Astronomy test 2

213 terms by c_ruiz

Create a new folder

Advertisement Upgrade to remove ads

Which of these colors of light passes most easily through interstellar clouds?

yellow light

A protostar is a __________.

star that is still in the process of forming

Recall that a main-sequence star is what we usually think of as a "normal" star, meaning one that generates energy through hydrogen fusion in its core. On the H-R diagram shown in this activity, main-sequence stars can be found __________.

along the well-defined curve running from the upper left to the lower right

The position of a star along the main sequence is determined by the star's __________.

mass

The position of a star (or protostar) on the H-R diagram tell us its __________.

surface temperature and luminosity

A group of stars with the same luminosity would form a _____ line on the H-R diagram.

horizontal

Suppose one star is directly above another on the H-R diagram. What can you conclude about the two stars?

Both stars have the same surface temperature, but the one higher up is more luminous.

Suppose two protostars form at the same time, one with a mass of 0.5 and the other with a mass of 15. Which of the following statements are true?

The 15 protostar will be much more luminous than the 0.5 protostar.
The 15 star will end its main-sequence life before the 0.5 star even completes its protostar stage.

Star clusters are extremely useful to astronomers for two key reasons:
All the stars in a cluster lie at about the same distance from Earth.
All the stars in the cluster formed from the same interstellar cloud and therefore began to form at about the same time.
Astronomers can therefore use star clusters as laboratories for comparing the properties of stars at about the same distance or of about the same age.

By observing and comparing protostars and stars of different masses within a single star cluster.

A molecular cloud fragment is __________.

a piece of a larger star-forming cloud in which one or a few stars will form.

In general, a contracting cloud will heat up only if __________.

it is dense enough to trap light inside it.

A contracting cloud loses gravitational potential energy as it contracts in size. What happens to this energy?

It is converted to light and to heat within the cloud.

Angular momentum must be conserved as a cloud contracts. Therefore, in a contracting cloud, __________.

the rotation rate must increase as it shrinks in size.

From the H-R diagram we can directly read off __________.

an object's surface temperature and luminosity

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

On the H-R diagram, hotter objects are plotted __________ than cooler objects.

farther to the left

On the H-R diagram, more luminous objects are plotted __________ on the graph than less luminous objects.

higher up

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 change as it approaches the main sequence?

Its surface temperature increases, but its luminosity decreases.

When does a newly forming star have the greatest luminosity?

when it is a shrinking protostar with no internal fusion

In the interactive figure, the red dot represents an object at its maximum luminosity when the dot appears __________.

at its highest point on the H-R diagram

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

gravitational contraction

Protostars shine with energy generated by _____.

gravitational contraction

What happens within a contracting cloud in which gravity is stronger than pressure and temperature remains constant?

It breaks into smaller fragments.

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

trapping of thermal energy inside the protostar

For main-sequence stars, which of the following lists the spectral types in order of decreasing mass?

OBAFGKM

Radiation pressure is produced by __________.

photons

Among stars within about 50 light-years of our solar system, __________.

very low-mass stars are the most common, and higher-mass stars are increasingly rare

Definition of a molecular cloud

a cool, dense interstellar cloud in which the low temperatures allow hydrogen atoms to pair up into hydrogen molecules.

Definition of thermal pressure

is the ordinary pressure in a gas, arising from motions of particles, that can be attributed to the object's temperature.

Definition of a protostellar disk

is a disk of material surrounding a forming star that has not yet reached the point where sustained fusion can occur in its core; it is essentially the same as a proto-planetary disk, but may not necessarily lead to planet formation

Definition of a protostellar wind

is the relatively strong wind from a forming star that has not yet reached the point where sustained fusion can occur in its core.

Definition of a jet

is a high-speed stream of gas ejected from an object into space.

Definition of a close binary

is a binary star system in which the two stars are very close together.

