Astronomy Exam 4 Flashcards

Questions and Answers

The overall brightness of a star differs from luminosity in that ________

brightness depends on the distance to the star

The brightness of a star at 10 parsecs is called the star's ________.

absolute magnitude

The temperature and composition of a star's photosphere can be determined from the properties of its starlight.

True

Molecular absorption lines indicate a star is which of the following spectral types?

L Signup and view all the answers

The hotter the star, the bluer it appears. This is a consequence of ________.

Wien's Law Signup and view all the answers

The technique of combining the light from two or more smaller telescopes to obtain an image equivalent to that of a much larger telescope is called ________.

interferometry Signup and view all the answers

The total amount of energy that a star emits each second is called its ________.

luminosity Signup and view all the answers

Two orbiting stars revolve around a point of balance called the ________.

center of mass Signup and view all the answers

The star temperature classification that is just cooler than the sun is the F-class star.

False Signup and view all the answers

Measuring the orbital period and semimajor axis of a binary star will give us each star's own mass.

False Signup and view all the answers

If you know a star's temperature and use the Stefan-Boltzmann law you can find ________.

luminosity Signup and view all the answers

Binary stars are used to measure ________.

mass Signup and view all the answers

Stars whose absorption lines move back and forth are called ________.

spectroscopic binaries Signup and view all the answers

Our sun is a G-type star.

True Signup and view all the answers

The absorption lines in a star's spectral signature give insight into its composition because ________.

different elemental gases absorb photon energy on different frequencies Signup and view all the answers

An eclipsing binary can tell us each star's radius if we observe ________.

the eclipse duration and orbital speed Signup and view all the answers

New interferometry techniques have measured many sizes of stars far from Earth.

False Signup and view all the answers

We can measure the temperature of a star by ________.

determining its spectral type Signup and view all the answers

This type of binary star system is detected by using the Doppler shift: ________.

spectral binary Signup and view all the answers

The Balmer lines in a spectrum are the signature of ________.

hydrogen Signup and view all the answers

Using the Stefan-Boltzmann law to find luminosity requires ________.

radius and temperature Signup and view all the answers

40 percent of visible stars are binary systems.

True Signup and view all the answers

The surface temperature of an O-type star is around ________.

30,000 K Signup and view all the answers

A technique to find diameters of stars using short exposures is called ________.

speckle interferometry Signup and view all the answers

The person who first started the magnitude scale for stars was ________.

Hipparchus Signup and view all the answers

Scientists have recently defined three new stellar spectral types, L, T, and Y, which describe objects ________.

called brown dwarfs Signup and view all the answers

M-type stars have a surface temperature of about ________.

3000 K Signup and view all the answers

In astronomy, a standard candle is a star ________.

whose luminosity is well-determined Signup and view all the answers

Eclipsing binaries cannot be used to measure masses of stars.

False Signup and view all the answers

Absolute magnitude is the brightness of a star in the night sky.

False Signup and view all the answers

Apparent double stars are two stars going around each other.

False Signup and view all the answers

Our sun will die as a white dwarf.

True Signup and view all the answers

Stars that are forming are called ________.

protostars Signup and view all the answers

The lower limit for a normal star is about 0.1 solar masses.

True Signup and view all the answers

What are the main components of comet nuclei?

Ice Signup and view all the answers

Stars near the same position on the H-R diagram have approximately the same mass.

True Signup and view all the answers

On the H-R diagram, the radius and surface area of stars ________.

increases toward the upper left quadrant Signup and view all the answers

Most stars are not on the main sequence.

False Signup and view all the answers

The North Star, Polaris, is a ________.

yellow giant, variable star Signup and view all the answers

A cloud of ejected gas surrounding a dying star is called a(n) ________.

planetary nebula Signup and view all the answers

Stars that pulsate in and out are called ________.

variable stars Signup and view all the answers

________ are small, bright, dead cores of stars like our sun.

white dwarfs Signup and view all the answers

When a new star ejects gas in opposite directions, this is known as ________.

bipolar flow Signup and view all the answers

Stellar computer models help us trace a star's life from birth to death.

True Signup and view all the answers

A star's first energy source comes from gravitational collapse.

