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