Exam 3 Review

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If a star is 20 parsecs away, its parallax must be: ½ arcsecond 20 arcseconds 2 arcseconds 1/20th of an arcsecond This can't be figured out from the information given

1/20th of an arcsecond

If a star is 10 parsecs away, how long ago did the light we see from it tonight begins its journey toward us? 0.1 years 10 years 6100 years 32.6 years 10,000 years

32.6 years

How far away would a star with a parallax of 0.2 arcsec be from us? 0.5 parsecs 0.2 parsecs 5 parsecs 2 parsecs We need more information to answer this question

5 parsecs

A star that is quite hot and has a very small radius compared to most stars is called An M-type star A main sequence star A red giant An O-type star A white dwarf

A white dwarf

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: Edwin Hubble Annie Cannon Cecilia Payne Joseph Fraunhofer James Lick

Annie Cannon

The period-luminosity relationship for Cepheid variables was discovered by Henrietta Leavitt Edward Pickering John Goodricke Annie Cannon Henry Norris Russell

Henrietta Leavitt

What was the first evidence that gravity outside our solar system worked the same way as it does inside? Canon measured different lines in the Spectra of different types of stars Herschel measured the two stars that make up the Castor system moved around each other you can't fool me, but you still don't know whether gravity around other stars works the same way as it does here comet haley returned after a 76 year absence Galileo saw through his early telescope that the Milky Way consisted of many stars

Herschel measured the two stars that make up the Castor system moved around each other

Who was the astronomer who is the H" in H-R diagram?" Huggins Hertzsprung Humason Hubble Hoyle

Hertzsprung

The first astronomer who did photometry in a systematic way (even though he did not have a telescope) was Hipparchus Ptolemy Kepler Galileo Hubble

Hipparchus

Which law do astronomers use to determine the masses of the stars in a spectroscopic binary system? Hubble's Law Kepler's Third Law Wien's Law Jenny Craig's Law Stefan-Botzmann's Law

Kepler's Third Law

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: O B A M we need more information; lines from molecules can be found in stars of every spectral type

M

Which of the following types of star is the coolest (has the lowest surface temperature)? O A M F G

M

Which of the following stars is a Cepheid variable? Polaris Betelgeuse Rigel Mizar Sirius

Polaris

What is the closest star to the Sun? Proxima Centauri Sirius We won't know the astronomer to this until we can travel to the stars The Earth Barnards Star

Proxima Centauri

To establish the scale of the solar system, we need to measure the distance to one object orbiting the Sun. Venus was first used for this purpose, but in the 1930's astronomers organized an international campaign to measure the distance to: Pluto because of its distance from the sun Mars Mercury The Moon The asteroid Eros

The asteroid Eros

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 an M type dwarf an O type dwarf the Sun Any star with high proper motion

a brown dwarf

Which of the following has the smallest mass? the Sun a brown dwarf a planet You can't fool me, all the above have roughly the same mass the smallest mass star that can still have fusion of hydrogen to helium in the core

a planet

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? an X-ray telescope, in orbit above the Earth's atmosphere a sensitive infra-red telescope a small visible light telescope (something even an amateur astronomer or small college might have) a CCD attached to an ultraviolet telescope a swimming pool sized VAT of commercial cleaning fluid, deep in an abandoned mine

a sensitive infra-red telescope

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) a significant increase in its apparent brightness (magnitude) More and more helium lines as it approaches us a shift in the spectral lines toward the red end (as compared to the laboratory positions of these lines) no change that can be measured with our present day instruments

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

Which of the following looks the brightest in the sky? a star with magnitude 10 a star with magnitude 1 a star with magnitude 6 a star with magnitude -1 You can't fool me, all of the above look equally bright from the earth

a star with magnitude -1

In an H-R diagram, where can you see the spectral type of a star (whether it is an O type star or a G type star, for example)? H-R Diagrams have nothing to say about spectral types only the main sequence along the bottom (the horizontal axis) along the right (vertical axis) only in the red giant region

along the bottom (the horizontal axis)

One of your good friends who is on a diet asks you to point out the stars with the smallest mass on an H-R diagram that you are studying. Where are you sure to find the stars with the lowest mass on any H-R diagram? Among the stars at the top left of the main sequence stars with low mass can be located anywhere at all in the H-R diagram among the Super giants among the white dwarfs among the stars at the bottom right of the main sequence

among the stars at the bottom right of the main sequence

Which of the following statements about spectroscopic binary stars is FALSE? an analysis of the ways the lines in the spectrum change allows us to calculate the star's distance directly we can use the spectrum to determine the sum of the masses of the two stars We can often use the changes in the position of the spectral lines to measure the radical velocity of the stars in the system visually we can only see one star some of the lines in the spectrum are double, with the spacing changing overtime

an analysis of the ways the lines in the spectrum change allows us to calculate the star's distance directly

