What is the use of terrestrial telescope?

Draw a labelled ray diagram of an astronomical telescope in the near point adjustment position.

A giant refracting telescope at an observatory has an objective lens of focal length $15 \mathrm{m}$ and an eyepiece of focal length $1.0 \mathrm{cm}$. If this telescope is used to view the Moon, find the diameter of the image of the Moon formed by the objective lens. The diameter of the Moon is $3.48\times {10}^6 \mathrm{m}$, and the radius of the lunar orbit is $3.8\times {10}^8 \mathrm{m}$.

The focal lengths of objective lens and eye lens of a Galilean Telescope are respectively 30 cm and 3.0 cm. Telescope produces virtual, erect image of an object situated far away from it at least distance of distinct vision from the eye lens. In this condition the Magnifying Power of the Galilean Telescope should be :

Draw a levelled ray diagram showing the image formation in an astronomical telescope. Define its magnifying power and write expression for it.

Draw the schematic diagram of a Cassegrain telescope.