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