Smartwork Ch 4
This radio message was beamed toward globular star cluster M13 in the year 1974, for a total broadcast of less than three minutes. Assume M13 is exactly 25,000 light-years away from us. If life within the globular cluster received our message and immediately sent back a response, in what year would we receive it
51974 Explanation: M13 is fairly distant from us; expect no response any time soon.
The presence of dark lines at specific wavelengths in an otherwise continuous spectrum can be explained most easily by which of the following?
A cool gas between observer and source is absorbing light at the wavelengths corresponding to the missing photons Explanation: Dark lines mean that some of the light that was in the spectrum could not reach your detector. Given that the spectrum is nearly continuous (with only a few missing colors), the light source is most likely a continuous light source, and the missing colors are being absorbed by a gas cloud between us and the light source.
Which of the following statements about the habitable zone is correct?
A world that is found to exist in the habitable zone of another star may have a higher probability of having life on it than those outside of this zone. Explanation: However, just because a world is in the habitable zone doesn't mean it actually has liquid water on its surface, and even if it does, that doesn't necessarily mean there is life there—it might be hard for life to begin, or there might be other conditions on the world that make life impossible.
The results of the Miller-Urey experiment supported which of the following conclusions about the early Earth?
Amino acids and organic compounds would have formed readily. Explanation: The Miller-Urey experiment created prebiotic molecules such as amino acids and organic compounds from simple compounds.
Why is the 21-cm line believed to be a prime candidate for the wavelength an extraterrestrial would send or recognize if sent?
An advanced civilization would be aware of its relevance. It is radiated by hydrogen, the most abundant element in the Universe. It falls in the radio part of the spectrum, whose long wavelengths are the most likely to travel unimpeded over large distances. Explanation: The 21-cm line is radiated by hydrogen, which is the most abundant element in the Universe. Because of this, many astronomers think it is reasonable that an advanced civilization would also be aware of it. Radio waves are also capable of traveling large distances unimpeded in the galaxy, making it a prime candidate for interstellar communication attempts.
The solar neutrino problem is accurately described in which of the following statements?
Experimental results found fewer neutrinos than models of nuclear fusion suggested would exist. Explanation: Only about one-third of the predicted number of neutrinos were detected before the realization that neutrinos could transform into two other types that would not have been detected.
For the following criteria, sort whether they are part of the definition of a "habitable zone" around a star or not.
For the following criteria, sort whether they are part of the definition of a "habitable zone" around a star or not. Explanation: Astronomers and astrobiologists think that the temperature of the star, distance from the star, and presence of water are all important criteria to define a habitable zone. The presence of carbon and the known existence of life are not taken into account for calculating the habitable zone.
A typical amateur telescope is a 10-inch reflector (where "10-inch" refers to the diameter of the telescope's mirror). How does the light-gathering power of the Hooker 100-inch reflector on Mount Wilson compare with that of the amateur telescope?
It is 100× greater.
A spectrum of a distant object reveals a sequence of known absorption lines that are all shifted to shorter wavelengths. What can be concluded about the object?
It must be moving toward us.
Ground-based telescopes are limited not only by their size but by the fact that the light from astronomical objects must pass through Earth's atmosphere. One effect of this is that the path of light from a source does not travel in a straight line, but it is refracted as it passes through air cells of varying temperature. This effect is called seeing. This slow-motion animation shows how the image of an object changes with time due to this effect. If the integration time is long enough to collect the light from this entire animation, what effect would seeing have on the image of the object?
It would blur the light from the object, effectively increasing the angular resolution of the telescope. Explanation: Every point (pixel) of the detector that receives light during the integration time will record that light, and as the light from the star moves around on the detector, the image will be blurred and the object will look larger than it really is.
Which of the following statements about natural selection is not true?
Less-adaptive traits die out in one generation. Explanation: The process of natural selection is a process that takes many generations for better-adapted traits to win out over less-adaptive traits. Less-adaptive traits may continue to be passed on from one generation to the next but usually in decreasing numbers until they eventually die out.
