, the older and further away it is from Earth.</p> <hr class="hidden-separator"> <div class="panel panel-turquoise panel-has-colored-body"> <div class="panel-heading"> <div> <p>Key Concepts</p> </div> </div> <div class="panel-body"> <div> <h4><img alt="" src="../../astro/andromeda-small.jpg" style="float: right; width: 200px; height: 150px;">Galaxy</h4> <p>A galaxy is a collection of hundreds of billions of stars. They orbit a black hole at the centre of the galaxy. A black hole is defined as having such a strong gravitational field that the escape velocity for a ballistic object exceeds the speed of light.</p> <p>We are located in the Milky Way galaxy. This image shows the Andromeda galaxy, the closest neighbour to our own.</p> <p>Hundreds or thousands of galaxies can group together under gravity to form <em>clusters</em>. These clusters may then group to form <em>superclusters</em>. As an example, the Milky Way is a galaxy in the Local Group galaxy cluster, which in turn is part of the Laniakea Supercluster.</p> <hr class="hidden-separator"> <h4><img alt="" src="../../astro/solar-system.jpg" style="float: left; height: 200px; width: 266px;">Planetary system</h4> <p>A planetary system consists of a star with bodies orbitting it, such as <em>planets</em> and <em>comets</em>. Both planets and comets have elliptical orbits but planets' orbits are nearly circular, whereas comets' are highly eccentric. Planets can be made of rock (like Earth) or gas (like Jupiter). Objects too small to be called planets are referred to as <em>dwarf planets </em>(you might recall Pluto's demotion) or <em>asteroids</em>. Comets are made from ice and dust.</p> <p>Bodies that orbit planets are called <em>satellites</em>. Most of those orbitting Earth are man-made satellites, but we have one natural satellite too - the Moon.</p> <p><img alt="" src="../../astro/moon-small.png" style="float: right; width: 150px; height: 150px;">Often depicted as a squashed up safari of big, bright spheres, our Solar System is rarely shown to scale. The correct relative sizes are too extreme to be shown here, but check out this <a href="http://joshworth.com/dev/pixelspace/pixelspace_solarsystem.html" target="_blank">tediously accurate model</a>.</p> <p>In order, our planets go outward from the sun as follows to make up the Solar System:</p> <ul> <li>Mercury</li> <li>Venus</li> <li>Earth</li> <li>Mars</li> <li>(Asteroid belt)</li> <li>Jupiter</li> <li>Saturn</li> <li>Uranus</li> <li>Neptune</li> <li>(Kuiper belt, including Pluto)</li> </ul> <hr class="hidden-separator"> <h4><img alt="" src="../../astro/proxima-centauri.jpg" style="float: left; width: 267px; height: 200px;">Stars</h4> <p>A star is a body of extremely large mass and high temperature, with nuclear fusion taking place at the core. A star is formed from a <em>nebula</em>, a cloud of dust and gas that collapses under its own gravity. </p> <p>Stars experience a lifecycle, from birth as a protostar to the main sequence to the giant phase. The death of a large star is an explosive supernova with two further possible outcomes, whereas small stars form dwarfs.</p> <p>A star exists longest in the <em>main sequence</em>, in which the inward force of gravity is balanced by the outward radiation pressure.</p> <ul> </ul> </div> </div> <div class="panel-footer"> <div> </div> </div> </div> <div class="panel panel-has-colored-body panel-yellow"> <div class="panel-heading"><a class="expander" href="#"><span class="fa fa-plus"></span></a> <div> <p>Essentials</p> </div> </div> <div class="panel-body"> <div> <p><img alt="" src="../../astro/nebula-small.png" style="float: right; width: 170px; height: 200px;">There are a few key terms to be aware of:</p> <ul> <li>Two stars in mutual orbit are referred to as <em>binary</em>. Star Wars fans might recall that Tatooine is a planet orbitting a binary star planetary system.</li> <li>Stars with constant relative positions in the night sky have been gazed and marvelled at by mankind for millenia. These are known as <em>constellations </em>and still inspire myth and astrological fortune telling across the world today.