Why does the objective lens of an astronomical telescope have a large light gathering  power?

8 Differentiate between a microscope and a telescope based on its use. 9 How is the length of the telescope tube related to the distance between the objective and the eyepiece of the telescope? How can the  magnification of the telescope be increased? 11 Explain clearly the working of a human eye? 12 How does the eye adjust itself to deal with light of varying intensity?