MasteringAstronomy Assignment #10

Visual Activity Exploring the Habitable Zone around a Central Star
As the mass of the central star increases, the distance to the habitable zone __________ and the size (width) of the habitable zone __________.
increases / increases

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.

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


Searching for Signs of Intelligence (Process of Science)

Part A
Currently, astronomers are observing the universe across many different regions of the electromagnetic spectrum, from gamma rays to radio waves. One of the primary issues when considering communication with potential life outside our planet is how an extraterrestrial signal would be distinguished from natural radiation sources. Sort the following source properties by whether they might be considered as originating from intelligence or simply be natural phenomena.

Part B
In searching for signs of intelligence elsewhere in the universe, scientists begin with assumptions based on biological and chemical properties of Earth. They also examine how signals from Earth might appear to an observer in space. Select the statements that correctly describe what an extraterrestrial observer outside our Galaxy might see when viewing Earth.
a pulsating radio signal that varies in intensity during each cycle
spectral evidence that nitrogen and oxygen are the most abundant gases
natural emissions minimized in the 18-cm to 21-cm wavelength range called the "water hole"



Process of Science: Estimating the Number of Advanced Civilizations in our Galaxy
Part A
Each factor within the Drake equation can be estimated individually. However, some factors are largely grounded in astronomical data, while others are based on speculation of how life evolved on the Earth. Identify which factors in the Drake equation are estimated from astronomical observations and which are based on speculation.

Part B
The third factor of the Drake equation is an estimate of the number of habitable planets each planetary system might contain. Two key parameters that need to be considered when determining a planet’s ability to sustain life are the planet’s distance from its parent star, which determines whether the planet is in the stellar habitable zone, and the parent star’s distance from the galactic center, which determines if the star is in the galactic habitable zone. Consider the following sets of conditions, and sort each set according to whether it has a high or low probability of supporting life.

Part C
The last few factors in the Drake equation cannot be scientifically evaluated using current technologies. Astronomers can only estimate their values from either a pessimistic or an optimistic point of view. Choose the statements from the list below that indicate a high probability (optimistic estimate) that life exists elsewhere in the universe.
Environments suitable for the creation of organic molecules are common.
Chemical reactions leading to complex molecules are common.
Planets with conditions that remain stable over long periods of time are common.

Part D
The key factor in the Drake equation that determines whether humans will ever make contact with intelligent life in the universe is the average lifetime of technologically advanced societies. Assume that the life expectancy of advanced civilizations is generally low. Which of the following statements explain why it is unlikely that we will ever communicate with other civilizations?
There are too few advanced civilizations in the galaxy.
The distance between advanced civilizations in light-years is greater than their lifetimes in years.

Process of Science: The Solar Interior

Explain how studies of the solar surface provide information about the Sun’s interior.Astronomers can make direct observations of the Sun’s atmosphere and photosphere, but since they cannot directly observe the Sun’s interior, they must obtain information from indirect observations and mathematical modeling. This tutorial will explore how astronomers learn about the solar interior using these indirect methods.

Part A - The standard solar model
Drag the appropriate labels to their respective targets.


Part B - Helioseismology
The Sun’s surface vibrates from internal pressure waves reflecting off of the photosphere and passing through the solar interior. Since these waves penetrate deep inside the Sun, an analysis of the vibrations these waves cause at the surface can reveal unique information about the solar interior. The science of studying the vibrations on the surface of the Sun is known as helioseismology. If you were a helioseismologist, which of the following observational methods could you use to obtain information about the solar interior?
Measure Doppler shifts in solar spectral lines
Determine the wavelengths and frequencies of individual pressure waves

Part C - Energy transport inside the Sun
The energy generated in the core of the Sun is transported to the surface by radiation in the radiation zone and then by convection in the convection zone. Radiation occurs when atoms in the interior of the Sun transfer energy by absorbing and reemitting photons in random directions. Convection occurs when energy is transported by a region of hot gas rising up and a region of cooler gas sinking down to take the place of the hotter gas. Since radiation takes place deep within the Sun’s interior, it cannot be directly observed. However, convection can be observed due to its effects on the solar surface. Which of the following surface features provide evidence for solar convection?
supergranulation
granulation

Vocabulary in Context: Structure of the Sun

Part A

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.

