ASTR 5- Chapter 3 HW
The fact that the elements of life were produced in stars suggests the following two things:
(1) These elements have become more common as the universe has grown older. (2) These elements should be found in nearly all star systems
Match the words in the left-hand column to the appropriate blank in the sentences in the right-hand column. Use each word only once.
Correct
Match the words in the left-hand column to the appropriate blanks in the sentences in the right-hand column. Use each word only once.
Correct.
Which of the following is not a general difference between a planet and a star?
Planets are made of rock and stars are made of gas.
A light-year is ________.
about 10 trillion kilometers
According to current scientific estimates, when did the Big Bang occur?
about 14 billion years ago
Based on the nebular theory as it explains our own solar system, which of the following should we expect to be true for other star systems?
- Planetary systems should generally have all planets orbiting in nearly the same plane. - Jovian planets always form farther from their star than terrestrial planets. - Many extrasolar planets should fall into the terrestrial or jovian categories. - Planetary systems should be common.
Assume that the migration hypothesis is the correct explanation for the hot Jupiters. In that case, the revised nebular theory looks just like the old theory, except that it now allows for the possibility of migration. Which of the following statements are consistent with this revised theory?
- Terrestrial planets always form in the warm, inner regions of their star system. - Jovian planets can migrate inward and disrupt the orbits of terrestrial planets. - Jovian planets always form in the cold, outer regions of their star system.
Which of the following best describes the structure of an atom?
A tiny nucleus, made of protons and neutrons, surrounded by a "cloud" of electrons that give the atom its physical size
Suppose that the Sun were to collapse from its current radius of about 700,000 km to a radius of only about 6000 km (about the radius of Earth). What would you expect to happen as a result?
A tremendous amount of gravitational potential energy would be converted into other forms of energy, and the Sun would spin much more rapidly.
On a scale in which the Sun is about the size of a grapefruit and the Earth is about 15 meters away, how far away are the nearest stars besides the Sun?
About the distance across the United States
As you've seen, the nebular theory predicts that a cloud that gives birth to planets should have the shape of a spinning disk. Which observable property of our solar system supports this prediction?
All the planets orbit the Sun in the same direction and in nearly the same plane.
Listed following are several objects in the solar system. Rank these objects from left to right based on the distance from the Sun at which they are presumed to have formed, from nearest to farthest.
Although Oort cloud comets are now located far beyond the Kuiper belt, they are thought to have formed in the region of the jovian planets. They were then "kicked out" to their current orbits by gravitational encounters with the jovian planets
As the cloud shrinks in size, its central temperature __________ as a result of its __________.
As the cloud shrinks in size, its gravitational potential energy decreases. Because energy cannot simply disappear, the "lost" gravitational potential energy must be converted into some other form. Some of it is converted into thermal energy, which raises the temperature of the gas cloud. The rest is mostly converted into radiative energy, which is released into space as light.
Listed following are several objects in the solar system. Rank these objects from left to right based on their orbital period around the Sun from shortest to longest.
Be sure to notice that these objects obey Kepler's laws, so the more distant objects have longer orbital periods.
Rank the following items that describe distances from longest distance (left) to shortest distance (right). (If two distances are equal, drag the second item on top of the first item.)
Be sure to remember that 1 AU is the average distance from Earth to the Sun of about 150 million kilometers, while 1 light-year is nearly 10 trillion kilometers. In other words, a light-year is a distance more than 60,000 times as large as an astronomical unit.
The nebular theory also predicts that the cloud will flatten into a disk as it shrinks in size. Which of the following best explains why the collapsing cloud should form a disk?
Colliding cloud particles exchange angular momentum and, on average, end up with the rotation pattern for the cloud as a whole
Today, the leading hypothesis for the existence of hot Jupiters is that they formed in their outer solar systems and then migrated inward. Why did this hypothesis gain favor over alternative ideas?
Computer models that simulate planetary formation show that interactions between young planets and other material in the surrounding disk can cause planetary migration.
Sort the following hypothetical discoveries into the appropriate bins as follows: Consistent with theory: The statement describes a discovery that we could reasonably expect to find if the nebular theory is correct. Not consistent with theory: The statement describes a discovery that would force us to modify or discard the nebular theory.
Continue to the remaining questions to explore how these hypothetical discoveries could be used to test the nebular theory.
Each of the following statements applies either to the formation of terrestrial planets or of jovian planets (but not both), based on our current theory of solar system formation. Drag the statements into the appropriate bin.
