Light and Telescopes

LIGHT: THE BASICS

Longer Wavelengths vs. Shorter Wavelengths

Wavelength: the distance from the crest of one wave to the crest of the successive wave

Frequency: longer wavelengths corresponds to lower frequency and lower energy, shorter wavelengths correspond to high frequency and higher energy

Radiation: transmission of energy through space

Transmission: light rays or electromagnetic waves bending through a different medium

  • All waves have a source (e.g. electromagnetic waves originate from vibrating charged particles)
  • All waves, except electromagnetic waves, transmit through a medium

Wavelengths in Visible Light

Electromagnetic Spectrum: electromagnetic waves ranging from low frequency,  low energy, and long wavelength to high frequency, high energy, and short wavelength that originate from vibrating charges from the Sun; all electromagnetic waves travel at the same speed, or the speed of light (c = 300,000 km/sec or 186,000 miles/sec)

PROPERTIES OF LIGHT

Reflection: light rays or electromagnetic waves bouncing off reflective surfaces (e.g. mirror)

Refraction: light rays or electromagnetic waves bending through a different medium (e.g. air to water)

PROBLEMS WITH LIGHT AND MIRRORS

Spherical Aberration

Spherical Aberration: when light rays incident on the edges of the spherical mirror are focused at a different point from light rays incident closer to the center of the mirror –> blurry images; corrected by using parabolic mirrors

Chromatic Aberration

Chromatic Aberration: as light rays travel through a lens, different wavelength rays are bent by different amounts, resulting in different focal points

OPTICAL TELESCOPES

Three Types: 1. Reflective (mirrors), 2. Refractive (lens); 3. Combined or Catadioptic (both mirrors and lens): combines advantages of refractive and reflective telescopes, while avoiding disadvantages

  • Objective: main lens or mirror
  • Eyepiece: lens that magnifies images
  • Focal Length: distance between the center of the lens and the its focus
  • Aperture: diameter of objective

Functions of Telescopes: to collect light, to resolve details, to magnify, to measure, to record

Problems of Optical Telescopes: “seeing” (Earth’s atmosphere refracts light), air transparency, light pollution

Hubble Space Telescope

Unusual Telescopes

  • Radio: Arecibo, VLA, COBE
  • Microwave, or RadarPIONEER, COBE
  • InfraredSIRTF, IRAS, SPITZER
  • UltravioletCOPERNICUS, IUE
  • X-rayHEAO, EXOSAT, CHANDRA
  • Gamma RayGRO, EINSTEIN, COMPTON
  • OrbitalHUBBLE
  • Multiple MirrorsKECK
  • Interferometry: VLA, VLT
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2 thoughts on “Light and Telescopes

  1. It’s also the only reliable way for us to measure something to incredible accuracies. There is no other touch or manual probed instruments that can yield better accuracy than a light through a borescope.

    • Right, ever since Galileo modified the telescope 400 years ago, scientists have yet to deviate. Perhaps in the future engineers will build some more advanced than a “borescope”! Haha
      Tina

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