Optics and Telescopes

Important Terms

Optical Telescopes

• Optical Elements
   
  • Mirrors and reflection

For plane (flat) mirrors, the angle of
incidence is equal to the angle of reflection.

For curved mirrors, all the light rays
can be brought to a common focus.

• Light in different materials and refraction

Light travels at different speeds in different materials.
The incident and refracted angles are related by:
n₁ sin θ₁ = n₂ sin θ₂

Light of different colors also travels at different speeds, even
in the same material. This is why prisms produce a spectrum.

• Lenses and images

Lenses are also able to bring light to a common focus.

The focal length is the distance from the center of the lens
or mirror to the point where light rays come together.

 The images formed by lenses depend on the kind
of lens, the focal length, and the distance of the
object from the lens.

• Telescopes

• Depending on the optical elements, telescopes are also classified as refracting or reflecting.
  
  
  • Click here to see how refracting telescopes operate.
    
  • Click here to see how reflecting telescopes operate.
     
• Since in a lens blue light is bent more than red light, refracting telescopes suffer from chromatic aberration. By combining one convex and one concave lens together into an achromatic lens, chromatic aberration is reduced, but not entirely eliminated.

• There is only one fundamental design for refracting telescopes. On the other hand, reflecting telescopes come in a wide range of designs.

• Light-gathering power – the bigger the better!

• The Industrial Revolution has in some ways made things very difficult for astronomers – light pollution!

• Modern, very large telescopes have innovative mirrors that use both active & adaptive optics.

• The 8.4-meter primary mirror of the Large Binocular Telescope (LBT) – yikes!