Astronomy

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 grav

Why do sunspots appear darker than their surroundings?

They are cooler than their surroundings

Why do sunspots appear darker than their surroundings?

They are cooler than their surroundings.

Why are the ionization nebulae so bright

They are regions where gas is ionized by hot, young stars The gas in ionization nebulae is ionized by hot, young stars. That is why they are found in star-formation regions of the galaxy.

What is the common trait of all main seq stars?

They generate energy through hydrogen fusion in their core

What is the common trait of all main seq stars

They generate energy through hydrogen fusion in their core.

Which of the following statements is probably true about the very first stars in the universe?

They were made only from hydrogen and helium

The star gas star cycle will continue forever because stars are continually recycling gas

false

What makes up the interstellar medium?

gas and dust

If the star Alpha Centauri were moved to a distance 10 times farther than it is now, its parallax angle would

get smaller

When a newly forming star is at its greatest luminosity, what is its energy source

gravitational contraction. From Part C, you know that a newly forming star is most luminous during its protostar stage. The source of energy for protostars is the energy released by gravitational contraction

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

gravitational force and outward

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

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

4.5 billion years

According to modern science, approx how old is the sun

4.5 billion yrs old

Why are the very first stars thought to have been much more massive than the Sun

The temperatures of the clouds that made them were higher because they consisted entirely of hydrogen and helium

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 grav

what slows down the contraction of a star forming cloud when it makes a protostar

trapping of thermal energy inside the protostar

Clouds that appear dark in visible light often glow when observed at long infrared wavelengths

true

On HR, where would we find stars that are cool and luminous

upper right

On HR, where would we find stars that have largest radii

upper right

To estimate the central temp of the Sun, scientists

use computer models to predict interior conditions

To estimate the central temperature of the Sun, scientists

use computer models to predict interior conditions

Since all stars begin their lives with the same basic composition, what characteristic most determines how they will differ?

mass they are formed with

Which kind of pressure prevents stars of extremely large mass from forming

radiation pressure

Infer indirectly

surface temperature, luminosity, mass, radius

What is the approx range of masses that newborn main seq stars can have

.1 to 150 solar masses

Approx what is the parallax angle of a star that is 20 light yrs away

.16 arcsec p=3.26/20=0.163 arcsecond.

Approx what is the parallax angle of a star that is 20 light years away

.16 arcsecond Using a distance of d = 20 light-years, this formula gives the parallax angle to be p=3.26/20=0.163 arcsecond.

What percentage of a molecular cloud's mass is interstellar dust?

1%

Which is closest to the temp of the core of the Sun

10 million K

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

10 million K

Five stars are shown on the following HR 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 luminositty, drag one star on top of the others.

10,000--100--1--.01--.001 Luminosity is shown along the vertical axis, with stars higher up more luminous than those lower down. Note that each tickmark along the luminosity axis represents a change by a factor of 10 from the prior tickmark, so the range of luminosities is quite large. Continue to Parts D and E to investigate surface temperature and luminosity for a different set of five stars.

Suppose that a star had a parallax angle of exactly 1 arcsecond. Approx how far away would it be, in light years

3.3 light years A more precise animation would show that the distance of an object with a parallax angle of 1 arcsecond is 3.26 light-years, which astronomers call a parsec (short for "parallax second"). One parsec is defined as the distance of an object with a parallax angle of exactly 1 arcsecond, and its value in light-years is 1 parsec = 3.26 light-years. This is the reason why there is the 3.26 in the parallax formula given at the end of Part E.

Suppose that a star had a parallax angle of exactly 1 arcsecond. Approx how far away would it be, in light years?

3.3 light years One parsec is defined as the distance of an object with a parallax angle of exactly 1 arcsecond, and its value in light-years is 1 parsec = 3.26 light-years. This is the reason why there is the 3.26 in the parallax formula given at the end of Part E.

Approx, what basic composition are all stars born with?

