Astronomy Final
A star at a distance of 5 parsecs must have a parallax of
0.2 arc seconds
The graph of apparent magnitude versus time for an RR Lyrae star is shown. What is the approximate pulsational period of the star?
0.45 day
Which of the following objects is the largest in diameter?
1.0 M sun white dwarf
If a star has a parallax of 0.1 arc seconds, it must be at a distance of
10 parsecs
The data illustrates data on Kepler's third law for the first six planets. Use it to estimate the orbital period of object Chiron, which has a semi-major axis of 13.7 AU.
50.2 years
A star is 530 light years away. The light we see tonight from that star left it
530 years ago
The two images of the same star field were taken 20 years apart. Which star demonstrates the smallest proper motion?
A
Which one of the following pairs of masses exerts the largest gravitational force on each other?
A (M=2 m=2 and no lines in between)
Which pie chart best shows the composition of the cloud from which our solar system was born?
A (majority H/He)
Which of the following main-sequence stars would have the largest mass?
A (on the main sequence, the higher the star, the greater the mass)
The graph shows blackbody curves for stars with different temperature surfaces. To the human eye, which of the stars is bluest?
A (tallest flux and peak has shorter wavelength)
A hypothetical solar system has planets evenly spaced in circular orbits. The planet masses are given (in terms of Jupiter's mass, MJ). Which of the planets below exerts the smallest gravitational force on the star?
B (3 Mj and 2 AU )
A binary system is shown looking down onto the plane of the system. Which label corresponds to the correct positions and directions of the two stars?
B (going the same direction but a opposite sides of their ellipse)
An incandescent bulb and a thin gas cloud are in space. From which point of view would an observer see an emission spectrum?
B (looking up to the thin gas cloud)
The evolutionary track of a low-mass star is shown on the HR diagram. Which position on the track corresponds to the cut-away core diagram shown (where an arrow indicates fusion)?
C (H-> He, He-> C)
The evolutionary track of a low-mass star is shown on the HR diagram. Which cut-away core diagram (A-D) correctly illustrates the source of fusion energy (an arrow indicates fusion) when the star is at the indicated position? (Dot is close to the end)
D (H-> He, He-> C, C)
Which labeled position on the light curve corresponds the binary star system at the time depicted when the red star is behind the blue star?
D (behind the blue star)
If the center of mass of this binary star system is indicated by the location of the green X, what is the mass of the star on the left?
D (center of the mass is closer to bigger star)
Which of the following conceptual diagrams correctly represents the HR diagram? Arrows point in the directions of increasing values.
D (luminosity ^ y axis, temperature <- on x axis, radius diagonal ->)
The turnoff points for four different star clusters (A-D) are shown on the main sequence of the HR diagram. Which of the clusters is the oldest?
D (the lower the star on the main sequence, the older)
An energy level diagram for hydrogen is shown below. In which transition is a photon with the smallest frequency emitted?
E (shortest line pointing down)
The Kepler Space Telescope is searching for exoplanets by the transit method. It is necessary for Kepler to monitor a large number of stars because
E, both b and C (only a small percentage of systems have the correct orbital tilt for transits to be observed./Planets will be transiting the star for only a small percentage of the orbit
Sirius is a type A1 star. Which of the following spectral types is slightly cooler than Sirius?
F1
The period-luminosity relationship for Cepheid variables was discovered by
Henrietta Leavitt
Who was the astronomer who is the "H" in H-R diagram?
Hertzsprung
The first astronomer who did photometry (measuring brightness) in a systematic way (even though he did not have a telescope) was
Hipparchus
Why is an absorption spectrum especially useful for astronomers?
It has dark lines in it that allow astronomers to determine what elements are in the star
The scientist who worked out the mathematics of the connections between electricity, magnetism, and light in the 19th century was:
James Clerk Maxwell
The scientist who formulated the three laws of planetary motion by analyzing the data on the precise location of planets in the sky was:
Johannes Kepler
Which of the following best describes what would happen if Mercury and Jupiter were to switch places in their orbits about the Sun?
Jupiter, the larger planet, would have a shorter orbital period than before.
Which star will live the longest time on the main sequence?
M type
The idea that atoms radiate photon energy only when their electrons move from higher to lower energy levels was first advanced by:
Niels Bohr
The block diagram below shows the major evolutionary stages of stars with masses like the Sun. Which stage is the longest?
