1. The Universe
Integrated Science I

2. What is the Big Bang Theory?
The Big Bang Model the most widely accepted theory for the start of our universe
It hypothesizes that the universe began 12 to 14 billion years ago
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

3. Continued…
Then it suddenly exploded – 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 and it kept on growing at a fantastic rate
It is still expanding today
After the big bang, the universe expanded quickly (and continues to expand) and then cooled down enough for atoms to form.
Gravity pulled the atoms together into gas clouds that eventually became stars, which comprise young galaxies

4. How Do We Know the Universe is Expanding?
Remember this!!?!
The Doppler Effect! It isn’t going away…

5. How Does The Doppler Effect relate to the Universe Expanding?
Stars and galaxies are not getting bigger; rather, the space between all objects is expanding with time
The expansion of the universe was discovered in 1929, by American astronomer Edwin Hubble
When Edwin Hubble, the astronomer for whom the Hubble Space Telescope is named, measured the spectrum of distant stars and galaxies, he observed extra amounts of red light (red shifting). 

6. What is the red shift?
Red shift occurs when a light-emitting body moves away from us. Light waves traveling in front of a body bunch up as it travels; light waves at the trailing end stretch out. The stretched-out light waves are said to be red shifting. Hubble concluded that the red shift means the stars and galaxies are actually moving away, which led him to develop the theory of an expanding universe. 

7. Expansion of the Universe
Proven by the Doppler shift
Starlight moving towards Earth is bluish
Starlight moving away from Earth is reddish
All galaxies outside the our galaxy indicate a red shift – therefore they are moving away from us

8. galaxies
A galaxy is a group of billions of individual stars, star systems, star clusters, dust and gas (hydrogen and helium) bound together by gravity
There are billions of galaxies in the universe, and they are classified by size and shape
Earth is in the Milky Way galaxy
There are about 200 billion stars in the Milky Way
100,000 light years wide!

9. Different Types of Galaxies
There are 3 types of galaxies: elliptical, spiral, and irregular
Elliptical
Most common type of galaxy
Shaped like large, 3-D ellipse (looks like a football)
Spiral (like the Milky Way) – have spiral arms that wind out, youngest stars at the center of the spiral
Normal – arms start close to center
Barred – arms extend from a large bar
Irregular – many different shapes
Smaller and less common

11. Stars
When heated to a sufficiently high temperature by gravitational attraction, stars begin nuclear reactions (NUCLEAR FUSION!), which convert matter to energy and fuse the lighter elements into heavier ones
These and other fusion processes in stars have led to the formation of all the other elements (heavier ones than Hydrogen and Helium)
All of the elements, except for hydrogen and helium, originated from the nuclear fusion reactions of stars

12. Lifetime of a star
The overall lifespan of a star is determined by its mass
Stars spend roughly 90% of their lives burning hydrogen into helium on the main sequence
Massive stars need higher central temperatures and pressures to support themselves against gravitational collapse, and for this reason, fusion reactions in these stars proceed at a faster rate than in lower mass stars
IMPORTANT: The result is that massive stars use up their core hydrogen fuel rapidly and spend less time on the main sequence before evolving into a red giant star.

13. How to Classify Stars
Stars are classified by their color, size, luminosity and mass
A Hertzprung-Russell (H-R) diagram must be used to estimate the sizes of stars and predict how stars will evolve
Most stars fall on the main sequence of the H-R diagram
A diagonal band running from the bright hot stars on the upper left to the dim cool stars on the lower right

14. Hertzsprung-Russell Diagram
Supergiants
Where is our Sun?
-Main Sequence
Brightness
Main Sequence
Giants
White Dwarfs
Temperature

15. Lifetime of a Star
When hydrogen fuel is used up, nuclear fusion can no longer occur and the star begins to “die”
Stages of a Low-mass star’s life:
Nebula – star beginning, a cloud of gas and dust condense together
Main Sequence – fusion causes pressure that is balanced
-A star’s mass determines the star’s place on the main sequence and how long it will stay there
Giant – when hydrogen is exhausted, a balance no longer exists, star expands and cools
White Dwarf – after core uses up helium, expands more and outer layers escape into space, leaving a very hot, dense core (about the size of Earth)
** If the star is a high-mass star, it could become a black hole