ASTR101: Test #2
for an object producing thermal spectrum, a higher item causes the spectrum to have ______.
a peak intensity located at shorter wavelength.
the sun will exhaust its nuclear fuel in about--
5 billion years
what is the fate of an isolated brown dwarf?
It will remain a brown dwarf forever.
What observations characterize solar maximum?
There are many sunspots visible on the surface of the Sun.
the ultimate fate of our sun is...
become a white dwarf that will slowly cool with time
layers of the sun from innermost to outermost
core, radiation zone, convection zone, photosphere, chromosphere, corona
what is the 4th most abundant element?
carbon
Suppose we want to know what the Sun is made of. What should we do?
compare the wavelengths of lines in the sun's spectrum to the wavelengths of lines produced by chemical elements in the lab
Red light has a lower energy per photon than blue light. Therefore, red light has
lower frequency, longer wavelength than blue light
a main-sequence star twice as massive as the sun would last ______.
much less than half as long as the sun
what is the approx luminosity of a main-sequence M star?
0.01 solar
the approximate abundance of oxygen atoms in the galaxy is ______.
1/1000 that of hydrogen
a star of spectral type G will last approximately how long on the main sequence?
10 billion years
you observe a star cluster with a main-sequence turn-off point at spectral type G2 (the same spectral type as the sun). what is the age of this star cluster?
10 billion yrs
you measure the parallax angle for a star to be 0.1 arc seconds. the distance to the star is
10 parsecs
Rigel's luminosity is about ______ times the sun's luminosity
100,000
a star with a parallax angle of 0.1 arcsecond is ______ away from us.
32.6 light years
a star with a parallax angle of 0.01 arcsecond is ______ away from us.
326 light years
the basic fusion reaction through which the sun produces energy is _______.
4 hydrogen nuclei fuse to make 1 helium nucleus
According to modern science, approximately how old is the Sun?
4.5 billion years old
what is the approximate temp of the sun's core?
5,800 K
approximately, what is the sun made of (by mass)?
70% hydrogen, 28% helium, 2% other elements
the typical temp of a sunspot is about 4000 K.... use Wien's law to calculate the wavelength of peak thermal emission from a sunspot.
725 nm
Rigel's radius is about ______ times the Sun's radius.
80
what percentage of a star's total lifetime is spent on the main sequence?
90%
sort each item into the appropriate bin based on which type of spectrum is represents
CONTINUOUS SPECTRUM a graph of this spectrum shows a smooth curve arises from relatively dense objects like light bulb filaments, rocks, and people the only one of the spectra below that does not give us information about chemical comp. EMISSION LINE SPECTRUM a graph of this spectrum has upward spikes produces by thin or low-density clouds of gas ABSORPTION LINE SPECTRUM a graph of this spectrum is a curve with star, downward dips produced when starlight passes through a thin or low-density clouds of gas
The ______ allows us to determine how fast mars is moving toward or away from us.
Doppler effect
why does the sun emit neutrinos?
Fusion in the Sun's core creates neutrinos as a byproduct.
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 the sun generates energy by fusing hydrogen into helium in its core. the core temp is 10 million K. the comp of the photosphere is the same as that of the gas cloud that gave birth to our solar system. the convection zone is cooler than the radiation zone.
classify each property as either something that we can observe or measure directly or something that we must infer directly.
OBSERVE color, parallax angle, spectral type, apparent brightness INFER luminosity, radius, surface temp, mass
individual stars or characteristics of stars. match these
RED GIANT//SUPERGIANT very cool but vert luminous. found in the upper right of the HR diagram. MAIN-SEQUENCE the sun. the majority of stars in our galaxy. the hottest and most luminous stars. WHITE DWARFS very hot but very dim not much larger in radius than earth.
which of the following statements about apparent and absolute magnitudes is true?
The absolute magnitude of a star is dependent upon its luminosity.// A star's absolute magnitude is the apparent magnitude it would have if it were at a distance of 10 parsecs from Earth.// A star with an apparent magnitude of 1 appears brighter than a star with an apparent magnitude of 2.// The magnitude system that we use now is based on a system used by the ancient Greeks over 2,000 years ago that classified stars by how bright they appeared.
which of the following are forms of light (electromagnetic radiation)?
