Complex sentence: Historically, the zenith of naked-eye astronomy was the work of Tycho Brahe (1546--1601), who built an extensive observatory to make precise measurements of the heavens without any instruments for magnification.
Split into simpler sentences: Historically, the zenith of naked-eye astronomy was the work of Tycho Brahe (1546--1601). He built an extensive observatory to make precise measurements of the heavens without any instruments for magnification.