Astronomy chapter 8

Part A: The Sun's mass is about 2×1030kg; this mass was about 70% hydrogen when the Sun formed, with about 13% of this hydrogen ever becomes available for eventual fusion in the core.

*1.8*10^29 kg *Correct answer is shown. Your answer 1.82⋅1029kg was either rounded differently or used a different number of significant figures than required for this part. The mass of hydrogen available for fusion over the Sun's lifetime is about 10 times the mass of Jupiter.

About what is Rigel's surface temperature?

*10,000 K

Rigel's luminosity is about _____ times the Sun's luminosity.

*100,000

Part B: The Sun fuses about 600 billion kilograms of hydrogen each second. Based on your result from the previous part, calculate how long the Sun's initial supply of hydrogen can last.

*3.03*10^17 *Correct answer is shown. Your answer 3.03⋅10^17 = 3.03×10^17 s was either rounded differently or used a different number of significant figures than required for this part.

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

*4 1/2 billion years *The Sun is the same age as the rest of our solar system.

Give your answer from the previous part in years.

*9.62*10^9

Consider the four stars shown following. Rank the stars based on their surface temperature from highest to lowest.

*A blue white dwarf star, Sun, An orange main-sequence star, A red supergiant star

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 (Also known as a million years ago)

Study the graph of the intensity of light versus wavelength for continuous spectra, observing how it changes with the temperature of the light bulb. Recall that one of the laws of thermal radiation states that a higher-temperature object emits photons with higher average energy (Wien's law). This law is illustrated by the fact that for a higher temperature object, the graph peaks at __________.

*A shorter wavelength. *Wien's law states that the thermal radiation from a hotter object peaks at a shorter wavelength.

Suppose you look at a detailed spectrum of visible light from some object. How can you decide whether it is an emission line spectrum or an absorption line spectrum?

*An emission line spectrum consists of bright lines on a dark background, whereas an absorption line spectrum consists of dark lines on a rainbow background. *In other words, you can tell just by looking at the spectrum.

Most continuous spectra are examples of what we also call thermal radiation spectra. Why do we call them "thermal" spectra?

*Because the peak wavelength of the spectrum depends on the temperature of the object producing the spectrum. *Notice that the word "thermal" comes from a Greek root meaning "heat."

Most interstellar clouds are made mostly of hydrogen (because hydrogen is the most common element in the universe). Why are these clouds usually dominated by the color red?

*Because the strongest visible emission lines from hydrogen are red. *As shown in the video, hydrogen clouds produce several visible emission lines, but the red lines are generally the strongest.

Suppose we want to know what the Sun is made of. What should we do?

*Compare the wavelengths of lines in the Sun's spectrum to the wavelengths of lines produced by chemical elements in the laboratory.

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

*Core

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

*Core, Radiation Zone, Convection Zone, Photosphere, Chromosphere, Corona. *As your answer correctly indicates, the density of the Sun decreases from the center outward. The core has the highest density and the corona has the lowest density.

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

*Core, Radiation Zone, Convective Zone, Photosphere.

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

*Core, Radiation Zone, Convective Zone, 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.

*Corona, Chromosphere, Photosphere

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.

*Corona, Chromosphere, Photosphere, Convection Zone, Radiation Zone, Core. *Now proceed to Part B to see if you can rank these layers by density.

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.

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.

*Corona, Chromosphere, 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.

Five stars are shown on the following H-R diagrams. Rank the stars based on their surface temperature from highest to lowest. If two (or more) stars have the same surface temperature, drag one star on top of the other(s). Part D:

*Dot over the O to the very left and then goes in order all the way to M on the very right.

Comte was proven wrong in his claim that we could never learn the composition of stars. What do we know today that Comte did not know when making his claim, and that makes it possible for us to learn the chemical compositions of stars?

*Every chemical element produces a unique spectral fingerprint. *If Comte had known that every element leaves a unique spectral fingerprint on light, he presumably could have guessed that we'd ultimately learn the chemical compositions of stars.

Which of these groups of particles has the greatest mass?

*Four individual protons. *In a hydrogen fusion reaction, four protons fuse (over the course of several steps) to make a helium nucleus and energy. A tiny amount of mass is converted to energy during this reaction, which means the starting set of four protons must have more mass than the end-product of helium.

Five stars are shown on the following H-R diagrams. Rank the stars based on their surface temperature from highest to lowest. If two (or more) stars have the same surface temperature, drag one star on top of the other(s).

*Group all together

A Time magazine cover once suggested that an "angry Sun" was becoming more active as human activity changed Earth's climate. It's certainly possible for the Sun to become more active at the same time that humans are affecting Earth, but is it possible that the Sun could be responding to human activity? Why or why not?