Stellar Distances

Part A - Triangulating distances

One of the most fundamental techniques used to determine distances is triangulation. This same method is used to detect a star’s parallax and corresponding distance. Triangulation involves observing the same object from two vantage points, so that the object, along with the two vantage points, forms a triangle in space. In the figure, label the essential components used to triangulate the distance to a building located on the opposite side of an empty lot.

Part B - Stellar parallax

When triangulation is used to detect stellar parallax, observations are made from different parts of Earth's orbit around the Sun. The figure shows observations taken in January and July, corresponding to opposite sides of Earth's orbit. Identify the key parameters used to determine the star's distance from Earth.

Part C - Stellar motions

In addition to the apparent motion of stars caused by parallax, stars also have real motions through space that differ from that of the Sun and the solar system. The annual motion of a star across the sky as seen from Earth is called its proper motion. Once a star's distance and proper motion are known, they can be used to calculate a star's transverse velocity. Using Doppler shift measurements, astronomers can calculate a star's radial velocity, and then combine it with the transverse velocity to determine the star's true space velocity, or how fast it actually moves through space.

Match the words in the left column to the appropriate blanks in the sentences on the right.

Ranking Task: H-R Diagram, Luminosity, and Temperature

Part A

Consider the four stars shown following. Rank the stars based on their surface temperature from highest to lowest.

From Highest to Lowest:

Blue  Blue-white  White  White-yellow  Yellow  Orange  Red

Part B

Five stars are shown on the following H-R diagrams. Rank the stars based on their surface temperature from highest to lowest. If two (or more) stars have the same surface temperature, drag one star on top of the other(s).

(A star's luminosity is it's brightness, not temperature.)

Part C

Five stars are shown on the following H-R diagrams; notice that these are the same five stars shown in Part B. Rank the stars based on their luminosity from highest to lowest. If two (or more) stars have the same luminosity, drag one star on top of the other(s).

Part D

Five stars are shown on the following H-R diagrams. Rank the stars based on their surface temperature from highest to lowest. If two (or more) stars have the same surface temperature, drag one star on top of the other(s).

(Increase right to left)

Part E

Five stars are shown on the following H-R diagrams. Rank the stars based on their luminosity from highest to lowest; notice that these are the same five stars shown in Part D. If two (or more) stars have the same luminosity, drag one star on top of the other(s).

Part F

Five stars are shown on the following H-R diagrams. Rank the stars based on their surface temperature from highest to lowest. If two (or more) stars have the same surface temperature, drag one star on top of the other(s).

(Increase right to left)

Part G

Five stars are shown on the following H-R diagrams; notice that these are the same five stars shown in Part F. Rank the stars based on their luminosity from highest to lowest. If two (or more) stars have the same luminosity, drag one star on top of the other(s).

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Which of the following is NOT one of the steps involved in the development of life that has been successfully performed in laboratory experiments?
production of DNA by assembly of amino acids and precursor proteins

Which of the following is NOT a general characteristic of life?
needs oxygen

In what sense are viruses on the border between material that we consider living and that we consider nonliving?
Viruses cannot reproduce on their own but must make use of the genetic machinery of the cells they invade to multiply.

Which of the following objects are considered the three most likely solar system candidates for extraterrestrial life?
Mars, Europa, and Titan

Scientists say that silicon-based life may be possible but not probable. Why is silicon not as good a choice as carbon for organic molecules?
Silicon's bonds aren't as strong as carbon's, so it may not be able to build complex molecules.

Which term of the Drake equation is completely unknown and the hardest to determine?
lifetime of a technological civilization

What question does the Drake equation attempt to answer?
What is the number of technological civilizations in the Galaxy?

Which of the following is NOT a term of the Drake equation used to calculate the number of current technological civilizations in our Galaxy?
the fraction of planets orbiting G-type stars

What is the "stellar habitable zone"?
the range of distances from a star in which an Earth-like planet could sustain liquid water

Do astronomers expect to find planets around binary stars that are stable enough for life to develop? Why?
No. While it is possible for planets to form stable orbits in binary star systems, those orbits do not provide stable conditions for life.

If we communicated with a civilization from another star, how long would a conversation with them take?
years

Which of the following is NOT an advantage of using radio frequencies near the hydrogen and hydroxyl wavelengths of 18 and 21 cm, respectively, to search for signals from beyond our planet?
Since radio waves are comparatively long, it is easy to achieve good angular resolution with even a small radio telescope compared to optical telescopes, making it easier to pinpoint a potential source.

