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 layers of the Sun does nuclear fusion occur?
core
Classify each statement as an observation or as an inference based on the current, accepted model for the Sun.
observation: the photosphere is made mostly of hydrogen and helium, the photosphere emits mostly visible light, the sun emits neutrions, the corona is hotter than the photosphere
Classify each statement as an observation or as an inference based on the current, accepted model for the Sun.
inferences from a model: core temperature is 10 million k, the convection zone is cooler than the radiation zone, the sun generates energy by fusing hydrogen into helium in its core, the composition of the photosphere is the same as that of the gas cloud
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.
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).
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
Observations of neutrinos coming from the Sun
and
Measurements of the Sun's total energy output into space
What is the approximate chemical composition (by mass) with which all stars are born?
three quarters hydrogen, one quarter helium, no more than 2% heavier elements
The total amount of power (in watts, for example) that a star radiates into space is called its _________.
luminosity
According to the inverse square law of light, how will the apparent brightness of an object change if its distance to us triples?
its apparent brightness will decrease by a factor of 9
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.
If star A is closer to us than star B, then Star A's parallax angle is _________.
Larger than that of star B
Ten parsecs is about _________.
32.6 light-years
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 A
From hottest to coolest, the order of the spectral types of stars is _________.
OBAFGKM
Our Sun is a star of spectral type _________.
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 a member of a binary star system
Which of the following terms is given to a pair of stars that we can determine are orbiting each other only by measuring their periodic Doppler shifts?
Spectroscopic binary
The axes on a Hertzsprung-Russell (H-R) diagram represent _________.
luminosity and surface temperature
What can we infer, at least roughly, from a star's luminosity class?
its size (radius)
On an H-R diagram, stellar radii _________.
increase diagonally from the lower left to the upper right
On an H-R diagram, stellar masses _________.
can be determined for main sequence stars but not for other types of stars
How is the lifetime of a star related to its mass?
More massive stars live much shorter lives than less massive stars.
Each choice below lists a spectral type and luminosity class for a star. Which one is a red supergiant?
Spectral type M2, luminosity class I
What is the common trait of all main sequence stars?
They generate energy through hydrogen fusion in their core.
Suppose our Sun were suddenly replaced by a supergiant star. Which of the following would be true?
Earth would be inside the supergiant.
What is a white dwarf?
the remains of a star that ran out of fuel for nuclear fusion
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.
observe directly
color, apparent brightness, parallax angle, spectral type
infer indirectly
lumionsity, mass, radius, surface temperature
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
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 found that mass must be inferred for the star described in Part A. However, we can measure a star's mass directly if __________.
it is a member of an eclipsing binary system
we cannot apply Newton's version of Kepler's third law. Which of the following must be true if the star's inferred mass is to be accurate?
We have determined that the star is a main-sequence star.
and
We have measured the star's spectral type.
the _______ is greater for high mass stars than it is for low mass stars
main-sequence lifetime
the stars known as ___ are the very brightest and very largest of all the stars
supergiants
most of the stars near the sun are
main - sequence stars
stars are classified on the basis of their spectacal type and _______
luminosity class
cepheids are examples of
pulsating variable stars
____ are no longer generating energy through nuclear fusion
white dwarfs
stars that are cooler than the sun yet 100 to 1,000 times as luminous as the sun are classified as ______
giants