3/4 hydrogen, 1/4 helium, no more than 2 percent heavier elements

Overall results of the proton-proton chain is that

4 H becomes 1 He + energy

The overall result of the proton-proton chain is that

4 H becomes 1 He and energy

What is the average temperature of the surface of the Sun

6,000 K

Which of these stars has the greatest surface temp

A 30Msun main sequence star

Which of these star cluster is oldest

A cluster whose brightest main seq are yellow

Which of these star clusters is oldest?

A cluster whose brightest main seq stars are yellow

Which of these stars has the longest lifetime

A main sequence M star

What do astronomers consider heavy elements?

All elements besides hydrogen and helium

Five stars are shown on the following HR. Rank these 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 others.

All five stars appear at the same place along the horizontal axis showing spectral type. Because spectral type is related to surface temperature, all five stars must have the same surface temperature. Now proceed to Part C to determine how these stars vary in luminosity.

Rank the stars based on their luminosity from highest to lowest; notice that these are the same five stars shown in Part D.

All five stars have the same luminosity because they are all at the same height along the vertical (luminosity) axis. Continue to Parts F and G for more practice in reading surface temperature and luminosity on the HR diagram.

Five stars are shown on the following HR. Rank the stars based on their surface temp from highest to lowest. If two or more stars have the same surface temp, drag one star on top of the others.

All the same. All five stars appear at the same place along the horizontal axis showing spectral type. Because spectral type is related to surface temperature, all five stars must have the same surface temperature. Now proceed to Part C to determine how these stars vary in luminosity.

Rank the stars based on their luminosity from highest to lowest.

All the same. All five stars have the same luminosity because they are all at the same height along the vertical (luminosity) axis. Continue to Parts F and G for more practice in reading surface temperature and luminosity on the HR diagram

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

An increase in core temp, a decrease in the core radius 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 changes would cause the fusion rate in the Sun's core to increase

An increase in the core temp/ a decrease in the core radius 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.

Rank based on luminosity

As always, the H-R diagram shows surface temperature along the horizontal axis and luminosity along the vertical axis.

Rank the stars based on their luminosity from highest to lowest.

As always, the H-R diagram shows surface temperature along the horizontal axis and luminosity along the vertical axis.

The life tracks shown on the diagram for different mass protostars are based on computer models. Observationally, how can astronomers test whether these models are correct?

By observing and comparing protostars and stars of different masses within a single star cluster. A star cluster forms from a large molecular cloud, so all the stars in a cluster begin to form at nearly the same time. We can therefore learn about how stars progress through their lives by comparing different stars within a cluster.

What law explains why a collapsing cloud usually forms a protostellar disk around a protostar?

Conservation of angular momentum

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

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

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 As you have correctly answered, the Sun's pressure is highest at its center and drops steadily from the core to the surface. This fact reflects what we call 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.

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

Corona, chromosphere, photosphere

Rank the layers of the Sun's atmos based on their temp, from highest to lowest

Corona, chromosphere, photosphere Scientists were quite surprised when they first learned that the temperature increases with altitude in the Sun's atmosphere, and even today the heating mechanism is not fully understood. However, we know that magnetic fields play an important role in transporting heat upward, making the chromosphere hotter than the photosphere and the corona hotter still.

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

Corona, chromosphere, photosphere Scientists were quite surprised when they first learned that the temperature increases with altitude in the Sun's atmosphere, and even today the heating mechanism is not fully understood. However, we know that magnetic fields play an important role in transporting heat upward, making the chromosphere hotter than the photosphere and the corona hotter still.

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

Corona, chromosphere, photosphere The energy of the emitted light rises with temperature, so the ranking for this question is the same as that of Part C. In fact, the photosphere emits primarily visible light, the chromosphere primarily ultraviolet light, and the corona primarily X rays. This is why astronomers study the corona with X-ray telescopes and the chromosphere with ultraviolet telescopes, while we observe the photosphere with visible-light telescopes.

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

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 comm and knock out sensitive equipment

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.

