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According to modern science, approximately how old is the Sun?

4.5 billion years

The Sun will exhaust its nuclear fuel in about

5 billion years

Which of the following correctly describes how the process of gravitational contraction can make a star hot?

When a star contracts in size, gravitational potential energy is converted to thermal energy

What two physical processes balance each other to create the condition known as gravitational equilibrium?

gravitational force and outward pressure

The source of energy that keeps the Sun shining today is ______

nuclear fusion

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 core and the rate at which the sun's surface radiates energy into space

When we say that the Sun is a ball of plasma we mean that ______.

the Sun consists of gas in which many or most atoms are ionized (missing electrons).

What is the sun made of (by mass)?

70% hydrogen, 28% helium, 2% other elements

From center outward, which of the following lists the layers of the Sun in the correct order?

Core, radiation zone, convection zone, photosphere, chromosphere, corona

What are the appropriate units for the Sun's luminosity?

watts

The Sun's surface, as we see it through our eyes, is called the _______.

photosphere

The Sun's average surface (photosphere) temperature is about _____.

5800 K

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

4 H becomes 1 He + energy

To estimate the central temperature of the Sun, scientists

use computer 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 the 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 have in common?

They are all strongly influenced by magnetic fields on the Sun.

Which of the following is NOT a characteristic of the 11 year sunspot cycle?

The sunspot cycle is very steady, so that each 11 year cycle is nearly identical to 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 Helmhotz suggested that the Sun stayed hot due to gravitational contraction. What was the major drawback to this idea?

It predicted that the Sun could shine for about 25 million years, but geologists had already found that Earth is much older than this.

When is/was gravitational contraction an important energy 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 equlibrium?

There is a balance with the Sun between the outward push of pressure and the inward pull of gravity

Which of the following is the best answer to "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 the Earth's mass?

The sun's mass is about 300,000 times that of Earth

Which of the following best describes why the Sun emits most of its energy in the form of visible light?

Like all objects, the sun emits thermal radiation with a spectrum that depends on its temperature, and 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

Which of the following 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 planets generate energy by the fission of larger nuclei

Every second, the Sun converts about 600 million tons of hydrogen into 596 million tons of helium. The remaining 4 million tons of mass is _________.

converted to an amount of energy equal to 4 million tons times the speed of light squared

Which of the following 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 shrank a little bit, what would happen in 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 emits neutrinos

If the Sun suddenly stopped emitting neutrinos, what might we infer (after checking that our neutrino detectors were still operational)?

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 its luminosity is about 1.6 times that of the sun. What can we conclude?

Alpha Centauri A fuses hydrogen into helium in its core at a higher rate than our Sun.

How can we best 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 of magnetic fields on the sun?

by looking for the splitting of spectral lines on the sun

Satellites in low-earth orbits are more 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

Which of the following choices is NOT a way by which we can study the inside of the sun?

we can send a space probe into the sun's photosphere

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

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