X-rays, radio waves, visible light, microwaves, infrared, ultraviolet, gamma rays
which of these star clusters is oldest?
a cluster whose brightest main-sequence stars are yellow.
for a higher temperature object, the graph peaks at ____.
a shorter wavelength
which of the following statements about spectral types of stars is true?
a star w spectral type F2 is hotter than a star w spectral type F3. a star with spectral type A is cooler than a star with spectral type B. the spectral type of a star can be used to determine its color. the spectral type of a star can be used to determine its surface temp.
at the end of its life, the remaining core of this star will be left behind as
a white dwarf made primarily of silicon and iron
Doppler shifted hydrogen absorption lines are seen in the spectrum of a star. The hydrogen line at 656.28 nm is seen to be shifted to 656.08 nm. How fast is the star moving?
about 100 km/s away from us
The brightest main-sequence star in a cluster has a temperature of 10,000 K and a luminosity about 10 times greater than the sun. What is the approximate age of the cluster?
about 10^9 years
it takes ____ for the sun to progress through one sunspot cycle from a maximin area covered with sunspots, to a min, and back to a max.
about 11 yrs
approximately how many neutrinos pass through your body each second?
about a thousand trillion
imagine that you are trying to stop neutrinos with a lead shield how thick would you need to make this shield to ensure that it can stop an average neutrino?
about one light-year
blue light hitting a red sweatshirt is an example of
absorption
carbon dioxide in mars's atmosphere produces ____ in the infrared portion of its spectrum
absorption lines
which of the following statements about open clusters is true?
all stars in the cluster are approx the same age.
which of the following is the most numerous type of main-sequence star?
an M star
what type of visible light spectrum does the sun produce?
an absorption line spectrum
when the atom's electrons step down to lower energy levels in a thin cloud of hot gas, what is produced?
an emission line spectrum
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
which statement about photons of light is true?
an infrared photon has less energy than an X-ray photon, but travels at the same speed.
a forming star spins more rapidly as it collapses because of conservation of ________.
angular motion
why do O stars exhibit hydrogen absorption lines?
at these high temps, nearly all the hydrogen is ionized, and is therefore unable to interact with light.
most continuous spectra are examples of what we also call thermal radiation spectra. why do we call them "thermal" spectra?
because the peak wavelength of the spectrum depends on the temp of the object producing the spectrum.
most interstellar clouds are made mostly of hydrogen. why are these clouds usually dominated by the color red?
because the strongest visible emission lines from hydrogen are red.
Rank the stars based on their surface temperature from highest to lowest.
blue white dwarf, sun, orange main-sequence star, red supergiant star
if a protostar has a mass too small for it to sustain nuclear fusion, it becomes the type of object known as a _________.
brown dwarf
on the main sequence, stars obtain their energy
by converting hydrogen to helium
various stages during the life of a high-mass star. rank from first to last
contracting cloud of gas and dust, protostar, main sequence O star, red supergiant, supernova, neutron star
Compared to a high-luminosity main-sequence star, stars in the upper right of the H-R diagram are __________.
cooler and larger in radius
in which of the following layers of the sun does nuclear fusion occur?
core
rank the layers of the sun based on the pressure within them, from highest to lowest
core, radiation zone, convection zone, photosphere
rank the layers of the sun based on their temperature, from highest to lowest
core, radiation zone, convection zone, photosphere
rank the layers of the sun based on their density, from highest to lowest
core, radiation zone, convection zone, photosphere, chromosphere, corona
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 sun spot 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.
Which of the following best explains the current state of agreement between theoretical models of star formation and observations of star formation?
current models can reproduce general features of star birth, but not all the details.
the collapse of a protostar with less than .08 times the mass of the sun is halted by __________.
degeneracy pressure
which of the following hypothetical observations would contradict our theories about the formation and evolution of white dwarfs?
discovery of a white dwarf with a mass 1.5 times that of the sun (1.5 Msun)
which of the following statements about the stages of nuclear burning in a massive star is not true?
each successive stage lasts for approximately as long as the first, hydrogen fusion stage.
suppose our sun were suddenly replaced by a red supergiant. which would be true?
earth would be inside a supergiant
which of the following makes it possible for us to observe stellar parallax?
earth's orbit around the sun
satellites in low-earth orbits are more likely to crash to earth when the sunspot cycle is near solar maximum because______.
earth's upper atmosphere tends to expand during solar maximum, entering more drag on satellites in low orbits
what kind of pressure supports a white dwarf?
electron degeneracy pressure
Notice that nitrogen is less abundant than either carbon or oxygen. this is an example of the more general observation that ________.
elements w even atomic numbers are more abundant that elements w odd atomic numbers that come between them.
what is the general trend in elemental abundance?
elements with more protons are less abundant
hot gas un mars's upper atmosphere produces _____ in the ultraviolet portion of its spectrum.
