Astronomy 100 Final Pt. 2
____ is similar in size to Pluto and also considered a dwarf planet.
Eris
Jupiter has three moons for which there is evidence of a global, subsurface ocean of liquid water, with the strongest evidence favoring an ocean on ____ .
Europa
Which of the following best describes how the Drake equation is useful?
It helps us understand what we need to know in order to determine the likelihood of finding other civilizations in our galaxy.
What do we mean by the event horizon of a black hole?
It is the point beyond which neither light nor anything else can escape
Which statement about the cosmic microwave background is NOT true?
It is the result of a mixture of radiation from many independent sources, such as stars and galaxies.
What do we mean by the main-sequence turnoff point of a star cluster, and what does it tell us?
It is the spectral type of the hottest main sequence star in a star cluster, and it tells us the cluster's age.
Given that the fossil record provides the key evidence for evolution, what is the importance of the theory of evolution?
It represents our understanding of the process by which evolution occurs.
How would you expect a star that formed recently in the disk of the galaxy to differ from one that formed early in the history of the disk?
It should have a higher fraction of elements heavier than hydrogen and helium.
How did oxygen (O2) get into Earth's atmosphere?
It was released by life through the process of photosynthesis.
How do the orbits of known extrasolar planets differ from those of planets in our solar system?
Many of orbits of extrasolar planets were much more eccentric and much nearer their stars than the jovian planets of our solar system.
____ has no surface liquid water today, but shows clear evidence of such water in the distant past.
Mars
All of the following statements are true. Which one explains why Mars has lost so much more interior heat than Earth. - Mars is farther from the Sun than Earth. - Mars is smaller than Earth. - Mars has a much weaker greenhouse effect than Earth. - Mars has lost much more atmospheric gas than Earth. - Mars lacks a large moon. Submit
Mars is smaller than Earth.
According to the diagram, the approximate abundance of oxygen atoms in the galaxy is __________.
1/1000 that of hydrogen
A Cepheid with a period of 30 days has an average luminosity that is about __________ times the luminosity of the Sun. (You will have to click on the blue Cepheids link on the main screen of the Interactive Figure to get back to the relevant plot.)
10,000
The following equation, derived from Newton's version of Kepler's third law, allows us to calculate the mass (M) of a central object, in solar masses, from an orbiting object's period (p) in years and semimajor axis (a) in astronomical units: M=a3p2 Using this formula with the values you found in Parts C and D, what is the approximate mass of the central object?
4 million solar masses
What is the approximate luminosity of the Cepheid whose light curve is shown in the graph?
9000 LSun
Which of the following is not an expected consequence of the rising carbon dioxide concentration or global warming?
Animal deaths due to carbon dioxide poisoning.
In principle, if we could see all the way back in time we could see the Big Bang taking place. However, our view is blocked for times prior to about 380,000 years after the Big Bang. Why?
Before that time, the gas in the universe was dense and ionized and therefore did not allow light to travel freely.
The requirement of liquid water is the most severe constraint on the development of life.
True
____ has an axis tilt that gives it very extreme seasons.
Uranus
The two jovian planets that contain the highest proportions of hydrogen compounds are ___________.
Uranus and Neptune
Spiral galaxy rotation curves are generally fairly flat out to large distances. Suppose that spiral galaxies did not contain dark matter. How would their rotation curves be different?
The orbital speeds would fall off sharply with increasing distance from the galactic center.
Which of the following statements best describes the general pattern of composition among the four jovian planets?
Uranus and Neptune contain relatively more rock and hydrogen compounds than Jupiter and Saturn.
How does gravitational lensing tell us about the mass of a galaxy cluster?
Using Einstein's general theory of relativity, we can calculate the cluster's mass from the precise way in which it distorts the light of galaxies behind it.
The star Vega has an absolute magnitude of about 4 and an apparent magnitude of about 0. Based on the definitions of absolute and apparent magnitude, we can conclude that ________.