How would Earth appear at radio wavelengths to extraterrestrial astronomers?
as periodic blasts of transmissions that repeat roughly every 24 hours

MasteringAstronomy Assignment #9

Sorting Task: Comets, Meteors, and Asteroids
Part A
Listed following are some distinguishing characteristics of comets, meteors, and asteroids. Match these to the appropriate category of objects.

Visual Activity Exploring the Formation of Comet Structures
A comet entering the inner solar system from afar will __________.
form a coma and some time later form a tail

During the time that a comet passes through the inner solar system, the comet can appear quite bright because __________.
sunlight reflects off the comet’s tail and coma

A comet’s plasma tail always points directly away from the Sun because __________.
of pressure exerted by the fast-moving charged particles in the solar wind


Vocabulary in Context: Comets
Part A
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.

Ranking Task: Basic Properties of Extrasolar Planets
Part A
The following images show four identical Sun-like stars and their companion planets, all traveling in circular orbits. In each case, the mass of the planet is given in Jupiter masses and the orbital distance is given in Astronomical Units (AU). Rank each case based on the strength of the gravitational force exerted by the extrasolar planet on its central star, from weakest to strongest. If you think that two (or more) diagrams should be ranked as equal, drag one on top of the other(s) to show this equality. (Not to scale)

Part B
The following figures show four identical Sun-like stars and their companion planets. Each planet’s orbital distance is given in Astronomical Units (AU); note that in this case, all four planets have the same mass. Rank the extrasolar planets based on the amount of time it takes each to complete one orbit, from shortest to longest. (Not to scale)

Part C
The following images show the set of four stars and planets as in Part B. Imagine that an Earth-based observer could see the motion of each of the stars edge-on. Rank each star based on the amount of Doppler shift we’d see in its spectrum as it moves in response to the gravitational tug of its planet, from smallest to largest. (Not to scale)

Ranking Task: Velocity Curves for Stars with a Single Orbiting Planet
Part A
The following four graphs show the velocities, toward and away from Earth, of four identical stars. Assume that all four stars have extrasolar planets orbiting them at the same distance, and that the velocities are inferred by measuring Doppler shifts in the spectra of the stars. Rank the graphs from left to right based on the amount of orbital Doppler shift observed in each star’s spectrum, from smallest to largest.

Part B
The following four graphs show the velocities, toward and away from Earth, of four identical stars (the same graphs shown in Part A). Assume that all four stars have extrasolar planets orbiting them at the same distance. Rank the graphs from left to right based on the amount of time that it takes the extrasolar planet orbiting each star to complete one orbit, from shortest to longest. If you think that two (or more) of the graphs should be ranked as equal, drag one on top of the other(s) to show this equality.

Part C
The following four graphs show the velocities, toward and away from Earth, of four identical stars (the same graphs shown in Parts A and B). Assume that all four identical stars have extrasolar planets orbiting them at the same distance. Rank the graphs from left to right based on the mass of the extrasolar planet that orbits the star, from smallest to largest.

Visual Activity: Measuring Properties of Extrasolar Planets
Which of the following properties can be inferred from the star’s orbital period?
the planet’s orbital radius

Is it possible to determine the planet's mass from the star's velocity curve?
yes, by measuring both the star's orbital period and its change in velocity over the orbit

Consider the planet that causes the stellar motion shown in Plot 2 (be sure you have clicked the “Plot 2” button in the lower window of the animation). What can be said about a different planet orbiting the same star with an orbital period of 500 days?
The planet must be closer to the star.

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What is the most important defining property of the Trojan asteroids?
They orbit the Sun in the same path as Jupiter and 60° ahead of and behind it.

Which of the following characterizes the Kuiper belt?
It is a disk-like region between the outer planets and the Oort cloud.

The ingredients of a typical comet's nucleus are most likely ________.
dust and rocky particles trapped in methane, ammonia, and water ice

How was Pluto discovered?
It was simple luck and hard work.

Which of the following is NOT one of the criteria necessary to classify an object as a major planet?
It must have at least one moon orbiting around it.

