Simplify the following text for a Grade 13 native English-speaking person.
Original: De revolutionibus orbium coelestium ( On the Revolutions of the Heavenly Spheres ) is the seminal work on the heliocentric theory of the Renaissance astronomer Nicolaus Copernicus ( 1473 â `` 1543 ) .
Simplified: De revolutionibus orbium coelestium ( On the revolutions of the heavenly spheres ) is great work of the Renaissance astronomer Nicolaus Copernicus ( 1473 â `` 1543 ) .