Consider a sun like a star at a distance of . When it is seen through a telescope with magnification, what should be angular size of the star? Sun appears to be from the earth due to atmospheric fluctuations, eye cannot resolve objects smaller than arc minute.
Mars has approximately half of earth's diameter. When it is closest to earth, it is at about A.U. from the earth. Calculate what size it will appear when seen through the same telescope. (Comment: This is to illustrate why a telescope can magnify planets but not stars.)