Protostar
Of these which is the closest to us?
The Moon
Of these, which is the largest?
The Universe
You find the distance to a star with a spectral type F, luminosity class V, and apparent magnitude 8. Afterwards, you find out that the luminosity class is really III. How does this change the value of distance you estimated?
The new distance is larger
The 17th century astronomer who kept a roughly 20-year continuous record of the positions of the Sun, Moon, and planets was:
Tycho Brahe
To establish the scale of the solar system, we need to measure the distance to one object orbiting the Sun. What object was first used for this purpose?
Venus
Which of the following has the greatest average energy of random atomic and molecular motion?
a cube of the Sun
An ambulance siren has a frequency of 500 Hz. As it recedes from your house, you would hear...
a frequency lower than 500 Hz
A type of star cluster that contains mostly very old stars is
a globular star cluster
At the end of the p-p chain of nuclear fusion in the Sun, hydrogen nuclei have been converted into:
a helium nucleus
A graduate student is given the assignment to find stars with dusty disks around them.
a large telescope that detects infrared radiation
Which of the following particles has the lowest mass
a neutrino
Which of the following has the smallest mass?
a planet
Light sometimes acts like a photon. What is a photon?
a self-contained "packet" of electro-magnetic energy
Which of these stars will take the SHORTEST time to go from the earliest protostar stage to the main sequence?
a star ten times the mass of our Sun
Which of the following looks the brightest in the sky?
a star with magnitude -1
Elements heavier than iron can be created during:
a supernova explosion
A star that is quite hot and has a very small radius compared to most stars is called
a white dwarf
An astronomer observes two ordinary stars. The first one turns out to be twice as hot as the second. This means that the first one radiates:
about 16 times the energy of the second
To go from a lower level in an atom to a higher level, an electron must a. give off a photon of energy
absorb a photon of energy
Why is it so difficult for astronomers to see new stars in the process of birth?
all of the above (birth happens very quickly, so it is hard to "catch" stars "in the act", most stars are born inside dusty clouds, which block any light that may be coming from the stars, the size of a newly forming star is typically quite small and thus hard to make out, protostars which are not yet doing fusion do not give off a lot of visible light)
Two stars are giving off electromagnetic radiation. The hotter star will:
all the above (give off more radiation at all wavelengths, will have a higher average frequency of radiation, will radiate energy at more than one wavelength, will give off a continuous spectrum of waves
The smallest piece of an element (like gold or lead) is called
an atom
We now know that the orbit of a stable planet around a star like the Sun is always in the shape of:
an ellipse
The gravitational force is a(n) _____ force between two objects that have _____.
attractive; mass
Imagine that a brilliant but quirky scientist in the biology department manages to put you in a deep freeze and you wake up in a million years. Which of the following statements about the sky you would see in that future time is correct?
because of proper motion, several the familiar constellations will look somewhat different in a million years
Why are astronomers much more interested in the luminosity of a star than its apparent brightness?
because the luminosity tells us how bright a star really is, while apparent brightness only tells us how bright it happens to look from Earth
Why can a star with a mass like our Sun not fuse (produce) further elements beyond carbon and oxygen?
because they just cannot get hot enough for the fusion of heavier nuclei
Because white dwarfs are small, as their name implies, they are hard to see. What is a way astronomers have to find white dwarfs that distinguishes them from main sequence stars?
because white dwarfs get really hot, we can search for their ultraviolet radiation
Two stars that are physically associated (move together through space) are called
binary stars
Which color star is likely to be the hottest?
blue-violet
Today, astronomers can measure distances directly to worlds like Venus, Mars, the Moon, or the satellites of Jupiter by
bouncing radar beams off them
According to Kepler's third law, there is a relationship between the time a planet takes to revolve (orbit) around the Sun and its
distance from the Sun
The way scientists know that a hypothesis in astronomy is a reasonable description of nature is to
do experiments and observations about the predictions of the hypothesis
For what type of star can astronomers measure the diameter with relative ease?
eclipsing binary stars
The orbit of a comet around the Sun is shown. If the comet takes two years to move from point 1 to point 2, and two years to move from point 3 to point 4, then area B must be ____ area A.