Rank them based on the time each takes, from longest to shortest, to go from a protostar to a main seq star during the formation process

Correct ranking has the stars in order from lowest to highest mass (remember that for main seq stars, mass follows the spectral seq order OBAFGKM) less massive stars take longer to go through all stages of life than do more massive stars, so they also take longer to reach main seq

What is the cause of the stellar parallax

Earth's orbit around the Sun Stellar parallax occurs because we see stars from different vantage points as Earth orbits the Sun. This causes the positions of nearby stars to appear to shift relative to the positions of more distant objects. To see the idea clearly, click on the blue strip labeled "Parallax" in the Interactive Figure, then select "Stellar Parallax" and watch the animation.

What is the cause of the stellar parallax

Earth's orbit around the Sun Stellar parallax occurs because we see stars from different vantage points as Earth orbits the Sun. This causes the positions of nearby stars to appear to shift relative to the positions of more distant objects. To see the idea clearly, click on the blue strip labeled "Parallax" in the Interactive Figure, then select "Stellar Parallax" and watch the animation.

Which of the following is a valid way of demonstrating parallax for yourself?

Hold up your hand in front of your face, and alternately close your left and right eyes. Notice that parallax is an apparent shift caused by a change in the way you are looking at your hand, not an actual motion. Parallax is an apparent motion, not an actual motion. To see the idea, click on the blue strip labeled "Parallax" in the Interactive Figure, select "Introduction to Parallax," then click "Next" until you reach the third screen.

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. Increasing the fusion rate releases more energy into the core, which raises the temperature and increases the internal pressure, causing the core to expand. Decreasing the fusion rate means less energy is released, so the temperature and internal pressure decreases. As you can see in the interactive figure, the solar thermostat keeps the fusion rate fairly steady in a star like the Sun because a temperature increase causes the core to expand while a temperature decrease causes the core to contract.

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 Increasing the fusion rate releases more energy into the core, which raises the temperature and increases the internal pressure, causing the core to expand. Decreasing the fusion rate means less energy is released, so the temperature and internal pressure decreases. As you can see in the interactive figure, the solar thermostat keeps the fusion rate fairly steady in a star like the Sun because a temperature increase causes the core to expand while a temperature decrease causes the core to contract.

How does the interstellar medium obscure our view of most of the galaxy

It absorbs visible, UV, and some infrared light

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 member of an eclipsing binary system We can use Newton's version of Kepler's third law to calculate the masses of distant objects, but only if we know the period and distance of an orbiting object. This is possible for an eclipsing binary system, because the two stars orbit each other (and the eclipses tell us that we are viewing the orbit edge-on).

What do we mean by the star gas star cycle?

It is the continuous recycling of gas in the galactic disk between stars and the interstellar medium

What do we mean by the main sequence turnoff of a star cluster, and what does it tell us?

It is the spectral type of the hottest main seq star in a star cluster, and it tells us the cluster's age

What do we mean by the main-sequence turnoff point of a star cluster, and what does it tell us?

It is the spectral type of the hottest main sequence star in a star cluster, and it tells us the cluster's age.

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

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

It's apparent brightness will decrease by a factor of 9

According to 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 3

Watch the red dot representing the protostar in the animation. After it reaches its highest point on the diagram, how do the protostar's surface temperature and luminosity chage as it approaches the main seq?

Its surface temperature increases, but its luminosity decreases Notice that in the red dot in the animation moves left and down after it passes passes it highest point and begins to approach the main seq. Left means increasing surface temp, and down means decreasing luminosity

Which of these stars has the coolest surface temp

K star

Provided following are four different ranges of stellar masses. Rank the stellar mass ranges based on how many star in each range you would expect to be born in a star cluster, from highest number to lowest number

Less than 1 solar mass, between 1 and 10 solar masses, between 10 and 30 solar masses, between 30 and 60 solar masses Low mass stars are born in far greater numbers than higher mass stars, so clusters almost inevitably contain mostly low mass stars and fewer and fewer stars of higher masses.

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).

Luminosity is shown along the vertical axis, with stars higher up more luminous than those lower down. Note that each tickmark along the luminosity axis represents a change by a factor of 10 from the prior tickmark, so the range of luminosities is quite large. Continue to Parts D and E to investigate surface temperature and luminosity for a different set of five stars.

