Astrophysics Flashcards
Definition of Principal Focus (Focal Point)
The point on the principal axis of the lens through which light parallel to the principal axis passes.
Focal Length
The distance between the centre of the lens and the focal point.
Spherical Aberration LENS
Where parallel rays at different distances from principal axis are brought to focus at different points (on principal axis).
Spherical Aberration MIRROR
Where parallel rays furthest from the principal axis are brought to focus closer to reflector than rays nearer to principal axis.
How can spherical aberration be prevented in a mirror?
Using a PARABOLIC mirror
Effect on image of Spherical Aberration
Image is blurred
Chromatic Aberration
Where different wavelengths are refracted by different amounts resulting in different focal lengths for different wavelengths (colours).
Effect on image of Chromatic Aberration
Images have multicoloured, blurred edges
Minimum Angular Resolution (Resolving Power)
The smallest angular separation that two point objects can still be discerned as separate.
Resolving Power
Measure of ability of a telescope to distinguish between adjacent objects.
Better resolving power means can distinguish objects closer together so the minimum angular resolution will be smaller.
Rayleigh Criteria
Two point objects can just be resolved when the central maximum of the diffraction pattern of one object lies over the first minimum of the diffraction pattern of the other.
Airy Disc
The bright central maximum (spot) of the diffraction pattern produced when light from a point source passes through a circular aperture.