The following images are a sequence illustrating what happens to a population of gray and white rabbits in a snowy environment when attacked by wolves. Which of the four basic processes would lead to there being more white rabbits than gray rabbits?
Natural selection is the process by which some traits may make one individual more likely to survive in its environment and pass those genes on to the next generation.
The pattern of nucleobases in a strand of DNA is TGCAACG. When the strand splits for reproduction, which nucleobases will attach, in what sequence?
Nucleobases can only attach in specific pairs, AT and GC. So if the strand is TGCAACG, it will only bond with ACGTTGC, thus making the appropriate pairs.
Star I is observed to be brighter than Star II. Which of the following is/are true?
Star II may be bigger than Star I, If they are the same size and distance from the observer, Star I is hotter, If their luminosity is the same, Star I must be closer.
Telescopes that use lenses to focus light are called refracting telescopes. Bigger is better, but there is a limit to how big a lens can get before gravity distorts its shape and it can no longer focus light properly. Reflecting telescopes use curved mirrors to focus light. Gravity will also distort a mirror's shape if it gets too big. Since light passes through a lens, but bounces off a mirror, there is a fundamental difference in the way these two telescope types are designed. Mirrors are supported at the bottom, while lenses are supported at the sides by the tube surrounding them. Given that gravity pulls downward at every point on the lens or mirror, select the telescope type that can get larger (more massive) and still retain its shape.
Telescopes could be made much larger after the technology to make precision curved mirrors was developed. Larger telescopes result in better light-gathering power and resolution, so most professional telescopes today are reflecting telescopes.
There will be no change in the spectral lines of an object that is moving transversely from an observer. An object moving toward an observer will have its spectral lines blueshifted.
The Doppler shift of an object tells us whether the object is moving toward us (blueshifted) or away from us (redshifted) but nothing about the side-to-side transverse motion of the object.
Sort the following steps into the correct sequence in which life evolved on Earth.
The earliest life forms were single-celled organisms. After that came the eukaryotes, which were more complex. Next came oxygen breathers after the Great Oxygenation Event. Finally, multicelled organisms formed.
Choose all of the effects that would automatically happen if the wavelength of light were increased.
The energy of the light would decrease. The frequency of the light would decrease.
rank the elements below by their nuclear binding energy per nucleon from least to most.
The mass numbers of As75 and Bi209 indicate that the number of nucleons (the x-axis on the graph) in each nucleus is 75 and 209, respectively. This puts them between Fe56 and U238 on the graph, where the binding energy per nucleon steadily decreases with increasing number of nucleons. You might have also inferred this from checking a periodic table to see that As and Bi lie between Fe and U in atomic number, which tends to increase with mass number.
Why do stars twinkle?
The motion of Earth's atmosphere creates the appearance of twinkling.
Life continuously supplies oxygen to Earth's atmosphere: While we breathe in oxygen and expel carbon dioxide, some other species (like some bacteria and plants) expel oxygen. Yet, it took time for the amount of oxygen in the air to build up to the levels with which we are familiar now. The following figure shows the oxygen levels that existed in the Earth's atmosphere throughout its 4.5-billion-year history.
The oxygen levels we are breathing today have only existed for a small percentage of the history of the Earth (note that the horizontal axis on this graph displays time exponentially)
Compare the spectra of blackbodies with different temperatures. Which of the following is true?
The peak of the emission in the spectrum of the cooler object is at a longer wavelength.
Which statement about energy from nuclear fusion is correct?
The proportion of hydrogen converted to energy in nuclear fusion is 0.7 percent. Explanation: Mass is such a dense source of energy, even converting a small amount is very powerful.
