Essential Cosmic Perspective
9th Edition
ISBN: 9780135795033
Author: Bennett
Publisher: PEARSON
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Chapter 15, Problem 39EAP
Galactic Ecosystem. We have likened the star−gas−star cycle in our Milky Way to the ecosystem that sustains life on Earth. Here on our planet, water molecules cycle from the sea to the sky to the ground and back to the sea. Our bodies convert atmospheric oxy-gen molecules into carbon dioxide, and plants convert carbon dioxide back into oxygen molecules. How are the cycles of mat-ter on Earth similar to the cycles of matter in the galaxy? How do they differ? Do you think the term ecosystem is appropriate in discussions of the galaxy?
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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
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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.
Planetary Nebula Age.
Suppose a planetary nebula is 1 pc in radius. If the Doppler shifts in its spectrum show it is expanding at 20 km/s, how old is it? (Note that 1 pc equals 3.1x1013 km, and 1 year equals 3.2x107 seconds, to two significant figures.)
Please round your answer to two significant digits.
At =
years
Chapter 15 Solutions
Essential Cosmic Perspective
Ch. 15 - Prob. 1VSCCh. 15 - Prob. 2VSCCh. 15 - Prob. 3VSCCh. 15 - Prob. 4VSCCh. 15 - Prob. 5VSCCh. 15 - Prob. 6VSCCh. 15 - Prob. 1EAPCh. 15 - Prob. 2EAPCh. 15 - 3. Describe and contrast stellar orbits in the...Ch. 15 - Prob. 4EAP
Ch. 15 - Prob. 5EAPCh. 15 - Prob. 6EAPCh. 15 - Prob. 7EAPCh. 15 - Prob. 8EAPCh. 15 - Prob. 9EAPCh. 15 - Prob. 10EAPCh. 15 - Prob. 11EAPCh. 15 - Prob. 12EAPCh. 15 - Prob. 13EAPCh. 15 - Prob. 14EAPCh. 15 - Prob. 15EAPCh. 15 - We did not understand the true size and shape of...Ch. 15 - Prob. 17EAPCh. 15 - Prob. 18EAPCh. 15 - Prob. 19EAPCh. 15 - Prob. 20EAPCh. 15 - Prob. 21EAPCh. 15 - Prob. 22EAPCh. 15 - Prob. 23EAPCh. 15 - Prob. 24EAPCh. 15 - Prob. 25EAPCh. 15 - Prob. 26EAPCh. 15 - Prob. 27EAPCh. 15 - Prob. 28EAPCh. 15 - Prob. 29EAPCh. 15 - Prob. 30EAPCh. 15 - Prob. 31EAPCh. 15 - Prob. 32EAPCh. 15 - Prob. 33EAPCh. 15 - Prob. 34EAPCh. 15 - Prob. 35EAPCh. 15 - Prob. 37EAPCh. 15 - Prob. 38EAPCh. 15 - Galactic Ecosystem. We have likened the...Ch. 15 - Galaxy Stuff. In the chapters on stars, we learned...Ch. 15 - Prob. 42EAPCh. 15 - Prob. 43EAPCh. 15 - Prob. 44EAPCh. 15 - Prob. 45EAPCh. 15 - Prob. 46EAPCh. 15 - Prob. 47EAPCh. 15 - Prob. 48EAPCh. 15 - Prob. 50EAPCh. 15 - Prob. 51EAPCh. 15 - Prob. 52EAPCh. 15 - Prob. 53EAP
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