occupation perseus 
In ___MASK3___ , an orbit is the gravitationally curved path of an object around a point in space , for example the orbit of a planet about a star or a natural satellite around a planet . Normally , orbit refers to a regularly repeating path around a body , although it may occasionally be used for a non recurring trajectory or a path around a point in space . To a close approximation , planets and satellites follow elliptical orbits , with the central mass being orbited at a focal point of the ellipse , as described by Kepler ' s laws of planetary motion . Geometry ( from the ; " geo -" " earth ", "- metron " " measurement ") is a branch of mathematics concerned with questions of shape , size , relative position of figures , and the properties of space . A ___MASK19___ who works in the field of geometry is called a geometer . A hypothesis ( plural hypotheses ) is a proposed explanation for a phenomenon . For a hypothesis to be a scientific hypothesis , the scientific method requires that one can test it . Scientists generally base scientific hypotheses on previous observations that cannot satisfactorily be explained with the available scientific theories . Even though the words " hypothesis " and " theory " are often used synonymously , a scientific hypothesis is not the same as a scientific theory . A working hypothesis is a provisionally accepted hypothesis proposed for further ___MASK50___ . Apollonius of Perga ( c . 262  c . 190 BC ) was a Greek geometer and ___MASK92___ noted for his writings on conic sections . His innovative methodology and terminology , especially in the field of conics , influenced many later scholars including Ptolemy , Francesco Maurolico , Johannes Kepler , Isaac Newton , and René Descartes . Apollonius gave the ellipse , the parabola , and the hyperbola their modern names . The hypothesis of eccentric orbits , or equivalently , deferent and epicycles , to explain the apparent motion of the planets and the varying speed of the Moon , is also attributed to him . Ptolemy describes Apollonius ' theorem in the " Almagest " XII . 1 . The crater Apollonius on the Moon is named in his honor . Francesco Maurolico ( Greek :   , " Frangiskos Mavrolikos "; Latin : " Franciscus Maurolycus "; " Francisci Maurolyci "; Italian : " Francesco Maurolico "; September 16 , 1494 - July 21 or July 22 , 1575 ) was a ___MASK19___ and astronomer from Sicily . Born to a Greek family and immersed in the study of classical Greek texts , throughout his lifetime he made contributions to the fields of geometry , optics , conics , mechanics , music , and astronomy . He edited the works of classical authors including Archimedes , Apollonius , Autolycus , Theodosius and Serenus . He also composed his own unique treatises on mathematics and mathematical science . An ___MASK92___ is a ___MASK61___ in the field of astronomy who concentrates their studies on a specific question or field outside of the scope of Earth . They look at stars , planets , moons , comets and galaxies , as well as many other celestial objects  either in observational astronomy , in analyzing the data or in theoretical astronomy . Examples of topics or fields astronomers work on include : planetary science , solar astronomy , the origin or evolution of stars , or the formation of galaxies . There are also related but distinct subjects like physical cosmology which studies the Universe as a whole . In the Hipparchian and Ptolemaic systems of astronomy , the epicycle ( from , literally " on the circle ", meaning " circle moving on another circle ") was a geometric ___MASK9___ used to explain the variations in speed and direction of the apparent motion of the Moon , Sun , and planets . In particular it explained the apparent retrograde motion of the five planets known at the time . Secondarily , it also explained changes in the apparent distances of the planets from Earth . Johannes Kepler ( December 27 , 1571  November 15 , 1630 ) was a German ___MASK19___ , astronomer , and astrologer . A key figure in the 17th century scientific revolution , he is best known for his laws of planetary motion , based on his works " Astronomia nova ", " Harmonices Mundi ", and " Epitome of Copernican Astronomy ". These works also provided one of the foundations for Isaac Newton ' s theory of universal gravitation . Sir Isaac Newton ( 25 December 1642  20 March 1726 / 27 ) was an English ___MASK19___ , astronomer , and physicist ( described in his own day as a " natural philosopher ") who is widely recognised as one of the most influential scientists of all time and a key figure in the scientific revolution . His book " Philosophiæ Naturalis Principia Mathematica " (" Mathematical Principles of Natural Philosophy "), first published in 1687 , laid the foundations of classical mechanics . Newton also made seminal contributions to optics , and he shares credit with Gottfried Wilhelm Leibniz for developing the infinitesimal calculus . Claudius Ptolemy (" Klaúdios Ptolemaîos ", ; ) was a Greek ___MASK60___ , known as a ___MASK19___ , astronomer , geographer , astrologer , and poet of a single epigram in the Greek Anthology . He lived in the city of Alexandria in the Roman province of Egypt , wrote in Koine Greek , and held Roman citizenship . Beyond that , few reliable details of his life are known . His birthplace has been given as Ptolemais Hermiou in the Thebaid in an uncorroborated statement by the 14th - century astronomer Theodore Meliteniotes . This is a very late attestation , however , and there is no other reason to suppose that he ever lived anywhere else than Alexandria , where he died around AD 168 . René Descartes ( Latinized : Renatus Cartesius ; adjectival form : " Cartesian "; 31 March 159611 February 1650 ) was a French ___MASK99___ , ___MASK19___ , and ___MASK61___ . Dubbed the ___MASK76___ of modern western philosophy , much of subsequent Western philosophy is a response to his writings , which are studied closely to this day . He spent about 20 years of his life in the Dutch Republic . In geometry , a spiric section , sometimes called a spiric of Perseus , is a quartic plane curve defined by equations of the form The work known as the Almagest , named "" ("") in Ancient Greek , and also called Syntaxis Mathematica or Almagestum in Latin , is a 2nd - century Greek - language mathematical and astronomical treatise on the apparent motions of the stars and planetary paths , written by Claudius Ptolemy . One of the most influential scientific texts of all time , its geocentric ___MASK9___ was accepted for more than 1200 years from its origin in Hellenistic Alexandria , in the medieval Byzantine and Islamic worlds , and in Western Europe through the Middle Ages and early Renaissance until Copernicus . Perseus ( c . 150 BC ) was an ancient Greek geometer , who invented the concept of spiric sections , in analogy to the conic sections studied by Apollonius of Perga .