He was appointed lucasian mathematician in 1669 on barrows recommendation. In 1666, Newton observed the spectrum of colours exiting a prism is an oblong. Even when the light ray entering the prism is circular, which is to say, the prism reacts different colours by different angled.
Newton also created a refracting telescope would suffer from the dispersion (chromatic aberration). As proof of his concept, he constructed a telescope using a mirror to bypass that problem (he called it a Newtonian telescope).
Isaac Newton studied the irregularities in the motion of the moon which provided a theory which determined orbits of comets and much more. Newton made clear his heliocentric view of the solar system. Developed in a somewhat modern way, because already in the mid 1680s he recognised the deviation of the sun from the centre of gravity in the solar system.