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Author Question: If they existed, and if they were watching, a civilization at the center of the Milky Way could have ... (Read 18 times)

ghost!

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on: Jul 27, 2018
If they existed, and if they were watching, a civilization at the center of the Milky Way could have detected our first TV signals by now.
 
  Indicate whether the statement is true or false

Question 2

Explain how we estimate that there are about 50-100 billion galaxies in the observable universe.
 
  What will be an ideal response?


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tandmlomax84

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Reply #1 on: Jul 27, 2018
Answer to Question 1

FALSE

Answer to Question 2

Obviously it's impossible to count so many galaxies one by one, but by observing a small part in detail, we can extrapolate to get the total number. As an example, the Hubble deep field shows thousands of galaxies in a very small angular area of the sky (about equal to the size of a grain of sand held at arm's length). Multiplying the number of galaxies by the ratio of the angular area of the entire sky to the angular area of the deep field then gives an estimate of the total number of galaxies in the observable universe.


ghost!

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Reply #2 on: Jul 27, 2018
Thank you!


tandmlomax84

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Reply #3 on: Jul 27, 2018
Always glad to help...


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