ASTR Exam 4 Study guide

Some objects in space just don't have what it takes to be a star (just like many hopefuls in Hollywood don't.) Which of the following is a "failed star", an object with too little mass to qualify as a star?

A brown dwarf

Which of the following is NOT a product of the first step in the p-p chain of nuclear fusion?

A form of helium

At the end of the p-p chain of nuclear fusion in the Sun, hydrogen nuclei have been converted into:

A helium nucleus

According to the formula E=mc2,

A little bit of mass can be converted into a substantial amount of energy

Who pays the bill for the energy generated by nuclear fusion in the Sun? In other words, where does the energy pouring out of the Sun come from ultimately?

A little bit of mass is lost in each fusion reaction and is turned into energy (the Sun is losing mass)

Which of the following particles has the lowest mass?

A neutrino

Which of the following, produced at the core of the Sun, will take the shortest time to emerge from the Sun's photosphere (surface)?

A neutrino

A star moving toward the Sun will show:

A shift in the spectral lines toward the blue end (as compared to the laboratory positions of these lines)

Physicists Kelvin and Helmholtz in the last century proposed that the source of the Sun's energy could be:

A slow contraction

Which of the following looks the brightest in the sky?

A star with a magnitude -1

Astronomers have found that the level of the Sun's activity varies over the centuries. How did they come to realize that this is so:

All of the above

The astronomer who, at the turn of the century, measured the spectra of hundreds of thousands of stars, leaving a catalog that astronomers used for the rest of the century, was:

Annie Cannon

Which color star is likely to be the hottest?

Blue-violet

At an astronomical conference, an astronomer gives a report on a star that interests astronomers because of hints that it may have a planet around it. In his report the astronomer gives the average speed with which this star is moving away from the Sun. How did the astronomer measure this speed?

By looking at the Doppler shift in the lines of the star's spectrum.

The hotter region directly above the Sun's visible surface is called the

Chromosphere

When great currents of hot material rise inside the Sun (and cooler material sinks downward), energy is being transferred by a process known as:

Convection

Astronomers arrange the stars into groups called spectral classes (or types) according to the kinds of lines they find in their spectra. These spectral classes are arranged in order of:

Decreasing surface temperature

Recently, some engineers and scientists have proposed building spaceships with enormous "sails" that catch the solar wind and use it to move the ship. What kinds of particles would be hitting this sail (i.e., what is the solar wind mostly made of):

Electrons and protons

In the Sun, when a positron and an electron collide, they will produce:

Energy in the form of 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

The first astronomer who did photometry in a systematic way (even though he did not have a telescope) was

Hipparchus

When an astronomer rambles on and on about the luminosity of a star she is studying, she is talking about:

How much energy that star gives off each second

Studies of the spectra of stars have revealed that the element that makes up the majority of the stars (75% by mass) is

Hydrogen

The most common element in the Sun is

Hydrogen

If hydrogen is the most common element in the universe, why do we not see the lines of hydrogen in the spectra of the hottest stars?

In the hottest stars, hydrogen atoms are ionized, so there are no electrons to produce lines in the spectrum.

One similarity in the spectra of T dwarf stars and giant planets in our solar system is that their spectra show:

Indications of methane

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 rays energy

A Canadian college student who has taken an astronomy class goes home for the holidays and persuades his parents to let him borrow the family car. When he returns, he finds that his parents are very angry with him, claiming he left the garage door open. Yet he remembers that he carefully closed the garage door with the electronic remote control in the car. After consulting with his astronomy instructor, he comes up with an alternative explanation for why the garage door is open. Which of the following is PART of that explanation?

It was a time of solar maximum, and there had been a big flare on the Sun earlier

After a lot of work, a group of graduate students has finally measured the wavelengths of many dozens of lines in the spectrum of a distant star. If a number of the lines come from molecules such as titanium oxide, the star is likely to be which spectral type:

M

Which of the following types of star is the coolest (has the lowest surface temperature)?

M

An exhausted-looking astronomer comes off the mountain where her observatory is located and tells you she has been doing photometry all night. What has she been up to?

Measuring the brightness of different stars

Most of the stars we can see with the unaided eye from Earth are

More luminous (inartistically brighter) than the sun

In an earlier era, some scientists suggested that the energy of the Sun comes from meteorites (or, more properly, meteoroids) falling into it and converting their falling motion into heat. Which of the following is part of the argument that shows this mechanism will not work?