*It is impossible. The sheer size of the Sun and the 150 million kilometer distance from Earth to the Sun make any human activity totally negligible compared to the processes inside it.

According to the inverse square law of light, how will the apparent brightness of an object change if its distance to us triples?

*Its apparent brightness will decrease by a factor of 9. *The inverse square law for light tells us that the light gets dimmer with increasing distance by the square of the distance, so tripling the distance decreases the brightness by a factor of 3^2 = 9.

In the illustration of the solar spectrum, the upper left portion of the spectrum shows the __________ visible light.

*Lowest frequency *Red light is the longest wavelength visible light, and longer wavelength means lower frequency (because of light wavelength × Frequency=speed of light)

The total amount of power (in watts, for example) that a star radiates into space is called its __________.

*Luminosity *For example, the luminosity of the Sun is 3.8 × 10^26 watts.

How is the lifetime of a star related to its mass?

*More massive stars live much shorter lives than less massive stars.

Based on its location on the HR diagram, what can we say about Rigel's mass and lifetime?

*Nothing, because it is not on the main sequence.

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.

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

*Nuclear fusion of hydrogen into helium. *Each complete reaction converts four hydrogen nuclei (protons) into one helium nucleus, although the reaction proceeds through several smaller steps.

From hottest to coolest, the order of the spectral types of stars is __________.

*OBAFGKM *It is worth memorizing this sequence for your astronomy class.

Which of the following procedures would allow you to make a spectrum of the Sun similar to the one shown, though with less detail?

*Pass a narrow beam of sunlight through a prism.

Solar energy leaves the core of the Sun in the form of

*Photons *Photons created during the fusion travel through the core and adjacent regions in a random walk due to collisions with the material. Region of that random walk is called radiation zone, and a photon could bounce inside that zone for about 200,000 years.

Which of these layers of the Sun is coolest?

*Photosphere *The photosphere, with a temperature of about 5,800 K, is the coolest layer of the Sun, even though it is not the uppermost one.

The Sun's visible surface (that is, the surface we can see 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.

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

*Photosphere, Chromosphere, Corona.

Any spectrum can be displayed either in photographic form as shown to the left or as a graph. Which of the following graphs could represent a portion of the Sun's visible light spectrum?

*Smooth on the top and then has dips coming from the line going down. *The smooth part of the curve represents the graph of the background rainbow of color; the dips in the curve represent the black lines where light is missing from the rainbow.

Which of the following best describes why the Sun's spectrum contains black lines over an underlying rainbow?

*The Sun's hot interior produces a continuous rainbow of color, but cooler gas at the surface absorbs light at particular wavelengths.

The "extraordinary" part of Comte's claim was his statement that we could never learn the composition of stars. Which of the following best summarizes the key lesson we should learn from the fact that his claim was ultimately proven wrong?

*The advance of science and technology may someday provide ways to answer questions that seem unanswerable today.

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. *In general, higher temperature gas emits higher energy light. The fact that the corona emits primarily in X rays therefore indicates that it consists of higher temperature gas than visible-light-emitting photosphere.

Astronomers can measure a star's mass only in certain cases. Which one of the following cases might allow astronomers to measure a star's mass?

*The star is a member of a binary star system. *If we can measure the orbital properties of the star around its companion, then we can measure the mass with Newton's version of Kepler's third law.

Why do sunspots appear darker than their surroundings?

*They are cooler than their surroundings. *According to the Stefan-Boltzmann law, a cooler object emits light of lower energy, which makes sunspots (4,000 K) dimmer than the surrounding gas (5,800 K).

What is the common trait of all main-sequence stars?

*They generate energy through hydrogen fusion in their core. *A star becomes a main-sequence star when it first starts fusing hydrogen into helium, and it ends its main-sequence life when it exhausts its central core supply of hydrogen for fusion.

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).

Which of these stars has the coolest surface temperature?

*a K star *The spectral sequence OBAFGKM goes from the hottest to the coolest temperatures. A K star is the coolest from the choices above. Type K stars are usually have temperature about 3700-5200 K.

What is the sunspot cycle?

*a cycle in which the number of sunspots on the Sun at any one time gradually rises and falls. *The sunspot cycle has an average of 11 years between the times when sunspots are most numerous.

Which of these stars is the most massive?

*a main-sequence A star. *At the main sequence, hotter stars have greater masses. Therefore, the spectral sequence OBAFGKM is also the order of masses for main-sequence stars. Type A stars with temperature about 7500-10000 K have the greatest mass among the choices above.