emission lines
a star is born when it comes into _________ in which energy released by fusion matches the energy it radiates into space.
energy balance
what is a planetary nebula?
gas ejected from a star in the final stage of its life
What is the source of luminosity for protostars that have not yet become hot enough for fusion in their cores?
gravitational energy released by infalling matter
a gas cloud in which gravity is perfectly balanced against pressure is said to be in _________.
gravitational equilibrium
where does the energy that heats the cloud come from?
gravitational potential energy that the cloud loses as it shrinks
what two items on the list below are in balance in what we call gravitational equilibrium?
gravity & gas pressure
the basic requirements for a cloud to collapse to form a star is that _____.
gravity must be strong enough to overpower the cloud's internal pressure.
spectrum from neutral atoms compared with spectra from ionized atoms of the same element
have different sets of spectral lines
the spectra of most galaxies show redshifts. this means that their spectral lines _____.
have wavelengths that are longer than normal
Provided following are various elements that can be produced during fusion in the core of a high mass main sequence star. Rank these elements based on when they are produced, from first to last.
helium, carbon, oxygen, iron
at the center of the sun, nuclear fusion converts hydrogen into
helium, gamma rays, and neutrinos
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
Compared to a low-luminosity main-sequence star, stars in the lower left of the H-R diagram are __________.
hotter and smaller in radius
what does the apparent magnitude of a star tell us about that star?
how bright it appears from the earth
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
Why is a star's birth mass its most fundamental property?
important predictor of a star's lifetime. a star born w high mass will have a short lifespan; a star born with low mass will have a significantly longer lifespan.
the particles erected from the sun during a coronal mass ejection, if directed at earth, will reach us...
in several days
why do incandescent bulbs require more energy to shine with the same amount of visible light as LED bulbs?
incandescent bulbs emit most of their energy as infrared light
Star-forming clouds appear dark in visible-light photos because the light of stars behind them is absorbed by __________.
interstellar dust
An atom that has fewer electrons than protons is called a/an _________.
ion
Which element has the lowest mass per nuclear particle and therefore cannot release energy by either fusion or fission?
iron
most abundant element w an atomic number greater than or equal to 20?
iron
which of the following statements is true of green grass
it absorbs red light and reflects green light
the star alpha Centauri A is the same type of star as the sun, but its luminosity is about 1.6 times that of the sun. what can we conclude?
it fuses hydrogen into helium in its core at a higher rate than our sun
you observe a red giant star. what is happening to that star?
it is increasing in size, and is fusing hydrogen in a shell around its core.
why does mars appear reddish in color?
it reflects most of the sun's red light while absorbing most of its blue light.
why is Supernova 1987A particularly important to astronomers?
it was the nearest supernova detected in nearly 400 yrs.
imagine being on the moon and looking at the thermal radiation spectrum of earth. how would it compare to the spectra shown on the graph in the video?
it would be very similar to the spectrum of the human.
If the Sun somehow acquired more hydrogen and helium and doubled in mass, what would happen to it?
it would evolve more quickly than it is now.
we can measure a star's mass directly if __________.
it's a member of an eclipsing binary system.
thermal radiation gets its name because ________.
its spectrum depends on the temperature of the object emitting it.
Compared to a main-sequence star with a short lifetime, a main-sequence star with a long lifetime is __________.
less luminous, cooler, smaller, and less massive
when an electron drops to a lower energy level in an atom...
light at a wavelength specific to the change in energy levels is emitted
how do the properties of long-lives 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.
red light has a ____ wavelength and a _____ frequency than does blue light.
longer, lower
in the solar spectrum, the upper left portion of the spectrum shows the ____ visible light.
lowest frequency
which of the following stellar properties has the greatest range in values?
luminosity
All the phenomena of solar activity — including sunspots, flares, coronal mass ejections, and the sunspot cycle — are tied to changes in the Sun's __________.
magnetic field
a star is observed with a surface temp of 3,000 K and a luminosity of 10^5. what is the approx mass of this star?
mass cannot be determined.
which of the following observation 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. & observation of neutrinos coming from the sun
which of the following statements about globular clusters is true?
most stars in the cluster are yellow or reddish in color.
