The document provides an overview of how telescopes work, including their history and the key components and principles of refracting and reflecting telescopes. Refracting telescopes use lenses to bend light rays and form an image, while reflecting telescopes use mirrors. Both collect light and use additional lenses or mirrors to magnify the image for viewing. The size of the objective lens or mirror determines how much light is collected, while different eyepieces allow changing the magnification. Filters can enhance viewing of certain objects. Modern telescopes also observe wavelengths beyond visible light.

1. Telescopes How do they work?

2. 1. History 2. Lenses & Hardware 3. Reflecting Telescopes 4. Refracting Telescopes

8. Diagram of a simple telescope. Parallel light rays enter from the left, pass through the objective lens, come to a focus at the focal plane, and exit through the eyepiece lens. The focal length of the objective is F , and the focal length of the eyepiece is f . www.ifa.hawaii.edu

13. A closer look at eyepieces View through an eyepiece. Note that the image is upside-down.

18. This is the simplest telescope design you could have. A big lens gathers the light and directs it to a focal point and a small lens brings the image to your eye.

19. Refracting telescopes are not used for astronomical research (anymore) because they are large and have heavy lenses (i.e. expensive).

21. Reflecting telescopes focus light by bending them with mirrors

24. Very Large Array (VLA) radio telescopes