According to modern science, approximately how old is the Sun?
4 1/2 Billion years (It is the same age as the rest of our solar system, which from earlier chapters is 4.5 billion years.)
The Sun will exhaust it's nuclear fuel in about ____?
5 billion years (The Sun's total life time is about 10 billion years, and the Sun I only halfway through this lifetime at present.)
What is the process of gravitational contraction that can make a star hot?
When a star contracts in size, gravitational potential energy is converted to thermal energy. (This process is called gravitational contraction because gravity is what makes the star contract.)
What two physical processes balance each other to create the condition known as gravitational equilibrium in stars?
Gravitational force and outward pressure. (This dynamic is important for understanding stellar structure and stellar evolution.)
The source of energy that keeps the Sun shining today is ____.
Nuclear fusion. (The Sun shines by fusing hydrogen into helium, a process in which a small amount of the mass is converted into energy.)
Energy balance in the Sun refers to a balance between____.
The rate at which fusion generates energy in the Sun's core and the rate at which the sun's surface radiates energy into space. (Together, energy balance and gravitational equilibrium keep the Sun stable.)
When we say that the Sun is a ball of Plasma, we mean that____.
The Sun consists of gas in which many or most of the atoms are ionized [missing electrons]. (A plasma is an ionized gas, and the Sun is so hot that most of its gas is ionized.)
What is the Sun made of (by mass)?
70% hydrogen, 28% helium, 2% other elements. (This is also the approximate overall chemical composition of the Milky Way Galaxy and the rest of the universe today.)
From the center outward, what are the "layers" of the Sun in the correct order?
Core, radiation alone, convection zone, photosphere, chromosphere, and corona.
What are the appropriate units for the Sun's luminosity?
Watts. (Luminosity measures energy output per second, which corresponds to units of watts.)
The Sun's surface, as we see it with our eyes, is called the _____.
Photosphere. (The prefix photo means "light"- usually taken to imply visible light- so the photosphere is the visible surface (sphere) of the Sun.)
The Sun's average surface (photosphere) temperature is about ______.
5,800 K. (Note that this is a temperature at which most thermal radiation is in the visible part of the spectrum- which is why the Sun radiates most of its energy as visible light.)
What is the solar wind?
A stream of charged particles flowing outward from the surface of the Sun.
The fundamental nuclear reaction occurring in the core of the Sun is____.
Nuclear fusion of hydrogen into helium.
The proton-proton chain is ____.
The specific set of nuclear reactions through which the Sun fuses hydrogen into helium.
The overall result of the proton-proton chain is:
4H becomes 1He+energy.
To estimate the central temperature of the Sun, scientists _____.
Use computers models to predict interior conditions.
Why are neutrinos so difficult to detect?
They have a tendency to pass through just about any material without any interactions.
The light radiated from the Sun's surface reaches Earth in about 8 minutes, but the energy of that light was released by fusion in the solar core about _____.
A few hundred thousand years ago.
What happens to energy in the Sun's convection zone?
Energy is transported outward by the rising of hot plasma and sinking of cooler plasma.
What do sunspots, solar prominences, and solar flares all have in common?
They are all strongly influenced by magnetic fields on the Sun.
What is not a characteristic of the 11-year sunspot cycle?
The sunspot cycle is vey steady, so that each 11-year cycle is nearly identical o every other 11-year cycle.
How is the sunspot cycle directly relevant to us here on Earth?
Coronal mass ejections and other activity associated with the sunspot cycle can disrupt radio communications and knock out sensitive electronic equipment.
In the late 1800s, Kelvin and Helmholtz suggested that Sun stayed hot due to gravitational contraction. What is the major drawback to this idea?
It predicted that the Sun could shine for about 25 million years, but geologists had already found thy Earth I much older than this.
When is/was gravitational contraction an important energy generation mechanism for the Sun?
It was important when the Sun was forming from a shrinking interstellar cloud of gas.
What do we mean when we say that the Sun is in gravitational equilibrium?
There is a balance within the Sun between the outward push of pressure and the inward pull of gravity.
Which of the following is the best answer to the question, "Why does the Sun shine?"
As the Sun was forming, gravitational contraction increased the Sun's temperature until the core became hot enough for nuclear fusion, which ever since has generated the heat that makes the Sun shine.
How does the Sun's mass compare to Earth's mass?
The Sun's mass is about 300,00 times the mass of the Earth.
Which of the following best describes why the Sun emits most o it's energy in the form of visible light?
Lil all objects, the Sun emits thermal radiation with a spectrum that depends on its temperature, an the Sun's surface temperature is just right for emitting mostly visible light.
The Sun's surface seethes and churns with a bubbling pattern. Why?
We are seeing hot gas rising and cool gas falling due to the convection that occurs beneath the surface.
What correctly compares the Sun's energy generation process to the energy generation process in human-built nuclear power plants?
The Sun generates energy by fusing small nuclei into larger ones, while our power plants generate energy by the fission of large nuclei.
Every second, the Sun converts about 600 million ons of hydrogen into 596 million tons of helium. The remaining 4 million ton of mass is _____.
Converted to an amount of energy equal to 4 million tons times the speed of light squared.
What best explains why nuclear fusion requires bringing nuclei extremely close together?
Nuclei normally repel because they are all positively charged and can be made to stick only when brought close enough for the strong force to take hold.
If the Sun's core suddenly shrank a little bit, what would happen to the Sun?
The core would heat up, fusion rates would increase, the core would re-expand.
Why does the Sun emit neutrinos?
Fusion in the Sun's core creates neutrinos.
If the Sun suddenly stopped emitting neutrinos, what might we infer?
Fusion reactions in the Sun have ceased.
Why do sunspots appear dark in pictures of the Sun?
They actually are fairly bright, but appear dark against the even brighter background of the surrounding photosphere.
The star Alpha Centauri A is the same type of star as the Sun, but it's luminosity is about 1.6 times that of the Sun. What can be concluded?
Alpha Centauri A fuses hydrogen into helium in its core at a higher rate than our Sun.
How can we beat observe the Sun's chromosphere and corona?
The chromosphere is best observed with ultraviolet telescopes and the corona is best observed with X-ray telescopes.
The intricate patterns visible in an X-ray image of the Sun generally show _____.
Extremely hot plasma flowing along magnetic field lines.
How can we measure the strength f magnetic fields on the Sun?
By looking for the splitting of spectral lines in the Sun's spectrum.
Satellites in low-Earth orbits are not e likely to crash to Earth when the sunspot cycle is near solar maximum because _____.
Earth's upper atmosphere tends to expand during solar maximum, exerting drag on satellites in low orbits.
What is not a way by which we can study inside of the Sun?
We can send a space probe into the Sun's photosphere. Duh.
A computer accessory salesman attempts to convince you to purchase a "solar neutrino" shield for your new computer. Why do you turn down this excellent offer?
Neutrinos rarely, if ever, interact with your computer.