Observations show that elements with atomic mass numbers divisible by 4 (such as oxygen-16, neon-20, and magnesium-24) tend to be more abundant in the universe than elements with atomic mass numbers in between. Why do we think this is the case?
near the end of a high-mass star's life, it produces new elements through a series of helium capture reactions.
the neon "open" sign appears reddish-orange because _______.
neon atoms emit many more yellow and red photons than blue and violet photons.
is a protostar in energy balance?
no bc its core generates less energy than its surface radiates into space.
based on its location on the HR diagram, what can we say about Rigel's mass and lifetime?
nothing, because it's not in main sequence.
the source of energy that keeps the sun shining today is _____.
nuclear fusion
Which two energy sources can help a star maintain its internal thermal pressure?
nuclear fusion and gravitational contraction
What keeps the Sun's outer layers from continuing to fall inward in a gravitational collapse?
outward pressure due to super-heated gas
the third most abundant element is
oxygen
which of the following procedures would allow you to make a spectrum of the sun similar to the one shown, though with less detail?
pass a narrow beam of sunlight through a prism
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
a star that has not yet finished forming is called a ______.
protostar
which of the following sequences correctly describes the stages of life for a one solar mass star?
protostar, main-sequence, red giant, white dwarf
If you have a telescope that is observing light with wavelengths of a few meters, you are observing __________.
radio waves
from lowest energy to highest energy, which of the following correctly orders the different categories of electromagnetic radiation?
radio, infrared, visible light, ultraviolet, X-rays, gamma rays
a star's luminosity depends primarily on its
radius and surface temperature
what color does this wavelength correspond to in the visible light spectrum?
red
white light hitting white paper is an example of
reflection or scattering
the light radiated from the sun's surface reaches earth in about 8 minutes. however the energy of this light was released by fusion in the sun's core about...
several hundred thousand years ago
xray photons have a ____ wavelength, _____ frequency, and ____ energy than do ultraviolet photons
shorter, higher, higher
compared to a colder object, a hotter object of the same size emits most of its light at ___ wavelengths and emits ____ light overall.
shorter, more
compared to a nearer star, a more distant star will have a _____.
smaller parallax angle
What must we measure directly so that we can infer a star's surface temperature?
spectral type
You see two main-sequence stars with the same spectral type. Star 1 is dimmer in apparent brightness than Star 2 by a factor of 100. What can you conclude, assuming there is no absorption of either star's light by interstellar gas or dust?
star 1 is 100 times more distant than star 2.
If stars A and B are both main-sequence stars and star A has a greater fusion rate than star B, which of the following statements hold(s)?
star A must be more massive and luminous than star B
one star is emitting primarily visible light and another star is emitting primarily infrared light. which star is hotter?
star emitting visible light
Star X has an apparent magnitude of 3, and star Y has an apparent magnitude of 13. How do they compare in observed brightness?
star is 10,000 times brighter than star Y.
which of the following are true about star-forming clouds?
star-forming clouds have the same overall chemical comp. as the galaxy as a whole. most of the hydrogen in star-forming clouds is in the form of a hydrogen molecule. the darkness of these clouds is due primarily to light absorption by tiny grains of interstellar dust. the densest cloud regions appear dark to visible light telescopes but we can see into these regions with infrared telescopes. star-forming clouds glow w visible light in regions where the gas is heated by radiation from nearby stars.
luminosity is shown along the vertical axis, so....
stars higher up are more luminous than those lower down.
sunspots are cooler than surrounding gas in the photosphere because
strong magnetic fields slow convection and prevent hot plasma from entering the region
which of the following is not true about differences between novae and supernovae?
supernovae eject gas into space, but novae do not.
Overall, careful study of the patterns revealed in the graph of measured element abundances has allowed scientists to __________.
test and validate models of how elements are produced by stars.
imagine comparing a 1.2 solar mass white dwarf to a 1.0 solar mass white dwarf. which of the following must be true?
the 1.2 solar mass white dwarf has a smaller radius.
notice that the sun's spectrum appears brightest in the yellow-green region. this fact tells us ______.
the approx. temperature of the sun's surface.
Suppose you see two stars: a blue star and a red star. Which of the following can you conclude about the two stars? Assume that no Doppler shifts are involved. (Hint: Think about the laws of thermal radiation.)
the blue star has a hotter surface temperature than the red star.
