1. 8.8 A and B Components the Universe and the Sun
The student is expected to describe components of the universe, including stars, nebulae, and galaxies, and use models such as the Hertzsprung-Russell Diagram for classification.
AND
recognize that the Sun is a medium-sized star near the edge of a spiral- shaped galaxy of stars, and that the Sun is many thousands of times closer to Earth than any other star.

2. The Universe
The universe is all of space, time, matter, and energy that exist.

3. Components of the Universe-Galaxies
Billions of galaxies in the universe
Each galaxy contains billions of stars, dust, and gas.
Stars, gas and dust are held together in a galaxy by the force of gravity.
The 3 main types of galaxies are spiral, elliptical, and irregular.

4. Milky Way Galaxy
Our solar system consists of the Sun, its planets, moons, and other celestial objects.
Our Sun is located in an outer arm of the Milky Way, which is a spiral galaxy.

5. Milky Way Galaxy
Since Earth is a part of the Milky Way galaxy, we cannot see its entire shape.
This is similar to the fact that you cannot see your entire body (unless you are looking in the mirror) because you are contained inside your body.

6. Stars
A star is a large ball of gas that generates its own energy and is held together by its own gravity.
Stars fuse hydrogen gas into helium, releasing massive amounts of heat and light in the process.
Some are very luminous (bright); others are dimmer.
Their colors range from blue and white to yellow and red

7. Stars Some are very large, whereas others are relatively small.
Some are extremely hot; others are cooler. Some emit great amounts of energy; others emit less energy.
Stars may be young, middle-aged, old, or dying.
They may be composed primarily of hydrogen, or they may contain mostly helium and heavier elements

8. Hertzsprung-Russell Diagram- a way to classify stars according to their luminosity, temperature, and color

9. H-R Diagram
Stars in the main sequence make up the vast majority of stars in the universe. In general, the hotter a star is on the main sequence, the brighter and bluer it is.
As stars age, they fall outside the main sequence and become giants or supergiants, depending on their mass.
As less-massive stars die, they become relatively tiny white dwarfs.
More massive stars die by exploding into a powerful supernova.

10. Life Cycle of Stars
Hot clouds of gaseous elements and compounds called nebulae serve as nurseries for stars.
As these nebulae spin, they slowly condense, raising their temperature and forming protostars, or beginning stars.

11. Life Cycle of Stars
Fill out the graphic organizer for the Life Cycle of Stars and glue into your notebook.
Note that the small/medium stars have a different cycle from massive stars, but they both begin as protostars in nebulae.

12. Practice with Hertzsprung Russell
Use the H-R diagram to answer the questions on the HR Worksheet.
Then answer the fundamental questions.

13. The Sun
Sun is a medium-sized star located near the edge of the Milky Way
The Sun appears brighter than any other star because it is many thousands of times closer to Earth than any other star.
The Sun is a yellow main sequence star.
According to the H-R diagram, the Sun’s surface temperature is between 5000K and 7500K
The Sun is the central gravitational point in our solar system

14. The Sun
It takes about 8.3 minutes for light from the Sun to travel the approximately 150 million kilometer distance between the Sun and Earth. This distance is called 1 astronomical unit (AU).
Light from all other stars takes much longer to reach Earth because the Sun is many thousands of times closer to Earth than any other star.

15. Fundamental Questions:
What are the components of the universe?
All space, time, matter, and energy.
What are the components of a galaxy?
Galaxies are composed of billions of stars along with dust, gas, and other objects such as planets.
What are the 3 main types of galaxies and what is the name of our galaxy?
They are elliptical, irregular, and spiral. Ours is the Milky Way.
Where are we located within the Milky Way?
We are located in an outer arm of the spiral.

16. Fundamental Questions:
What are nebulae and why are they important to the life cycle of a star? Nebulae are clouds of dust and interstellar gas. They are important because all stars begin as stellar nebulae.
What is the first stage of any star’s life cycle?
Stellar nebulae
Describe the life cycle for a small/medium star.
Stellar nebula to average star to red giant to planetary nebula to white dwarf

17. Fundamental Questions
Describe the life cycle of a large star.
Stellar nebula to massive star to red supergiant to supernova to either black home or neutron star.
What gaseous element fuels a star through nuclear fusion, and what type of gas does it become?
Hydrogen fuels the star when it undergoes fusion to form helium.
What 3 characteristics are used to classify stars on the H-R diagram?
Surface temperature, luminosity, and color
What have scientists learned about stars by classifying them on the H-R diagram? Most stars spend most of their life on the main sequence. Within the main sequence the hotter the surface temperature of the star, the more luminous the star.

18. Fundamental Questions
The Sun is a medium sized, main sequence star. Describe its location on the H-R diagram in terms of luminosity, temperature, and color.
It has medium luminosity and surface temperature and yellow color.
Why does the Sun appear brighter to us than all other stars?
It is closest to us.
How long does it take for the light emitted from the Sun to reach the Earth?
It takes about 8 minutes to reach the Earth.

19. Fundamental Questions
Why can we only see a portion of the Milky Way Galaxy from Earth?
We are a part of the Milky Way, so we can never see the entire galaxy, just a portion of it.
Where is the Sun found within the Milky Way Galaxy?
It is found in an outer arm of the spiral.