Why Is the Sun a Star?
The Sun is the center of our Solar System. It is so massive that its strong gravity attracts all the planets and their moons, comets, asteroids and meteors into orbit around it. Its light provides Earth with 99% of all the energy used on our planet and we see its reflected light on all the planets as far away as Pluto and beyond when we look up at the night sky. But what makes it a star? If an object is massive enough its gravity will be strong enough to begin crushing the matter at the core and a star is “born”. Imagine that we could pile everything we could get our hands on and throw it into a pile in the center of the grass field at school. Eventually if our pile got big enough, the gravity from the mass (the amount of matter) of all that “stuff” would begin crushing the matter at its core and we would create a star! But it would be a pile of stuff many thousands of times the mass of the Earth! When those atoms (matter is atoms!) are crushed together their nuclei fuse (protons and neutrons crushed together) and a tiny bit of the atoms are converted into a fantastic amount of energy that radiates out as light. This most fundamental of all the properties of our Universe is called nuclear fusion. Einstein discovered the equation that describes what happens: E=mc2. The equation says that a tiny bit of matter can become a huge amount of energy! Any object can become a star if it becomes massive enough. How massive is enough? If Jupiter were about 75 times more massive its gravity would increase enough for nuclear fusion to begin and we would have a second Sun in our solar system! Interestingly, scientists recently discovered a new class of stars that are between 20 – 70 Jupiter masses that are fusing some atoms and radiating some energy, but not in the fantastic amounts like true stars. These stars are known as brown dwarfs since they emit some light but are not as bright as the smallest true stars. They are dimly glowing like a cooling campfire ember. When you look out into the night sky across vast light years of distance, remember that each star is another “Sun” and that some are much larger and some much smaller. And many, if not most of those other “Suns” have planets of their own and so they are “solar” systems too. Our Sun is comfortably right in the middle of the range (it’s an average star) in terms of its mass and size, and lucky for us, it’s perfect for life as we know it on Earth.
Answer the questions below based on what you read.
1. What is the center of our solar system? What astronomical objects does the Sun attract due to its strong gravity?
3. What percentage of the Earth’s energy is provided by the Sun? When we see the planets shining in the night sky what light are we seeing reflected back at us?
5. Gravity and mass (the amount of matter that makes up an object) are related. How?
6. Stars are not alive, although we say a star is “born” when what begins to happen to matter at its core?
7. How could we make a star? How big would our pile of “stuff” have to be?
8. What does the word mass mean? What is the scientific word for “stuff”?
9. Describe what happens during the fundamental process of nuclear fusion?
10. Who discovered the equation that describes nuclear fusion? What is the equation?
11. How many masses of Jupiter are needed to make a star?
12. What are brown dwarfs? What is the range of Jupiter masses for brown dwarfs?
13. Do other stars have their own planets? What kind of star is our Sun?
Sketch the Sun
Draw the picture of the Sun on page 549 in the textbook. You don’t have to color your picture, unless you want to, and your picture does not have to be perfect. Just do the best you can. Be sure to label all the parts of the Sun as shown on page 549. Finally answer the questions below.
1. Where does nuclear fusion occur in the Sun?
2. What zone of the Sun radiates electromagnetic radiation (light!)? How long can it take electromagnetic radiation to move through this zone?
3. What layer of the Sun has gasses rising and cooling?
4. What two features of the Sun’s atmosphere can be seen during a total solar eclipse?
5. How do sunspots demonstrate the Sun rotates on an axis? Sunspots vary over how many years?