Vega is nearer than 10 parsecs from Earth
____ has a surface hot enough to melt lead as a result of an extremely strong greenhouse effect.
Venus
Which model is most strongly supported by the data on the graph?
accelerating
Which model predicts the largest average distance between galaxies 6 billion years ago?
accelerating
We cannot see tidal forces or tidal heating; rather, we predict that they must occur based on the orbital characteristics of the moons. What observational evidence confirms that tidal heating is important on Io?
active volcanoes on Io
Scientists have confidence in the predictions of today's best climate models because they __________.
agree well with actual data for recent decades
What type of visible light spectrum does the Sun produce?
an absorption line spectrum
Where would you expect terrestrial planets to form in the solar nebula?
anywhere between the innermost regions (within about the inner 0.3 AU) and the frost line
A typical white dwarf is _________.
as massive as the Sun but only about as large in size as Earth
Orbital resonance also gives Europa an elliptical orbit, so it experiences tidal heating, too. However, Europa experiences less tidal heating than Io, because Europa __________
is farther from Jupiter
Io experiences tidal heating primarily because __________.
its elliptical orbit causes the tidal force to vary as Io orbits Jupiter.
All stars are born with the same basic composition, yet stars can look quite different from one another. Which two factors primarily determine the characteristics of a star?
its mass and its stage of life
Which one of the following can the transit method tell us about a planet?
its size
The existence of a core-mantle-crust interior structure tells us that a world __________.
once had a molten interior
The jovian planets are thought to have formed as gravity drew hydrogen and helium gas around planetesimals made of __________.
rocks, metals, and ices
What substances were found in the innermost regions (within about the inner 0.3 AU) of the solar system before planets began to form?
rocks, metals, hydrogen compounds, hydrogen, and helium, all in gaseous form
Based on DNA studies, it seems that all life on Earth ________.
shares a common ancestor
X ray photons have a _____ wavelength, _____ frequency, and _____ energy than do ultraviolet photons.
shorter, higher, higher
Which of the following are the best candidates to search for planets that might harbor extraterrestrial life?
solar-mass stars, because they have both a large habitable zone and a long stellar lifetime.
During the history of the universe, what important event occurred about 0.001 seconds after the Big Bang?
Most matter was annihilated by antimatter.
Which of the following statements correctly describes the motion of the particles in Saturn's rings?
Particles in the inner rings orbit Saturn at a faster speed than particles in the outer rings.
____ is orbited by at least two geologically active moons: Titan and Enceladus.
Saturn
Which of the following important events occurred earliest in the history of the universe?
Space-time rapidly expanded during a brief period of inflation.
As a general rule, smaller planets __________ than larger planets.
cool more rapidly
vCompared to a high-luminosity main-sequence star, stars in the upper right of the H-R diagram are __________.
cooler and larger in radius
Each data point represents a single white dwarf supernova that has been observed. The data points that appear farthest to the left on the graph represent the white dwarf supernovae that are the __________.
farthest away from us
According to the diagram, what is the most abundant element with an atomic number greater than or equal to 20?
iron
The primary way in which we learn about the history of life on Earth is through ___________.
the study of fossils
To determine a planet's average density, we can use
the transit and Doppler methods together.
The first of the two "undeniable facts" is that any localized population of a species has the potential to produce far more offspring than the local environment can support. This fact is important to understanding evolution because it means that __________.
there is competition for survival among the individuals of the population
Dark matter is inferred to exist because:
we can observe its gravitational influence on visible matter.
Not surprising
- A white dwarf supernova in a galaxy of only old stars - Two massive star supernovae occur in the same young star cluster. - A massive star supernova leaves behind no detectable compact object. - A massive star in a binary system explodes.
Surprising
- An isolated star like our Sun explodes as a white dwarf supernova. - A young (5 million years) star explodes as a white dwarf supernova.
Massive star supernova
- Black hole or neutron star left behind - Can only occur in a galaxy with ongoing star formation
White dwarf supernova
- Can only occur in a binary system - Spectra always lack strong hydrogen lines. - Can occur in a very old star cluster - Star explodes completely, leaving no compact object behind. - Has a brighter peak luminosity
Volcanism
- Created the smooth lunar maria. - Erased virtually all craters on Io. - Responsible for the existence of Earth's atmosphere and oceans
All the following statements are true. Which two represent the two facts that lead us to expect Earth to be warming up as a result of human activity? Be sure to choose two of the statements below. - If the polar caps melted, sea level would be much higher than it is today. - Temperatures are generally warmer in summer and cooler in winter. - Human activity is increasing the concentration of carbon dioxide and other greenhouse gases in the atmosphere. - Greenhouse gases make Earth warmer than it would be otherwise. - Water vapor is a greenhouse gas, but nitrogen and oxygen are not. - Venus has a much stronger greenhouse effect than Earth.
