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 Radar: PIONEER, COBE
- Infrared: SIRTF, IRAS, SPITZER
- Ultraviolet: COPERNICUS, IUE
- X-ray: HEAO, EXOSAT, CHANDRA
- Gamma Ray: GRO, EINSTEIN, COMPTON
- Orbital: HUBBLE
- Multiple Mirrors: KECK
- Interferometry: VLA, VLT