The axes on a Hertzsprung-Russell diagram represent

Lumninosity and surface temp

What kinds of stars are most common in a newly formed star cluster

M stars

Which of these stars has the longest lifetime

Main sequenc M star

Since all stars begin their lives with the same basic composition, what characteristic most determines how they will differ.

Mass they are formed with

A solar model is used to calculate the expected temperature and density at all depth 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 Sun shines with energy generated by fusion, so the total rate at which the Sun emits energy into space must be equal to the rate at which it generates energy by fusion in the core. Neutrinos are a product of fusion reactions, so they provide direct evidence concerning fusion in the core.

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 Sun shines with energy generated by fusion, so the total rate at which the Sun emits energy into space must be equal to the rate at which it generates energy by fusion in the core. Neutrinos are a product of fusion reactions, so they provide direct evidence concerning fusion in the core.

How is the lifetime of a star related to its mass

More massive stars live much shorter lives than less massive stars

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

More massive stars live much shorter lives than less massive stars

Rank stars based on strength of the radiation pressure that pushes outward as they are forming, from highest pressure to lowest pressure.

Notice that the correct ranking has the stars in order from highest to lowest mass (for main seq stars mass follows the spectral sequence order OBAFGKM), because radiation pressure is stronger in more mmasive stars. In fact, it is so strong for very massive stars that it prevents stars with masses above about 150 solar masses from forming at all.

TO understand the interplay of observations and models you must first be able to distinguish between things that we onbserve things that infer from moderls. 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 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 Inferences from a model: The Sun generates energy by fusing hydrogen into helium in its core. The core temp 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.

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: 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. Inferences: The Sun generates energy by fusing hydrogen into helium in its core. The convection zone is cooler than the radiation zone. The core temp is 10 million K. The composition of the photosphere is the same as that of the gas cloud that gave birth to our solar system

Solar energy leaves the core of the Sun in the form

Photons

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

Photosphere, chromosphere, corona As your answer correctly indicates, the density of the Sun's atmosphere decreases with altitude above the 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.

Photosphere, chromosphere, corona 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 HR diagrams. Rank the stars based on their surface temp from highest to lowest.

Spectral type is related to surface temperature, with stars of spectral type O having the highest surface temperature and stars of spectral type M having the lowest surface temperature. In other words, spectral type increases to the left on the H-R diagram.

Rank the stars based on their surface temp from highest to lowest. If two stars have the same surface temperature, drag one star on top of the other.

Spectral type is related to surface temperature, with stars of spectral type O having the highest surface temperature and stars of spectral type M having the lowest surface temperature. In other words, spectral type increases to the left on the H-R diagram.

Five stars are shown on the following HR. Rank based on their surface temp from highest to lowest. If two or more stars have same surface temp, drag one star on top of the others.

Spectral type is related to surface temperature, with stars of spectral type O having the highest surface temperature and stars of spectral type M having the lowest surface temperature. In other words, spectral type increases to the left on the H-R diagram. Now proceed to Part E to determine how these stars compare in luminosity.

Suppose two protostars form at the same time, one with a mass of .5 Msun and the other with a mass of 15 Msun. Which of the following statements are true?

The 15MSun protostar will be much more luminous than the 0.5MSun protostar. The 15MSun star will end its main-sequence life before the 0.5MSun star even completes its protostar stage. High-mass stars proceed through all stages of their lives much faster than low-mass stars—so much faster that when a star cluster forms, the high-mass stars can live and die before the low-mass stars are "born" at the ends of their protostar stages.

Based on the protostar tracks on the diagram, which statement must be true about the Sun?

The Sun was much more luminous when it was a protostar than it is today. You can see this fact by looking at the life track for the Sun's protostar stage. Note that it starts (at the right) much higher up at than it ends (where it reaches the main sequence), and higher on the H-R diagram means more luminous.

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 As you know from Part B, an increase in the fusion rate will cause the core to expand in a normal (or main-sequence) star like the Sun, and this expansion will restore core equilibrium. But if for some reason the core could not expand, the higher temperature would make the fusion rate increase even more, creating a positive feedback loop in which the fusion rate and temperature would keep getting higher and higher. (That is, there would be no equilibrium.) In fact, as you'll learn when you study stellar life cycles, this is essentially what will occur when the Sun is near the end of its life.