</li> <li>Stars can group together to form <em>stellar clusters</em>. <em>Globular</em> clusters contain tens of thousands of old stars with tight gravitational attraction and are found in the halo of a galaxy. <em>Open</em> clusters contain hundreds or thousands of stars with weaker gravitational attraction. Found in the disk of galaxies, open clusters have active star formation taking place<small><em>.</em></small></li> </ul> </div> </div> <div class="panel-footer"> <div> </div> </div> </div> <div class="panel panel-has-colored-body panel-green"> <div class="panel-heading"><a class="expander" href="#"><span class="fa fa-plus"></span></a> <div> <p>Test Yourself</p> </div> </div> <div class="panel-body"> <div> <p><i>Use flashcards to practise your recall.</i></p> <div class="tib-flashcard"><a class="show-flashcards btn btn-success btn-xs-block btn-block " data-levels="1" data-mode="Normal" data-topics="832" data-subject-id="6" data-n-flashcards="15" style="text-align:center">Show flashcards</a></div><hr> <p><i>Use quizzes to practise application of theory.</i> </p> <br><a class="btn btn-primary btn-block text-center" data-toggle="modal" href="#fbb6a3ea"><i class="fa fa-play"></i> START QUIZ!</a><div class="modal fade modal-slide-quiz" id="fbb6a3ea"> <div class="modal-dialog" style="width: 95vw; max-width: 960px"> <div class="modal-content"> <div class="modal-header slide-quiz-title"> <h4 class="modal-title" style="width: 100%;"> Objects in the universe <strong class="q-number pull-right"> <span class="counter">1</span>/<span class="total">1</span> </strong> </h4> </div> <div class="modal-body p-xs-3"> <div class="slide-quiz" data-stats="6-306-830" style="opacity: 0"> <div class="exercise shadow-bottom"><div class="q-question"><p>The size of the observable universe is:</p></div><div class="q-answer"><p><label class="radio"> <input type="radio"> <span>10<sup>56</sup> ly</span></label> </p><p><label class="radio"> <input type="radio"> <span>infinite</span></label> </p><p><label class="radio"> <input class="c" type="radio"> <span>10<sup>11</sup> ly</span></label> </p><p><label class="radio"> <input type="radio"> <span>10<sup>27</sup> ly</span></label> </p></div><div class="q-explanation"><p>The whole universe is infinite (probably). The observable universe is what we can see, in the order 10<sup>11</sup> ly. You will notice that this is larger than 13.8 billion years, the age of the universe, as photons were emitted before rapid expansion of the universe.</p></div><div class="slide-q-actions"><button class="btn btn-default btn-sm btn-xs-block text-xs-center check"><i class="fa fa-check-square-o"></i> Check</button></div></div><div class="exercise shadow-bottom"><div class="q-question"><p>The size of the universe is:</p></div><div class="q-answer"><p><label class="radio"> <input type="radio"> <span>10<sup>56</sup> ly</span></label> </p><p><label class="radio"> <input class="c" type="radio"> <span>infinite</span></label> </p><p><label class="radio"> <input type="radio"> <span>10<sup>11</sup> ly</span></label> </p><p><label class="radio"> <input type="radio"> <span>10<sup>27</sup> ly</span></label> </p></div><div class="q-explanation"><p>Probably!</p></div><div class="slide-q-actions"><button class="btn btn-default btn-sm btn-xs-block text-xs-center check"><i class="fa fa-check-square-o"></i> Check</button></div></div><div class="exercise shadow-bottom"><div class="q-question"><p>This photograph shows the constellation, Orion.</p><p style="text-align: center;"><img alt="" height="278" src="../../astro/orion_spinelli_c1.jpg" width="326"></p><p>The three bright stars in the centre of this photo are...</p></div><div class="q-answer"><p><label class="radio"> <input type="radio"> <span>the same distance from the Earth</span></label> </p><p><label class="radio"> <input type="radio"> <span>the same diameter</span></label> </p><p><label class="radio"> <input type="radio"> <span>close to each other</span></label> </p><p><label class="radio"> <input class="c" type="radio"> <span>unconnected</span></label> </p></div><div class="q-explanation"><p>Beware of confusing Astrophysics with Astrology.