Which of these stars has the longest lifetime?

*a main-sequence M star. *Main sequence M stars are the least luminous, so they use their fuel at the slowest rate and have very long lifetimes.

For an object producing a thermal spectrum, a higher temperature causes the spectrum to have ___________.

*a peak intensity located at shorter wavelength. *This is one of the two laws of thermal radiation, also called Wien's law: Hotter objects produce photons with higher average energy, which means the peak intensity is located at shorter average wavelength.

What is the solar wind?

*a stream of charged particles flowing outward from the surface of the Sun. *The solar wind blows outward in all directions and has important effects on the planets, especially through interactions with planetary magnetospheres.

Which of these stars has the largest radius?

*a supergiant M star.

What type of visible light spectrum does the Sun produce?

*an absorption line spectrum.

What do we need to measure in order to determine a star's luminosity?

*apparent brightness and distance. *The inverse square law for light relates apparent brightness and distance with luminosity. If you know any two of these variables, you can calculate the third.

The absorption line spectrum shows what we see when we look at a hot light source (such as a star or light bulb) directly behind a cooler cloud of gas. Suppose instead that we are looking at the gas cloud but the light source is off to the side instead of directly behind it. In that case, the spectrum would __________.

*be an emission line spectrum.

Assuming that we can measure the apparent brightness of a star, what does the inverse square law for light allow us to do?

*calculate the star's luminosity if we know its distance, or calculate its distance if we know its luminosity.

On an H-R diagram, stellar masses __________.

*can be determined for main-sequence stars but not for other types of stars. *Along the main sequence, mass decreases from upper left to lower right, but there is no clear pattern for masses of stars that are not on the main sequence.

Compared to a high-luminosity main-sequence star, stars in the upper right of the H-R diagram are __________.

*cooler and larger in radius.

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. *Be sure to study the figure in your text to make sure you understand the structures of these layers.

At the center of the Sun, fusion converts hydrogen into

*helium and energy. *The overall fusion reaction in the Sun converts hydrogen into helium and energy emitted as light.

Compared to a low-luminosity main-sequence star, stars in the lower left of the H-R diagram are __________.

*hotter and smaller in radius.

On an H-R diagram, stellar radii __________.

*increase diagonally from the lower left to the upper right. *Small-radius white dwarfs appear near the lower left, while large-radius supergiants are in the upper right.

We found that mass must be inferred for the star described in Part A. However, we can measure a star's mass directly if __________.

*it is a member of an eclipsing binary system.

Compared to a main-sequence star with a short lifetime, a main-sequence star with a long lifetime is __________.

*less luminous, cooler, smaller, and less massive.

The axes on a Hertzsprung-Russell (H-R) diagram represent __________.

*luminosity and surface temperature. *We plot luminosity on the vertical axis and surface temperature (or spectral type) on the horizontal axis.

Scientists estimate the central temperature of the Sun using

*mathematical models of the Sun.

Click "show" for the emission line spectrum, then click "choose gases" and study the emission line spectrum for neon. The neon "OPEN" sign appears reddish-orange because __________.

*neon atoms emit many more yellow and red photons than blue and violet photons.

From Part A, you know that surface temperature is a stellar property that we infer indirectly. What must we measure directly so that we can infer a star's surface temperature?

*spectral type

Notice that the Sun's spectrum appears brightest (or most intense) in the yellow-green region. This fact tells us __________.

*the approximate temperature of the Sun's surface.

What two pieces of information would you need in order to measure the masses of stars in an eclipsing binary system?

*the time between eclipses and the average distance between the stars. *Newton's version of Kepler's third law relates the period, average distance, and total mass of a binary system. Time between the eclipses is the period, and knowing it and average distance we can obtain the mass of the system.

Suppose you want to know the chemical composition of a distant star. Which piece of information is most useful to you?

*the wavelengths of spectral lines in the star's spectrum. *Different chemical elements and ions produce different sets of spectral lines.

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?

-Observations of neutrinos coming from the Sun. -Measurements of the Sun's total energy output into space.

You should now see that the reason the mass of the star in Part A must be inferred is that the star has no known orbiting objects, which means we cannot apply Newton's version of Kepler's third law. Which of the following must be true if the star's inferred mass is to be accurate?

-We have determined that the star is a main-sequence star. -We have measured the star's spectral type.

Which of the following must be true if we are to infer (calculate) a star's luminosity directly from the inverse square law for light?

-We have measured the star's apparent brightness. -We have measured the star's distance. -No interstellar gas or dust absorbs or scatters light between us and the star.

Match the words in the left-hand column to the appropriate blank in the sentences in the right-hand column. Use each word only once.

