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Chapter 9 : Telescope

Telescope arrow_upward

  • An object that uses lenses or reflecting surfaces to collect light from a distant object.

  • What a Telescope Does? arrow_upward

  • A Telescope collects photons, so fainter objects can be seen.
  • A telescope magnifies angular sizes.
  • It gathers light from faint distant objects and magnifies these objects.
  • There are different telescope designs but the basic idea remains the same in all of them.
    •  A lens or mirror gathers light and concentrates it so the image can be examined by a magnifying eyepiece.

  • A flat surface reflects incident light at the same angle.
  • A curved surface can focus light.
  • A telescope uses mirrors or lenses to collect and focus light.
  • The area of the lens or mirror can be considerably larger than the area of the eye’s pupil. Hence, much fainter objects can be seen.
  • The largest lenses that can be built have a diameter of about 1 m, and have very long focal lengths.
  • A lens must be held by its edges, and large lenses sag under their own weight.  Also lots of light is lost in the glass.
  • For these and more reasons, all modern telescopes use mirrors.
  • Using an objective mirror, and some additional mirrors and lenses, light are collected and focused to a point.
  • A telescope’s main job is collecting photons.
  • The light gathering power is proportional to the area of the mirror or lens.

  • How a Telescope works? arrow_upward

  • There are two main types of telescopes:
    • Refracting Telescopes use lenses to focus light to a point.
    • Reflecting Telescopes use mirrors to focus the light.

    • Catadioptric Telescopes are a combination of the two.

    Anatomy of a Telescope arrow_upward

  • There are many types of telescopes; all have some basic key parts:
    • Aperture
    • Primary
    • Secondary
    • Eyepiece
    • Optical Tube
    • Finder
    • Detector
  • The Aperture is simply the part of the telescope that lets light in.
  • The Primary bends the light, bringing the rays to a point.
  • The Secondary aids in this process.
  • The Optical Tube protects the rest of the telescope and blocks stray rays of light.
  • The Finder is a small telescope used for locating an object.
  • The Detector is the thing that actually records the light.

  • Focusing Light arrow_upward

  • The idea of focusing light is important-
    • Telescopes collect light from a large area.
    • By focusing the light, we concentrate its power.
  • The Focal Plane is the plane where the light rays meet.
  • The Focal Length is the distance from the primary lens to the focal plane.

  • Resolution of Telescope arrow_upward

  • The resolution of a telescope defines how much detail can be seen.
  • All optical systems have some resolution limit.
    • The separation between the objects becomes too small for us to see.
    • Telescopes have a much improved resolution, but there is a limit.
    • The resolving power of a telescope cannot be greater than R= (1.22×λ)/D

    Angular Size arrow_upward

  • The separation of objects is measured in terms of angles.
    • There are 360° in a full circle.
    • There are 60 arc minutes in a degree, and 60 arc seconds in an arc minute.

    Thank You from Kimavi arrow_upward

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