Discuss about astronomical telescope.

Explanation

(i) An astronomical telescope is used to get the magnification of distant astronomical objects like stars, planets, moon etc. the image formed by astronomical telescope will be inverted. (ii) It has an objective of long focal length and a much larger aperture than the eyepiece. (iii) Light from a distant object enters the objective and a real image is formed in the tube at its second focal point. (iv) The · eyepiece magnifies this image producing a final inverted image.
Magnification of astronomical telescope :
The magnification m is the ratio of the angle `beta` subtended at the eye by the final image to the angle `alpha` which the object subtends at the lens or the eye.
` m = beta/ alpha`
From the diagram, m ` = (h//f_e)/(h//f_0)`
`m = (f_0)/(f_e)`
The length of the telescope is approximately,
`L = f_0 + f_e`