Correct
Listed following are characteristics that can identify a planet as either terrestrial or jovian. Match these to the appropriate category. Consider only the planets of our own solar system.
Correct.
From shortest to longest wavelength, which of the following correctly orders the different categories of electromagnetic radiation?
Gamma rays, X rays, ultraviolet, visible light, infrared, radio
Which of the following types of material can condense into what we call ice at low temperatures?
Hydrogen compounds
The solar system has two types of planets, terrestrial and jovian. According to the nebular theory, why did terrestrial planets form in the inner solar system and jovian planets in the outer solar system?
Ices condensed only in the outer solar system, where some icy planetesimals grew large enough to attract gas from the nebula, while only metal and rock condensed in the inner solar system, making terrestrial planets.
The materials that made up the solar nebula can be categorized into these four general types. Rank these materials from left to right based on the temperature at which each would condense into a solid, from highest to lowest. Note: For a substance that does not condense at all, rank it as very low temperature.
In fact, hydrogen and helium gas never condense into solid form under the conditions that exist in interstellar clouds such as the solar nebula. Continue on to Part C to see how the condensation temperatures of the other materials explain why different materials condensed in different regions of the young solar system.
According to the nebular theory of solar system formation, which of the following best explains why the solar nebula ended up with a disk shape as it collapsed?
It flattened as a natural consequence of collisions between particles in the nebula.
According to the nebular theory of solar system formation, what three major changes occurred in the solar nebula as it shrank in size?
It got hotter, its rate of rotation increased, and it flattened into a disk.
Which of the following statements about nuclear fusion is not true?
It refers solely to the process of converting hydrogen into helium.
Suppose that two asteroids are orbiting the Sun on nearly identical orbits, and they happen to pass close enough to each other to have their orbits altered by this gravitational encounter. If one of the asteroids ends up moving to an orbit that is closer to the Sun, what happens to the other asteroid?
It will end up on an orbit that is farther from the Sun.
Suppose you know the frequency of a photon and the speed of light. What else can you determine about the photon?
Its wavelength and energy
The materials that made up the solar nebula can be categorized into the four general types as follows. Rank these materials from left to right based on their abundance in the solar nebula, from highest to lowest.
Knowing this ranking order is useful, but even more important is to recognize the vast differences in abundance: Hydrogen and helium gas constituted about 98 percent of the mass in the solar nebula. Most of the rest was hydrogen compounds, which were nearly three times as abundant as rock and metal combined.
Which of the following facts most definitively rules out the possibility that planets form when stars collide?
Many stars have planets.
Which of the following is not a major pattern of motion in the solar system?
Nearly all comets orbit the Sun in same direction and roughly the same plane.
Using the ideas discussed in the text, in what sense are we "star stuff"?
Nearly every atom from which we are made was once inside of a star.
Rank the forms of light from left to right in order of increasing energy. To rank items as equivalent, overlap them
Notice that the energy order is the same as the frequency order from Part B, which means it is opposite the wavelength order from Part A. The reason is that the energy of a photon of light is proportional to its frequency: energy = Planck's constant × frequency
Rank the forms of light from left to right in order of increasing frequency. To rank items as equivalent, overlap them.
Notice that the frequency order is the opposite of the wavelength order from Part A. You can understand why if you recall that wavelength times frequency always equals the speed of light. Because the speed of light is a constant, longer wavelengths must mean lower frequencies, and vice versa.
We divide the electromagnetic spectrum into six major categories of light, listed below. Rank these forms of light from left to right in order of increasing wavelength. To rank items as equivalent, overlap them.
Notice that these wavelengths span an enormous range. The wavelengths of gamma rays can be smaller than the size of an atomic nucleus, while the wavelengths of radio waves can be many meters (or even kilometers) long. Visible light spans only a very narrow range of wavelengths, from about 400 nanometersnanometers at the blue (violet) end to about 700 nanometersnanometers at the red end.
Rank the following items according to their size (diameter) from left to right, from largest to smallest.
Now continue to Part B to check that you understand levels of structure in the universe when we discuss them in terms of distances, using units such as AU and light-years.
Consider the indicated events in the history of the universe that have helped make human life possible. Rank the events based on when they occurred, from longest ago to most recent. To rank items as equivalent, overlap them. Note: If two events occurred within seconds of each other, rank them as equivalent.
Now that you know the order in which these events occurred, continue on to check whether you know approximately when they occurred
Provided following are stages that occurred during the formation of our solar system. Rank these stages from left to right based on when they occurred, from first to last.
