21st Century Astronomy
6th Edition
ISBN: 9780393428063
Author: Kay
Publisher: NORTON
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Question
Chapter 1, Problem 28QP
To determine
Whether the scientist’s statement that it is a known fact that life does not exist beyond Earth is reputable.
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Tutorial
A radio broadcast left Earth in 1923. How far in light
years has it traveled?
If there is, on average, 1 star system per 400 cubic light
years, how many star systems has this broadcast
reached?
Assume that the fraction of these star systems that
have planets is 0.50 and that, in a given planetary
system, the average number of planets that have
orbited in the habitable zone for 4 billion years is 0.40.
How many possible planets with life could have heard
this signal?
Part 1 of 3
To figure out how many light years a signal has
traveled we need to know how long since the signal left
Earth. If the signal left in 1923, distance in light years =
time since broadcast left Earth.
d = tnow - broadcast
d = 97
97 light years
Part 2 of 3
Since the radio signal travels in all directions, it
expanded as a sphere with a radius equal to the
distance it has traveled so far. To determine the
number of star systems this signal has reached, we
need to determine the volume of that sphere.
V, =
Vb…
A radio broadcast left Earth in 1911. How far in light years has it traveled?
If there is, on average, 1 star system per 400 cubic light years, how many star systems has this broadcast reached?
Assume that the fraction of these star systems that have planets is 0.50 and that, in a given planetary system, the average number of planets that have orbited in the habitable zone for 4 billion years is 0.20. How many possible planets with life could have heard this signal?
200 years has passed and now it is year 2220. The Earth is out of basic resourcesas they have been drastically drained in the past 200 years. The president of theUnited World Council (UWC) has approved you and your crew’s Mission toMars. You will pilot the most advanced spaceship the world has ever known, theExcelsior! It will carry equipment that will help to transform Mars so as toresemble the Earth, especially so that it can support human life.Before the mission can launch a few items need to be figured out. What is thecapacity of the fuel tank? How long should the fuel burn to achieve escapevelocity (otherwise the Excelsior will be stuck in the Earth’s gravitational pull)?How long will it take the Excelsior to arrive at Mars?1. The ground crew is filling the fuel tanks. You know th
Chapter 1 Solutions
21st Century Astronomy
Ch. 1.1 - Prob. 1.1CYUCh. 1.2 - Prob. 1.2CYUCh. 1.3 - Prob. 1.3CYUCh. 1 - Prob. 1QPCh. 1 - Prob. 2QPCh. 1 - Prob. 3QPCh. 1 - Prob. 4QPCh. 1 - Prob. 5QPCh. 1 - Prob. 6QPCh. 1 - Prob. 7QP
Ch. 1 - Prob. 8QPCh. 1 - Prob. 9QPCh. 1 - Prob. 10QPCh. 1 - Prob. 11QPCh. 1 - Prob. 12QPCh. 1 - Prob. 13QPCh. 1 - Prob. 14QPCh. 1 - Prob. 15QPCh. 1 - Prob. 16QPCh. 1 - Prob. 17QPCh. 1 - Prob. 18QPCh. 1 - Prob. 19QPCh. 1 - Prob. 20QPCh. 1 - Prob. 21QPCh. 1 - Prob. 22QPCh. 1 - Prob. 23QPCh. 1 - Prob. 24QPCh. 1 - Prob. 25QPCh. 1 - Prob. 26QPCh. 1 - Prob. 27QPCh. 1 - Prob. 28QPCh. 1 - Prob. 29QPCh. 1 - Prob. 30QPCh. 1 - Prob. 31QPCh. 1 - Prob. 32QPCh. 1 - Prob. 33QPCh. 1 - Prob. 34QPCh. 1 - Prob. 35QPCh. 1 - Prob. 36QPCh. 1 - Prob. 37QPCh. 1 - Prob. 38QPCh. 1 - Prob. 39QPCh. 1 - Prob. 40QPCh. 1 - Prob. 41QPCh. 1 - Prob. 42QPCh. 1 - Prob. 43QPCh. 1 - Prob. 44QPCh. 1 - Prob. 45QP
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- Life on Earth exists because of oxygen in Earths atmosphere. True false? Explain your answer.arrow_forwardWhat are the advantages to using radio waves for communication between civilizations that live around different stars? List as many as you can.arrow_forwardSuppose astronomers discover a radio message from a civilization whose planet orbits a star 35 lightyears away. Their message encourages us to send a radio answer, which we decide to do. Suppose our governing bodies take 2 years to decide whether and how to answer. When our answer arrives there, their governing bodies also take two of our years to frame an answer to us. How long after we get their first message can we hope to get their reply to ours? (A question for further thinking: Once communication gets going, should we continue to wait for a reply before we send the next message?)arrow_forward
