Geocentric model The stars, it was assumed, moved on a celestial sphere around the outside of the planetary spheres centered on a stationary Earth. Claudius Ptolemy a Roman national (born AD 90 and died AD 168 in Alexandria, Egypt). His model of the solar system and heavenly sphere was a refinement of previous models developed by Greek astronomers. Elements of Ptolemaic astronomy, showing a planet on an epicycle (small dashed circle), a deferent (large dashed circle) , the eccentric (X) and an equant (black dot). 150 BC, Greek astronomer Hipparchus modeled: Planets, each has a uniform velocity about the eccentric. Sun has no epicycle. Other planets are on an epicycle. AD 150 , Alexandrian astronomer, Claudius Ptolemy, modeled the path of the epicycle center was circular about the eccentric but its velocity is uniform in is motion about a new point called the equant. Copernicus published an early description of his "heliocentric" model of the solar system in Commentariolus (1512). In life, Brahe had jealously guarded his data, not even letting his prized pupil Johannes Kepler gain access. However: "I confess that when Tycho died, I quickly took advantage of the absence, or lack of circumspection, of the heirs, by taking the observations under my care, or perhaps usurping them." parsec = 3.26 light years The nearest star is proxima centauri, which exhibits a parallax of 0.762 arcsec, and therefore is 1.31 parsecs away Herschel observed Uranus on March 13, 1781 English astronomer John Couch Adams made the mathematical calculations of where Neptune should be and German astronomer Johann Galle observed it in 1846. (1571-1630). Kepler’s First Law Galileo Galilei (1564-1642) Phases of Venus discovered and sketched by Galileo The ecliptic is the apparent path of the Sun on the celestial sphere which is coplanar with both the orbit of the Earth around the Sun and the apparent orbit of the Sun around the Earth. Closest at Furthest at .