What is a telescope? Discuss the types of telescopes that are used in general.

(N/A) The word 'tele' means 'away' and 'scope' means 'to see'. Hence,the name 'telescope' is given to an instrument used to see objects that are far away.
An optical instrument used to observe objects that are at a large distance is called a telescope.
Types of telescopes:
$1)$ Astronomical telescope: Objects that are very far away,such as the $Sun$,$Stars$,and $Planets$,can be observed using this telescope. The final image obtained is inverted and diminished,but since these celestial objects are spherical,the inversion does not affect the observation.
$2)$ Terrestrial telescope: This telescope includes an additional pair of inverting lenses to make the final image erect. Galileo's telescope used a combination of convex and concave lenses.
$3)$ Reflecting telescope: $A$ concave mirror is used in this telescope instead of a refractive objective lens to avoid chromatic aberration. Example: Cassegrain telescope.