More than one of the above

Two stars have the same luminosity, but star B is three times farther away from us than star A. Compared to star A, star B will look

Nine times fainter

When a large nucleus breaks apart (or is broken apart) into two smaller pieces, this is called

Nuclear fission

Today we realize that the source of energy for the Sun is a process called

Nuclear fusion

The Sun is an enormous ball of gas. Left to itself, a ball of so many atoms should collapse under its own tremendous gravity. Why is our Sun not collapsing?

Nuclear fusion in the core keeps the temperature and the pressure inside the Sun at a high enough level so that gravity is balanced

Where in the Sun does fusion of hydrogen occur?

Only in the core

You are out on the beach, enjoying the warm sunshine with friends. As you glance up at the Sun (only briefly we hope), the part of the Sun that you can see directly is called its:

Photosphere

When we use the light of atoms such as hydrogen and calcium to examine the Sun's outer layers, we can see bright "clouds" in the chromosphere right around the location of sunspots. These bright clouds are given the name:

Plages

The material inside the Sun is in the form of a

Plasma

The antimatter version of an electron is called a

Positron

Which of the following is NOT one of the fundamental particles that we find inside atoms?

Positrons

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

The Sun's chromosphere contains many jet-like projections that stick up into the transition region. These spikes of gas are called:

Spicules

What is the best reason astronomers have come up with to explain why sunspots are cooler and look darker?

Sunspots are places where the strong magnetic fields in the Sun resist the upward motion of bubbling hot gases from underneath

Which of the following best describes the first set of experiments, using chlorine traps, that were searching for electron neutrinos from the Sun?

The chlorine experiments found only 1/3 the number of electron neutrinos arriving from the Sun that our models predicted

Which part of the Sun has the greatest density?

The core

A friend (who does not have the new awareness which you have gained from this course) suggests that the mechanism that keeps the Sun shining as brightly as it does is the burning of coal. You brilliantly challenge his theory! Your challenge comes in several related steps; which of the following is one of those steps?

The dating of radioactive rocks show that the Earth and thus the Sun are billions of years old

How do astronomers know how strong the magnetic field of the Sun is?

The measure of the Zeeman effect (the splitting of spectral lines)

The strongest force we know is

The nuclear force which holds nucleui together

Astronomers have concluded that the Sun's activity varies in an 11-year cycle. Which of the following statements about this cycle is TRUE:

The number sunspots gets larger and smaller over the course of 11 years

The Sun's photosphere is

The part of the sun from which the light comes from that we see when we look at the sun with our eyes

Which of the following statements about the Sun's photosphere is NOT TRUE?

The photosphere is significantly hotter than all the layers of the Sun beneath it (further inward)

When did scientist begin to understand how the Sun produces all the energy that it does?

The process was not well understood until the 1930s

In the formula E=mc2, the letter c stands for

The speed of light

Which statement about the Sun's rotation is TRUE?

The sun rotates at different rates at different latitudes on the sun

Sunspots are darker than the regions of the Sun around them because

They are cooler than the material around them (although still very hot compared to earth temperatures)

The process of fusion that keeps our Sun shining begins with which building blocks?

Two protons

How do astronomers know what the outer layers of the Sun are made of?

We take an absorption line spectrum of the Sun; these absorption lines tell us what elements are present in the outer layers.

In recent decades, astronomers discovered stars even cooler than the traditional spectral type M stars recently. Astronomers gave these cool stars a new spectral type, L. If you wanted to go out and find more such type L stars, what kind of instrument would it be smart to use?

a sensitive infra-red telescope

Which of the following statements about the violent events on the Sun called flares is FALSE?

astronomers think that flares are connected with sudden changes in the magnetic field of the sun

Solar wind particles can be captured by the Earth's magnetosphere. When these particles spiral down along the magnetic field into the atmosphere, they are responsible for:

aurorae (northern and southern lights)

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, a number of the familiar constellations will look somewhat different in a million years

Some "superstars" give off more than 50,000 times the energy of the Sun. Why are there no such stars among the stars that are close to the Sun?

because such very luminous stars are extremely rare, and thus any small neighborhood in the Galaxy is unlikely to contain one of them

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 Which color star is likely to be the hottest

