The celestial sphere appears to move fastest above the ________. ...

[bcretired]

The celestial sphere appears to move fastest above the ________.
 
  Fill in the blank(s) with correct word

Question 2

How did scientists use Titan to guide Cassini on a tour of Saturn's moon system?
 
  What will be an ideal response?

[aprice35067]

Answer to Question 1

equator

Answer to Question 2

Titan was used to give gravitational assists to increase and decrease the semi-major axis of the probe's orbit. When Cassini passes Titan inside its orbit of Saturn, Cassini's orbital semi-major axis is decreased. When Cassini passes Titan outside its orbit of Saturn, Cassini's orbital semi-major axis is increased. Using this, Cassini's controllers are able to guide the spacecraft on a tour of Saturn's moon system even though the spacecraft doesn't have much of its own power.

[bcretired]

TYSM

[xiazhe]

Excellent