What is the water hole? Why is it so promising to radio ...

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What is the water hole? Why is it so promising to radio astronomers?
 
  What will be an ideal response?

Question 2

The radial velocity method is less likely to detect low mass planets than high mass planets because low mass planets cause smaller ________ fluctuations.
 
  Fill in the blank(s) with correct word

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Answer to Question 1

The water hole is the region of the radio spectrum between 18 cm (natural wavelength of the hydroxyl, OH, molecule) and 21 cm (natural wavelength of atomic hydrogen, H). Hydroxyl and hydrogen combine to form water, and the 18 cm to 21 cm region of the spectrum is relatively free of background noise. Thus it is believed that the so-called water hole is a natural band for communication between galactic civilizations.

Answer to Question 2

velocity