Light

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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