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Galaxies • The basic structural unit of matter in the universe is the galaxy • A galaxy is a collection of billions of _____________ stars , gas, and dust held together by gravity ____________________ • An average galaxy will have over ___________________________ billion stars 100 Galaxies • Galaxies are classified by their shape • The three most common shapes are: – ________________________ Elliptical (football shaped) – ________________________ Irregular – ________________________ Spiral **based on the speed at which they rotate Milky Way Galaxy spiral • Our solar system is part of a ________________ galaxy called the Milky Way Galaxy • The Milky Way galaxy has about _________ billion stars fast • It is rotating very ___________ 200 Milky Way Galaxy 2 main spiral “arms” Stars •https://www.youtube.co m/watch?v=5az0W4Y1n uU Stars • The majority of the visible matter in the universe is made up of gas clouds, dust, and stars ____________ • Definition: gas held together by – A star is a large ball of __________ gravity – Stars produce tremendous amount of ________________ energy and shine Stars • The majority of the visible matter in the universe is made up of gas clouds, dust, and stars ____________ • Definition: gas held together by – A star is a large ball of __________ gravity – Stars produce tremendous amount of ________________ energy and shine Sun • The star associated with the Earth and the Sun rest of our Solar System is called the ________ • The Sun is the main gravitational ____________ force holding the Solar System together • Most stars have a solar system revolving around it Energy in Stars • Stars produce a tremendous amount of energy! • Stars create energy as a result of nuclear cores fusion in their ___________ Nuclear Fusion • Nuclear Fusion is the process of combining smaller atoms to the nuclei of two ____________________________ create an atom with one larger nuclei Nuclear Fusion • What is a nucleus? – Dense region at the center of an atom that neutrons consists of protons _______________ and __________________ • Let’s look at an atom vof Hydrogen! Nuclear Fusion • Below is an atom of Hydrogen: How many protons are in the nucleus? 1! Nuclear Fusion • During Nuclear Fusion, two Hydrogen atoms will be combined to form an atom with 2 protons in its nucleus + = Nuclear Fusion • During the combination of nuclei, some of mass left over is converted into the ____________ energy _________________ • Our Sun converts hydrogen nuclei into helium nuclei similar to the example Nuclear Fusion • Nuclear Fusion can only occur in extremely temperature and high high ________________________ pressure conditions ____________________ • http://www.bing.com/videos/search?q=nucl ear+fusion+in+stars+youtube&qpvt=nuclear+ fusion+in+stars+youtube&FORM=VDRE#view =detail&mid=97FD5A55FA8317BCF55597FD5 A55FA8317BCF555 Star Classification • Stars are classified by two main conditions: 1. Surface Temperature 2. Luminosity Surface Temperature • The differences of surface temperature of color stars is reflected by their ______________ Think about a candle flame, the hottest part is the closest to the wick – which is blue! The same pattern can be seen with stars. The hotter the star, the bluer it appears. Less hot stars are more yellow/orange. Luminosity • Luminosity is the ___________________ brightness of a star • However, when we observe distant stars from Earth, we are seeing its apparent brightness, not its luminosity • The farther the star is away from us, the less bright it will appear __________ Characteristics of Stars • Reference Table – Page 15! • Characteristics of Stars 1. Look at the X axis, what is the variable? What is it measured in? 2. Look at the Y axis, what is the variable? 3. As you increase along the X axis, what happens to temperature? Characteristics of Stars 4. Which star is more luminous – Alpha Centauri or Rigel? 5. Which star has a higher surface temperature – Spica or Polaris? 6. Read what’s in the parenthesis under Luminosity – explain why this is so. 7. Find Polaris on the table. Does it have a high luminosity? Is this what you would have expected? Characteristics of Stars 8. What is the approximate color of Procyon B? 9. Is there any relationship between luminosity and color of the star? Star Types • There are 5 main types of stars: – Main Sequence Stars – Giant Stars – Super Giants – White Dwarfs – Black Dwarfs Main Sequence • About 90% of all stars are Main Sequence stars • Main Sequence stars are generally average _____________ size • For all Main Sequence stars, as surface temperature starts to increase, luminosity increases also _________________ • Most stars spend the majority of their life as Main Sequence stars Main Sequence • The increase in luminosity that Main Sequence stars go through is a result of