# Reflecting telescope optics problem-Angle on the sky to angle on a mirror

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1. Dec 2, 2012

### Desafino

1. The problem statement, all variables and given/known data

When viewed from Earth, the Moon subtends an angle of 0.5° in the sky. How large an image of the Moon will be formed by the 3.6 m diameter mirror of the Canada-France-Hawaii Telescope, which has a focal length of 8.5 m?

2. Relevant equations

1/s + 1/s' = 1/f, but I'm not sure what else.

3. The attempt at a solution

I'm really not sure where to begin. My book only talks about refracting telescopes and we've yet to talk about reflecting telescopes in class. I thought initially it might have something to do with the distance to and radius of the moon but I couldn't figure out how to work those into the problems. I'd appreciate any help you have. Thanks!

2. Dec 3, 2012

### Basic_Physics

The angle the object subtended at the mirror is the same angle that the image subtends - just like for refracting telescopes.

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Last edited: Dec 3, 2012