AS101 LESSON 6
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38 Terms
Light
Electromagnetic transverse wave and main tool of astronomy
Why light is important in astronomy
Most information about universe comes from analyzing light
Electromagnetic spectrum
All forms of light including radio, infrared, visible, ultraviolet, X-ray, gamma ray
Visible light
Small part of full electromagnetic spectrum
Wave properties of light
Wavelength, frequency, speed
Light wave formula
Frequency × wavelength
Speed of light
3 × 10^8 m/s (300,000 km/s)
Wavelength measured in
Nanometres (nm)
Frequency measured in
Hertz (Hz)
Long wavelength means
Lower frequency and lower energy
Short wavelength means
Higher frequency and higher energy
Photon
Packet of light energy
Photon energy
Directly proportional to frequency
Light interactions with matter
Absorbed, reflected, transmitted, refracted, emitted
Refraction
Bending of light when entering new medium
Prism effect
Separates white light into spectrum
Source of light
Atomic or molecular energy transitions
Emission spectrum
Unique set of spectral lines for each element
Use of spectra in astronomy
Determine composition, temperature, motion
Doppler Effect
Change in observed wavelength/frequency due to motion
Redshift
Object moving away; wavelengths stretched longer
Blueshift
Object moving toward; wavelengths shortened
Use of Doppler Effect in astronomy
Measure radial motion of stars/galaxies
Optical device common features
Collect light, focus light, detect light
Human eye parts
Pupil, lens, retina
Camera parts
Lens, aperture, shutter, detector/film
CCD
Electronic light detector with high efficiency used in astronomy
Quantum efficiency highest
CCD (better than eye or film)
Two basic visible-light telescopes
Refracting and reflecting
Refracting telescope
Uses lens to focus light
Reflecting telescope
Uses mirror to focus light
Main telescope properties
Light-gathering power and resolving power
Light-gathering power
Ability to collect faint light; larger aperture is better
Resolving power
Ability to distinguish close objects
Magnification
Not most important telescope property
Ground telescopes problems
Atmosphere, weather, light pollution
Hubble Space Telescope significance
Above atmosphere gives clearer images and major discoveries
Space telescope advantage
Can observe wavelengths blocked/distorted by atmosphe