True Signup and view all the answers

A star's life cycle ultimately depends upon its mass.

True Signup and view all the answers

A molecular cloud contains mainly hot gases.

False Signup and view all the answers

More luminous stars on the main sequence are smaller in size.

False Signup and view all the answers

________ of stars will lie on the main sequence.

90% Signup and view all the answers

A main sequence star has a luminosity class of ________.

V Signup and view all the answers

These small dark areas in molecular gas clouds may be prime stellar formation areas: ________.

Bok Globules Signup and view all the answers

A protostar becomes a main-sequence star when ________.

hydrogen begins fusing into helium within its core Signup and view all the answers

Objects with masses between about 0.08 and 0.016 times the mass of the Sun are called ________.

brown dwarfs Signup and view all the answers

The best place to find star formation is in a ________.

molecular cloud Signup and view all the answers

A plot of surface temperature vs. luminosity for stars is known as the ________.

Hertzsprung-Russell (H-R) diagram Signup and view all the answers

According to the Stefan-Boltzmann Law, if two stars with the same surface temperature have different luminosities, then ________.

the more luminous one must have a larger radius Signup and view all the answers

A protostar is heated to fusing temperature by ________.

compression and accretion of materials due to gravitational collapse Signup and view all the answers

The pulsation period of very luminous Cepheid variable stars can be used with the standard candle formula to measure distances to galaxies millions of light-years away.

True Signup and view all the answers

Once core hydrogen is used up, gravitational contraction heats hydrogen in ________ to fusion temperatures.

a layer outside the core called a shell Signup and view all the answers

The stars with the shortest main sequence lifetimes will be ________.

the highest mass stars. Signup and view all the answers

The Sun will ascend into the giant region of the H-R diagram ________.

twice Signup and view all the answers

As soon as any star's core becomes degenerate, it collapses into a black hole.

False Signup and view all the answers

Many of the pulsating stars in the instability strip have an unstable layer that is responsible for alternately absorbing and releasing the energy flowing from the center of the star. This layer is made up of ________.

partially ionized helium. Signup and view all the answers

Cepheid variable stars have pulsation periods in the range of ________.

1-70 days Signup and view all the answers

The sun is expected to live about ________ years.

10 billion Signup and view all the answers

The more luminous a Cepheid variable star is, the slower it pulsates.

True Signup and view all the answers

For helium fusion to occur, a low-mass star must be compressed ________ a high-mass star.

more than Signup and view all the answers

Stars with less than about 0.4 times the mass of the Sun are probably ________.

fully convective. Signup and view all the answers

Without a source of energy, the Sun would ________.

collapse due to gravitational forces. Signup and view all the answers

We can use the ________ relation to help measure the distance to a Cepheid variable star.

period-luminosity Signup and view all the answers

The time stars spend as a giant during their life cycle is equal to the time spent as a main sequence star.

False Signup and view all the answers

The Sun's luminosity will continue to increase to around double its current value in the next 5 billion years.

True Signup and view all the answers

As the Sun's core heats up, helium will begin to fuse in a process called ________.

triple alpha fusion Signup and view all the answers

Geological studies show Earth's temperature has remained stable due to constant increases in greenhouse gases.

False Signup and view all the answers

When electrons are forced very close together, they can stop the collapse of a star. This is known as ________.

electron degeneracy Signup and view all the answers

Pulsating variable stars experience regular changes in luminosities while maintaining a constant diameter.

False Signup and view all the answers

Before it leaves the main sequence, the Sun's luminosity will ________.

double Signup and view all the answers

Very massive stars live relatively short lives.

True Signup and view all the answers

On the H-R diagram, most variable stars in the instability strip are ________ stars.

yellow Signup and view all the answers

Stars with a core temperature in excess of 20 million K probably have this hydrogen fusion type: ________.

CNO Signup and view all the answers

A protostar becomes a main-sequence star when ________.

hydrogen begins fusing into helium within its core Signup and view all the answers

When the core of our Sun begins to fuse helium, ________.

it will compress and turn yellow Signup and view all the answers

A type ________ supernova can result when a white dwarf receives enough extra mass from its companion star to fuse carbon and oxygen.