One key difference that astronomers use to distinguish between brown dwarfs and high-mass planets is that:

brown dwarfs are able to do deuterium fusion in their cores,while planets cant

Astronomers first detected the presence of a wind of particles coming from the Sun by

by noting the winds effects on the trails of comets

Coronal Mass Ejections from the Sun have many serious effects on or near the Earth. Which of the following is NOT one of these effects?

causing huge cyclones around the equator of the Earth

The hottest zone in the Sun is the

core

Which part of the Sun's atmosphere has the lowest density (number of atoms per unit volume)?

corona

Which part of the Sun's atmosphere is the hottest?

corona

The ten million tons of particles that escape the Sun each year in the form of the solar wind get out mainly through regions called

coronal holes

The Sun's chromosphere and corona were discovered

during total eclipses of the sun

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

Which of the following is not part of some active regions on the Sun?

granulation

Which of the following statements about helioseismology experiments is FALSE:

helioseismology measures waves that are set up by the motion of neutrinos from the core of the Sun

The granulation pattern that astronomers have observed on the surface of the Sun tells us that:

hot material must be rising from the Sun's hotter interior

As astronomers have learned more about the structure of the Sun, they have found that it

is made entirely of hot gas

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

Which of the following is NOT an experiment that is searching for neutrinos coming from the Sun?

looking for changes in the Doppler shift of lines in the atmosphere of the Sun

Astronomers now realize that active regions on the Sun are connected with

loops of magnetic field emerging from the surface of the Sun

The most common kinds of stars in the Galaxy have

low luminosity compared to the sun

The Global Oscillations Network Group (GONG) Project is engaged in:

measuring the pulsations of the Sun from stations around the world

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

When two light elements collide to undergo nuclear fusion,

some of the energy in their mass is released

Two stars have the exact same luminosity, but star Y is four times dimmer looking that star X. This means that

star Y is twice as far away as star X

An astronomer whose secret hobby is riding merry-go-rounds has dedicated his career to finding the stars that rotate the most rapidly. But the stars are all very far away, so none of them can be seen to spin even when he looks through the largest telescopes. How then can he identify the stars that rotate rapidly?

stars that rotate have much wider lines in their spectra than stars that do not

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

What mechanisms do astronomers believe is responsible for making the Sun's outer atmosphere so much hotter than its photosphere?

the Sun's magnetic field interacting with the charged particles that make up the atmosphere

As you go upwards from the Sun's photosphere,

the density (number of atoms in a unit volume) decreases

When an astronomer measures a color index for a star, what is she measuring?

the difference between how bright a star looks at two different wavelength regions

A college friend of yours who has been postponing taking any science courses hears you talking about the generation of nuclear energy in the Sun and makes the following observation: "The whole idea of the atomic nucleus is pretty ridiculous. If an oxygen nucleus consists of eight protons and eight neutrons, the charge on that nucleus is positive. Since even I learned in high school that like charges repel, such a nucleus would find all its positive protons repelling and quickly fall apart." How would you answer his argument?

the nuclear force, which is attractive over short distances like the nucleus, and stronger than electricity, holds the nucleus together

If it takes an average of 14 billion years before any proton inside the Sun will undergo fusion, and the Sun is only about 5 billion years old, why do astronomers believe that fusion is going on there now?

there are an enormous number of protons inside the Sun, and some of them will fuse much sooner than the average

Most of the really bright stars in our sky are NOT among the stars that are very close to us. Why then do they look so bright to us?

these stars are intrinsically so luminous, that they can easily be seen even across great distances

Starting in 2009, astronomers have been discovering really cool objects out there (cool here meaning low-temperature, as well as really interesting), which they have called Y dwarfs. What distinguishes these brown dwarfs from others that astronomers have discovered?

they show absorption lines from the ammonia molecule in their spectra

Astronomers and physicists now believe they know what is happening to the missing neutrinos from the Sun (the neutrinos that our theories say should be emerging from the Sun, but our experiments in that underground mine could not find). These neutrinos are:

turning into a different type of neutrino in a neutrino oscillation

Which of the following statements about antimatter is true ?

when a particle of matter and the corresponding particle of antimatter meet, they become pure energy

Which of the following can astronomers NOT learn from studying the spectrum of a star?

you can't fool me, all of the above can be learned from studying the spectrum