(A) Astronomers often speak of the "ability of a telescope to separate closely–spaced stellar images".
Answer the following with reference to an optical telescope used with light of wavelength lying in the visible region.
(i) Define the term resolving power of an astronomical telescope and hence state what is meant by its limit of resolution.
(ii) Without performing a full mathematical derivation, explain qualitatively why the resolving power of the telescope (a) increases when its objective diameter is made larger, and (b) decreases when observations are carried out with red light instead of blue light.
(iii) The same telescope is used first with a green filter (central wavelength 550nm) and then with a red filter (700nm). Which filter will give the sharper separation of two neighbouring stars? Justify your answer on the basis of the ideas explained in part (ii).