Definition of degeneracy pressure

is a type of pressure unrelated to an object's temperature, which arises when electrons (electron degeneracy pressure) or neutrons (neutron degeneracy pressure) are packed so tightly that the exclusion and uncertainty principles come into play.

Definition of a brown dwarf

is an object too small to become an ordinary star because electron degeneracy pressure halts its gravitational collapse before fusion becomes self-sustaining; brown dwarfs have mass less than 0.08

Which two processes can generate energy to help a star or gas cloud maintain its internal thermal pressure?

nuclear fusion and gravitational contraction

About what percentage of the mass of a molecular cloud is in the form of dust?

1%

How do we learn the chemical composition of the interstellar medium?

By studying spectra of interstellar gas clouds.

What happens to the visible light radiated by stars located within a dusty gas cloud?

It is absorbed by dust, which heats the dust grains so that they emit the absorbed energy as infrared light.

Under which circumstances can you be sure that the thermal pressure within a gas cloud is increasing?

the cloud's temperature and density are both increasing

Which process is required to allow a gravitationally-collapsing gas cloud to continue to collapse?

The cloud must radiate away much of its thermal energy.

According to current understanding, how did the first generation of stars differ from stars born today?

They were much more massive than most stars born today.

Angular momentum plays an important role in star formation. Which of the following characteristics of a protostellar system is probably not strongly affected by the star's angular momentum?

the onset of core hydrogen fusion

Close binary star systems are thought to form when _____.

gravity pulls two neighboring protostars quite close together, but angular momentum causes them to orbit each other rather than colliding.

Generally speaking, how does the surface temperature and luminosity of a protostar compare to the surface temperature and luminosity of the main-sequence star it becomes?

A main-sequence star is hotter and dimmer than it was as a protostar.

Where does a 1-solar-mass protostar appear on an H-R diagram?

to the right of the main sequence, and higher up than the Sun

Why does the rotation of a protostar slow down over time?

Magnetic fields can transfer angular momentum to the protostellar disk and protostellar winds can carry angular momentum away

The surface of a protostar radiates energy while its core ________.

shrinks and heats

The core of a protostar that will eventually become a brown dwarf shrinks until ______.

the type of pressure called degeneracy pressure becomes important

If a star is extremely massive (well over 100 solar masses), why isn't it likely to survive for long?

It may blow itself apart because of radiation pressure.

Consider a large molecular cloud that will give birth to a cluster of stars. Which of the following would you expect to be true?

A few massive stars will form, live, and die before the majority of the star's clusters even complete their protostar stage

We do not know for certain whether the general trends we observe in stellar birth masses also apply to brown dwarfs. But if they do, then which of the following would be true?

Brown dwarfs would outnumber all ordinary stars.

Where would a brown dwarf be located on an H-R diagram?

below and to the right of the lowest part of the main sequence

What do we mean by the interstellar medium?

the gas and dust that lies in between the stars in the Milky Way galaxy

The interstellar clouds called molecular clouds are _______.

the cool clouds in which stars form

Which of the following types of molecule is the most abundant in an interstellar molecular cloud?

H2

Interstellar dust consists mostly of _____.

microscopic particles of carbon and silicon

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

infrared

Suppose you look by eye at a star near the edge of a dusty interstellar cloud. The star will look _______ than it would if it were outside the cloud.

dimmer and redder

Most interstellar clouds remain stable in size because the force of gravity is opposed by _______ within the cloud.

thermal pressure

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

a cold, dense gas cloud

What effect are magnetic fields thought to have on star formation in molecular clouds?

They can help resist gravity, so that more total mass is needed before the cloud can collapse to form stars.

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

They were made only from hydrogen and helium.

What is a protostar?

a star that is still in the process of forming

Which of the following phenomena is not commonly associated with the star formation process?

intense ultraviolet radiation coming from a protostar

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

conservation of angular momentum

What can we learn about a star from a life track on an H-R diagram?

the surface temperature and luminosity the star will have at each stage of its life

When does a protostar become a main-sequence star?

when the rate of hydrogen fusion becomes high enough to balance the rate at which the star radiates energy into space

Approximately what core temperature is required before hydrogen fusion can begin in a star?