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? All the stars and constellations would look exactly the same as they do now all the stars we can see in the sky today will have died in a million years if you could see them up close, almost all the stars in the sky today would have changed their color significantly in a million years because of proper motion, a number of the familiar constellations will look somewhat different in a million years at the present time astronomers do not know enough about the universe to say what the sky will be like in a million years

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

Some superstars" give off more than 50000 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 because such superstars are really several hundred stars blending their light together (but so far away we can't distinguish individual stars); nearby stars are easy to separate because conditions in the "neighborhood" of the sign only permit low mass (low luminosity) stars to form because such superstars only give off a lot of energy for a year or so, before they die because All Stars in the vicinity of the sun have planets, and planets rob a star of its brightness

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 luminosity can be measured exactly, but apparent brightness can only be roughly estimated 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 because the luminosity also tells us what elements the star is made of, while apparent brightness cannot tell us a stars chemical makeup because luminosity can tell us how bright it is inside the stars core, while apparent brightness only tells us about its outside layers you cannot fool me there is no difference between luminosity and apparent brightness, they are merely different terms for the same property of a star

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 did it take astronomers until 1838 to measure the parallax of the stars? because cepheid variable stars had not been discovered earlier because the stars are so far away that their annual shift of position in the sky is too small to see without a good telescope because no one before then could conceive of the earth moving around the sun because most stars are too faint to see without a good telescope because detecting parallax requires measuring a spectrum, which only became possible in the 1830s

because the stars are so far away that their annual shift of position in the sky is too small to see without a good telescope

Two stars that are physically associated (move together through space) are called main sequence stars binary stars first contact stars double stars brown dwarf stars

binary stars

Which color star is likely to be the hottest? red green blue-violet yellow orange

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 using the Hubble Space Telescope to triangulate with sending graduate students out with very long tape measures using Cepheid variable stars that lie behind the planets using X-ray telescopes

bouncing radar beams off them

Stars that do not have what it takes to succeed as a star (i.e. do not have enough mass to fuse hydrogen into helium at their centers) are called: main sequence stars extras brown dwarfs red giants spectroscopic stars

brown dwarfs

One key difference that astronomers use to distinguish between brown dwarfs and high-mass planets is that: brown dwarfs are much larger in diameter than any planet brown dwarfs shining quite brightly in visible light, while planets are mostly visible from the light they reflect brown dwarfs are able to do deuterium fusion in their cores, while planets can't brown dwarfs are much lower in mass than planets like Jupiter brown dwarfs have much lower luminosity than any planets

brown dwarfs are able to do deuterium fusion in their cores, while planets can't

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 seeing how the luminosity of this star has been decreasing as it moves farther and farther away by seeing the whole star become much redder than it used to be by measuring the diameter of the star (which is easy to do) and noticing that it is getting smaller and smaller by looking at the Doppler shift in the lines of the star's spectrum this astronomer must be making up stories to impress his colleagues; there is no way to measure the speed with which stars move away or towards us

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

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 increasing mass increasing amount of hydrogen decreasing distance from us you can't fool me, there is no order to the spectral types (that's why the letters are not in alphabetical order)

decreasing surface temperature

For what type of star can astronomers measure the diameter with relative ease? any star that is not a brown dwarf main sequence stars eclipsing binary stars white dwarf stars visual double stars

eclipsing binary stars

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: use Kepler's laws as modified by Newton find the star's luminosity class from its spectrum and read the luminosity from an H-R diagram only throw up her hands in desperation, there is no way to even estimate the distance to such a star search for planets around the star since it is much easier to get the distance to planets use the stars light curve

find the star's luminosity class from its spectrum and read the luminosity from an H-R diagram

Astronomers identify the main sequence on the H-R diagram with what activity in the course of a star's life? dying you can't fool me, so many stars are on the main sequence that there is no special stage in the stars life that can be identified with that fusing hydrogen into helium in their cores forming a from a reservoir of cosmic materials letting go of a huge outer layer

fusing hydrogen into helium in their cores

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 are located in many different regions of the Milky Way have different temperatures are made of significantly different elements sometimes have atmospheres and sometimes do not change their Spectra as they age, and so young stars have very different Spectra from older ones

have different temperatures

When an astronomer rambles on and on about the luminosity of a star she is studying, she is talking about: What color the star is the total amount of mass in the star the stars apparent size (the size seen from earth) how much energy the star gives off each second the elements she can see in the stars spectrum

how much energy the 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 stellarium hydrogen helium carbon einsteinium

