active optics

magnification (magnifying power)

adaptive optics

medium (plural media)

angular resolution

Newtonian reflector

baseline

objective lens

Cassegrain focus

objective mirror (primary mirror)

charge-coupled device (CCD)

optical telescope

chromatic aberration

optical window (in Earth’s atmosphere)

coma

photometry

coudé focus

pixel

diffraction

prime focus

diffraction grating

radio telescope

eyepiece lens

radio window (in Earth’s atmosphere)

false color

reflecting telescope (reflector)

focal length

reflection

focal plane

refracting telescope (refractor)

focal point

refraction

focus (of a lens or mirror)

seeing disk

imaging

spectrograph

interferometry

spectroscopy

lens

spherical aberration

light-gathering power

very-long-baseline interferometry (VLBI)

light pollution