... Armagh Observatory, College Hill, Armagh BT61 9DG, +44 (0)28 3752 2928 . ... Though made without the aid of a telescope, his careful observations together with those of others and his physical intuition, lead to a revolution in our understanding of the mechanics of the solar system. The new heliocentric theory which he propounded maintained that the Earth moved around the Sun once per year and rotated on its own axis once per day. ... Tycho's Observatory built in 1584 at Uraniborg in Denmark. ...