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.

Given that our solar system is now about 4.6 billion years old, in which time will the Sun run out of hydrogen for fusion?

5020000000 billion years

Rigel's radius is about _____ times the Sun's radius.

80

Five stars are shown on the following H-R diagrams. Rank the stars based on their luminosity from highest to lowest; notice that these are the same five stars shown in Part D. If two (or more) stars have the same luminosity, drag one star on top of the other(s). Part E:

All stacked on top of each other

The following figure shows how four identical stars appear in the night sky seen from Earth. The shading is used to indicate how bright (white) or dim (dark gray) the star would appear in the sky from Earth. Rank the stars based on their distance from Earth, from farthest to closest.

Brightest is closest, dimmest (or darkest) is most distant.

Listed following are several fictitious stars with their luminosities given in terms of the Sun's luminosity (LSun) and their distances from Earth given in light-years (ly). Rank the stars based on how bright each would appear in the sky as seen from Earth, from brightest to dimmest. If two (or more) stars have the same brightness in the sky, show this equality by dragging one star on top of the other(s).

Brightest: Nismo, then (overlapping because they're the same) Shelby and Ferdinand, then Enzo, then Lotus (dimmest)

Suppose we obtain a single, detailed (high-resolution) spectrum of a star located many light-years away. What can we learn about the star? Sort each of the following characteristics of a star into the correct bin based on whether we can or cannot learn it from the single spectrum.

CAN LEARN: -surface temperature -speed toward or away from us -chemical composition (surface) CANNOT LEARN: -mass -distance -interior temperature -size (diameter) -speed across our line of sight

Sort each item into the appropriate bin based on which type of spectrum it represents.

CONTINUOUS SPECTRUM: -a graph of this spectrum shows a smooth curve. -arises from relatively dense objects like light bulb filaments, rocks, and people. -the only one of the spectra below that does not give us information about chemical comp. EMISSION LINE SPECTRUM: -a graph of this spectrum has upward spikes. -produces by thin or low-density clouds of gas. ABSORPTION LINE SPECTRUM: -a graph of this spectrum is a curve with star, downward dips. -produced when starlight passes through a thin or low-density clouds of gas.

Five stars are shown on the following H-R diagrams; notice that these are the same five stars shown in Part B. Rank the stars based on their luminosity from highest to lowest. If two (or more) stars have the same luminosity, drag one star on top of the other(s).

Dot at the very top going down in order to the dot in the very bottom.

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 is made mostly of hydrogen and helium. -The corona is hotter than the photosphere. -The photosphere emits mostly visible light. Inferences from a model: -The core temperature 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. -The composition of the photosphere is the same as that of the gas cloud that gave birth to our solar system.

Consider a relatively nearby, single star, that is, a star that is not a member of a binary system and has no known orbiting planets. Listed below are a few properties of this star. Classify each property as either something that we can observe or measure directly (with the aid of a telescope and instruments such as cameras or spectrographs) or something that we must infer indirectly (and hence is correct only if all of our assumptions are correct).

Observe: - color, parallax angle, spectral type, apparent brightness Infer Indirectly: - luminosity, surface temperature, mass, radius

Listed following is a set of statements describing individual stars or characteristics of stars. Match these to the appropriate object category.

Red giant or supergiant stars: -Very cool but very luminous. -Found in the upper right of the H-R diagram. Main-sequence stars: -The majority of stars in our galaxy. -The Sun, for example. -The hottest and most luminous stars. White dwarfs: -Not much larger in radius than Earth. -Very hot but very dim.

Listed following is the same set of fictitious stars given in Part A. Rank the stars based on how bright each would appear in the sky as seen from Jupiter, from brightest to dimmest.

Same as part A. Brightest: Nismo, then (overlapping because they're the same) Shelby and Ferdinand, then Enzo, then Lotus (dimmest)

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.

Solar 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. Solar Minimum: -Occurs about 5 to 6 years after a solar maximum.

Five stars are shown on the following H-R diagrams. Rank the stars based on their surface temperature from highest to lowest. If two (or more) stars have the same surface temperature, drag one star on top of the other(s). Part F:

The two O's stacked on top of each other to the right the A in the middle and the M's stacked on top of each other to the left

Five stars are shown on the following H-R diagrams; notice that these are the same five stars shown in Part F. Rank the stars based on their luminosity from highest to lowest. If two (or more) stars have the same luminosity, drag one star on top of the other(s). Part G:

The two dots at the 10,000 mark on the very right stacked then the middle one is the one marked at A and the the two at the very bottom at the .0001 mark at the very right stacked