instrument for observing distant objects by collecting electromagnetic radiation
optical telescope: refracting (lens) or reflecting (mirror), invented 1608
radio telescope: dish antenna collecting radio waves, reveals cold gas and pulsars
space telescopes: above atmospheric distortion (Hubble, James Webb, Chandra)
aperture determines resolving power; larger aperture captures more photons
extends human vision from planetary scale to cosmic scale (13.8 billion light-years)
interferometry links multiple telescopes for effective aperture spanning continents
adaptive optics corrects atmospheric turbulence in real time using semiconductor sensors
complementary to microscope: one reaches outward, the other inward
energy source for deep-space instruments: solar panels and radioisotope generators