Working as an astronomer in Rhodes, I invented instruments involving graduated circles that allowed me to catalogue the celestial coordinates of 800 stars.

My main astronomical discovery was the precession of the equinoxes but I also improved estimates of the sizes and distances of the sun and moon...despite my rejection of Aristarchus' proposed sun-centered planetary system.

I "redid" Eratosthenes geographical work by more precisely estimating latitudes and longitudes for a given position.

And, I basically founded trigonometry via my computation of a table of sines via a table of chords of angles ranging from 0^o to 180^o....which included the discovery of common trig identities.