equal to (distances are the same on each side in photo)
By the term universe, astronomers mean
everything that we can observe
According to Kepler's 2nd Law, comets (which have eccentric orbits) should spend a lot more of their time:
far from the Sun
If an astronomer wants to find the distance to a star that is not variable and is located too far away for parallax measurements, she can:
find the star's luminosity class from its spectrum and read the luminosity from an H-R diagram
If the "fuel" for nuclear fusion is nuclei of hydrogen, and the Earth's oceans are filled with hydrogen atoms in water all being jostled together, why isn't there a lot of fusion happening in our oceans?
for hydrogen nuclei to fuse, they must get very close to each other, which the nuclei in the oceans cannot do
Astronomers identify the main sequence on the H-R diagram with what activity during a star's life?
fusing hydrogen into helium in their cores
Which of the following bands of the electromagnetic spectrum has photons with the largest energy?
gamma ray
A team of astronomers takes spectra of thousands of different stars in different parts of the sky. The spectra show significant differences. The main reason the spectra of the stars do not all look alike is that the stars...
have different temperatures
As the nebula (cloud) evolved to form our solar system, it
heated up
If stars with masses like our Sun's cannot make elements heavier than oxygen, where are heavier elements like silicon produced in the universe?
heavier elements are made in the cores of significantly more massive stars than the Sun, which can get hotter in the middle
The brightest stars we can see with our eyes are best described as:
high luminosity stars
Atoms typically consist of electrons, protons, and neutrons. The most common isotope of one element, however, only has two of these three types of particles. This element is:
hydrogen
Studies of the spectra of stars have revealed that the element that makes up the majority of the stars (75% by mass) is
hydrogen
A star with a mass like the Sun which will soon die is observed to be surrounded by a large amount of dust and gas -- all material it has expelled in the late stages of its life. If astronomers want to observe the radiation from such a giant star surrounded by its own debris, which of the following bands of the spectrum would be the best to use to observe it?
infrared
Using a good pair of binoculars, you observe a section of the sky where there are stars of many different apparent brightnesses. You find one star that appears especially dim. This star looks dim because it is:
it could be more than one of the above; there is no way to tell which answer is right by just looking at the star
What happens to the positron created during the p-p chain of nuclear reactions inside the Sun?
it quickly collides with an electron and turns into gamma-ray energy
How did astronomers determine that the planet orbiting the star HD 209458 is a gas giant like Jupiter and not made mostly of rocks or metals?
it took more than one of the above measurements to figure out the density
Which of the following statements about the force of gravity is FALSE?
its strength is inversely proportional to the mass: the more mass, the less gravity
How do astronomers learn what elements are present in a given star?
look at the absorption lines in its spectrum
The most common kinds of stars in the Galaxy have
low luminosity compared to the Sun
When the Sun becomes a red giant for the second time, its
luminosity increases and temperature increases
Stars on the main sequence obey a mass-luminosity relation. According to this relation,
luminosity is proportional to mass to the fourth power (luminosity increases strongly with mass)
In figuring out the evolutionary tracks on the H-R diagram, astronomers
make model stars on a computer and then follow how their characteristics will change with time
The laws of nature (as determined by scientists)
more than one of the above
When a planet, in its orbit, is closer to the Sun, it:
moves faster than average
Which of the following is the smallest in diameter?
neutron star
Today we realize that the source of energy for the Sun is a process called
nuclear fusion
As astronomers use the term, the parallax of a star is
one half the angle that a star shifts when seen from opposite sides of the Earth's orbit
Where in the Sun does fusion of hydrogen occur?
only in the core
Where on the H-R Diagram would we find stars that look red when seen through a telescope?
only on the right side of the diagram and never on the left
The big surprise about the first planet discovered around another regular star was that it
orbited so close to its star it took only 4 days to go around
The Doppler method (radial velocity technique) of exoplanet detection doesn't work well for systems where the
planet is very far from the star
The material inside the Sun is in the form of a
plasma (ionized gas)
The antimatter version of an electron is called a
positron
Astronomers call the motion of a star across the sky (perpendicular to our line of sight) its
proper motion
When energy is first produced by fusion deep in the core of the star, that energy moves outward mostly by what process?
radiation
Not all wavelengths of electromagnetic radiation can penetrate the Earth's atmosphere. Of the following types of waves that come from space, which one are you likely to be able to detect most easily from our planet's surface
radio waves
Which of the following has the longest wavelength?