- Human activity is increasing the concentration of carbon dioxide and other greenhouse gases in the atmosphere. - Greenhouse gases make Earth warmer than it would be otherwise.
Which of the following must occur for a star's core to reach equilibrium after an initial change in fusion rate?
- If the fusion rate initially increases, then the core expands. - If the fusion rate initially decreases, then the core contracts
Impact Cratering
- Mostly occurred during heavy bombardment. - Affected all solid worlds similarly.
Tectonics
- On Earth, involves motion of plates. - Includes surface compression that builds mountains.
Early Mars (more than 3 billion years ago)
- Some craters held lakes of water. - Strong greenhouse effect. - Substantial volcanism and outgassing. - Strong magnetosphere. - Core convection.
Red giant or supergiant stars
- very cool but very luminous - found in the upper right of the H-R diagram
The theory of evolution has gained even further support since that time, because it has successfully passed many other observational tests. Which of the following statements represent successful tests of the theory of evolution by natural selection?
- Species often show unique adaptations that are suited to the specific environment in which they live and might be detrimental in other environments. - Genetic comparisons show that the DNA of closely related species is more similar than that of more distantly related species. - Over time, bacteria tend to acquire resistance to antibiotic drugs.
Mars Today
- Surface pressure too low for stable liquid water. - Very weak greenhouse effect. - Solar wind strips atmospheric gas.
Which of the following statements about galactic centers are true?
- The mass of a galaxy's central black hole is closely linked to the mass of a galaxy's bulge. - The power source for active galactic nuclei is thought to be the accretion disk around a central black hole. - Evidence suggests that many or most galaxies have a supermassive black hole in their centers.
Which of the following statements about the "tree of life" are correct?
- The tree is constructed by mapping evolutionary (genetic) relationships among species. - The tree suggests that all life on Earth arose from a common ancestor. - Many organisms on the tree can survive conditions that would be lethal to humans.
Which of the following statements about our solar system's terrestrial worlds are true?
- They are all of nearly the same age. - Their interiors all have a core, mantle, and crust. - They are all made primarily of rock and metal.
Consider the first image shown in the video, which is the Hubble Extreme Deep Field. Which of the following statements about this image are true?
- We see the more distant galaxies as they were when they were quite young. - The image includes galaxies that are elliptical, spiral, and irregular. - Careful study of the image shows that the youngest galaxies were mostly irregular in shape.
Which of the models predict that galaxies should be getting farther apart now? (Keep in mind that now is located at at time=0years on the graph.)
- accelerating - coasting - critical - recollapsing
Terrestrial Planets
- accreted from planetesimals of rock and metal - surfaces dramatically altered during the heavy bombardment
Which of the following changes would cause the fusion rate in the Sun's core to increase?
- an increase in the core temperature - a decrease in the core radius
all four jovian planets
- approximately 10 Earth-mass core - orbited by rings of ice and rock - magnetic field stronger than Earth's - strong atmospheric winds and storms
Uranus and Neptune only
- blue color because of methane - composed mostly hydrogen compounds
Which of the following are likely to play a role in determining whether a galaxy is spiral or elliptical?