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 nuclei are forced to break apart into smaller nuclei in the hottest stars, all hydrogen in the star has quickly fused into helium in the hottest stars, hydrogen can quickly combine with oxygen to make H2O, whose spectrum consist of completely different lines in the hottest stars, the hydrogen atoms experience a huge Doppler shift, which moves the lines in the spectrum to a completely unrecognizable place in the hottest stars, hydrogen atoms are ionized, and so there are no electrons to produce lines in the spectrum

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

Imagine that powerful telescopes in the future give us a truly representative sampling of all the stars in the Sun's cosmic neighborhood. Where on the H-R diagram would most of the stars in our immediate vicinity lie? in the lower left, among the white dwarfs in the upper left, among the bright main sequence stars In the upper right, among the Super giants In the middle of the main sequence, roughly where the sun is in the lower right, among the least luminous main sequence stars

in the lower right, among the least luminous main sequence stars

One similarity in the spectra of T dwarf stars and giant planets in our solar system is that their spectra show: lots of free oxygen lines of ionized magnesium and iron indications of methane nothing that shows that hydrogen was ever present in them temperatures at which human beings could survive unprotected

indications of methane

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: very far away very low luminosity radiating most of its energy in the infrared region of the spectrum partly obscured by a cloud 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

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

Measurements show a certain star has a very high luminosity (100,000 x the Sun's) while its temperature is quite cool (3500o K). How can this be? it must be quite large in size it must be a brown dwarf and not a regular star it must be quite small in size it must be a main sequence star this must be an error in observations; no such star can exist

it must be quite large in size

Astronomers must often know the distance to a star before they can fully understand its characteristics. Which of the following properties of a star typically requires a knowledge of distance before it can be determined? its temperature its luminosity its apparent brightness all of the above its radial velocity

its luminosity

Which of the following characteristics of a single star (one that moves through space alone) is it difficult to measure directly? You can't fool me, all of these are quite easy to measure directly it's apparent brightness its mass it's chemical composition its temperature

its mass

The most common kinds of stars in the Galaxy have low luminosity compared to the Sun a dozen or more stars in close orbit around them diameter is thousands of times greater than the Suns Spectra that showed they contained mostly carbon enormous mass compared to the sun

low luminosity compared to the Sun

Stars on the main sequence obey a mass-luminosity relation. According to this relation, if you double the mask, you get double the luminosity luminosity is proportional to mass to the fourth power (luminosity increases strongly with mass) the lower the mass, the higher the luminosity bright stars have more mass around them in the form of planets, comets, and asteroids the brightest stars are made of such light materials they hardly have any mass at all

luminosity is proportional to mass to the fourth power (luminosity increases strongly with mass)

Stars that lie in different places on the main sequence of the H-R diagram differ from each other mainly by having different: internal structure radial velocities compositions masses Ways that they formed

masses

Kepler's Laws can give us the relative distance of objects in the solar system. To convert these relative distances into actual distances, we need to: measure the distance directly to any object orbiting the Sun measure the exact time it takes for the earth to spin once on its axis measure the mass of the sun measure the size of the earth measure the length of the year exactly

measure the distance directly to any object orbiting the Sun

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? taking photos through bedroom windows in the valley below measuring the positions of stars on photographic plates taken over many years putting the light of stars through a spectrograph to measure what elements are present measuring the brightness of different stars counting the number of stars in different star clusters (groups)

measuring the brightness of different stars

An astronomer is observing a single star (and one which does not vary) which she knows is located about 30 light-years away. What was the most likely method she or her colleagues used to obtain that distance? Hubble's law measuring the star's parallax Kepler's law bouncing radar beams off the star the period luminosity relationship

measuring the star's parallax

Most of the stars we can see with the unaided eye from Earth are more luminous (intrinsically brighter) than the Sun Very close to us (among the closest stars) intrinsically fainter than the sun only visible to our eyes because they actually consist of three or more stars blending their light together undergoing some sort of explosion which makes their outer layers unusually bright

more luminous (intrinsically brighter) than the Sun

Which of the following is a method for measuring the diameter of a star? more than one of the above measuring the spectrum of a spectroscopic binary Watching the body of the moon go across the stars comparing the colour of a star seen high above our heads and then again when it's near the horizon getting the light curve of an eclipsing binary star

