STARS AND GALAXY

Which is closest to the temperature of the core of the Sun?

10 million K

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

4 1/2 billion years

The overall result of the proton-proton chain is:

4 H becomes 1 He + energy

The overall fusion reaction by which the Sun currently produces energy is

4 H ⇒ 1 He + energy.

How much mass does the Sun lose through nuclear fusion per second?

4 million tons

The Sun will exhaust its nuclear fuel in about ______.

5 billion years

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

5,800 K

What is the average temperature of the surface of the Sun?

6,000 K

What is the Sun made of?

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

What is the Sun made of (by mass)?

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

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.

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

An increase in the core temperature increases the fusion rate because the fusion rate is very sensitive to temperature. A decrease in the core radius causes the core to heat up and increase in density, which therefore leads to an increased fusion rate.

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.

How do we know what goes on under the surface of the Sun?

Astronomers create mathematical models that use the laws of physics, the Sun's observed composition and mass, and computers to predict internal conditions. AND By measuring Doppler shifts, we observe vibrations of the Sun's surface that are created deep within the Sun.

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.

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

Core of the sun.

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

Core, Radiation Zone, Convection Zone, Photosphere (It doesn't include the chromosphere or corona because they have high temps despite their low densities)

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

Core, Radiation Zone, Convection Zone, Photosphere, Chromosphere, Corona,

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

Core, Radiation Zone, Convection Zone, Photosphere. (The Sun's pressure is highest at its center and drops steadily from the core to the surface. This is gravitational equilibrium — the idea that the inward pull of gravity (or, equivalently, the weight of overlying layers bearing down) must at all points be balanced by the outward push of pressure.)

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

Which of the following layers of the Sun can be seen with some type of telescope?

Corona, Chromosphere and Photosphere. The photosphere can be seen with visible-light telescopes, while the chromosphere is most easily observed with ultraviolet telescopes and the corona with X-ray telescopes.

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

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.

Corona, Chromosphere, Photosphere

Rank the layers of the sun 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.

Corona, Chromosphere, Photosphere

Rank the layers of the sun based on their distance from the sun's center, from greatest to least.

Corona, Chromosphere, Photosphere, Convection Zone, Radiation Zone, Core

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 statement best describes what was called the solar neutrino problem?

Early experiments designed to detect solar neutrinos found them, but in fewer numbers than had been expected.

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

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 happens to energy in the convection zone of the Sun?

Energy is transported outward by the rising of hot plasma and the sinking of cooler plasma.

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.

Why does the Sun emit neutrinos?

Fusion in the Sun's core creates neutrinos.

Why must the Sun's rate of fusion gradually rise over billions of years?

Fusion reactions decrease the overall number of particles in the core, causing the core to shrink, converting gravitational potential energy into thermal energy, and increasing the rate of fusion.

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.

Based on its surface temperature of 5,800 K, what color are most of the photons that leave the Sun's surface?

Green

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?

Green arrows(going in) represent gravity; red arrows (coming out) represent pressure; longer arrows represent a stronger push or pull.

Suppose that, for some unknown reason, the core of the Sun suddenly became hotter. Which of the following best describes what would happen?

Higher temperature would cause the rate of nuclear fusion to rise, which would increase the internal pressure, causing the core to expand and cool until the fusion rate returned to normal.

What is going on in the bright regions of the Earth's photosphere?

Hot gas is rising up from the solar interior.

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 OR If the fusion rate initially decreases, then the core contracts.

The first step in the proton-proton chain produces an antielectron, or positron. What happens to the positron?

It is rapidly converted to energy when it meets an ordinary electron, resulting in matter-antimatter annihilation.

In the late 1800s, Kelvin and Helmholtz suggested that the Sun stayed hot thanks to gravitational contraction. What was the major drawback of this idea?

It predicted that the Sun could last only about 25 million years, which is far less than the age of Earth.

In the late 1800s, Kelvin and Helmholtz 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 generation mechanism for the Sun?

It was important when the Sun was forming from a shrinking interstellar cloud of gas.

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.

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 and observations of neutrinos coming from the Sun.

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

Neutrinos rarely, if ever, interact with your computer.

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.

What are some things that we observe and things that we infer from models?

