Tycho advocated as an alternative to the Ptolemaic geocentric system a "geoheliocentric" system (now known as the Tychonic system), which he developed in the late 1570s. In such a system, the Sun, Moon, and stars circle a central Earth, while the five planets orbit the Sun. The essential difference between the heavens (including the planets) and the Earth remained: Motion stayed in the aethereal heavens; immobility stayed with the heavy sluggish Earth. It was a system that Tycho said violated neither the laws of physics nor sacred scripture—with stars located just beyond Saturn and of reasonable size.