10 million K

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

a 1 solar mass star

What is the approximate range of masses that newborn main sequence stars can have?

0.1 to 150 solar masses

The vast majority of stars in a newly formed star cluster are ______.

less massive than the Sun

Which of the following statements about brown dwarfs is not true?

Brown dwarfs eventually collapse to become white dwarfs.

The Sun's photosphere is __________.

the visible surface of the Sun

The word corona, as in the Sun's corona, means _____.

crown

As you go upward in altitude through Earth's atmosphere __________.

the density steadily decreases

How do we observe different layers of the Sun's atmosphere?

We use visible-light telescopes to observe the photosphere, ultraviolet telescopes to observe the chromosphere, and X-ray telescopes to observe the corona.

When we observe the Sun with an X-ray telescope, we see the _____.

corona

The layer of the Sun's atmosphere that is best observed with an ultraviolet telescope is the _____.

chromosphere

The Sun's photosphere is __________.

the visible surface of the Sun.

Fusion requires bringing two positively charged nuclei so close together that the strong nuclear force can hold them against the electromagnetic repulsion of their positive charges. What conditions make fusion possible?

extremely high temperature and high density

When the Sun's core contracts, the core temperature _____.

increases

What equilibrium for the core of a star means

The core of a star is in equilibrium when its temperature, size, and the rate of nuclear fusion all hold steady.

Suppose you could somehow start nuclear fusion in a box that stayed the same size. Increasing the fusion rate would cause the temperature inside the box to _____.

increase

If you heat up a balloon, what happens to it?

The gas particles inside it move faster, causing it to expand until it stabilizes at a new, larger size.

If you heat up a balloon, what happens to it?

The gas particles inside it move faster, causing it to expand until it stabilizes at a new, larger size.

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

Our current understanding of nuclear fusion in the Sun's core is based primarily on __________.

applying the laws of physics to calculate what must be occurring inside the Sun

Which of the following lists the Sun's layers in the correct order (staring from the Sun's center and going outward)?

core, radiation zone, convection zone, photosphere, chromosphere, corona

Which of the following statements accurately describes how we can best study different layers of the Sun with telescopes either on the ground or in space?

We observe the photosphere with visible-light telescopes, the chromosphere with ultraviolet-light telescopes, and the corona with X-ray telescopes.

Definition of a neutrino

a lightweight (almost massless) particle that is a by-product of nuclear reactions and radioactive decay.

Which of the following lists the Sun's layers in the correct order (staring from the Sun's center and going outward)?

core, radiation zone, convection zone, photosphere, chromosphere, corona

Which of the following statements accurately describes how we can best study different layers of the Sun with telescopes either on the ground or in space?

We observe the photosphere with visible-light telescopes, the chromosphere with ultraviolet-light telescopes, and the corona with X-ray 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

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

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

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

Core, Radiation Zone, Convection Zone, Photosphere

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

Core, Radiation Zone, Convection Zone, Photosphere

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

Core

The Sun is in gravitational equilibrium throughout its interior, which means that ___________.

the inward pull of gravity is everywhere balanced by the outward push of pressure inside the Sun

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

Photosphere, Chromosphere, Corona

What a convection zone is

a region in which energy is transported outward by convection, which means hot material will rise and cooler material will fall

What a chromosphere is

the layer of the Sun's atmosphere below the corona; most of the Sun's ultraviolet light is emitted from this region, in which the temperature is about 10,000 K.

What a photosphere is

the visible surface of the Sun, where the temperature averages just under 6,000 K.

What a radiation zone is

a region of the interior of a star in which energy is transported primarily by radiative diffusion.

What a core is

the central region of a star, in which nuclear fusion can occur

What a corona is

the tenuous uppermost layer of the Sun's atmosphere; most of the Sun's X rays are emitted from this region, in which the temperature is about 1 million K.

the average time from one solar minimum to the next is approximately _____.