Once the solar wind helped clear away the remaining gas in the solar nebula, the era of planet formation was essentially over. Remember that all these stages occurred over a period of millions of years, ending about 4 1/2 billion years ago.
You examine the thermal radiation from two different planets. Planet A has a thermal radiation spectrum that peaks at a shorter wavelength than Planet B. What can you conclude?
Planet A has a hotter surface than Planet B.
The discovery of extrasolar planets has provided strong validation for the nebular theory, but it also forced scientists to recognize that the theory was incomplete. Which idea was added to the theory after the discovery that some massive planets orbit very close to their stars?
Planets can migrate inward or outward from the orbits on which they originally formed.
If you could count stars at a rate of about one per second, how long would it take to count all the stars in the Milky Way Galaxy?
Several thousand years
Which of the following is not a general distinction between terrestrial planets and jovian planets?
Terrestrial planets have oceans of liquid water and jovian planets do not.
Listed following are several objects in the solar system. Rank these objects from left to right based on their distance from the Sun, from closest to farthest.
The asteroid belt is located between Mars and Jupiter. The Kuiper belt is a region beginning just beyond the orbit of Neptune. The Oort cloud is located far beyond the orbits of the planets.
Imagine that we receive a radio message from a civilization living on a planet around another star, and the message tells us that they have seen a television show from Earth that was broadcast in 1962. Which of the following statements can not be true?
The civilization is located 100 light-years away.
A rock held above the ground has potential energy. As the rock falls, this potential energy is converted to kinetic energy. Finally, the rock hits the ground and stays there. What has happened to the energy?
The energy goes to producing sound and to heating the ground, rock, and surrounding air.
Drag words indicating what happens to the first blank and indicating the reason to the second blank.
The force of gravity between any two particles increases as the particles come closer together. Therefore, as the cloud shrinks and particles move closer together, the force of gravity strengthens. This will tend to accelerate the collapse as long as no other force resists it. This is the case during the early stages of the collapse before the internal gas pressure builds up. (Once the gas pressure builds up, the outward push of the pressure can counteract the inward pull of gravity, which is why the cloud eventually stops contracting.)
What do we mean by accretion in the context of planet formation?
The growth of planetesimals from smaller solid particles that collided and stuck together
According to the nebular theory of solar system formation, which law best explains why the solar nebula spun faster as it shrank in size?
The law of conservation of angular momentum
Drag words indicating what happens to the first blank and indicating the reason to the second blank.
The law of conservation of angular momentum states that, in the absence of external influences (torques), the angular momentum of an object or a system of objects stays constant. Since the angular momentum of an object depends on both its size and rate of rotation, the cloud's rate of rotation will increase as its size (or radius) decreases in order to conserve angular momentum.
Suppose we make a scale model of our solar system, with the Sun the size of a grapefruit. Which of the following best describes the planets in this model?
The planets are all much smaller than the Sun. Four planets are within about 20 meters of the Sun, and the rest of the planets are spread much farther apart.
Rank the forms of light from left to right in order of increasing speed. To rank items as equivalent, overlap them.
The speed of light is a constant (in empty space) for all forms of light, meaning that all forms of light travel at the same speed, regardless of wavelength, frequency, or energy.
Which of the following best describes why we think the terrestrial planets formed in the inner solar system and the jovian planets formed in the outer solar system?
The terrestrial planets grew from "seeds" of metal and rock, whereas the jovian planets grew from seeds that also contained hydrogen compounds that condensed only in the cold outer solar system.
Suppose you want to know the chemical composition of a distant star. Which piece of information is most useful to you?
The wavelengths of spectral lines in the star's spectrum
The discovery of hot Jupiters led scientists to reconsider the nebuar theory. Which of the following best explains why the nebular theory(as it stood before the discoveries of extrasolar planets) had not predicted the existence of hot Jupiters?
There are no hot Jupiters in our solar system.
The region of our solar system between Mercury and Mars has very few asteroids, whereas the region between Mars and Jupiter has many asteroids. Based on what you have learned, what is the most likely explanation for the lack of asteroids between Mercury and Mars?
There were very few planetary leftovers in this region because most of the solid material was accreted by the terrestrial planets as the planets formed.
As you've learned from Part B, hydrogen and helium gas never condense under conditions found in the solar nebula. The remaining three categories of material in the solar nebula are shown again here. Rank these materials from left to right based on the distance from the Sun at which they could condense into a solid in the solar nebula, from farthest to closest.
