About Optical/Infrared Telescopes

1. About Optical/Infrared Telescopes ASTR 1, 4, & 14

3. Overview • The Electromagnetic Spectrum • Atmospheric Transparency • Optical Telescope Types • Three Important Concepts

4. The Electromagnetic Spectrum

5. Atmospheric Transparency

6. Optical Telescope Types Reflector – Use mirrors to gather and focus light to the detector. • 3 Types of Reflector • Cassegrain Focus • Newtonian Focus • Coude Focus Refractor – Use lenses to gather and focus light to the detector.

7. Three Important Concepts - I • Magnification or Magnifying Power of a telescope is the ratio of an object’s angular diameter seen through the telescope to its naked-eye angular diameter. The magnification can be estimated by computing the ratio of the primary (objective) lens or mirror focal length to its eyepiece focal length.

8. Three Important Concepts - II • Light-gathering power of a telescope is directly proportional to the area of the primary lens or mirror, which in turn is proportional to the square of the lens or mirror diameter.

9. Three Important Concepts - IIIa • TheAngular Resolutionof a telescope indicates the sharpness of the telescope’s image; i.e., the smallest angular separation that two stars can be discernible. Generally, the larger the diameter of the primary lens or mirror of a telescope, the higher angular resolution it is.

10. Three Important Concepts - IIIb • Ground-based optical/infrared telescopes cannot achieve the theoretical angular resolution limits because of the problem of seeing – turbulence in the air causes star images to jiggle around and twinkle. A measure of the blurring is called the seeing disk. Adaptive optics is applied to compensate the seeing.

11. Telescopes in the World