- collisions or other interactions that the galaxy has had with other galaxies in the past - the rotation rate of the protogalactic cloud from which the galaxy was born - the density of the protogalactic cloud from which the galaxy was born
Europa
- double-ridged surface features strongly suggest a subsurface ocean below - ice covered surface with few impact craters
main-sequence phase
- energy generated by nuclear fusion - lasts about 10 billion years - surface radiates energy at same rate that core generates energy
Halo stars
- globular clusters - stars with the smallest abundance of heavy elements - oldest stars -stars whose orbits can be inclined at any angle
Main-sequence stars
- he majority of stars in our galaxy - the Sun, for example - the hottest and most luminous stars
White dwarf
- in a binary system, it can explode as a supernova - has a mass no greater than 1.4 MSun - typically about the size (diameter) of Earth - supported by electron degeneracy pressure
Jupiter and Saturn only
- interior is mostly liquid or metallic hydrogen - composed mostly of hydrogen and helium
Jovian Planets
- large moons formed in surrounding disks of material - ejected icy planetesimals that are now Oort cloud comets - formed in a region of the solar system with lower orbital speeds - accreted from icy planetesimals - formed in regions cold enough for water to freeze
Ganymede
- largest moon in the solar system - heavily cratered terrain adjacent to fairly smooth terrain
protostar phase
- luminosity much greater than the Sun - radius much larger than the Sun - pressure and gravity are not precisely balanced - energy generated by gravitational contraction
White dwarfs
- not much larger in radius than Earth - very hot but very dim
Solar minimum
- occurs about 5 to 6 years after a solar maximum (on average)
no jovian planets
- solid surface under a thick atmosphere
Neutron star
- sometimes appears as a pulsar - usually has a very strong magnetic field
Io
- source of ionized gas in the donut-shaped charged particle belt around Jupiter - hot, glowing lava visible in some photos - volcanoes currently erupting
Solar maximum
- sunspots are most numerous on the Sun - occurs about 11 years after a solar maximum (on average) - orbiting satellites are most at risk - auroras are most likely in Earth's skies - solar flares are most common
Black hole
- viewed from afar, time stops at its event horizon - size defined by its Schwarzschild radius
Disk stars
- youngest stars - the Sun - stars that all orbit in nearly the same plane - high-mass stars
The figure above shows the geological times scale. Animals have been present on land for approximately ________ of the Earth's history.
1/10
Look again at the orbit of the star with the highlighted orbit. By comparing the orbit to the scale bar shown on the diagram, you can estimate that this orbit has a semimajor axis of about _____.
1150 AU
We see a galaxy with a lookback time of 12 billion years when its age could not have been more than ____.
2 billion years
Based on this apparent brightness and the luminosity you found in Part D, what is the approximate distance to this Cepheid?
2.5 million light-years
To determine the mass of the central object, we must apply Newton's version of Kepler's third law, which requires knowing the orbital period and average orbital distance (semimajor axis) for at least one star. We could consider any of the stars shown in the figure, so let's consider the star with the highlighted orbit (chosen because its dots are relatively easy to distinguish). What is the approximate orbital period of this star?
20 yr
What is a mutation?
A change in a living cell's DNA
Consider a large molecular cloud that will give birth to a cluster of stars. Which of the following would you expect to be true?
A few massive stars will form, live, and die before the majority of the star's clusters even complete their protostar stage.
Why do astronomers hypothesize that a massive black hole lies at the center of M87?
A very small region at the center of M87 releases an enormous amount of energy.
Why do virtually all the galaxies in the universe appear to be moving away from our own?
Because expansion causes all galaxies to move away from nearly all others.
Why does the rotation curve for the solar system show speeds that become slower with increasing distance from the Sun?
Because the Sun contains most of the mass of the solar system
With our current technology, how could we detect life on a planet orbiting a distant star?
By analyzing the spectral lines created by the planet's atmosphere as it crosses in front of the star
The Interactive Figure (in red) shows a graph of the Cepheid period-luminosity relation. This graph indicates that __________.
Cepheids with longer periods have higher luminosities
Spacecraft images show fountains of ice spraying into space from Saturn's moon ____.
Enceladus
As you found in Part A, early Mars had both core convection and a strong magnetosphere. What is the connection between these two things?
Core convection helps generate a magnetic field, and the magnetic field creates the magnetosphere.
Some people wish that we lived in a recollapsing universe that would eventually stop expanding and start contracting. For this to be the case, which of the following would have to be true (based on current understanding)?
Dark energy does not exist and there is much more dark matter than we are aware of to date.
____ has a single moon that is surprisingly large compared to its planet.
Earth
Nearly all of the oxygen in the Earth's atmosphere was originally produced by photosynthesis in the leaves of trees that covered the continents 3.5 billion years ago.
False
The habitable zone around a star refers to the places where living organisms are found.
False
The two moons that are larger than the planet Mercury are Titan and ____ , which is also the largest of Jupiter's moons (and largest moon in the solar system).
Ganymede
Which of the following is not a possible solution to the Fermi Paradox?
Given the current age of our galaxy, there has not been enough time for a galactic civilization to develop.