What eventually halts the gravitational collapse of an interstellar gas cloud if it is massive enough to become a star?
the central object becoming hot enough to sustain nuclear fusion in its core
what happens after the helium flash in the core of a star?
the core quickly heats up and expands as helium fusion begins all at once throughout the core
"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
the energy that is released in the hydrogen fusion reaction comes from ______.
the difference in mass between the four hydrogen nuclei and the single resulting helium nucleus
what is the solution to the solar neutrino problem?
the electron neutrinos created in the sun's core change into another type of neutrino that we did not originally detect.
what two items on the list below are in balance with what we call energy balance?
the energy released into space & the energy produced by fusion
a white dwarf is
the exposed core of a dead star, supported by electron degeneracy pressure.
which of the following facts about stars in a cluster make it possible to determine the approx age of the cluster?
the mass of a star determines how long it'll be on the main sequence. all the stars in a cluster are at about the same distance from us. stars in a cluster all formed at approx the same time.
why is there an upper limit to the mass of a white dwarf?
the more massive the white dwarf, the greater the degeneracy pressure and the faster the speeds of its electrons. near 1.4 solar masses, the speeds of the electrons approach the speed of light, and no more mass can be supported.
what events bring the forming star into energy balance?
the onset of nuclear fusion in the core
which of the following best describes why we say that light is an electromagnetic wave?
the passage of a light wave can cause electrically charged particles to move up and down
suppose that mars had a higher surface temp. how would its spectrum be different?
the peak in the infrared would be at shorter wavelength.
which of the following describes the light that can be detected from a person?
the person reflects many wavelengths of visible light and emits a continuum of wavelengths of infrared light
if we observe one edge of a planet to be redshifted and the opposite edge to be blue shifted, what can we conclude about the planet?
the planet is rotating
what would happen to the core of the sun if its temperature rose slightly?
the rate at which fusion occurs would increase, leading to an expansion of the core, which would in turn cause the temperature to drop back down.
what is a white dwarf?
the remains of a star that ra out of furl for nuclear fusion.
consider a planet orbiting another star that is very similar to our sun. assume the planet is about the size of the earth and has an earth-like orbit around its star. which of the following statements are true about the light coming from the star and planet?
the star emits much more total light than the planet the planet emits virtually all its light as infrared light the star's spectrum peaks in visible light
what is the only force that can overcome the repulsion between two positively charged nuclei and bind them together?
the strong force
which event marks the beginning of a supernova?
the sudden collapse of an iron into a compact ball of neutrons
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 hear up, and the rate of fusion would increase even more.
the color of mars in our sky is determined by the _____ of mars's spectrum
the visible portion
suppose you want to know the chemical composition of a distant star. which piece of information is most useful to you?
the wavelengths of spectral lines in the star's spectrum
the fundamental lesson we learn from the life track is that the star's outward appearance at any moment in its life reflects ________.
the way it is generating energy in its core.
which of the following processes is involved in the sunspot cycle?
the winding up of magnetic field lines inside the sun due to its differential rotation
why are the very lowest mass stars unable to fuse helium in their cores?
their cores will never get hot enough to fuse helium
as a protostar shrinks in size, its central temp rises along with its _______.
thermal pressure
we determine mars's surface temperature from the peak wavelength of the _____ it emits.
thermal radiation
why does it make sense for star forming clouds to be cold and dense?
these conditions help gravity overcome gas pressure
if stars are at the same place along the horizontal axis on HR, then.....
they all must have the same surface temperature.
what is the common trait of all main-sequence stars?
they generate energy through hydrogen fusion in their core.
In science, it is now well accepted that the speed of light is always the same and therefore nothing can travel faster than light. These ideas gained acceptance primarily because __________.
they have been verified through actual observations and experiments.
why are hydrogen and helium so much more abundant?
they were produced in the Big Bang.
why are sunspots dark?
they're regions that are significantly cooler than the rest of the photosphere
at the time the hypothesis was suggested, what major problem was identified with the idea that the sun was powered by gravitational contraction?
this process would power the sun for only about 25 million years, but geologists already had evidence that earth was much older than that.
the GAIA spacecraft is capable of measuring parallax angles as small as about 0.00002 arcsecond. based on this fact, the GAIA should in principle be able to measure the distances of stars located _______.
throughout the Milky Way galaxy, but not in the Andromeda galaxy or other more distant galaxies.
Based on its surface temperature of 6,000 K, most photons that leave the Sun's surface lie in which region of the electromagnetic spectrum?
visible
what must be true if we are to infer (calculate) a star's luminosity directly from the inverse square law for light?
we have measure the star's apparent brightness, we have measured the star's distance, no interstellar gas or dust absorbs or scatters light between us and the star.
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.
What can we learn about a star from its life track on an H-R diagram?
what surface temp and luminosity it will have each stage of its life.
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.
when does a star become a main-sequence star?
when the rate of hydrogen fusion in the star's core is high enough to sustain gravitational equilibrium
which of the following represents key observational evidence that stars are born in clouds of gas and dust?
younger star clusters are always associated with clouds of gas and dust