</p></div><div class="slide-q-actions"><button class="btn btn-default btn-sm btn-xs-block text-xs-center check"><i class="fa fa-check-square-o"></i> Check</button></div></div><div class="exercise shadow-bottom"><div class="q-question"><p>This illustration is a poor scale model of the solar system.</p><p style="text-align: center;"><img alt="" height="243" src="../../astro/solar-system.jpg" width="324"></p><p>Which of the following statements is not true about the planets?</p></div><div class="q-answer"><p><label class="radio"> <input class="c" type="radio"> <span>They are all solid</span></label> </p><p><label class="radio"> <input type="radio"> <span>They all orbit the Sun</span></label> </p><p><label class="radio"> <input type="radio"> <span>They are all roughly spherical</span></label> </p><p><label class="radio"> <input type="radio"> <span>They all dominate the gravitational field of their <span class="scayt-misspell-word" data-scayt-word="neighbourhood" data-wsc-lang="en_US">neighbourhood</span></span></label> </p></div><div class="q-explanation"><p>Taking these in turn:</p><ul><li>The planets have existed for long enough to have become roughly spherical due to gravitation, collisions and combinations.</li><li>The Sun is the most massive body in the solar system. All planets (and asteroids and comets) orbit the Sun.</li><li>Even the planets of lower mass dominate their neighbourhood, which is why we can observe them as distinct (rather than one among many asteroids).</li><li>Only Mercury, Venus, Earth and Mars are solid. The planets outward from Jupiter are made of gas.</li></ul></div><div class="slide-q-actions"><button class="btn btn-default btn-sm btn-xs-block text-xs-center check"><i class="fa fa-check-square-o"></i> Check</button></div></div><div class="exercise shadow-bottom"><div class="q-question"><p>This illustration is a poor scale model of the solar system.</p><p style="text-align: center;"><img alt="" height="243" src="../../astro/solar-system.jpg" width="324"></p><p>The furthest planet from the Sun is:</p></div><div class="q-answer"><p><label class="radio"> <input class="c" type="radio"> <span>Neptune</span></label> </p><p><label class="radio"> <input type="radio"> <span>Mars</span></label> </p><p><label class="radio"> <input type="radio"> <span>Jupiter</span></label> </p><p><label class="radio"> <input type="radio"> <span>Pluto</span></label> </p></div><div class="q-explanation"><p>Pluto is the object in this list that is furthest from the Sun. However, it was declassified as a planet on the basis of its smaller diameter (larger objects exist in the asteroid belt!).</p></div><div class="slide-q-actions"><button class="btn btn-default btn-sm btn-xs-block text-xs-center check"><i class="fa fa-check-square-o"></i> Check</button></div></div><div class="exercise shadow-bottom"><div class="q-question"><p>The time taken for light to cross the solar system is approximately...</p></div><div class="q-answer"><p><label class="radio"> <input type="radio"> <span>1 year</span></label> </p><p><label class="radio"> <input class="c" type="radio"> <span>1 day</span></label> </p><p><label class="radio"> <input type="radio"> <span>10 years</span></label> </p><p><label class="radio"> <input type="radio"> <span>1 second</span></label> </p></div><div class="q-explanation"><p>The diameter of solar system is about 1 light day.</p><p>A common piece of general knowledge is the time taken for light to travel from the Sun to the Earth: approximately 8 minutes. The solar system is much larger than this, but not so extreme as to take a year!