Chapter 14 Mastering Astronomy

What is the solar wind

a stream of charged particles flowing outward from the surface of the Sun

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

5,800 K

The Sun's visible surface (that is, the surface we can see with our eyes) is called the __________.

Photosphere

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

Watts

From the 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 is the Sun's approximate composition (by mass)?

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

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)

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

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

gravitational force and outward pressure

The source of energy that keeps the Sun shining today is _________.

nuclear fusion

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

The Sun will exhaust its nuclear fuel in about __________.

5 Billion Years

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

4.5 billion years

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

Why are neutrinos so difficult to detect?

They have a tendency to pass through just about any material without any interactions.

To estimate the central temperature of the Sun, scientists __________.

use computer models to predict interior conditions

What is the overall result of the proton-proton chain?

4 H becomes 1 He + energy

The proton-proton chain is __________.

the specific set of nuclear reactions through which the Sun fuses hydrogen into helium

The fundamental nuclear reaction occurring in the core of the Sun is __________.

nuclear fusion of hydrogen into helium

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

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

The sunspot cycle is 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.

Which of the following changes would cause the fusion rate in the Sun's core to increase?

-increase in core temp

-decrease in core radius

Which of the following must occur for a star's core to reach equilibrium after an initial change in fusion rate?

-If the fusion rate initially increases, then the core expands.

-If the fusion rate initially decreases, then the core contracts

What would happen if the fusion rate in the core of the Sun were increased but the core could not expand?

The Sun's core would start to heat up, and the rate of fusion would increase even more

What is the overall fusion reaction that converts mass into other forms of energy in the Sun's core?

4 hydrogen nuclei become 1 helium nucleus

When we refer to the solar thermostat, we are referring to the idea that __________.

the Sun's core temperature naturally stays stable

The energy balance that contributes to the solar thermostat is a balance between __________.

the energy released in the core by fusion and the energy radiated from the Sun's surface into space

To understand the interplay of observations and models you must first be able to distinguish between things that we observe and things that we infer from models. Consider the following statements about the Sun. Classify each statement as an observation or as an inference based on the current, accepted model for the Sun.

OBSERVATIONS:

-The Sun emits neutrinos.

-The photosphere emits mostly visible light.

-The photosphere is made mostly of hydrogen and helium.

-The corona is hotter than the photosphere.

INTERFERENCES:

-The Sun generates energy by fusing hydrogen into helium in its core.

-The core temperature is 10 million K.

-The convection zone is cooler than the radiation zone.

-The composition of the photosphere is the same as that of the gas cloud that gave birth to our solar system.

One statement about the Sun from Part A is "The corona is hotter than the photosphere." Which of the following statements provides observational evidence for this claim?

The corona primarily emits X rays while the photosphere primarily emits visible light.

Now consider the statements in Part A that are inferred from models. A solar model is used to calculate interior conditions based on certain "known" characteristics of the Sun, such the Sun's total mass. How do we know the Sun's mass?

We can calculate it by applying Newton's version of Kepler's third law with Earth's orbital period (1 year) and Earth's average distance from the Sun (1 AU).

A solar model is used to calculate the expected temperature and density at all depths within the Sun. These results are then used to calculate the expected fusion rate within the Sun. We have confidence that the model is correct because it agrees with the observed characteristics of the Sun. Which of the following observations can be used to check that we really do know the Sun's internal fusion rate?

-Measurements of the Sun's total energy output into space

-Observations of neutrinos coming from the Sun

The basic fusion reaction through which the Sun produces energy is __________.

4 hydrogen nuclei fuse to make 1 helium nucleus

The energy that is released in the hydrogen fusion reaction comes from __________.

The difference in mass between the four hydrogen nuclei and the single resulting helium nucleus.

What two items on the list below are in balance in what we call gravitational equilibrium?

-Gravity

-Gas Pressure

What two items on the list below are in balance in what we call energy balance?

-the energy released into space

-the energy produced by fusion

Place the layers of the Sun into the correct order from innermost at left to outermost at right

Core>Radiation Zone>Convection Zone>Photosphere>Chromosphere>Corona

All the phenomena of solar activity — including sunspots, flares, coronal mass ejections, and the sunspot cycle — are tied to changes in the Sun's __________.

magnetic field

Fill in the blank

-The proton 13proton chain is how hydrogen fuses into helium in Sun.

High temperatures enable nuclear fusion to happen in the core.

Patterns of vibration on the surface tell us about what the Sun is like inside.

Observations of solar neutrinos can tell us what's happening in core.

Energy gradually leaks out of radiation zone in form of randomly bouncing photons.

The solar thermostat keeps burning rate steady.

Select the correct corresponding

-Convection Zone: Where energy transported upward by rising hot plasma.

-Radiation Zone: Where energy transported upward by photons.

-Chromosphere: Middle layer of solar atmosphere, about 10,000 K to 100,000 K.

-Corona: Outermost layer of solar atmosphere, about 1 million K.

-Core: Where energy generated by nuclear fusion, about 15 million K

-Solar wind: A flow of charged particles from the surface of the Sun.

-Photosphere: Visible surface of Sun, about 6000 K.

Fill in the blank

-Charged particles spiral along magnetic field lines.

-Coronal mass ejections send bursts of energetic charged particles out through the solar system.

-The sunspot cycle has something to do with winding and twisting of the Sun's magnetic field.

-Charged particles streaming from the Sun can disrupt electrical power grids and can disable communications satellites.

-Sunspots are cooler than other parts of the Sun's surface.

-We can measure magnetic fields in sunspots by observing the splitting of spectral lines.

-Magnetic activity causes solar flares that send bursts of X rays and charged particles into space.