- Why are we limited to finding life on planets orbiting other stars to situations where the biosphere has created planet-scale changes?arrow_forwardImagine that we discovered a new planet that has the potential to support life. This planet has plenty of water on its surface and carbon dioxide in its atmosphere, and a nice, comfortable temperature similar to Earth. The only difference is that this planet orbits a star that produces green light only. If we took some plants from Earth and planted them on this new planet, would our plants be able to grow? Explain your answer.arrow_forwardIn a globular cluster, astronomers (someday) discover a star with the same mass as our Sun, but consisting entirely of hydrogen and helium. Is this star a good place to point our SETI antennas and search for radio signals from an advanced civilization? Group of answer choices No, because such a star (and any planets around it) would not have the heavier elements (carbon, nitrogen, oxygen, etc.) that we believe are necessary to start life as we know it. Yes, because globular clusters are among the closest star clusters to us, so that they would be easy to search for radio signals. Yes, because we have already found radio signals from another civilization living near a star in a globular cluster. No, because such a star would most likely not have a stable (main-sequence) stage that is long enough for a technological civilization to develop. Yes, because such a star is probably old and a technological civilization will have had a long time to evolve and develop there.arrow_forward
- can you imagine life without electricity? what would you be our if there is no advancement in technology like motors and generators?arrow_forwardWhich of the following seems least reasonable regarding life on Earth? Group of answer choices There is much scientific evidence suggesting that all creatures living on Earth today appear to have evolved from a common ancestor. Louis Pasteur discredited the concept of spontaneous generation by demonstrating that even bacteria and other microorganisms arise from parents resembling themselves. There is ample physical evidence that the earliest life forms on Earth were multicellular creatures, perhaps resembling some of our primitive fish. When the earth formed some 4.6 billion years ago, it was a lifeless, inhospitable place. Before the mid-17th century, most people believed that God had created humankind and other higher organisms and that insects, frogs, and other small creatures could arise spontaneously in mud or decaying matter About billion years into its development, the Earth it was teeming with organisms resembling blue-green algae.arrow_forwardMost of the stars we can see with the unaided eye in our night sky are hundreds or even thousands of lightyears away from Earth. (The very closest ones are only a few dozen lightyears away, but most are much further.) The vast majority of stars in our galaxy are many tens of thousands of lightyears away. IF intelligent life existed on planets orbiting some of these stars – and that’s a huge IF! – comment on the likelihood and practicality of (a) visiting, (b) communicating with, or (c) verifying the existence of those life forms. Describe how you might go about approaching EACH of these three tasks, or if you think they are even possible. (One or two sentences for each part would be appropriate.)arrow_forward
- Which of the following is least reasonable regarding the difficulty in contacting extraterrestrial life using space flight and radio communication. Group of answer choices Space flight to the nearest star would take thousands of years with current technology. Even if another intelligent civilization is within a few hundred light-years of us, conversations would be very slow with a turnaround time of decades or even centuries. The spacecraft that NASA sent to Proxima Centauri a few years ago should be approaching its target within a decade or two, depending on solar wind conditions. Earth has been broadcasting at radio wavelengths since the 1930's, so any civilization within a radius of about 100 light-years or so could have received the broadcast by now. Without some major breakthrough, interstellar space flight is totally impractical.arrow_forwardA newly discovered star was found to have a surface temperature of approximately 5185 K. If an astrologist wanted to look for potentially habitable planets, what is the maximum distance from the star to reach its solar system's 'Goldilocks Zone'?arrow_forward
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