9.0 Astrophysics Flashcards
Describe chromatic aberration
Differing focal lengths of different wavelengths cause coloured fringes
Describe spherical aberration
different focal lengths of different incident rays cause blurring and distortion
avoiding aberration
use a convex lens with a concave lens cemented together
lens power
how closely a lens can focus a beam
similarities between radio and optical telescopes
- same function process
- can be aimed
- parabolic dish
- can be ground based
differences between radio and optical telescopes
- radio much larger
- radio cheaper and simpler
- radio scans area
- radio must be isolated
collecting power
measure of a lens’ or mirrors ability to collect incident EM radiation
Resolving power
ability to produce two separate images of close together objects
Rayleigh criterion
two objects will not be resolved if any part of the central maxima of one coincides the minima ring of the other
CCD
charge-coupled devices - an array of light sensitive pixels that use the photoelectric effect to detect light
quantum efficiency
The percentage of incident photons that cause an electron to be released
CCD ~ 80%, Eye 4-5%
Spectral range
detectable range of wavelengths
CCD - Infrared, uv visible
eye - visible
pixel resolution
number of pixels that make up an image
CCD ~ 50 megapixels
CCD ~ 500 megapixels
spatial resolution
minimum distance between two objects to be distinguishable
CCD - 10 micrometers
eye - 100 micrometers
conveniance
how easily images form
CCD - set up & digital
eye - no extra equipment