more than one of the above

A team of astronomers discovers one of the most massive stars ever found. If this star is just settling down in that stage of its life where it will be peacefully converting hydrogen to helium in its core, where will we find it on the H-R diagram? a little bit below the sun on the main sequence among the Super giants, in the upper right near the very top of the main sequence, in the upper left among the most brilliant of the white dwarfs, in the lower left it could be anywhere on the diagram, we would just need more information to determine its place

near the very top of the main sequence, in the upper left

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 three times brighter nine times brighter nine times fainter three times fainter just as bright as A

nine times fainter

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 orbitthe time it takes for a start to move one second of Arc of proper motion always equal to 1 AU the time it takes a Cepheid variables start to go through one cycle of its brightness changes 1/2 of the Doppler shift due to its radial velocity

one half the angle that a star shifts when seen from opposite sides of the Earth's orbit

The original definition of a meter was the distance from the extended index finger of the Emperor Napoleon to his nose one ten-millionth of the distance from the Earth's equator to its pole one billionth the distance from the Earth to the Sun one thousandth the distance from Paris to London one thousandth the distance of the town Bayonne, New Jersey

one ten-millionth of the distance from the Earth's equator to its pole

Where on the H-R Diagram would we find stars that look red when seen through a telescope? Only near the top of the diagram and never near the bottom only on the right side of the diagram and never on the left anywhere in the diagram only near the left side of the diagram and never near the right only near the bottom of the diagram and never near the top

only on the right side of the diagram and never on the left

An astronomer is interested in a galaxy called M31, the nearest galaxy that resembles our Milky Way. It is about 2 million lightyears away. Which technique would be able to give us a distance to this galaxy? Kepler's Law period-luminosity relation for Cepheid variables radar reflections you can't pull me, there is no way at present to get a distance to an object so far away parallax

period-luminosity relation for Cepheid variables

Astronomers call the motion of a star across the sky (perpendicular to our line of sight) its radial velocity doppler shift light travel time proper motion spectral type

proper motion

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: there is most likely no helium anywhere in the star all the gallium must be in the core of the star; there is none of it in the outer regions since helium shows lines only in hot stars, this star must be relatively cool since helium is the kind of element that quickly bonds with others, all the helium in this star must be in the form of molecules the student was not surprised, because no star ever shows any lines of helium

since helium shows lines only in hot stars, this star must be relatively cool

A white dwarf, compared to a main sequence star with the same mass, would always be: the same size in diameter less massive larger in diameter smaller in diameter younger in age

smaller in diameter

Two stars have the exact same luminosity, but star Y is four times dimmer looking that star X. This means that star Y is four times as far away as star X star Y is 16 times as far away as star X star Y is half as far away as star X star Y is twice as far away as star X we cannot figure out the relative distance of the two stars from the information given

star Y is twice as far away as star X

Why can astronomers not measure the diameters of stars directly? you can't fool me, measuring the diameter of any stars a relatively easy process All Stars change their diameters regularly, and growing alternately larger and smaller stars are so far away, we cannot resolve (distinguish) their diameters Stars are so bright, their light burns out all the delicate instruments we would use to measure their diameters stars are all in binary systems, and we can only see the combined diameter of both stars

stars are so far away, we cannot resolve (distinguish) their diameters

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? all the stars that rotate show a huge Doppler shift toward the blue end of the spectrum stars that rotate have a significantly lower luminosity than stars that do not rotate stars that rotate have much wider lines in their spectra than stars that do not stars that rotate bring the light atoms (like hydrogen) spinning up to their surfaces; so they can be identified by the elements they contain this astronomer better spend some more time enjoying his hobby, because he is not doing well at his job; there is no way we know about today to identify stars that rotate

