A telescope is an optical device that makes distant dim objects appear larger and brighter.  The most popular form of telescope, called a Newtonian, uses a paraboloidal mirror to focus light onto an image plane that is then inspected by an eyepiece to gain magnification.  The paraboloidal mirror, and smaller flat secondary that is used to direct light out to the side of the tube, must be ground, polished, and figured to an accuracy of a couple of millionths of an inch.  That amateurs can do this by hand using simple test equipment is nothing short of amazing. Also amazing is the degree of penetration into the sky that amateurs now achieve.  Using a CCD camera and 12 inch aperture telescope, an amateur can equal the 200 inch Palomar telescope with film plates.   Digital cameras with cooled detectors must be exposed for many minutes to capture extremely faint objects.  During the exposure, the camera and telescope must precisely follow the stars in their slow apparent motion across the sky.