Astronomy
1st Edition
ISBN: 9781938168284
Author: Andrew Fraknoi; David Morrison; Sidney C. Wolff
Publisher: OpenStax
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Textbook Question
Chapter 30, Problem 31E
Think of our Milky Way Galaxy as a flat disk of diameter 100,000 light-years. Suppose we are one of 1000 civilizations, randomly distributed through the disk, interested in communicating via radio waves. How far away would the nearest such civilization be from us (on average)?
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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?
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…
Tutorial
A radio broadcast left Earth in 1925. 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 0.30 and that, in a given planetary
system, the average number of planets that have orbited in the habitable zone for 4 billion years is 0.85. 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 1925, distance in light years = time since broadcast left Earth.
d = tnow - tbroadcast
d =
light years
Submit
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Chapter 30 Solutions
Astronomy
Ch. 30 - What is the Copernican principle? Make a list of...Ch. 30 - Where in the solar system (and beyond) have...Ch. 30 - Give a short history of the atoms that are now in...Ch. 30 - What is a biomarker? Give some possible examples...Ch. 30 - Why are Mars and Europa the top targets for the...Ch. 30 - Why is traveling between the stars (by creatures...Ch. 30 - What are the advantages to using radio waves for...Ch. 30 - What is the “cosmic haystack problem”? List as...Ch. 30 - What is a habitable zone?Ch. 30 - Why is the simultaneous detection of methane and...
Ch. 30 - What are two characteristic properties of life...Ch. 30 - What are the three requirements that scientists...Ch. 30 - Can you name five environmental conditions that,...Ch. 30 - Would a human have been possible during the first...Ch. 30 - If we do find life on Mars, what might be some...Ch. 30 - What kind of evidence do you think would convince...Ch. 30 - What are some reasons that more advanced...Ch. 30 - What are some answers to the Fermi paradox? Can...Ch. 30 - Why is there so little evidence of Earth’s...Ch. 30 - Why was the development of photosynthesis a major...Ch. 30 - Does all life on Earth require sunshine?Ch. 30 - Why is life unlikely to be found on the surface of...Ch. 30 - In this chapter, we identify these characteristic...Ch. 30 - Given that no sunlight can penetrate Europa’s ice...Ch. 30 - Why is Saturn’s moon Enceladus such an exciting...Ch. 30 - In addition to an atmosphere dominated by...Ch. 30 - How can a planet’s atmosphere affect the width of...Ch. 30 - Why are we limited to finding life on planets...Ch. 30 - Suppose astronomers discover a radio message from...Ch. 30 - The light a planet receives from the Sun (per...Ch. 30 - Think of our Milky Way Galaxy as a flat disk of...
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Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, physics and related others by exploring similar questions and additional content below.Similar questions
- In 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_forwardSuppose there are 9000.0 civilizations broadcasting radio signals in the Milky Way Galaxy at the moment. On average, how many stars would have to be searched before a signal is heard? Assume that there are 8 × 1011 stars in the Galaxy and one civilization per star.arrow_forwardThink of our Milky Way Galaxy as a flat circular disk of diameter 100,000 light-years. Suppose we are one of 1000 civilizations, randomly distributed through the disk, interested in communicating via radio waves. How far away in light years would the nearest such civilization be from us on average? Show your working. (Hint: Begin by calculating the area of the disk. Find the area of one of a 1,000 squares. Consider the separation of the centres of two adjacent squares.)arrow_forward
- Why is traveling between the stars (by creatures like us) difficult?arrow_forwardWould a human have been possible during the first generation of stars that formed right after the Big Bang? Why or why not?arrow_forwardWhat is the difference between chemical evolution and biological evolution?arrow_forward
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