Assuming that the bright core of M87 is powered by a supermassive black hole, which of the following best describes the source of energy that makes the core appear so bright?
Gravitational potential energy is converted to thermal energy as matter from the surrounding gas disk spirals into the central black hole.
How does the transit method tell us planetary size, and in what cases can we also learn mass and density?
In the transit method, the fraction of light absorbed is the ratio of the planet's area to the star's area, so we can find the physical size of the planet. If we also measure its mass via radial velocity, we can calculate its density.
Erosion
Includes features sculpted by wind.
What key process underlies why Mars changed so much from its early conditions to its conditions today?
Interior cooling.
____ is the most volcanically active world in the solar system.
Io
This elliptical orbit, in turn, is a result of the orbital resonance among Io, Europa, and Ganymede. This orbital resonance causes Io to have a more elliptical orbit than it would otherwise, because __________.
Io, Europa and Ganymede periodically return to the same orbital positions, creating the same gravitational tugs
Why is iron significant to understanding how a supernova occurs?
Iron cannot release energy either by fission or fusion.
How does the amount of heat released in a planet's interior by radioactive decay change with time?
It drops off with time.
What makes us think that the star system Cygnus X-1 contains a black hole?
It emits X rays characteristic of an accretion disk, but the unseen star in the system is too massive to be a neutron star.
Why do we call dark matter "dark"?
It emits no radiation that we have been able to detect.
How has the MAVEN mission provided evidence for this hypothesis?
It has measured rates of gas loss from the atmosphere today.
Earth has a relatively strong magnetic field, but Mars does not. Which of the following probably explains why Mars lacks a strong magnetic field today?
Its core is too cool for convection
This diagram represents the life track of a 1 solar mass star. Refer to the life stages labeled with roman numerals. What will happen to the star after stage viii?
Its outer layers will be ejected as a planetary nebula and its core will become a white dwarf.
____ has a famous storm known as the Great Red Spot.
Jupiter
Based on the leading scientific theory of solar system formation, which of the following statements best explains why Uranus and Neptune have a significantly different composition than Jupiter and Saturn?
Jupiter and Saturn captured more gas from the solar nebula than Uranus and Neptune
Which of the following best explains why Jupiter's density is higher than Saturn's?
Jupiter is more massive than Saturn.
Which of the following statements accurately describes a key lesson we have learned from the geological time scale?
Life arose almost as early as it could have on Earth.
What evidence suggests that life arises relatively easily?
Life was present on Earth soon after the end of the heavy bombardment period
During the history of the universe, what important event occurred about 380,000 years after the Big Bang?
Light began to travel freely through the universe.
____ has a greater difference in temperature between its day and night sides than any other world.
Mercury
What additional data would be most valuable in helping scientists evaluate whether the accelerating model really is the best of the four models?
More observations of very distant white dwarf supernovae
When were the heat-trapping effects of gases that cause the greenhouse effect first measured by scientists?
More than 150 years ago.
____ has a large moon, Triton, that almost certainly once orbited the Sun independently.
Neptune
The only place outside of Earth for which there is irrefutable evidence for ancient, microbial life is
None of the abovethere is no irrefutable evidence for life beyond Earth
Imagine that our Sun were magically and suddenly replaced by a black hole of the same mass (1 solar mass). What would happen to Earth in its orbit?
Nothing—Earth's orbit would remain the same.
Suppose that our Sun was cool enough to include Mercury in its habitable zone. Which of the following would be true in that case?
Only Mercury would be in the Sun's habitable zone.
Which is more common: a star blows up as a supernova, or a star forms a planetary nebula/white dwarf system?
Planetary nebula formation is more common.
____ was studied up close in 2015 by the New Horizons spacecraft.
Pluto
What is the Fermi Paradox?
Reasonable assumptions predict that a galactic civilization should have already arisen in the Milky Way, yet we have absolutely no evidence for it.
In Part D, you saw that elements with even atomic numbers tend to be more abundant than neighboring elements with odd atomic numbers. What nuclear process explains why this is the case?
Starting from carbon (atomic number is 6), the most common nuclear reactions involve the fusion of an additional helium nucleus.
Which of the following statements best describes the pattern of the graph?
Starting from the center, speeds at first rise rapidly, and then become nearly constant with increasing distance.