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.

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).

To be sure you understand the concept, notice the following facts: (1) Nismo is clearly brighter in the sky than Shelby, because it has the same luminosity but is nearer to us. (2) Enzo is twice as luminous and twice as far as Shelby; the inverse square law for light tells us that doubling distance makes an object four times as dim, so Enzo must be dimmer than Shelby. (3) Similarly, because Lotus has twice the luminosity and twice the distance of Enzo, it must be dimmer than Enzo. (4) Ferdinand has four times the luminosity and twice the distance of Shelby, so the inverse square law for light tells us that they are equally bright in our sky. Putting all four facts together leads to the correct answer.

Almost all elements heavier than hydrogen and helium were made inside stars.

True

Molecular clouds appear more transparent at longer wavelengths

True

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) Recall that Newton's version of Kepler's third law allows us to calculate the mass of any object if we know the orbital period and distance of a much smaller object that orbits it. This means we can use not only Earth's period and distance to calculate the Sun's mass but the period and distance of any planet or even of a spaceship that we put into solar orbit.

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). Recall that Newton's version of Kepler's third law allows us to calculate the mass of any object if we know the orbital period and distance of a much smaller object that orbits it. This means we can use not only Earth's period and distance to calculate the Sun's mass but the period and distance of any planet or even of a spaceship that we put into solar orbit.

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 distance, no interstellar gas or dust absorbs or scatters light between us and the star. We have measured the star's apparent brightness We can use the inverse square law for light to calculate the star's luminosity from its apparent brightness and distance. However, this calculated value will be accurate only if there is no absorption or scattering of the light on its way from the star to us. (If there is interstellar dust between us and the star, we can sometimes measure the amount and therefore determine the star's luminosity by accounting for the light this dust absorbs or scatters.)

You should now see that the reasons 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 measured the star's spectral type, we have determined that the star is a main sequence star. All main seq stars of a particular spectral type have approximately the same mass. There, if we know the star's spectral type and know that it is a main sequence star, then we can infer its mass

When does a newly forming star have the greatest lumin

When it is a shrinking protostar with no internal fusion If you watch the position of the red dot on the HR diagram as the interactive figure plays, you will see that the dot is highest--meaning the object is most luminous--when it is a protostar and therefore does not yet have internal fusion. This fact can be a little surprising, but do not forget that luminosity dpends on both surface temp and size. Protostars are always much larger than the main seq star they will become, which is why they can be so luminous even though they are still cool

Why do we think the first generation of stars would be different from stars born today?

Without heavy elements, the clouds could not reach as low a temperature as today and had to be more massive to collapse

Which star spends the longest time in the protostellar phase of lifefe?

a 1 solar mass star

Which of these stars has the greatest surface temp

a 30Msun main seq star

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

a blue white dwarf star, Gun, an orange main sequence star, red supergiant star Notice that temperature is related to color, and follows the order of the colors in the rainbow: Blue (or violet) stars are the hottest, while red stars are the coolest. In the parts that follow, the H-R diagrams show the correlation between color and temperature on the horizontal axis.

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

a blue white dwarf star, Sun, an orange main seq star, a red supergiant star Notice that temperature is related to color, and follows the order of the colors in the rainbow: Blue (or violet) stars are the hottest, while red stars are the coolest. In the parts that follow, the H-R diagrams show the correlation between color and temperature on the horizontal axis.

What kind of gas cloud is most likely to give birth to stars

a cold, dense gas cloud

Astronomers estimate that new stars form in our galaxy at the rate of about

a few (2-3) per year

How does the number of neutrinos passing through your body at night compare with the number passing through your body during the day>

about the same

How does the number of neutrinos passing through your body at night compare with the number passing through your body during the day?

about the same

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

apparent brightness and distance

What is the most common form of gas in the interstellar medium

atomic hydrogen

What produces the 21 cm line that we use to map out the Milky Way Galaxy

atomic hydrogen

On the main sequence, stars obtain their energy

by converting hydrogen to helium

How can we see through the interstellar medium

by observing in high energy wavelengths such as X rays and long wavelengths of light such as radio waves

