32 The Telescope

“The early spectacle maker – today’s equivalent of an optometrist – set up shop in the open streets. The patient would try on different ‘spectacles’ to see which one provided the best improvement in vision.”The telescope . is an instrument designed to collect and magnify visible light and see detail . Detail refers to angular resolution ; think of resolving into finer details. Bigger telescopes collect more light and produce better resolution. However, the bigger the better is not always true; our atmosphere can limit a telescope’s resolving abilities.

Image of a telescope inside an observatory.
CC BY-SA 4.0 | Image courtesy of Wikimedia Author: H. Aziz KAYIHAN.

Before the Telescope

Specific discoveries led up to the invention of the telescope. Below they are divided in Year and Event.

  • 3000 BC – Glass first appears in Egypt
  • 1500 BC – Oldest known glass vessels made
  • 425 BC – Optical properties discussed
  • Before 79 AD – Pliney, other writers knew of “liquid lenses,” spheres filled with water
  • 1000 AD – Atmospheric Refraction explained
  • 1278 AD – Glass mirror invented; properties of reflection
  • 1285 AD – Spectacles – eyeglasses – invented

There are several basic terms we use when discussing telescopes. Optics is the science that deals with all aspects of visible light. Primary Objective refers to the main lens (refractor telescopes) or mirror (reflector telescopes) which gathers the incoming light. The Eyepiece is a lens or series of lenses which focuses the light from the telescope’s primary objective for the eye. Refraction is the bending of waves, such as light, when it passes from one substance to another, for example, from air through glass. Refraction is the primary method of a refracting telescope. Reflection is the bending of waves, such as light or sound waves, from a surface. Reflection is the primary method of a reflecting telescope.


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