</p></div><div class="slide-q-actions"><button class="btn btn-default btn-sm btn-xs-block text-xs-center check"><i class="fa fa-check-square-o"></i> Check</button></div></div><div class="exercise shadow-bottom"><div class="q-question"><p>The number of stars in a galaxy is approximately:</p></div><div class="q-answer"><p><label class="radio"> <input type="radio"> <span>10<sup>9</sup></span></label> </p><p><label class="radio"> <input class="c" type="radio"> <span>10<sup>11</sup></span></label> </p><p><label class="radio"> <input type="radio"> <span>10<sup>3</sup></span></label> </p><p><label class="radio"> <input type="radio"> <span>10<sup>6</sup></span></label> </p></div><div class="q-explanation"><p>There are hundreds of billions of stars in a typical galaxy.</p></div><div class="slide-q-actions"><button class="btn btn-default btn-sm btn-xs-block text-xs-center check"><i class="fa fa-check-square-o"></i> Check</button></div></div><div class="exercise shadow-bottom"><div class="q-question"><p>What is the correct sequence in the evolution of a star?</p></div><div class="q-answer"><p><label class="radio"> <input type="radio"> <span><span class="math-tex">\(\text{red giant - protostar - main sequence - supernova}\)</span></span></label></p><p><label class="radio"> <input class="c" type="radio"> <span><span class="math-tex">\(\text{protostar - main sequence - red giant - supernova}\)</span></span></label></p><p><label class="radio"> <input type="radio"> <span><span class="math-tex">\(\text{supernova - main sequence - protostar - red giant}\)</span></span></label></p><p><label class="radio"> <input type="radio"> <span><span class="math-tex">\(\text{main sequence - protostar - supernova - red giant}\)</span></span></label></p></div><div class="q-explanation"><p>A protostar has collapsed under gravity but not yet commenced nuclear fusion. The main sequence is the longest stage of the lifecycle, when gravitation balances with radiation pressure from fusion. A red giant comes next, followed by (for the largest stars) a supernova explosion.</p></div><div class="slide-q-actions"><button class="btn btn-default btn-sm btn-xs-block text-xs-center check"><i class="fa fa-check-square-o"></i> Check</button></div></div><div class="exercise shadow-bottom"><div class="q-question"><p>The size of a galaxy is approximately:</p><p style="text-align: center;"><img alt="" height="257" src="../../astro/andromeda-small.jpg" width="343"></p></div><div class="q-answer"><p><label class="radio"> <input class="c" type="radio"> <span>10<sup>5</sup> ly</span></label> </p><p><label class="radio"> <input type="radio"> <span>10<sup>7</sup> ly</span></label> </p><p><label class="radio"> <input type="radio"> <span>10 ly</span></label> </p><p><label class="radio"> <input type="radio"> <span>10<sup>3</sup> ly</span></label> </p></div><div class="q-explanation"><p>There are some galaxies with diameters larger and smaller than this, but the Milky Way has a diameter in the order 10<sup>5</sup> ly.</p></div><div class="slide-q-actions"><button class="btn btn-default btn-sm btn-xs-block text-xs-center check"><i class="fa fa-check-square-o"></i> Check</button></div></div><div class="exercise shadow-bottom"><div class="q-question"><p>How many Milky Ways are there in the observable universe?</p></div><div class="q-answer"><p><label class="radio"> <input type="radio"> <span>10<sup>6</sup></span></label> </p><p><label class="radio"> <input class="c" type="radio"> <span>1</span></label> </p><p><label class="radio"> <input type="radio"> <span>100</span></label> </p><p><label class="radio"> <input type="radio"> <span>10<sup>11</sup></span></label> </p></div><div class="q-explanation"><p> There are more than 10<sup>11</sup> galaxies. However, only one is called the Milky Way: ours.