Module 7 test
A _____ is a planet that is intermediate between the largest terrestrial planet in our solar system (Earth) and the smallest jovian planet (Neptune); generally, they have sizes between 2.8 and 4 times Earth's size
mini-Neptune
The largest types of clouds found in interstellar space are
molecular clouds with supplies of dust and molecules
Supposing we launched a very fast dart from the Space Shuttle, pointed in some direction away from any planet, so that it could travel beyond the solar system. What would it be most likely to hit first after traveling outward for a while?
an atom of interstellar gas
To get the distance to a Cepheid variable star, astronomers must take several steps. Which of the following is NOT one of these steps?
measure the star's Doppler shift from its spectrum
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?
measuring the star's parallax
A star whose temperature is increasing but whose luminosity is roughly constant moves in what direction on the H-R diagram?
to the left
_____ is when one astronomical object moves in front of another
transit
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
If a star is 20 parsecs away, its parallax must be:
1/20th of an arcsecond
How far away would a star with a parallax of 0.2 arcsec be from us?
5 parsecs
The _____ is the cycling of mass in and out of the interstellar medium, including accretion of gas from intergalactic space, loss of gas back into intergalactic space, and conversion of interstellar gas into stars
Baryon cycle
When astronomers carefully examine the planets found by Kepler and draw conclusions from the Kepler sample, what do they conclude about planets the size of Earth?
Earth-sized planets are common, but so are planets somewhat bigger than Earth
Our solar system has 8 planets orbiting the Sun. Based on the discoveries of exoplanets so far, what can we say about a star with 8 planets?
Even though planets were only discovered starting in 1995, so we can't yet find planets that take centuries to go around their star, we already know other stars with 8 planets and we are likely to find more
The _____ is the region of ionized hydrogen in interstellar space
H II region
A _____ refers to luminous knots of gas in an area of star formation that are set to glow by jets of material from a protostar
Herbig-Haro object
The red color we see on a lot of photographs of nebulae comes from which element?
Hydrogen
The star now called Kepler-444 is 11 billion years old (much older than the Sun) and has five planets orbiting close to it. What has this system taught astronomers about the history of star formation?
If such an old star has planets close to it, where it's really warm, those planets must be made of heavier elements. So heavier elements must have formed before the time this star formed.
Which of the following stars is a Cepheid variable?
Polaris
A _____ is a very young star still in the process of formation, before nuclear fusion begins
Protostar
What is the closest star to the Sun?
Proxima Centauri
____ is one of a class of giant pulsating stars with periods shorter than 1 day, useful for finding distances
RR Lyrae
The first (living) star other than our own Sun found to have more than one planet orbiting it is called
Upsilon Andromedae
An astronomer wants to observe a cloud of dust in a relatively close part of the Galaxy. Unfortunately, this dust cloud is not located in the direction of a crowded region of stars. What instrument would be the most help in finding this cloud.
a sensitive infra-red telescope in orbit around the Earth
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
Where is the outer rim of the Local Bubble located today?
about 200 light-years from the Sun, in the rough direction of the constellations of Orion, Perseus, and Auriga
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 and protostars which are not yet doing fusion do not give off a lot of visible light)
The light element lithium (which, on Earth, is part of medications that improve the lives of people with mental health illnesses) is more common in cosmic rays than it is in the Sun and the stars. What do astronomers think is the reason for this?
because cosmic rays move so fast, they can collide with atoms of carbon, nitrogen, and oxygen and break them apart, producing more light elements like lithium
Why did it take astronomers until 1838 to measure the parallax of the stars?
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
Today, astronomers can measure distances directly to worlds like Venus, Mars, the Moon, or the satellites of Jupiter by
bouncing radar beams off them
Which of the following is NOT a way astronomers discover clouds of interstellar matter that have a large amount of dust in them?
by giving off x-rays from hot gas surrounding the dust cloud
A _____ is a star that belongs to a class of yellow supergiant pulsating stars; these stars vary periodically in brightness, and the relationship between their periods and luminosities is useful in deriving distances to them
cepheid
Astronomers now understand that the dark regions or rifts visible in parts of our Galaxy that are otherwise crowded with stars are caused by:
clouds with a considerable amount of dust which blocks the light of the stars behind them
_____ are atomic nuclei (mostly protons) and electrons that are observed to strike Earth's atmosphere with exceedingly high energies
cosmic rays
Why can astronomers not tell from what direction a particular cosmic ray started toward the Earth?
cosmic rays are charged particles and are thus spiral around the Earth and the Galaxy's magnetic field
An _____ is a planet orbiting a star other than our Sun
exoplanet
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
_____ are large, cold interstellar clouds with diameters of dozens of light-years and typical masses of 10^5 solar masses; found in the spiral arms of galaxies, these clouds are where stars form
giant molecular clouds
Which of the following is not a place where astronomers believe interstellar dust grains can form?
in H II regions
You are an astronomer whose supervisor has just forbidden drinking alcoholic beverages near the observatory. In frustration, you under¬take a search for alcohol molecules in space. Where would your search be most likely to succeed?
in an interstellar cloud of gas and dust
If you want to find stars that are just being born, where are the best places to search?
in giant molecular clouds
_____ consists of tiny solid grains in interstellar space thought to consist of a core of rocklike material (silicates) or graphite surrounded by a mantle of ices; water, methane, and ammonia are probably the most abundant ices
interstellar dust
Which of the following descriptions of interstellar dust is FALSE?