-Magnetic activity also causes solar prominences that erupt high above the Sun's surface.

Listed following are the different layers of the Sun. Rank these layers based on their distance from the Sun's center, from greatest to least.

GREATEST:

Corona

Chromosphere

Photosphere

Convection Zone

Radiation Zone

Core

LEAST

Rank the layers of the Sun based on their density, from highest to lowest.

HIGHEST:

core

radiation

convection

photosphere

chromosphere

core

Rank the following layers of the Sun based on their temperature, from highest to lowest.

HIGHEST:

Core

Radiation Zone

Convective Zone

Photosphere

Rank the following layers of the Sun based on the pressure within them, from highest to lowest.

HIGHEST:

Core

Radiation Zone

Convective Zone

Photosphere

In which of the following layer(s) of the Sun does nuclear fusion occur?

Core

Which of the following layers of the Sun can be seen with some type of telescope? Consider all forms of light, but do not consider neutrinos or other particles.

Chromosphere

Corona

Photosphere

Following are the different layers of the Sun's atmosphere. Rank them based on the order in which a probe would encounter them when traveling from Earth to the Sun's surface, from first encountered to last.

FIRST:

Corona

Chromosphere

Photosphere

Rank the layers of the Sun's atmosphere based on their density, from highest to lowest.

HIGHEST:

Photosphere

Chromosphere

Corona

Rank the layers of the Sun's atmosphere based on their temperature, from highest to lowest.

HIGHEST:

Corona

Chromosphere

Photosphere

Rank the layers of the atmosphere based on the energy of the photons that are typically emitted there, from highest to lowest.

HIGHEST:

Corona

Chromosphere

Photosphere

Fill in the blank

1. Nuclear fusion of hydrogen into helium occurs in the core.

2. Energy moves through the Sun's convection zone by means of the rising of hot gas and falling of cooler gas.

3. Nearly all the visible light we see from the Sun is emitted from the photosphere.

4. Most of the Sun's ultraviolet light is emitted from the narrow layer called the chromosphere where temperature increases with altitude.

5. We can see the Sun's corona most easily during total solar eclipses.

6. The radiation zone is the layer of the Sun between its core and convection zone.

Listed following are events or phenomena that occur during either the part of the sunspot cycle known as solar minimum or the part known as solar maximum. Match these items to the correct part of the sunspot cycle.

MINIMUM:

-Occurs about 5 to 6 years after a solar maximum

MAXIMUM:

- Sunspots are most numerous on the Sun

- Solar flares are most common

- Orbiting satellites are most at risk

- Auroras are most likely in earth's skies

- Occurs about 11 years after a solar maximum

The arrows in this diagram are meant to show how gravitational equilibrium works in the Sun. What do the different colors and different arrow lengths represent?

Inward pointing green arrows represent gravity

Outward pointing red arrows represent pressure

Longer arrows represent a stronger push or pull

What layer of the Sun are we seeing in this photo?

photosphere

The dark spots in this photo (such as the one indicated by the arrow) represent what we call __________.

Sunspots

Which photo pair shows Earth correctly scaled in comparison to the Sun?

Earth looks like a tiiiiny dot photo

This photograph shows a small portion of the Sun's photosphere. What is going on in the bright regions (such as the bright region indicated by the arrow)?

Hot gas is rising up from the solar interior.

This x-ray image shows a loop of hot gas above the surface of the Sun. If we took a visible light photo that looked in the Sun's photosphere just under the two points where the loop of gas comes down (arrows), what would we find?

Sunspots

This x-ray image shows a loop of hot gas above the surface of the Sun. Suppose we took another photo looking at the same place 1 hour later. What would we see?

The loop would look about the same as it does in this photo.

What layer of the Sun are we seeing in this photograph, and in what wavelength band was it photographed?

corona, photographed in x-rays

Study this figure and its axis labels. What is this graph showing us?

The number of sunspots on the Sun tends to increase and decrease with an approximately 11-year cycle.

In terms of the global warming that has been occurring on Earth over the past few decades, what is the key message from this figure?

Changes in the Sun's energy output (irradiance) cannot explain the observed warming

The Sun's surface seethes and churns with a bubbling pattern. Why?

We are seeing hot gas rising and cool gas falling as a result of the convection that occurs beneath the surface.

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

How does the Sun's mass compare to Earth's mass?

300,000 times larger

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 become hot enough for nuclear fusion, which ever since has generated the heat that makes the Sun shine

What do we mean when we say that the Sun is in energy balance?

The amount of energy released by fusion in the Sun's core equals the amount of energy radiated from the Sun's surface into space

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

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.

In the late 1800s, Kelvin and Helmholtz suggested that the Sun stayed hot because of 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.

A salesman attempts to convince you to purchase a "solar neutrino shield" to protect you and your family. (It's even "on sale!") Why do you turn down this excellent offer?

Neutrinos rarely, if ever, interact with other matter.

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 within the past few minutes

Why does the Sun emit neutrinos?

Fusion in the Sun's core creates neutrinos.

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

Which of the following best explains why the Sun's luminosity gradually rises over billions of years?

Fusion gradually decreases the number of independent particles in the core, allowing gravity to compress and heat the core, which in turn increases the fusion rate and the Sun's luminosity

If the Sun's core suddenly shrank a little bit, what would happen in the Sun?

The core would heat up, fusion rates would increase, the core would re-expand.

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

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 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 (splitting) of large nuclei.

We can essentially rule out the Sun as a cause of global warming over the past few decades because __________.

the amount of incoming sunlight has decreased while Earth's average temperature has increased

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

How can we measure the strength of magnetic fields on the Sun?

By looking for the splitting of spectral lines in the Sun's spectrum

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 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

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.