In all cases, assume that the Cepheid's apparent brightness has been carefully measured through observations.
Step 1: Measure the period of the Cepheid's brightness variations. Step 2: Use the period-luminosity relation to determine the Cepheid's luminosity. Step 3: Calculate the Cepheid's distance from its luminosity and apparent brightness.
Why is Europa considered a good candidate for the possible existence of life?
Strong evidence suggests that it has a deep, subsurface ocean of liquid water.
What actually causes a Cepheid to vary in apparent brightness?
The Cepheid varies in radius, and its luminosity is greater when its radius is larger.
Why isn't the Moon considered to be a likely place for finding extraterrestrial life?
The Moon lacks liquid water.
____ generates energy deep in its core through the fusion of hydrogen into helium
The Sun
What would happen if the fusion rate in the core of the Sun were increased but the core could not expand?
The Sun's core would start to heat up, and the rate of fusion would increase even more.
The observational data for the element abundances agree quite well with what we expect based on our current understanding of nuclear fusion and stellar evolution. But imagine the data had turned out to be different. Which of the following differences, if it had actually been observed, would have forced us to rethink our entire picture of stellar evolution?
The abundance of elements heavier than uranium turned out to be greater than the abundance of carbon.
Based on current evidence, how does the actual average density of matter in the universe compare to the critical density?
The actual density, even with dark matter included, is only about one third of the critical density.
What was the significance of the end of the era of nucleosynthesis, when the universe was about 5 minutes old?
The basic chemical composition of the universe had been determined.
The third image in the video (with the most detailed view of the galactic center) is labeled "gas disk." Which of the following best describes what we are seeing in this photo?
The black hole is located deep within the bright central region, and around this region we see gas that is orbiting the central black hole.
Like any scientific theory, the theory of evolution is subject to revision or even to being discarded if future observations do not agree with its predictions. Which of the following hypothetical observations (none of which are real or likely) would force us to reconsider the theory of evolution?
The discovery of fossils of human-like primates dating to a time before the earliest dinosaurs existed.
Scientists think it is very unlikely that complex and large forms of life could evolve on planets that orbit stars that are much more massive than the Sun. Why?
The expected lifetime of a massive star is too short to allow for the evolution of complex life
The idea that life evolves through time was first suggested in ancient Greece, and it was favored by at least some scientists of the 18th and 19th centuries even before Charles Darwin proposed the theory of evolution. What is the key observational evidence that supports the idea that life on Earth has evolved through time?
The fossil record, revealed in geological layers of different ages, shows that life on Earth has become more complex over time.
Which of the following is NOT considered a potential solution to the question of why we lack any evidence of a galactic civilization?
The galactic civilization probably is undetectable because they operate under different laws of physics from the ones we know.
Which of the following is not considered a potential solution to the question of why we lack any evidence of a galactic civilization?
The galactic civilization probably is undetectable because they operate under different laws of physics from the ones we know.
How does the habitable zone around a star of spectral type M compare to that around a star of spectral type G?
The habitable zone around the M star is closer to the star.
Why don't we expect to find life on planets orbiting high-mass stars?
The lifetime of a high-mass star is too short.
Why do scientists think it unlikely that life would arise on a planet orbiting a 10-solar-mass star?
The lifetime of the star is too short.
In general, how does the size and location of a star's habitable zone depend on the star's mass?
The smaller (less massive) the star, the smaller and the closer-in the habitable zone.
How should we expect the Milky Way's interstellar medium to be different in 50 billion years than it is today?
The total amount of gas will be much less than it is today.
Which of the following statements best reflects our current knowledge about the term Flife in the equation Number of Civilizations = NHP × Flife × Fcivilization × Fnow?
The value of Flife is between 0 and 1.
Suppose that a white dwarf is gaining mass through accretion in a binary system. What happens if the mass someday reaches the 1.4 solar mass limit?
The white dwarf will explode completely as a white dwarf supernova.
Based on the diagram, which of the following statements best describes the observed pattern of abundances for elements with an atomic number between 6 and 20?
There is a general trend of decreasing abundance with increasing atomic number, but elements with even atomic numbers tend to be more abundant than those with odd atomic numbers.
Look at the average densities of the jovian planets given in Figure 1. Can you identify a trend in jovian planet densities with mass or distance from the Sun?
