astrophysics: comparing telescopes

define resolving power

a measure of how much detail you can see through a telescope

define minimum angular resolution

the smallest angular separation at which an instrument can distinguish 2 points

the [] the minimum angular resolution, the [] the resolving power of the telescope

smaller, better

what is resolution limited by?

diffraction

what happens if a beam of light passes through a circular aperture (such as a telescope lens)?

diffraction pattern of bright and dark maxima. central circle called airy disk.

what observation led to the rayleigh criterion?

two light sources can be distinguished if the centre of the airy disk is at least one minima away from the other.

what is the rayleigh criterion?

angular resolution is approximately the wavelength / D, where D is the diameter of the circular aperture.

name 4 cons when it comes to refracting telescopes

chromatic abberation AND spherical abberation, distortion in lenses due to only being supported on the edges, refracting telescopes need to be long to have a good magnification so they are expensive, bubbles/other impurities absorb and scatter some light causing blurriness in the image

name 2 cons when it comes to reflecting telescopes

spherical abberation, diffraction around secondary mirror/secondary mirror blocks light

name 2 pros when it comes to reflecting telescopes

cheaper, supported from underneath, so dont distort as much

where is chromatic aberration at its greatest?

chromatic abberation is greatest around the edges of the lens. it is least in the middle of the lens.