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

starsgravity100 billion

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

EllipticalIrregularSpiral

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 ___________

spiral200

fast

Milky Way Galaxy2 main spiral

“arms”

Stars

•https://www.youtube.com/watch?v=5az0W4Y1nuU

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

starsgas

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

starsgas

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

Sunforce

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!protons neutrons

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

massenergy

Nuclear Fusion• Nuclear Fusion can only occur in extremely

high ________________________ and high ____________________ conditions

temperaturepressure

• http://www.bing.com/videos/search?q=nuclear+fusion+in+stars+youtube&qpvt=nuclear+fusion+in+stars+youtube&FORM=VDRE#view=detail&mid=97FD5A55FA8317BCF55597FD5A55FA8317BCF555

Star Classification• Stars are classified by two main conditions:

1. Surface Temperature2. 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

temperatureyellow

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

lowblue

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

Life of a Star• https://www.youtube.com/watch?v=PM9CQDlQI0A

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

clumpgravitational

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!

temperaturepressure

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 livesmass

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 Gianthotter

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 ________________________

fusionWhite DwarfBlack 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

denselight

Smaller StarsGas 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

1.5shorter

large

Larger Stars• Next, they become _________________________• They eventually ___________________ in an event

called a Supernova

Super Giantsexplode

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!

explosioncollapses

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

denseNeutron Stars

Larger StarsGas 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 _____________________

densitylight

Black Hole