interstellar dust must be at a temperature equal to the outer layers of a star interstellar dust particles can sometimes be found in meteorites and can be identified
_____ is the attenuation or absorption of light by dust in the interstellar medium
interstellar extinction
_____, or interstellar matter, is the gas and dust between the stars in a galaxy
interstellar medium
Astronomers have found large quantities of cold, neutral hydrogen gas in our galaxy. How is this gas distributed?
it is found mostly in a flat layer extending throughout the disk of our galaxy
he closest star to the Sun, Proxima Centauri, was recently found to have a planet in its habitable zone. Proxima Centauri is a main sequence star with spectral type M. How would its habitable zone differ from the habitable zone of our Sun?
it would be significantly closer to Proxima Centauri than ours is to the Sun
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 luminosity
When a star settles down to a stable existence as a main-sequence star, what characteristics determines where on the main sequence in an H-R diagram the star will fall?
its mass
A _____ is a graph that displays the time variation of the light from a variable or eclipsing binary star or, more generally, from any other object whose radiation output changes with time
light curve
The _____, or Local Hot Bubble, is a region of low-density, million degree gas in which the Sun and solar system are currently
local bubble
The _____ is a slightly denser cloud inside the Local Bubble, inside which the Sun also lies
local fluff
Given the presence of dust throughout the disk of the Milky Way Galaxy, what is the best technique for learning about more distant regions of our galaxy's disk.
look for radiation at long wavelengths, for example in the infrared region of the spectrum
_____ is a classification of a star according to its luminosity within a given spectral class; our Sun, a G2V star, has _____ V, for example
luminosity class
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
What technique did astronomers use to make the first confirmed discovery of a planet around another star like the Sun?
measure the Doppler shift of the lines in the star's spectrum and look for periodic changes in this shift due to the pull of the planet as it orbits the star
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
Cosmic rays differ from other forms of interstellar matter by
moving much faster, at typical speeds of 90% the speed of light
Astronomers were surprised to find so many Jupiter-mass planets so close to their stars. According to their best theories and models, such "hot Jupiters"
must have formed further out from the star and must have "migrated inward" early on are absolutely impossible, so they must be mistaken observations
A _____ is a cloud of interstellar gas or dust; the term is most often used for clouds that are seen to glow with visible light or infrared
nebula
_____ is an apparent displacement of a nearby star that results from the motion of Earth around the Sun
parallax
A _____ is a unit of distance in astronomy, equal to 3.26 light-years; at a distance of 1 _____, a star has a parallax of 1 arcsecond
parsec
_____ is an empirical relation between the periods and luminosities of certain variable stars
period-luminosity relation
Which of the following is NOT one of the reasons planets around other stars are so difficult to detect?
planets only form very late in the life of a star, just when it is ready to die, and thus last only a very short fraction of the star's life
If an astronomer wanted to find some relatively complex molecules in space, what technique should she use?
point a radio telescope into regions in the galaxy where there is a lot of dust
A _____ is a variable star that pulsates in size and luminosity
pulsating variable star
The term _____ refers to the reddening of starlight passing through interstellar dust because dust scatters blue light more effectively than red
reddening
The amount of interstellar matter present in our Galaxy is always changing. Which of the following processes is NOT a major contributor to that change?
some atoms of gas combine in dusty clouds to make more complex molecules actually, none of the above is a major contributor to the change
_____ is the outflow of gas, sometimes at speeds as high as hundreds of kilometers per second, from a star
stellar wind
Which type of star has the least amount of pressure in its atmosphere?
supergiants
A type of star that has turned out to be extremely useful for measuring distances is
the Cepheid variables
With our current techniques, astronomers can typically only measure the minimum mass of a planet orbiting another star. To know the precise mass of the planet, they must also be able to determine
the angle at which the planet's orbit is tilted relative to 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
the clouds of the nebula that have a lot of dust in them
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
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 parallax
The higher the luminosity (intrinsic brightness) a Cepheid variable is,
the longer the period of its variations
Among interstellar clouds, the hotter the cloud, the
the lower the density of particles in it
To measure how dense a planet is (to know whether it is made of rock or gas and liquid) they must be able to measure the planet's mass from the Doppler shift and
the planet's radius using the transit method
Which of the following will show the smallest parallax shift?
the star 51 Pegasi, about 50 lightyears away
How do astronomers know that pulsating variable stars are actually expanding and contracting in diameter?
they can measure a regularly varying Doppler shift in the spectral lines
A light curve for a star measures how its brightness changes with
time
The dust in the dust clouds in interstellar space consists of
tiny solid grains
An astronomer is observing a star which puzzles her. The lines in the star's spectrum indicates that the star is very hot and should therefore be blue. But the star looks reddish in photographs and in measurements of the continuous spectrum. What is one possible explanation of this puzzle?
we are seeing the light of the star through layers of interstellar dust this star must be located high above the disk of the Milky Way Galaxy
Astronomers studying regions like the Orion Giant Molecular Cloud have observed that a wave of star formation can move through them over many millions of years. What sustains such a wave of star formation in a giant molecular cloud?
when massive stars form, their ultraviolet radiation and later their final explosions compress the gas in the cloud and cause a new group of stars to form
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
The luminosity class of a star tells an astronomer
whether the star is a supergiant, a giant, or a main-sequence star