radio waves
When a star or galaxy is moving away from us, we observe the Doppler effect by seeing the lines in its spectrum
red-shifted (shifted toward the red end of the light spectrum)
As the nebula (cloud) evolved to form our solar system, it (pt.2)
rotated more rapidly
We have two waves of light, A and B. Wave A has a higher frequency than wave B. Then wave A must have:
shorter wavelength
A graduate student has done a careful analysis of the spectrum of a star. While she has found lines from many elements, there was not a trace of the element helium in the spectra she has been analyzing. From this she can now conclude:
since helium shows lines only in hot stars, this star must be relatively cool
Two stars A and B have the same surface temperature. If star A has a greater luminosity than star B, then:
star A is larger than star B
Why can astronomers not measure the diameters of all stars directly?
stars are so far away, we cannot resolve (distinguish) their diameters
Which of the following is a way for astronomers to learn more about the interior of the Sun?
study the oscillations (pulsations) of the Sun's surface
An H-R Diagram plots the luminosity of stars against their:
surface temperature
The Stefan-Boltzmann Law relates the energy flux coming from a blackbody (such as a star) to its:
temperature
Wien's Law relates the wavelength at which a star gives off the greatest amount of energy to the star's
temperature
A type of star that has turned out to be extremely useful for measuring distances is
the Cepheid variables
The instrument astronomers are now using to make the most precise measurements of stellar parallax we have ever had is
the Gaia satellite in space
The telescope that allowed astronomers to discover most of the planets found with the transit method was called
the Kepler mission
Which of the following is the Earth located in?
the Milky Way Galaxy
The star that provides energy for life on Earth is
the Sun
An astronomical unit is:
the average distance between the Earth and the Sun
The Astronomical Unit (AU) as defined by astronomers is
the average distance between the Earth and the Sun
We observe a glowing cloud of gas in space with a spectroscope. We note that many of the familiar lines of hydrogen that we know on Earth seem to be in a different place. They are shifted toward the blue or violet end of the spectrum compared to their positions in the spectrum of glowing hydrogen gas on Earth. From this we can conclude that:
the cloud is moving toward us
You are an astronomy graduate student and you are observing the big Orion Nebula from an airplane that has a good-sized infrared telescope built into it (there really is such a plane.) On an infrared image of the Nebula, what would particularly stand out?
the clouds of the nebula that have a lot of dust in them
When a star first begins the long path toward becoming a red giant, a layer of hydrogen around the core begins to undergo fusion. If this layer was too cold to do fusion throughout the main sequence stage, why is it suddenly warm enough?
the core is collapsing under its own weight and heating up from the compression; this heats the next layer up
What observations about disks of dusty material around young stars suggest that planets may be forming in such disks?
the disks show lanes that are empty of dust within them
A light year is
the distance that light travels in one year
The higher the luminosity (intrinsic brightness) a Cepheid variable is,
the longer the period of its variations
For scientists, an element (like gold) is defined by
the number of protons in its atomic nucleus
Which of the following statements about electromagnetic radiation is FALSE?
the radiation consists of tiny, charged particles given off by the nuclei of atoms
When stars become giants, which of the following does NOT usually happen?
their mass grows significantly as they incorporate planets and interstellar matter near the star
(In the absence of a strong magnetic field,) what is the chief factor that determines what type of electromagnetic radiation objects give off:
their temperature
A light curve for a star measures how its brightness changes with
time
When the outer layers of a star like the Sun expand, and it becomes a giant, which way does it move on the H-R diagram?
toward the upper right
To figure out what you weigh on the surface of the Moon (how much gravity there pulls you downward), you need to know
two of the above factors
The process of fusion that keeps our Sun shining begins with which building blocks?
two protons
Astronomers identify the "birth" of a real star (as opposed to the activities of a protostar) with what activity in the star?
when nuclear fusion reactions begin inside its core
A Herbig-Haro (HH) object is
where a jet from a star in the process of being born collides with (and lights up) a nearby cloud of interstellar matter
The luminosity class of a star tells an astronomer
whether the star is a supergiant, a giant, or a main-sequence star
Which of the following has the highest frequency?
x-rays
Which of the following can astronomers NOT learn from studying the spectrum of a star?
you can't fool me, all the above can be learned from studying the spectrum
What is the baseline that astronomers use to measure the parallax (the distance) of the nearest stars?
½ the diameter of the Earth's orbit around the Sun