These condensation regions explain the makeup of objects at different distances from the Sun. In the inner regions of the solar nebula, where temperatures were high, only metal and rock could condense, which is why the inner planets ended up being made of metal and rock. Farther out, hydrogen compounds could condense into ices, which is why comets and outer solar system moons contain large amounts of ice. And because hydrogen compounds are more abundant than metal or rock, some of the solid objects in the outer solar system grew so large that their gravity could pull in hydrogen and helium gas, which explains how the jovian planets formed.
Two hypothetical discoveries in Part A deal with moons that, like Earth's moon, are relatively large compared to their planets. Which of the following best explains why finding 1 planet with such a moon is consistent with the nebular theory, while finding 6 planets with such moons is not consistent?
Unusually large moons form in giant impacts, which are relatively rare events.
The Milky Way Galaxy is ________.
a giant collection of more than 100 billion stars
The Andromeda Galaxy is faintly visible to the naked eye. When you look at the Andromeda Galaxy, the retina of your eye is absorbing light that has traveled through space for ______ to reach you.
about 2 ½ million years
The age of Earth is about ________ the age of the universe.
about one-third
Consider the hypothetical discovery from Part A reading: "A star's 5 terrestrial planets orbit in the opposite direction of its 3 jovian planets." This discovery would be inconsistent with the nebular theory because the theory holds that __________.
all the planets formed in a rotating, disk-shaped nebula
Suppose that someone in the Andromeda galaxy had a super-telescope through which they were looking at Earth right now. They would see Earth ______.
as it was about 2 ½ million years ago
A carbon atom with six protons, seven neutrons, and five electrons has ________.
atomic number = 6 and atomic mass number = 13
Each choice describes two atoms, but the two atoms are isotopes of one another in only one case. Which one?
carbon-12 and carbon-14
On the cosmic calendar, which compresses the history of the universe into a single year, about when did life arise on Earth?
in September
On the cosmic calendar, which compresses the history of the universe into a single year, about when did Earth form?
in early September
A television advertisement claiming that a product "is light-years ahead of its time" does not make sense because ________.
it is using "light-years" to talk about time
Our modern theory of solar system formation—the nebular theory—successfully accounts for all the major features of our own solar system. However, when the first hot Jupiters were discovered, their existence seemed inconsistent with the nebular theory because this theory predicts that
jovian planets can form only in the cold, outer regions of a solar system
On the cosmic calendar, which compresses the history of the universe into a single year, about when did early humans first walk on Earth?
just a few hours before midnight on December 31
The energy attributed to an object by virtue of its motion is known as ________.
kinetic energy
The term organic molecules generally refers to ________.
molecules containing carbon
Vaporization is the process in which ___________.
molecules go from the liquid or solid phase to the gas phase
In essence, the nebular theory holds that _________.
our solar system formed from the collapse of an interstellar cloud of gas and dust
When considering light as made up of individual "pieces," each characterized by a particular amount of energy, the pieces are called ________.
photons
Thermal radiation is defined as ________.
radiation with a spectrum whose shape depends only on the temperature of the emitting object
A carbon atom with six protons and six neutrons will be electrically neutral if it contains ________.
six electrons
On a scale in which the distance from the Sun to the Earth is about 15 meters, the distance from the Earth to the Moon is ________.
small enough to fit within your hand
Based on what we know about our own solar system, the discovery of hot Jupiters came as a surprise to scientists because these planets are __________.
so close to their stars
The "Big Bang" is the name we use for ________.
the event that marked the beginning of the expansion of the universe
Observations show that interstellar clouds can have almost any shape and, if they are rotating at all, their rotation is not perceptible. However, the nebular theory predicts that a cloud will rotate rapidly once it shrinks to a relatively small size. What physical law explains why a collapsed cloud will rotate rapidly?
the law of conservation of angular momentum
The nebular theory also predicts that the cloud should heat up as it collapses. What physical law explains why it heats up?
the law of conservation of energy
The total number of stars in the observable universe is about ________.
the same as the number of grains of sand on all the beaches on Earth
The idea that the universe began in a Big Bang is now well-supported by evidence but initially arose as a logical inference based on the fact that ________.
the universe is expanding
Consider the hypothetical discovery from Part A reading: "Beyond its jovian planets, a star has two ice-rich objects as large as Mars." This discovery is consistent with the nebular theory, because this theory predicts that _________.
this might have happened in our own solar system if it had taken longer for the solar wind to clear the solar nebula
If we imagine the history of the universe compressed into a 1-year "cosmic calendar," dinosaurs became extinct ________.
yesterday morning