11 years

Why do sunspots appear darker than their surroundings?

They are cooler than their surroundings

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

hydrogen

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

4 1/2 billion years

The Sun will exhaust its nuclear fuel in about ______.

5 billion years

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

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

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

gravitational force and outward pressure

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

nuclear fusion

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 the Sun made of (by mass)?

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

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

watts

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

photosphere

What is the solar wind?

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

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

nuclear fusion of hydrogen into helium

The proton-proton chain is _________.

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

The overall result of the proton-proton chain is:

4 H becomes 1 He + energy

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

use computer models to predict interior conditions

Why are neutrinos so difficult to detect?

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

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.

The light radiated from the Sun's surface reaches Earth in about 8 minutes, but the energy of that light was released by fusion in the solar core about _________.

a few hundred thousand years ago

What happens to energy in the Sun's convection zone?

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

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

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

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

The sunspot cycle is very steady, so that each 11-year cycle is nearly identical to every other 11-year cycle.

How is the sunspot cycle directly relevant to us here on Earth?

Coronal mass ejections and other activity associated with the sunspot cycle can disrupt radio communications and knock out sensitive electronic equipment

How do the properties of long-lived stars compare to those of short-lived stars?

both mass and luminosity

True or False? More massive main-sequence stars are less luminous than less massive main-sequence stars.

False

How do the properties of long-lived stars compare to those of short-lived stars?

Long-lived stars begin their lives with less mass and a smaller amount of hydrogen fuel

Long-lived stars are less luminous during their main-sequence lives

A main-sequence star twice as massive as the Sun will be about

ten times as luminous

A main-sequence star twice as massive as the Sun would last __________.

much less than half as long as the Sun

The fusion rate in the core of a main-sequence star will be greater if the core temperature and density are higher.

True

How do the life stages of a high-mass star compare to those of a low-mass star?

Both low- and high-mass stars are protostars until they can fuse hydrogen in their cores, then become hydrogen-burning main-sequence stars, and near the ends of their lives expand to become giants or supergiants.

Protostar is the name we give to __________.

a star that has not quite reached its "birth," meaning its core is not yet hot enough to sustain nuclear fusion

What makes a supergiant shine?

nuclear fusion of elements heavier than hydrogen (as well as of hydrogen in the shell)

Which of the following lists the elements in order of increasing atomic mass?

helium, carbon, oxygen, iron

A main-sequence star is __________.

a star in the longest stage of its life, in which it is fusing hydrogen into helium in its core

Protostar is the name we give to __________.

a star that has not quite reached its "birth," meaning its core is not yet hot enough to sustain nuclear fusion

A red giant shines with energy released by __________.

hydrogen fusion in a shell surrounding an inert helium core

A white dwarf is __________.

the dead remains of a low-mass star

On the H-R diagram, red giants are found __________.

toward the upper right, where stars are bright but cool

On the H-R diagram, white dwarfs are found __________.

in the lower left, where stars are dim but hot

Description of a supernova

is the complete explosion of a star

Description of a neutron star

the compact corpse of a high-mass star left over after a supernova. It typically contains a mass comparable to the mass of the Sun in a volume just a few kilometers in radius.

See More

Please allow access to your computer’s microphone to use Voice Recording.

Having trouble? Click here for help.

We can’t access your microphone!

Click the icon above to update your browser permissions above and try again

Example:

Reload the page to try again!

Reload

Press Cmd-0 to reset your zoom

Press Ctrl-0 to reset your zoom

It looks like your browser might be zoomed in or out. Your browser needs to be zoomed to a normal size to record audio.

Please upgrade Flash or install Chrome
to use Voice Recording.

For more help, see our troubleshooting page.

Your microphone is muted

For help fixing this issue, see this FAQ.

Star this term

You can study starred terms together

NEW! Voice Recording

Create Set