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 HR diagram, stellar masses

can be estimated for main seq stars but not for other types of stars

On an H-R diagram, stellar masses

can be estimated for main sequence stars but not for other types of stars

Observe directly

color, parallax angle, spectral type, apparent brightness

On the main sequence, stars obtain their energy

converting hydrogen to helium

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

cooler and large in radius Be sure to notice that luminosity increases upward on the diagram, surface temperature increases to the left, and radius increases diagonally from the lower left to the upper right. Therefore, stars in the upper right must be high in luminosity and radius, but low in surface temperature. These stars are called giants or supergiants because of their large radii.

Compared to a high luminosity main sequence star, stars in the upper right of the HR diagram are

cooler and larger in radius Be sure to notice that luminosity increases upward on the diagram, surface temperature increases to the left, and radius increases diagonally from the lower left to the upper right. Therefore, stars in the upper right must be high in luminosity and radius, but low in surface temperature. These stars are called giants or supergiants because of their large radii.

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

core Nuclear fusion occurs only in the core of the Sun, where the temperatures, pressures, and densities are highest.

rank these 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 As you have correctly answered, the Sun's pressure is highest at its center and drops steadily from the core to the surface. This fact reflects what we call 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.

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

core, radiation zone, convective zone, photosphere As you have correctly answered, the Sun's temperature drops from the core to the surface, which is the photosphere. Notice that this part did not include the chromosphere and corona as choices, because their temperatures are surprisingly high, despite their very low densities.

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

core. Nuclear fusion occurs only in the core of the Sun, where temperatures, pressures, and densities are highest

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

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

corona, chromosphere, photosphere The energy of the emitted light rises with temperature, so the ranking for this question is the same as that of Part C. In fact, the photosphere emits primarily visible light, the chromosphere primarily ultraviolet light, and the corona primarily X rays. This is why astronomers study the corona with X-ray telescopes and the chromosphere with ultraviolet telescopes, while we observe the photosphere with visible-light telescopes.

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

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

hotter and smaller in radius Notice that the stars in the lower left of the diagram are called white dwarfs: white because they are hot enough to appear "white hot" to our eyes, and dwarfs because of their small sizes. A typical white dwarf is no larger in size (radius) than our Earth, but has as much mass as the Sun.

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

hotter and smaller in radius. Notice that the stars in the lower left of the diagram are called white dwarfs: white because they are hot enough to appear "white hot" to our eyes, and dwarfs because of their small sizes. A typical white dwarf is no larger in size (radius) than our Earth, but has as much mass as the Sun.

As a clump of interstellar gas contracts to become a main-sequence star, its changing position on the H-R diagram tells us

how its outward appearance is changing An objects position on the HR diagram tells us its surface temp and lumin, which are essentially outward appear

What is the most common kind of element in the solar wind

hydrogen

Where would you be most likely to find an ionization nebula

in a spiral arm

Where does most star formation occur in the Milky Way Galaxy

in the spiral arms

where does most star formation occur in the Milky Way today?

in the spiral arms

where do most dust grains form

in the winds of red giant stars

HR diagram, stellar radii

increase diagonally from the lower left to the upper right

On an H-R diagram, stellar radii

increase diagonally from the lower left to the upper right

Which of these forms of radiation passes most easily through the disk of the Milky Way?

infrared

Which part of the electromagnetic spectrum generally gives us our best views of stars forming in dusty clouds?

infrared

If star A is closer to us than star B, then Star A's parallax angle is

larger than that of Star B

If star A is closer to us than star B, then Star A's parallax angle

larger than that of star b

Compared to a main seq star with a short lifetime, a main seq star with a long lifetime is

less luminous, cooler, cooler, smaller, and less massive Note that there are physical reasons why long-lived stars have these properties: They are less luminous because they burn their fuel at a much lower rate than short-lived stars; they burn it at this lower rate because they are less massive (which means less compression and hence a lower fusion rate in their cores); and their lower masses lead to their smaller sizes and lower surface temperatures.