Telescopes that observe nonvisible types of light work on the same principles as visible telescopes, but they might require different technologies. For instance, instead of lenses or mirrors, a radio telescope (such as the one in the figure) uses technology similar to the television satellite dish you might install on your roof. As with visible light telescopes, bigger radio telescopes yield greater light-gathering power and better angular resolution. However, the angular resolution (θ) of a telescope also depends on the wavelength of light (λ) based on the following equation, where D is the diameter of the telescope, and the resolution is in units of arcseconds (when D and λ have the same units). θ=2.06×105(λD)θ=2.06×105(λD) If there were two telescopes with the same diameter, but one is a visible light telescope and the other a radio telescope, how would the resolution of the images from each telescope compare? The wavelength of visible light is several hundred nanometers (1 nanometer = 10-9 meters), and radio can be several centimeters (1 cm = 10-2 meters) or several meters.
The radio telescope would have much worse angular resolution. Explantion: Because angular resolution is proportional to the wavelength of light being observed, larger wavelengths will have larger (worse) resolutions.
Space telescopes that exist in orbit above most of Earth's atmosphere are expensive, so they must therefore be supported with a very compelling motivation. If you were trying to justify funding for a space telescope in orbit around the Earth, which of the following would be the best argument to use?
The telescope could observe wavelengths of light that are not visible from the ground. Explanation: Astronomers need to observe objects across all wavelengths to learn the most about the universe. Many astronomical discoveries would not have been possible without space telescopes.
Which statement about the inputs to and outputs from nuclear fusion in the Sun is true?
The total mass of outputs is less than the corresponding inputs. Explanation: Some fraction of the total mass is converted to energy, so the total mass is decreased.
Based on life as we know it on Earth, which of the following is absolutely necessary for life to exist?
There are some life-forms on Earth that do not need an atmosphere, sunlight, or oxygen. This leads us to conclude that the subsurface oceans of Europa and other Jovian moons are potential locations for life in our Solar System.
One of the requirements for habitability for humans is a sufficient level of oxygen in the atmosphere to breathe. The table at right shows the percentage of oxygen in the atmospheres of Venus, Earth, and Mars. Oxygen is continuously removed from the atmosphere by oxidation reactions that combine it with other molecules, such as those in surface rocks. On the basis of this information, and your observations of the data in the table, which of the following is correct?
There is a special, continual source of oxygen that exists on Earth but not on any of the other planets. Explanation: Earth must have a special continual source of oxygen that adds more to the air, even as it is constantly being removed.
How will the composition of the Sun change over the next billion years?
There will be less hydrogen and more helium. Explanation: Correct! Nuclear fusion converts hydrogen into helium, so there will be less hydrogen and more helium.
Based on the time frames given in the above figure, which of the following are implications of the finite speed of light?
There would be a noticeable delay in communications at the speed of light between Earth and astronauts on the Moon. When we gaze at the Andromeda Galaxy, we are looking back in time to the way it used to appear millions of years ago. If the light of the Sun were suddenly extinguished, we wouldn't notice it from Earth for over 8 minutes.
Which of the following statements about sunspots is true?
They occur in predictable cycles. The number of sunspots, and the amount of solar activity in general, varies over an approximately 11-year cycle.
You find a polymer that contains the nucleobases A, G, and C. What kind of molecule can it be?
You find a polymer that contains the nucleobases A, G, and C. What kind of molecule can it be? Explanation: Both DNA and RNA contain A, G, and C nucleobases.
Larger lenses in telescopes offer better resolution. Resolution is defined as the closest angular distance two objects can be apart from one another before their light merges together and they look like just one object. Therefore, smaller resolutions are better (closer objects can be separated). The resolution of the human eye is 1 arcminute, or 1/60th of a degree. If the light of two street lamps in the distance is separated by 0.5 arcminute, what will you see with your eyes?
a single light, with the combined brightness of each street lamp Explanation: They are so close together that their light would blur into one single light, as seen by your eye.