</p></div><div class="slide-q-actions"><button class="btn btn-default btn-sm btn-xs-block text-xs-center check"><i class="fa fa-check-square-o"></i> Check</button></div></div><p>. </p> </div> </div> <div class="modal-footer slide-quiz-actions"> <div class=""> <div class="pull-left pull-xs-none mb-xs-3"> <button class="btn btn-default d-xs-none btn-prev"> <i class="fa fa-arrow-left"></i> Prev </button> </div> <div class="pull-right pull-xs-none"> <button class="btn btn-success btn-xs-block text-xs-center btn-results" style="display: none"> <i class="fa fa-bar-chart"></i> Check Results </button> <button class="btn btn-default d-xs-none btn-next"> Next <i class="fa fa-arrow-right"></i> </button> <button class="btn btn-default btn-xs-block text-xs-center btn-close" data-dismiss="modal" style="display: none"> Close </button> </div> </div> </div> </div> </div></div> </div> </div> <div class="panel-footer"> <div> </div> </div> </div> <div class="page-container panel-self-assessment" data-id="830"> <div class="panel-heading">MY PROGRESS</div> <div class="panel-body understanding-rate"> <div class="msg"></div> <label class="label-lg">Self-assessment</label><p>How much of <strong>Objects in the universe</strong> have you understood?</p><div class="slider-container text-center"><div id="self-assessment-slider" class="sib-slider self-assessment " data-value="1" data-percentage=""></div></div> <label class="label-lg">My notes</label> <textarea name="page-notes" class="form-control" rows="3" placeholder="Write your notes here..."></textarea> </div> <div class="panel-footer text-xs-center"> <span id="last-edited" class="mb-xs-3"> </span> <div class="actions mt-xs-3"> <button id="save-my-progress" type="button" class="btn btn-sm btn-primary text-center btn-xs-block"> <i class="fa fa-fw fa-floppy-o"></i> Save </button> </div> </div></div> <div id="modal-feedback" class="modal fade" tabindex="-1" role="dialog"> <div class="modal-dialog" role="document"> <div class="modal-content"> <div class="modal-header"> <h4 class="modal-title">Feedback</h4> <button type="button" class="close hidden-xs hidden-sm" data-dismiss="modal" aria-label="Close"> <span aria-hidden="true">×</span> </button> </div> <div class="modal-body"> <div class="errors"></div> <p><strong>Which of the following best describes your feedback?</strong></p> <form method="post" style="overflow: hidden"> <div class="form-group"> <div class="radio"><label style="color: #121212;"><input type="radio" name="feedback-type" value="Recommendation"> Recommend</label></div><div class="radio"><label style="color: #121212;"><input type="radio" name="feedback-type" value="Problem"> Report a problem</label></div><div class="radio"><label style="color: #121212;"><input type="radio" name="feedback-type" value="Improvement"> Suggest an improvement</label></div><div class="radio"><label style="color: #121212;"><input type="radio" name="feedback-type" value="Other"> Other</label></div> </div> <hr> <div class="row"> <div class="col-md-6"> <div class="form-group"> <label for="feedback-name">Name</label> <input type="text" class="form-control" name="feedback-name" placeholder="Name" value=" "> </div> </div> <div class="col-md-6"> <div class="form-group"> <label for="feedback-email">Email address</label> <input type="email" class="form-control" name="feedback-email" placeholder="Email" value="@airmail.cc"> </div> </div> </div> <div class="form-group"> <label for="feedback-comments">Comments</label> <textarea class="form-control" name="feedback-comments" style="resize: vertical;"></textarea> </div> <input type="hidden" name="feedback-ticket" value="082b9c9c4ae3624d"> <input type="hidden" name="feedback-url" value="https://studyib.net/physics/page/830/objects-in-the-universe"> <input type="hidden" name="feedback-subject" value="6"> <input type="hidden" name="feedback-subject-name" value="Physics"> <div class="pull-left"> </div> </form> </div> <div class="modal-footer"> <button type="button" class="btn btn-primary btn-xs-block feedback-submit mb-xs-3 pull-right"> <i class="fa fa-send"></i> Send </button> <button type="button" class="btn btn-default btn-xs-block m-xs-0 pull-left" data-dismiss="modal"> Close </button> </div> </div> </div></div> <div id="fc-viewer" class="modal fade modal-flashcard" tabindex="-1" role="dialog"><div class="modal-dialog" role="document"><div class="modal-content"><div class="modal-header" style="background-color: #fafafa;"><div class="row" style="width: 100%;"><div class="col-md-12 tags-heading"><div style="display: flex; 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