Refractive Astronomical Telescope:
It is an optical instrument which is used to see heavenly bodies such as stars, moon and planets is known as telescope.
Astronomical telescope having of a long metallic tube of variable length, two converging lens are mounted at its two ends.
Convex lens of large focal length and big aperture is known as objective.
Convex lens of shorter focal length and large aperture is known as eye piece.
Working:
The objective forms a real and inverted image of the object. This image is very small as compared to the object. The eye piece is used as magnifying glass. The final image is inverted and brighter than the object.