(opening through which light passes)
An aperture is an opening through which light passes,
the term being used to describe the light-collecting opening
of a telescope, and also used analogously for radio telescopes
and telescopes for other parts of the electromagnetic radiation spectrum.
The size is generally listed as a length, e.g., meters,
which presumes they are circular, which is generally but
not always the case. The size of the aperture affects the instruments
angular resolution due to diffraction.
The current technique of apodization consists of
deliberately reducing and/or reshaping the aperture in order
to change the resulting diffraction patterns and tease out
detail that diffraction would normally hide.
Arecibo Observatory (NAIC)
extremely large telescope (ELT)
European Southern Observatory Very Large Telescope (ESO VLT)
Fast Fourier Transform Telescope
Gran Telescopio Canarias (GTC)
Las Cumbres Observatory (LCO)
point-spread function (PSF)
Square Kilometre Array (SKA)