To consider the possibility of life on other planets, we must look at the only example we have—life on Earth. We can then apply what we learn there to other worlds to determine the likelihood that life could have arisen there as well. There is no life on the surface of Mars or Venus, which are lacking one very important substance that Earth has in large quantities: liquid water. The following plot shows the conditions necessary for water to exist in the solid, liquid, or vapor (gas) phase. On the basis of your observations of the plot, which of the following things are absolutely necessary for a world to have for liquid water to exist on its surface?
a sufficiently thick atmosphere a location just the right distance from the Sun (not too close or too far) Venus has a very thick atmosphere, but it is too close to the Sun and therefore too hot for liquid water. Mars's atmosphere is far too thin (and therefore the atmospheric pressure is too low) for liquid water to ever exist on the surface, no matter what the temperature.
The sequence of bases in DNA directs which function?
building proteins Explanation: The sequence of bases in DNA directs the building of proteins.
Which of the following can astronomers determine from the spectrum of an object?
composition speed toward or away from an observer temperature explanation:The spectrum of an object can tell us the temperature from the peak of its blackbody curve, the composition from the wavelengths of absorption or emission lines, and the speed toward or away from us from the Doppler shift of those lines.
Choose the correct order of the Sun's layers from the center outward.
core, radiative zone, convective zone, photosphere, chromosphere, corona Explanation: The core is at the center, then energy is transferred through the radiative and convective zones, the photosphere is the "surface," and then the chromosphere and corona.
Oxygen exists in our atmosphere as O2 (two oxygen atoms bonded together) and O3 (three oxygen atoms bonded together, known as ozone). Both can absorb ultraviolet light from the Sun, through the reactions shown in the following figure. Oxygen and an ozone layer surrounding a planet help to prevent ultraviolet radiation from reaching the ground. Which of the following would be the most likely place that life would first form on Earth?
deep under water Explanation: Without an ozone layer, early Earth's atmosphere wouldn't have been enough to protect most surface creatures from deadly ultraviolet radiation. Water is denser, so it would have been able to absorb enough light to provide the protection early life needed from the Sun.
A hotter star will be brighter and bluer than a cooler star
explanation: The temperature of an object determines what color of light it emits as well as how brightly it glows. Humans are cool enough that they glow relatively faintly in the infrared (invisible to the human eye), while stars are so hot that they glow much more brightly and at much shorter wavelengths.
If a star like the Sun did not have the ability to create energy by nuclear fusion,
it would have exhausted its energy long ago. Nuclear fusion produces energy that heats the Sun so thermal pressure balances gravity. A star would keep contracting and converting gravitational potential energy to thermal energy for support, but this energy source is limited and cannot last as long as nuclear fusion. The Sun does not have enough antimatter or heavy elements for recombination or nuclear fission to power it.
Which of the following is not a basic feature of all living things on Earth?
sexual reproduction Explanation:While all life must reproduce, sexual reproduction is not required by the definition of life on Earth.
Observations of excited gas in the lab show that every element, molecule, and ion has its own unique set of possible electron energy levels, as shown in the emission spectra below. Based on this fact, what can we find from the wavelengths of absorption lines seen in the spectrum of a star?
the composition of any gas between the light-emitting "surface" of the star and the observer The light emitted from the "surface" (photosphere) of a star has a pure, continuous blackbody spectrum. As that light passes through the gas in the atmosphere of the star and any other gas between the star and the observer, particular wavelengths of light will be absorbed and removed from the spectrum depending on what that gas is made of (its composition).
The formation of absorption lines in a spectrum emitted by a blackbody indicates which of the following?
the existence of an intervening cloud of material cooler than the emitting source the specific elements of the atoms present in an intervening cloud the interaction of matter and light the existence of an intervening cloud of material hotter than the emitting source
What property of neutrinos allows them to mostly pass right through matter?
their low probability of interaction with other particles Matter is a collection of particles, so the low probability of interaction with other particles allows neutrinos to pass through matter.
Using Earth's evolutionary history as a model, what is the probability of finding intelligent life on a planet that has liquid water at or just below its surface and is orbiting in the habitable zone of a 1-billion-year-old Sun-like star?
very unlikely, because of the age of the system Explanation: The Sun is over 4 billion years old. Intelligent life formed on Earth relatively recently. This tells us that if a star is only 1 billion years old, it is very unlikely that intelligent life would have had enough time to form.