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

Which type of star has the least amount of pressure in its atmosphere? main sequence stars giants supergiants you can't pull me, All Stars have roughly the same pressure subgiants

supergiants

An H-R Diagram plots the luminosity of stars against their: location in the sky diameter age surface temperature mass

surface temperature

I am measuring the spectrum of the stars in a spectroscopic binary system. When one of the stars is moving toward the Earth in its orbit, we observe that the lines in the spectrum get brighter that the lines in the spectrum merge with the lines of the other star that the lines in its spectrum show a blue-shift none of the above that is no longer possible to learn what elements are in the star

that the lines in its spectrum show a blue-shift

A type of star that has turned out to be extremely useful for measuring distances is the white dwarf stars the main sequence stars the Cepheid variables the stars that line in the constellation of Orion the eclipsing binaries

the Cepheid variables

The instrument astronomers are now using to make the most precise measurements of stellar parallax we have ever had is the five meter reflector on mount palomar the very large array of radio telescopes the Compton gamma ray observatory a swimming pool sized VAT of cleaning fluid deep in the shaft of a gold mine the Gaia satellite in space

the Gaia satellite in space

An astronomical unit is: the distance to the nearest star the distance covered by light in one month the average distance between the Earth and the Sun the time it takes for the solar system to turn once on its axis the distance covered by light in one year

the average distance between the Earth and the Sun

When an astronomer measures a color index for a star, what is she measuring? What color the human eye sees when people look at the star the difference between how bright a star looks at two different wavelength regions the total luminosity of the star in all parts of the electromagnetic spectrum the amount of hydrogen in the atmosphere of the star how would the color of the stars changed when its light passes through the Earth's atmosphere

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

Why do Cepheid variables have that strange name? the first such variable was discovered in a constellation called Cepheus the word Cepheid means changing in brightness in ancient Greek the astronomer who discovered them had a dog named Ceffie they were discovered by an astronomer named George Cepheid the first star discovered to be this kind of variable had the Latin name Cepheidus

the first such variable was discovered in a constellation called Cepheus

The measurement of cosmic distances was helped tremendously by the discovery, in the early part of the 20th century, that in Cepheid variable stars, the average luminosity was related to: the length of time they took to vary their radial velocity their parallax the abundance of hydrogen in their atmosphere their distance from the Sun

the length of time they took to vary

The higher the luminosity (intrinsic brightness) a Cepheid variable is, The larger the telescope we need to observe it the closer it is to us the longer the period of its variations the smaller its mass the lower it is on the main sequence of the H-R diagram

the longer the period of its variations

Ninety percent of all stars (if plotted on an H-R diagram) would fall into a region astronomers call: the twilight zone the supergiant region the visual region the main sequence The white dwarf region

the main sequence

The apparent brightness of stars in general tells us nothing about their distances; we cannot assume that the dimmer stars are farther away. In order for the apparent brightness of a star to be a good indicator of its distance, all the stars would have to be: the same luminosity the same composition by themselves instead of in binary or double star systems at the same direction a lot farther away than they presently are

the same luminosity

Which of the following will show the smallest parallax shift? the star 51 Pegasi, about 50 lightyears away the Moon the Planet Jupiter Proxima Centauri the Sun

the star 51 Pegasi, about 50 lightyears away

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? actually this is just an optical illusion; all the stars are really the same brightness We see them in crowded regions of stars, which gives us the impression that the stars there are brighter than they really are All the brightest stars are red, and the red color is much easier to see against the black night sky these stars are intrinsically so luminous, that they can easily be seen even across great distances these stars vary in brightness (flashing brighter and dimmer) and are thus easier to notice

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

How do astronomers know that pulsating variable stars are actually expanding and contracting in diameter? Discover this by looking at an H-R diagram astronomers are just guessing, at the distances of stars, there is no way to show that stars are expanding and contracting it is clear just by looking at the light curve they can measure the stars changing pull on a companion star round it they can measure a regularly varying Doppler shift in the spectral lines

they can measure a regularly varying Doppler shift in the spectral lines

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 they are hotter than other brown dwarfs they orbit hundreds of nearby stars and are much more common than other brown dwarfs they show strong evidence of helium in their Spectra they have much larger mass than other brown dwarfs

they show absorption lines from the ammonia molecule in their spectra

A light curve for a star measures how its brightness changes with distance age mass radial velocity time

time

The luminosity class of a star tells an astronomer none of the above how long ago the star formed whether or not the star is surrounded by planets whether the star is a supergiant, a giant, or a main-sequence star whether this starts close to us or far away

whether the star is a supergiant, a giant, or a main-sequence star

Which of the following can astronomers NOT learn from studying the spectrum of a star? its surface temperature it motioned toward or away from us whether it is rotating slow or fast whether it is a star the size of the sun or giant star you can't fool me, all of the above can be learned from studying the spectrum

you can't fool me, all of 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? the distance between the earth and the moon the distance between observatories in Greenwich England and Washington DC ½ the diameter of the Earth's orbit around the Sun the diameter of the earth no one can measure parallax for the stars, only for planets in the our solar system

½ the diameter of the Earth's orbit around the Sun


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