The _______________ time is the amount of time it took light to ...

[c0205847]

The _______________ time is the amount of time it took light to travel from a celestial object to Earth.
 
  Fill in the blank(s) with correct word

Question 2

Why are reflecting telescopes cheaper to build than refracting telescopes?
 
  What will be an ideal response?

[kthug]

Answer to Question 1

lookback
look-back

Answer to Question 2

Mirrors are much less expensive than lenses because light reflects off the front surface; therefore, only the front surface of a mirror needs to be made with a precise shape. Lenses are much more difficult to manufacture than a mirror of the same size. The interior of the glass must be flawless and pure, and must be made of two different kinds of glass requiring four precisely ground surfaces. Refracting telescopes larger than 1 m would be prohibitively expensive.

[c0205847]

Thank you!

[kthug]

Always glad to help...