its temperature increasing ________________________ • Our Sun is a Main Sequence star of yellow ____________ color Giant Stars • Giant Stars are often referred to as “The Red Giants” because of their _________________________________ red and orange coloring • These stars are extremely large! (about 10x the diameter of the Sun) • They have an extremely high luminosity __________________ but a low temperature Super Giants • Super Giant Stars can be anywhere from 100 to __________ times the diameter of the Sun! • These stars are extremely luminous • Super Giants usually explode in a tremendous event called a supernova _______________________ • In order for a star to eventually become a Super Giant, it must have started out much larger than the Sun 1000 White Dwarfs • White Dwarfs are _____________! small • They are usually about the size of the Earth • White Dwarfs can be anywhere from white to _________ blue in color low in luminosity • They are very hot but ________ • Represent the last luminous stage of a star Black Dwarfs • When a White Dwarf cools and no longer energy it is considered a emits any ______________-, “dead” star – or a Black Dwarf • These stars have stopped nuclear fusion and no longer produce any nuclear energy dense • They are extremely ____________ Life of a Star • https://www.youtube.com/watch ?v=PM9CQDlQI0A Life Cycle of Stars • Stars, like many objects on Earth, have a evolution of features, beginning, an _________________ and an ending • Just like us, stars are“born” ___________ Star Birth dust and • Stars originate from clouds of __________ gas molecules • These star forming clouds are called nebulas __________________ Nebulas • Nebulas were created from the masses of _________________ matter that were released during the Big Bang • Eventually, some of the gas and dust particles clump together in a nebula will begin to _____________ • As these clumps gain more mass, they build gravitational pull that up a stronger __________________________ causes more and more matter to be sucked into it Nebulas • Once this mass gains enough size (reaches about the size of Jupiter), the gravitational pull results in high enough temperature _____________________ and ___________________ pressure to start nuclear fusion! shine as it • The ball then begins to _____________ radiates energy --- thus, a star is born! Nebulas Main Sequence • Every star begins its journey on the Main Sequence after it is created in a nebula • All stars spend most of their lives as a Main Sequence star • These stars will range greatly in their mass __________,which will affect the rest of their lives Smaller Stars • Stars with a mass similar to our Sun and smaller will spend billions of years as a Main Sequence star and eventually will become a _____________________ Red Giant hotter and • As these stars age, they get ______________ luminous more ___________________ Smaller Stars • After billions of years, these stars eventually use up most of their nuclear fuel used for fusion and collapse to form a ____________ __________________________ White Dwarf • They will then slowly die as they run out of nuclear fuel completely and become a Black Dwarf ________________________ Smaller Stars dense • These Black Dwarfs are extremely ____________ and have a very strong gravitational pull light • However, they no longer emit any __________ because nuclear fusion has stopped Smaller Stars Gas and dust cloud - Nebula Black Dwarf Main Sequence Star Red Giant White Dwarf Red Super Giant Larger Stars 1.5 • Larger stars are any star that is ________times the mass of our Sun shorter • These stars exist for much _______________ periods of time (approximately 100 million years) large Main • These stars start as very ___________ Sequence stars Larger Stars Super Giants • Next, they become _________________________ explode in an event • They eventually ___________________ called a Supernova Larger Stars explosion • A supernova is a stellar __________________ • When nuclear fusion no longer takes place in collapses and the stars core, the core _________________ releases a huge about of energy • A Supernova will occur about once every 50 years in a galaxy the size of the Milky Way – which means they occur about every second in the universe! Larger Stars rapidly • During a Supernova, the star _____________ collapses, forming a mass much smaller than a White Dwarf dense that only • They get so small and ____________ neutrons can exist – these are called _________________________ Neutron Stars Larger Stars Gas and dust cloud - Nebula Main Sequence Star Red Super Giant Supernova Neutron Star HUGE Stars • When the most massive stars collapse, the density is so large that an extreme ______________ gravity field is created light or any form of energy can • No ____________ escape Black Hole • This is called a _____________________