What is the source of the material of a meteor shower?
Comets

The most common type of meteorite to strike Earth is ________.
rocky

Planetesimals were created through what process?
accretion

Which of the following objects is NOT best explained by some sort of unique impact event?
The asteroid belt

Which of the following methods have astronomers used to detect extrasolar planets?
Extrasolar planets have been detected using all of the methods listed here.

Planetary transits, coupled with radial velocity measurements, CANNOT unambiguously tell us which of the following about an extrasolar planet?
The planet's composition

If we lived in a solar system outside of our own, would we be able to detect Earth using Doppler measurements of our Sun's "wobble"?
No. The Doppler shifts would be too small for us to detect.

What is a "hot Jupiter?"
A planet with Jupiter's mass orbiting very close to its star.

What is a brown dwarf?
An object with more mass than Jupiter, but not enough mass to become a star.

What is a the best explanation for the hot Jupiters?
They formed far from their stars, and “migrated†inward because of interactions with the gas disk from which they formed.

MasteringAstronomy Assignment #8

Discovering Uranus and Neptune (Process of Science)
Part A
Many scientific discoveries are made by chance. While studying one phenomenon, a scientist may discover a different one. Such was the case when William Herschel discovered the planet Uranus in 1781. Herschel was charting faint stars in the sky, when he discovered something that was not a star. How can astronomers tell the difference between a star and a planet?

The following diagram depicts the sky as it would have appeared to Herschel when he first observed Uranus in 1781, as well as the same part of the sky over the next several nights. Label the indicated objects as stars or planets.

Part B
After the discovery of Uranus, astronomers calculated its orbit and predicted its position in the sky using Kepler's laws of planetary motion, which had been known since the early 17th century. However, they soon discovered a small discrepancy between the predicted and actual positions of Uranus. As a scientist, what should you do when presented with such a conflict between prediction and observation?
verify that your observations are correct
think about what else might cause the observed discrepancy
consider that Uranus may not be a planet
consider whether Kepler's laws need to be modified to account for the new observations

Part C
Starting with the hypothesis that a planet near Uranus was the cause of the orbital discrepancy, scientists had to develop a plan to find the unidentified planet. They started with what they knew about the discrepancies in the orbit of Uranus. Rank the steps in the order that scientists would take to discover the planet.

Ranking Task: Planet Temperature, Orbital Period, and Number of Moons
Part A
The following images show five planets in our solar system. Rank these planets from left to right based on their average surface (or cloud-top) temperature, from highest to lowest. (Not to scale.)

Part B
The following images show five planets in our solar system. Rank these planets from left to right based on the amount of time it takes them to orbit the Sun, from longest to shortest. (Not to scale.)

Part C
The following images show four planets in our solar system. Rank these planets from left to right based on the number of moons that orbit them, from highest to lowest. (Not to scale.)

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Why is Saturn's atmosphere almost three times thicker than Jupiter's?
Saturn is less massive than Jupiter; its gravity is weaker.

Which of the following statements is NOT true about Saturn's moon Titan?
Its surface temperature is about the same as that of Earth.

The Roche limit is that distance from a planet where ________.
tidal forces are equal to internal forces

Why did astronomers suspect there was an eighth planet beyond Uranus?
Irregularities in the motion of Uranus suggested that gravity from another planet was affecting it.

All but one of the following properties of Uranus's rings makes them different from the rings of Saturn. Which property is the same for both planets?
They are very thin.

Why is Neptune bluer than Uranus?
It has more methane.

What substance is responsible for the colors of Neptune and Uranus?
Methane

Which of the following statements is NOT true about the magnetic fields of Uranus and Neptune?
They are stronger than the magnetic field of Jupiter.

What evidence suggests that Triton is a captured moon?
It has a retrograde, highly inclined orbit.

Miranda's appearance suggests which of the following statements?
It has been catastrophically disrupted and reassembled several times.

Why are the moons of Uranus and Neptune so dark?
They are subject to radiation darkening.

What is the most significant difference between the Great Dark Spot of Neptune and the Great Red Spot of Jupiter?
The Great Dark Spot has disappeared, whereas the Great Red Spot has been seen for hundreds of years.

As a percentage of their total volumes, how do the cores of Uranus and Neptune compare with those of Saturn and Jupiter?
Their cores are larger than those of Jupiter and Saturn.

What has created Uranus's magnetic field?
A layer of conducting water

In 1781, Uranus was the first new planet to be discovered in how many years?
more than 2000