There is no clear trend in the densities with mass or distance
You've now found that the central object has a mass of about 4 million solar masses but is no more than about 70 AU in diameter—which means it cannot be much larger than the size of our planetary system. Why do these facts lead astronomers to conclude that the central object is a black hole?
There is no known way to pack so much mass into such a small volume without it collapsing into a black hole.
Jupiter and the other jovian planets are sometimes called "gas giants." In what sense is this term misleading?
They actually contain relatively little material in a gaseous state.
Which of the following best describes the nature of planetary rings?
They are composed of countless individual particles.
If there are other civilizations at present in the Milky Way Galaxy, which statement is almost undoubtedly true?
They are far more technologically advanced than we are.
Which of the following statements best explains why the densities of Uranus and Neptune are higher than that of Saturn, even though Saturn is much more massive?
They have a higher proportion of hydrogen compounds and rock.
Why are these orbits surprising?
This was surprising since our planet formation model suggests that planets should have nearly circular orbits and that jovian planets, which require ice to form, should form only farther out in the solar system.
Scientists have detected lakes of liquid methane and ethane on the surface of ____.
Titan
Which of the following best describes the predominant scientific view of the origin of life on Earth?
We may never know precisely how life arose, but current evidence suggests that life probably can arise naturally under the conditions that prevailed on the early Earth.
We now know of many Jupiter-size planets around other stars. Suppose that future observations show that one of these planets has two orbiting moons. What additional information, if any, would we need to decide whether these moons experience tidal heating?
We need to know their orbital periods.
How do we determine the conditions that existed in the very early universe?
We work backward from current conditions to calculate what temperatures and densities must have been when the observable universe was much smaller in size.
Recall that one of the laws of thermal radiation states that a higher-temperature object emits photons with higher average energy (Wien's law). This law is illustrated by the fact that for a higher temperature object, the graph peaks at __________.
a shorter wavelength
A typical neutron star is more massive than our Sun and about the size (radius) of _________.
a small asteroid (10 km in diameter)
Which kind of object is the best standard candle for measuring distances to extremely distant galaxies?
a white dwarf supernova
The absorption line spectrum shows what we see when we look at a hot light source (such as a star or light bulb) directly behind a cooler cloud of gas. Suppose instead that we are looking at the gas cloud but the light source is off to the side instead of directly behind it. In that case, the spectrum would __________.
be an emission line spectrum
Why do scientists say that evolution is a "theory"?
because it explains a great deal about life and is supported by an enormous body of evidence
The Rotation Curve of the Solar System animation shows the orbits of Mercury, Venus, Earth, and Mars. Click on each of the orbits, and watch the corresponding points appear on the graph below it. If a planet (or asteroid) orbited the Sun at three times the distance of Mars, its orbital speed would be __________.
between one-third and two-thirds the orbital speed of Mars
Star A is identical to Star B, except that Star A is twice as far from us as Star B. Therefore, ________.
both stars have the same luminosity, but the apparent brightness of Star B is four times that of Star A
How do we know the total mass of the Milky Way Galaxy that is contained within the Sun's orbital path?
by applying Newton's version of Kepler's third law (or the equivalent orbital velocity law) to the Sun's orbit around the center of the Galaxy
Essentially all the hydrogen nuclei that will ever exist in our universe were created __________.
by the time the universe was about 3 minutes old
At present, what is the primary way that astronomers carry out SETI programs (that is, search for extraterrestrial intelligence)?
by using radio telescopes to search for signals from extraterrestrial civilizations
This graph is what we call a rotation curve, because it plots the speed at which any point rotates around the center (the orbital speed) against the distance of that point from the center. Based on the graph, you can conclude that doubling the distance of a point from the center of the merry-go-round would __________.
double its orbital speed
Compared to when the cosmic microwave background was first released, the radiation of the cosmic microwave background today is __________.
fainter and has most of its photons at longer wavelengths
The two facts from Parts C and D lead to the "inescapable conclusion" that individuals in a population will have unequal reproductive success, so that those whose traits best enable them to survive will leave more offspring. Therefore, in any local environment, over time, __________.
heritable traits that enhance survival will become progressively more common in succeeding generations
Compared to a low-luminosity main-sequence star, stars in the lower left of the H-R diagram are __________.
