Chapter 15 home work 13 Surveying the Stars Flashcards
What is the approximate chemical composition (by mass) with which all stars are born?
half hydrogen and half helium 98% hydrogen, 2% helium 95% hydrogen, 4% helium, no more than 1% heavier elements three quarters hydrogen, one quarter helium, no more than 2% heavier elements
three quarters hydrogen, one quarter helium, no more than 2% heavier elements
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 3. Its apparent brightness will decrease by a factor of 9. Its apparent brightness will increase by a factor of 9. Its apparent brightness will increase by a factor of 3.
Its apparent brightness will decrease by a factor of 9.
Star A has an apparent magnitude of 3 and star B has an apparent magnitude of 5. Which star is brighter in our sky?
Star B The two stars have the same brightness in our sky, but Star A is closer to us than Star B. There is not enough information to answer the question. Star A
Star A
From hottest to coolest, the order of the spectral types of stars is _________.
ABCDEFG ABFGKMO OMGABFF!! OBAGFKM OBAFGKM
OBAFGKM
Our Sun is a star of spectral type _________.
S G F M
G
Astronomers can measure a star’s mass in only certain cases. Which one of the following cases might allow astronomers to measure a star’s mass?
The star is of spectral type G. We know the star's luminosity and distance. The star is of spectral type A. The star is a member of a binary star system.
The star is a member of a binary star system.
How is the lifetime of a star related to its mass?
More massive stars live much longer lives than less massive stars. More massive stars live much shorter lives than less massive stars. More massive stars live slightly shorter lives than less massive stars. More massive stars live slightly longer lives than less massive stars.
More massive stars live much shorter lives than less massive stars.
What is the common trait of all main sequence stars?
They are in the final stage of their lives. They are all spectral type G. They all have approximately the same mass. They generate energy through hydrogen fusion in their core.
They generate energy through hydrogen fusion in their core.
What is a white dwarf?
It is a star that follows a period-luminosity relation. a main sequence star of spectral type F, which tends to look white in color the remains of a star that ran out of fuel for nuclear fusion It is a type of star that produces energy by gravitational contraction.
the remains of a star that ran out of fuel for nuclear fusion
Compared to a main-sequence star with a short lifetime, a main-sequence star with a long lifetime is __________.
more luminous, hotter, larger, and more massive more luminous, hotter, smaller, and less massive less luminous, cooler, larger, and more massive less luminous, cooler, smaller, and less massive
less luminous, cooler, smaller, and less massive
Compared to a high-luminosity main-sequence star, stars in the upper right of the H-R diagram are __________.
hotter and larger in radius cooler and larger in radius cooler and smaller in radius hotter and smaller in radius
cooler and larger in radius
Compared to a low-luminosity main-sequence star, stars in the lower left of the H-R diagram are __________.
hotter and larger in radius cooler and larger in radius cooler and smaller in radius hotter and smaller in radius
hotter and smaller in 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 The majority of starts in our galaxy The sun for example The hottest and most luminous stars Very hot but very dim Not much larger in radius than earth.
Very cool but very luminous
Found in the upper right of the H-R diagram
Listed following is a set of statements describing individual stars or characteristics of stars. Match these to the appropriate object category. Main-sequence stars Very cool but very luminous Found in the upper right of the H-R diagram The majority of starts in our galaxy The sun for example The hottest and most luminous stars Very hot but very dim Not much larger in radius than earth.
The majority of starts in our galaxy
The sun for example
The hottest and most luminous stars
Listed following is a set of statements describing individual stars or characteristics of stars. Match these to the appropriate object category.White dwarfs Very cool but very luminous Found in the upper right of the H-R diagram The majority of starts in our galaxy The sun for example The hottest and most luminous stars Very hot but very dim Not much larger in radius than earth.
Very hot but very dim
Not much larger in radius than earth.
Star A is identical to Star B, except that Star A is twice as far from us as Star B. Therefore:
Both stars have the same luminosity, but the apparent brightness of Star B is four times that of Star A. Both stars have the same luminosity, but the apparent brightness of Star A is four times that of Star B. Both stars have the same apparent brightness, but the luminosity of Star B is four times that of Star A. Both stars have the same luminosity, but the apparent brightness of Star B is twice that of Star A.
Both stars have the same luminosity, but the apparent brightness of Star B is four times that of Star A.
Sirius is a star with spectral type A star and Rigel is a star with spectral type B star. What can we conclude?
Rigel has a higher core temperature than Sirius. Sirius has a higher core temperature than Rigel. Sirius has a higher surface temperature than Rigel. Rigel has a higher surface temperature than Sirius.
Rigel has a higher surface temperature than Sirius.
The approximate main-sequence lifetime of a star of spectral type O is _________.
3 million years 300 million years 10,000 years 10 billion years
3 million years
How did astronomers discover the relationship between spectral type and mass for main sequence stars?
By measuring stellar radii with very powerful telescopes. By measuring the masses and spectral types of main-sequence stars in binary systems. By comparing stars with the same spectral type but different luminosities. By using computer models of hydrogen fusion and stellar structure.
By measuring the masses and spectral types of main-sequence stars in binary systems
Before we can use parallax to measure the distance to a nearby star, we first need to know __________.
the month in which the star is observed the distance to the nearest star besides the Sun the Earth-Sun distance the Sun's mass
the Earth-Sun distance
Which of the following is a valid way of demonstrating parallax for yourself?
Get a camera, and photograph a person who is running back and forth. Hold up your hand in front of your face, and alternately close your left and right eyes. Hold up your hand in front of your face, and move it slowly back and forth. Look up at a star, and notice how it moves toward the western horizon during the night.
Hold up your hand in front of your face, and alternately close your left and right eyes.
What is the cause of stellar parallax?
Stellar parallax is caused by
the gradual motion of stars in the local solar neighborhood.
the varying speed of Earth in its orbit around the Sun.
the gradual change in the patterns of the constellations over thousands of years.
Earth’s orbit around the Sun.
Earth’s orbit around the Sun.
The more distant a star, the __________.
smaller its parallax angle slower its parallax occurs faster its parallax occurs larger its parallax angle
smaller its parallax angle
Suppose that a star had a parallax angle of exactly 1 arcsecond. Approximately how far away would it be, in light-years?
1 light-year 3. 3 light-years 2. 1 light-years 8. 7 light-years
3.3 light-years
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).
Observer directly
color parallax angle spectral type apparent brightness luminosity surface temperature mass radius
color
parallax angle
spectral type
apparent brightness
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).
Infer indirectly
color parallax angle spectral type apparent brightness luminosity surface temperature mass radius
luminosity
surface temperature
mass
radius
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 apparent brightness parallax angle mass
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?
Check all that apply.
We have measured the star’s apparent brightness. No interstellar gas or dust absorbs or scatters light between us and the star. The star must be a member of a binary system. We have measured the star’s spectral type. We have measured the star’s distance.
We have measured the star’s apparent brightness.
No interstellar gas or dust absorbs or scatters light between us and the star.
We have measured the star’s distance.
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 unusually high in mass we know its spectral type it is near enough for us to measure its distance with parallax it is a member of an eclipsing binary system
it is a member of an eclipsing binary system
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?
Check all that apply.
We have determined that the star is a main-sequence star. We have measured the star’s velocity. The star must be located within the Milky Way Galaxy and not in another galaxy. We have measured the star’s spectral type.
We have determined that the star is a main-sequence star.
We have measured the star’s spectral type.
