How are photographic techniques used in astronomy?
By placing a photographic film at the position of the observer’s eye, the telescope image can be preserved on a photograph for a permanent record. Moreover very faint telescope images can be intensified photographically by prolonged exposure using films very sensitive to light.
How powerful a telescope is required to observe all the planets?
Probably, the most elusive planet for observation is Pluto for which at least a 60 cm focal length telescope is required. Also it must have a 30 cm aperture for visual observation or a 10 cm aperture for photographic observation.
Why are larger aperture telescopes required for visual observation as compared to photographic observation?
A camera can record on smaller apertures by increasing the time of exposure or increasing the sensitivity of the film. This is not possible in the case of the human eye.
What is a radio telescope?
A radio telescope receives and amplifies radio waves instead of light waves. Instead of lenses or concave mirrors a radio telescope uses parabolic reflectors. Radio telescopes are used to study radio waves emitted by the heavenly bodies.
Is there a maximum physical limit to the size of a practical radio telescope?
It is possible to construct a radio telescope in sections, with each section located at a different place, the maximum limit of reparation being obviously the diameter of the Earth. The readings at the different locations are recorded independently, synchronized by atomic clocks, and integrated by processing the data in a computer.