Download Why Is the Sun a Star

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?