hotter and smaller in radius
If observations had shown that the cosmic microwave background was perfectly smooth (rather than having very slight variations in temperature), then we would have no way to account for ________.
how galaxies came to exist
To calculate the dashed orbits from the stellar positions, astronomers had to assume that __________.
if they observed for many more years, the dots would trace out ellipses
Scientists can estimate the age of a planetary surface by counting __________.
impact craters
According to current understanding, the two most abundant elements in the universe were made __________.
in the Big Bang
Where does most star formation occur in the Milky Way Galaxy?
in the spiral arms
As the mass of the central star increases, the distance to the habitable zone __________ and the size (width) of the habitable zone __________.
increases / increases
Compared to a main-sequence star with a short lifetime, a main-sequence star with a long lifetime is __________.
less luminous, cooler, smaller, and less massive
Saturn's rings look bright because __________.
light from the Sun reflects off the material in the rings
The key commonality required for all life on Earth to be able to grow and reproduce is __________.
liquid water
Red light has a _____ wavelength and a _____ frequency than does blue light.
longer, lower
Saturn's rings are composed of __________.
lots of individual particles of ice and rock
The neon "OPEN" sign appears reddish-orange because __________.
neon atoms emit many more yellow and red photons than blue and violet photons
Based on what you can see in the diagram, you can conclude that the diameter of the central mass is __________.
no more than about 70 AU
What substances existed as solid flakes within the innermost regions (within about the inner 0.3 AU) of the solar system before planets began to form?
none
Suppose that you had "X-ray vision" that allowed you to see X rays. What would you notice when you looked at a friend standing near you that you could not notice with your visible light vision alone?
nothing
Dark energy has been hypothesized to exist in order to explain:
observations suggesting that the expansion of the universe is accelerating.
The Schwarzschild radius of a black hole depends on ________.
only the mass of the black hole
The diagram indicates that the third most abundant element in the Milky Way Galaxy is _____.
oxygen
If we can measure the period of a star's "wobble" caused by an orbiting planet, we know the _______.
period of the planet's orbit.
If you have a telescope that is observing light with wavelengths of a few meters, you are observing __________.
radio waves
If life exists in the oceans on Jupiter's moon Europa, what would be its most likely energy source?
radioactive decay of heavy elements
Which model is most clearly ruled out by the data on the graph?
recollapsing
Which of the models predict that galaxies will eventually get closer together in the future?
recollapsing
The second of the two "undeniable facts" is that individuals in a population of any species vary in many heritable traits (traits passed from parents to offspring), so that no two individuals are exactly alike. This fact is important to understanding evolution because it means that
some individuals possess traits that make them better able than others to compete for food and other resources
From Part D, you know that the galaxy's rotation curve is nearly flat, even well beyond the point at which we see any stars in the galaxy. According to the law of gravity as we understand it today, the only explanation for these this flatness is that __________.
substantial amounts of mass must reside at great distances from the galactic center
Which region of Earth has warmed the most in recent decades?
the Arctic
Notice that some of the stars on the diagram are represented by a series of dots that are very close together, while others have their dots farther apart. Keeping in mind that all the stellar positions were measured at approximately one-year intervals, which stars are moving the fastest in their orbits during the time period indicated by the dots?
the dots farthest apart
Laboratory experiments conducted with particle accelerators confirm predictions made by the theory that unifies ________.
the electromagnetic and weak forces into the electroweak force
When we analyze whether a world is a possible home to life, the key thing we look for is ________.
the existence of liquid water
In the Drake equation (Number of Civilizations = N HP × f life × f civ × f now), what do we mean by f now?
the fraction of planets with civilizations at the present time (as opposed to only in the past or future)
To understand why the galaxy rotation curve in Part D is flat, we must first understand how gravity determines the orbital speeds of stars around the galactic center. Consider any star on a circular orbit around the center of the galaxy. The speed of the star's orbit depends on the star's distance from the galactic center and __________.
the mass of the galaxy that resides within the star's orbit
To estimate the central temperature of the Sun, scientists _________.
use computer models to predict interior conditions
When the universe was 380,000 years old, its thermal radiation spectrum consisted mostly of
visible and infrared photons.
Fermi's paradox is the name given to a question about why ___________.
we do not yet have clear evidence of alien civilizations