Observe: The photosphere is made mostly of hydrogen and helium. The photosphere emits mostly visible light. The corona is hotter than the photosphere. The sun emits neutrinos. Infer from models: The composition of the photosphere is the same as that of the gas cloud that gave birth to our solar system. The core temp is 10 million k. The sun generates energy by fusing hydrogen into helium in its core. The convection zone is cooler than the radiation zone.

In which of the following layers of the Sun does nuclear fusion occur?

Only in the core of the Sun, where the temperatures, pressures, and densities are highest.

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

Photosphere, Chromosphere, Corona

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

Photosphere.

The _________ __________ is the layer of the Sun between its core and convection zone.

Radiation Zone

Which items are in either the solar maximum or the solar minimum of the sunspot cycle?

Solar Maximum: Sunspots are most numerous on the Sun. Orbiting satellites are most at risk. Solar flares are most common. Occurs about 11 years after a solar maximum (on average). Auroras are most likely in Earth's skies. Solar Minimum: Occurs about 5-6 years after a solar maximum (on average)

Which statement best describes the solar neutrino problem?

Solar neutrinos have been detected, but in fewer numbers than predicted by theoretical models.

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. The loop is shaped by magnetic fields, and these loops generally are anchored to the strong magnetic fields of sunspots at each end.

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.

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.

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

The Sun's mass is about 300,000 times the mass of the Earth.

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.

Most of the energy produced in the Sun is released in the form of visible light from the photosphere. However, some energy is released from the upper layers of the solar atmosphere. Which of the following best describes where other forms of light are released?

The chromosphere is the source of ultraviolet light, and the corona is the source of X rays.

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.

"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.

What is a possible solution to the solar neutrino problem?

The electron neutrinos created in the Sun change into another type of neutrino that we do not detect.

Which of the following statements about neutrinos is not true?

The mass of a neutrino is 30 percent of the mass of an electron.

Which of the following statements about the sunspot cycle is not true?

The rate of nuclear fusion in the Sun peaks about every 11 years.

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.

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.

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 Sun.

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.

What do sunspots, solar prominences, and solar flares all have in common?

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

Why are neutrinos so difficult to detect?

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

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

Watts

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.

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).

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.

What observations characterize solar maximum?

We see many sunspots on the surface of the Sun.

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 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

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 million years ago.

What is the solar wind?

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

What are coronal holes?

areas of the corona where magnetic field lines project into space, allowing charged particles to escape the Sun, becoming part of the solar wind

Why are neutrinos so difficult to detect?

because they rarely interact with matter.

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

chromosphere

Energy moves through the Sun's _________ __________ by means of the rising of hot gas and falling of cooler gas.

convection zone.

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

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

corona

The intricate patterns visible in an X-ray image of the Sun generally show _________.

extremely hot plasma flowing along magnetic field lines

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

gravitational force and outward pressure

At the center of the Sun, fusion converts hydrogen into

helium, energy, and neutrinos.

The core of the Sun is

hotter and denser than the surface.

Hydrogen fusion in the Sun requires a temperature (in Kelvin) of

millions of degrees.

How do human-built nuclear power plants on Earth generate energy?

nuclear fission

How does the Sun generate energy today?

nuclear fusion

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

nuclear fusion

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

nuclear fusion of hydrogen into helium

Studies of sunquakes, or helioseismology, have revealed that

our mathematical models of the solar interior are fairly accurate.

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

photosphere

Which layer of the Sun do we normally see?

photosphere

The phase of matter in the Sun is

plasma.

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 _________.

reabsorbed as molecular hydrogen

Suppose you put two protons near each other. Because of the electromagnetic force, the two protons will

repel each other.

Humans have not sent a spacecraft into the interior of the Sun to confirm any models of the interior. What evidence then do we have to support our current ideas about the solar interior?

solar neutrinos

Which is the strongest of the fundamental forces in the universe?

strong force

Sunspots are cooler than the surrounding solar surface because

strong magnetic fields slow convection and prevent hot plasma from entering the region.

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)

What is granulation in the Sun?

the bubbling pattern on the photosphere produced by the underlying convection

The proton-proton chain is _________.

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

What processes are involved in the sunspot cycle?

the winding of magnetic field lines due to differential rotation

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

use computer models to predict interior conditions

When is/was gravitational contraction an important energy-generation mechanism for the Sun?

when the Sun was being formed from a collapsing cloud of gas