Compare to a main sequence star with a short lifetime, a main seq star with a long lifetime is

less luminous, cooler, smaller, and less massive Note that there are physical reasons why long-lived stars have these properties: They are less luminous because they burn their fuel at a much lower rate than short-lived stars; they burn it at this lower rate because they are less massive (which means less compression and hence a lower fusion rate in their cores); and their lower masses lead to their smaller sizes and lower surface temperatures.

The total amount of power that a star radiates into space is called its

luminosity

Total amount of power that a star radiates into space is called its

luminosity

The axes on a HR represent

luminosity and surface temp

The five colored curves on the diagram have arrows pointing to the left. Each of these five curves represents a star of a different

mass Notice that each star's mass is indicated by the purple numbers to the left of where each curve touches the main sequence.

A source of energy that keep the Sun shining today is

nuclear fusion

The source of energy that keeps the Sun shining today is

nuclear fusion

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

photons

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

photosphere, chromosphere, corona As your answer correctly indicates, the density of the Sun's atmosphere decreases with altitude above the 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.

photosphere, chromosphere, corona 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.

The phase of matter in the Sun is

plasma

The phase of matter in the Sun is

plasma motherf*cker

The arrows on each protostar's curve on the diagram's indicate that

protostars change in surface temp and luminosity as they develop Each curve is a life track (or evolutionary track) showing how the luminosity and temperature of a single protostar changes as it gradually develops into a main-sequence star.

Which protostars maintain nearly the same luminosity throughout the time that they are protostars?

protostars with masses about 10 or more times that of the Sun. Notice that the life tracks for the 9- and 15-solar-mass protostars are nearly horizontal, indicating that these high-mass stars maintain nearly constant luminosity throughout their protostar stages.

The more distant a star the

smaller its parallax angle Just as moving your finger farther from your face makes its parallax smaller as you alternately close each eye, a more distant star has a smaller amount of stellar parallax than a star that is closer to Earth.

The more distant a star, the

smaller its parallax angle Just as moving your finger farther from your face makes its parallax smaller as you alternately close each eye, a more distant star has a smaller amount of stellar parallax than a star that is closer to Earth.

What must we measure directly so that we can infer a star's surface temp

spectral type

FIve stars are shown on the following HR diagram. Rank the stars based on their surface temperature from highest to lowest. If two (or more) stars have the same surface temp, drag one star on top of the others

spectral type corresponds to temperature. high temp is O. H is low temp.

What are cosmic rays?

subatomic particles tht travel close to the speed of light

Before we can use parallax to measure the distance to a nearby star, we first need to know

the Earth Sun distance The Earth-Sun distance, or 1 AU, forms the baseline used in parallax measurements. We measure the Earth-Sun distance by using radar within our solar system to measure the distance to a planet, such Venus, from which we can then calculate the Earth-Sun distance.

Before we can use parallax to measure the distance to a nearby star, we first need to know

the Earth-Sun distance The Earth-Sun distance, or 1 AU, forms the baseline used in parallax measurements. We measure the Earth-Sun distance by using radar within our solar system to measure the distance to a planet, such Venus, from which we can then calculate the Earth-Sun distance.

The interstellar clouds called molecular clouds are ___

the cool clouds in which stars form

What two pieces of info 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

Most interstellar clouds remain stable in size because the force of grav is opposed by ______ within the cloud

thermal pressure

Approx, what basic composition are all stars both with?

three-quarters hydrogen, one-quarter helium, no more than 2 percent heavier elements

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

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

When does hydrogen first begin to fuse into helium in the star formation process?

when the protostar undergoes radiative contraction

Where are large dust clouds predominantly located in the galaxy M51

within or on the edges of spiral arms. As is generally true for spiral galaxies, large, star forming dust clouds are located primarily within or on the edges of spiral arms

Where are the ionization nebulae predom located in galaxy M51

within or on the edges of the spiral arms of the galaxy Like the dust clouds, ionization nebulae are located primarily within or on the edges of spiral arms. This is because spiral arms are regions of active star formation. Stars are born within dust clouds, and ionization nebulae are ionized by the intense light from massive, young stars.