Reflecting Telescopes

• What type of mirrors do reflecting telescopes use?

  Parabolic mirrors
• What is the most common type of reflector?

  Cassegrain telescope

  
• How do reflectors work?

  By the law of reflection
• What does the law of reflection state?

  The angle of incidence equals the angle of reflection
• What components do reflectors use instead of lenses?

  A primary mirror and a secondary mirror
• What shape is the primary mirror in a Cassegrain telescope?

  Concave

  
• Where does the incident light reflect in a Cassegrain telescope?

  Towards a focal point behind the secondary mirror

  
• What shape is the secondary mirror in a Cassegrain telescope?

  Convex

  
• What type of image does the secondary mirror form?

  A real, magnified image
• Where is the eyepiece lens located in a Cassegrain telescope?

  Behind the primary mirror

  
• What are the important features of the ray diagram for a Cassegrain telescope?

  • Rays enter parallel to the principal axis
  • Mirror curvatures do not have to be the same
  • Rays cross only in the aperture of the primary mirror
  • Shading indicates the non-reflective side of mirrors

  
• What is the first step in drawing a ray diagram for a Cassegrain telescope?

  Draw and label the principal axis

  
• What should be included at the center of the primary mirror in a ray diagram?

  The aperture (gap)
• What should be used to indicate the non-reflective side of each mirror?

  Lines or shading
• What should be drawn to show the reflection of rays by the primary mirror?

  Rays reflecting onto the secondary mirror

  
• What is the final step in checking a ray diagram?

  Ensure everything is included for marks
• What are common problems to avoid when drawing a ray diagram of a Cassegrain telescope?

  • Different curvatures on primary mirror halves
  • Drawing secondary mirror as a straight line
  • Forgetting to include the eyepiece lens
  • Rays crossing before hitting the secondary mirror

  
• Why are light rays from distant astronomical objects drawn as parallel?

  Because they are very far away
• What is a common misconception about the secondary mirror?

  It blocks light, missing central image
• What happens to light rays from a source on the mirror axis?

  They reach the secondary and are collected
• What is the only reflector arrangement to learn in this course?

  Cassegrain arrangement