Ia Signup and view all the answers

Stars like our Sun will become ________ stars in their final phases.

Mira variable. Signup and view all the answers

Eventually a white dwarf cools to a black dwarf.

True Signup and view all the answers

Type II supernovas are white dwarf explosions.

False Signup and view all the answers

Spiraling gas around a white dwarf is known as a(an) ________.

accretion disk Signup and view all the answers

Helium core fusion in the Sun will last about ________ years.

100 million Signup and view all the answers

High mass stars are those above ________ solar masses.

8 Signup and view all the answers

A type ________ supernova is a single massive star exploding.

II Signup and view all the answers

The production of heavy atoms from light atoms inside of a star is called ________.

stellar nucleosynthesis Signup and view all the answers

A white dwarf can explode in a supernova if it ________.

False Signup and view all the answers

The sun will become a supernova.

False Signup and view all the answers

A high-mass star typically begins its life as a ________.

blue main-sequence star Signup and view all the answers

A recurrent nova usually occurs in a binary star system.

True Signup and view all the answers

Large massive stars create a series of nested shells of fusion as they age.

True Signup and view all the answers

The Chandrasekhar limit is about ________.

1.4 times the mass of the Sun. Signup and view all the answers

Stars like our sun will leave this type of remnant after they die: ________.

white dwarf Signup and view all the answers

A white dwarf will stay hotter than the sun for about ________.

1,000,000,000 years Signup and view all the answers

The process that generates energy in a white dwarf is ________.

nonexistent. Signup and view all the answers

Study Notes

Brightness and Luminosity

Brightness of a star is distance-dependent, unlike luminosity, which is an intrinsic property.
Absolute magnitude defines a star's brightness at a standard distance of 10 parsecs.

Star Temperature and Composition

Properties of starlight allow determination of a star's photosphere temperature and composition.
Molecules contribute to spectral lines, indicating a star's spectral type.

Special Laws and Techniques

Wien's Law explains why hotter stars appear bluer.
Interferometry combines light from multiple telescopes for improved imaging.
The Stefan-Boltzmann law connects temperature to a star's luminosity.

Binary Stars

Binary systems revolve around a shared center of mass.
Spectroscopic binaries exhibit moving absorption lines.
Eclipsing binaries can reveal star radii from eclipse duration and speed.
Mass measurement in binary stars relies on orbital periods and axes.

Stellar Classification

Our sun is classified as a G-type star, while F-type stars are actually hotter.
Newly defined spectral types L, T, and Y describe brown dwarfs.
M-type stars have surface temperatures around 3000 K.

Main Sequence Characteristics

About 90% of stars are on the main sequence, where they fuse hydrogen.
Luminosity class V indicates a main sequence star.

Star Lifecycles

Stars form from molecular clouds and evolve based on their mass.
Protostars become main-sequence stars upon hydrogen fusion in their cores.
High-mass stars have shorter life cycles than low-mass stars.

Synthesis and Remnants

Stellar nucleosynthesis produces heavy elements from lighter ones within stars.
White dwarfs are remnants of stars like our sun; they can become black dwarfs over immense timescales.
Type II supernovae come from massive single stars, while Type Ia supernovae arise from white dwarfs gaining mass.

Variable Stars

Cepheid variables are pulsating stars vital for measuring galactic distances; their pulsation periods are 1-70 days.
Variables exhibit regular luminosity changes, but maintain constant diameters during pulsation.

Stellar End Stages

After exhausting core hydrogen, the sun's core will compress, leading to helium fusion (triple alpha process).
Electron degeneracy pressure prevents collapse of stellar cores under certain conditions.
The sun's final phases will lead to a Mira variable star status before becoming a white dwarf.

Miscellaneous Facts

The Chandrasekhar limit defines the maximum mass for a stable white dwarf at approximately 1.4 solar masses.
Bok Globules are dense regions in molecular gas clouds, potential sites for star formation.
The North Star, Polaris, is categorized as a yellow giant and variable star.

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Test your knowledge with these flashcards for Astronomy Exam 4. Each card covers important concepts related to star brightness, absolute magnitude, and starlight properties. Perfect for students looking to review crucial astronomical terms and definitions.