Two nearby objects or spectral lines are resolved if they appear as two images or two spectral lines. Normal human eye can see two objects separate if they subtend a minimum angle of 1´´ of arc on eye.
The seperation of close objects is termed as resolution and the ability of an optical instrument to produce separate image of two such objects is known as resolving power of the instrument. Two neighbouring point objects are resolved by the lens system such as telescope or microscope is known as Geometrical resolution. When two close spectral lines (i.e. wave lengths) are resolved with the help of a prism; grating etc. we have spectral resolution.
