Galaxies The basic structural unit of matter in the universe is the galaxy A galaxy is a collection of billions of _____________, gas, and dust held together by ____________________ An average galaxy will have over ___________________________ stars stars gravity 100 billion

Galaxies Galaxies are classified by their shape The three most common shapes are: – ________________________ (football shaped) – ________________________ **based on the speed at which they rotate Elliptical Irregular Spiral

Milky Way Galaxy Our solar system is part of a ________________ galaxy called the Milky Way Galaxy The Milky Way galaxy has about _________ billion stars It is rotating very ___________ spiral 200 fast

Milky Way Galaxy 2 main spiral “arms”

Stars

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Stars The majority of the visible matter in the universe is made up of gas clouds, dust, and ____________ Definition: – A star is a large ball of __________ held together by gravity – Stars produce tremendous amount of ________________ and shine stars gas energy

Stars The majority of the visible matter in the universe is made up of gas clouds, dust, and ____________ Definition: – A star is a large ball of __________ held together by gravity – Stars produce tremendous amount of ________________ and shine stars gas energy

Sun The star associated with the Earth and the rest of our Solar System is called the ________ The Sun is the main gravitational ____________ holding the Solar System together Most stars have a solar system revolving around it Sun force

Energy in Stars Stars produce a tremendous amount of energy! Stars create energy as a result of nuclear fusion in their ___________ cores

Nuclear Fusion Nuclear Fusion is the process of combining the nuclei of two ____________________________ to create an atom with one larger nuclei smaller atoms

v Nuclear Fusion What is a nucleus? – Dense region at the center of an atom that consists of _______________ and __________________ Let’s look at an atom of Hydrogen! protonsneutrons

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 the ____________ left over is converted into _________________ Our Sun converts hydrogen nuclei into helium nuclei similar to the example mass energy

Nuclear Fusion Nuclear Fusion can only occur in extremely high ________________________ and high ____________________ conditions temperature pressure

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Star Classification Stars are classified by two main conditions: 1.Surface Temperature 2.Luminosity

Surface Temperature The differences of surface temperature of 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. color

Luminosity Luminosity is the ___________________ 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 __________ bright it will appear brightness less

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 _____________ For all Main Sequence stars, as surface temperature starts to increase, luminosity also _________________ Most stars spend the majority of their life as Main Sequence stars size increases

Main Sequence The increase in luminosity that Main Sequence stars go through is a result of its increasing ________________________ Our Sun is a Main Sequence star of ____________ color temperature yellow

Giant Stars Giant Stars are often referred to as “The Red Giants” because of their _________________________________ coloring These stars are extremely large! (about 10x the diameter of the Sun) They have an extremely high __________________ but a low temperature red and orange luminosity

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 _______________________ In order for a star to eventually become a Super Giant, it must have started out much larger than the Sun supernova 1000

White Dwarfs White Dwarfs are _____________! They are usually about the size of the Earth White Dwarfs can be anywhere from white to _________ in color They are very hot but ________ in luminosity Represent the last luminous stage of a star small low blue

Black Dwarfs When a White Dwarf cools and no longer emits any ______________-, it is considered a “dead” star – or a Black Dwarf These stars have stopped nuclear fusion and no longer produce any nuclear energy They are extremely ____________ energy dense

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Life Cycle of Stars Stars, like many objects on Earth, have a beginning, an _________________ of features, and an ending Just like us, stars are ___________ evolution “born”

Star Birth Stars originate from clouds of __________ and gas molecules These star forming clouds are called __________________ dust nebulas

Nebulas Nebulas were created from the masses of _________________ that were released during the Big Bang Eventually, some of the gas and dust particles in a nebula will begin to _____________ together As these clumps gain more mass, they build up a stronger __________________________ pull that causes more and more matter to be sucked into it matter clump gravitational

Nebulas Once this mass gains enough size (reaches about the size of Jupiter), the gravitational pull results in high enough _____________________ and ___________________ to start nuclear fusion! The ball then begins to _____________ as it radiates energy --- thus, a star is born! temperature pressure shine

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 __________,which will affect the rest of their lives mass

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 _____________________ As these stars age, they get ______________ and more ___________________ Red Giant hotter luminous

Smaller Stars After billions of years, these stars eventually use up most of their nuclear fuel used for ____________ and collapse to form a __________________________ They will then slowly die as they run out of nuclear fuel completely and become a ________________________ fusion White Dwarf Black Dwarf

Smaller Stars These Black Dwarfs are extremely ____________ and have a very strong gravitational pull However, they no longer emit any __________ because nuclear fusion has stopped dense light

Smaller Stars Gas and dust cloud - Nebula Main Sequence Star Red Giant Red Super Giant White Dwarf Black Dwarf

Larger Stars Larger stars are any star that is ________times the mass of our Sun These stars exist for much _______________ periods of time (approximately 100 million years) These stars start as very ___________ Main Sequence stars 1.5 shorter large

Larger Stars Next, they become _________________________ They eventually ___________________ in an event called a Supernova Super Giants explode

Larger Stars A supernova is a stellar __________________ When nuclear fusion no longer takes place in the stars core, the core _________________ and 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! explosion collapses

Larger Stars During a Supernova, the star _____________ collapses, forming a mass much smaller than a White Dwarf They get so small and ____________ that only neutrons can exist – these are called _________________________ rapidly dense 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 ______________ is so large that an extreme gravity field is created No ____________ or any form of energy can escape This is called a _____________________ density light Black Hole