VIEWS: 4 PAGES: 25 POSTED ON: 11/17/2012
« Looking at the sky, night after night, man no doubt noticed very early that most of the brilliant dots he could see there retained their relative position. A triangle in that corner looked pretty much the same next night, and the night after that; and the same could be said of most of the figures he saw. But there were a few dots that moved against the fixed background of stars. These no doubt provoked great curiosity, and were the subject of very careful scrutiny. The ancient greeks dubbed them wanderers, and it is from this greek term that their modern name comes: Planets. » HISTORY of ASTRONOMY • Ancient peoples believed the celestial bodies to be linked to gods and spirits. • They credited the celestial bodies (and their movements) to different phenomenons like rain, the seasons and tides • It is generally believed that the first astronomers were priests, and their comprehension of the skies was seen as divine • Just imagine looking at the night sky and having no idea what you were seeing……. STONEHENGE • Built between 3100-2000 BC on the plain of Salisbury in England, Stonehenge is an intriguing astronomical site • The alignment of the heelstone with the rising sun on summer solstice(the 21st of June, longest day of the year) represents a true and precise astronomical alignment. • Like stonehenge, many ancient structures have astronomical alignments and probably had astronomical and religious functions Sundials were once the only available method for telling time Ancient peoples used the stars to determine direction, they relied on the location of certain asterisms for direction Asterisms are small groups of stars that form a distinct shape or pattern Constellations are huge groups of stars (80 or more) , these stars occupy an area in the night sky Astronomy becomes a science…… Pythagoras 6th Centruy BC • He believed that the planets were attached to crystaline spheres, one sphere for every planet • Pythagoras is also credited with discovering that both the morning and night star are actually the planet venus! Aristotle • In aristotle’s world, the Earth is situated in the centre of the universe (or solar system). He believed Earth to be composed of 4 elements: earth, air, water and fire • Aristotle adopted pythagoras’s model of concentric spheres for the planets, but added that the Earth was immobile…..he proposed the GEOCENTRIC model!! • Geocentric = EARTH centered (it’s all about us!) Geocentric Model Claudius Ptolemy (85-165 AD) • (Greek) mathematicien, geographer, et astronomer • He supported the geocentric model, and the principle of the movement of planets in perfect circles. • Ptolemy’s model was VERY complex – it used EPICYCLES to describe the movements of planets Ptolemy’s Work Epicycles (Ptolemy’s theory of planetary movement in the geocentric model) http://www.astro. utoronto.ca/~zhu/ ast210/geocentri c.html The development of the geocentric model: Geocentric = EARTH centered 1. Pythagoras introduced the theory of the planets being attached to crystalline spheres 2. The geocentric model was proposed by Aristotle using both his own ideas and the work of Pythagoras. 3. The geocentric model was further supported by Ptolemy who added the idea of epicycles to explain planetary motion. A popular model… The geocentric model was popular because it allowed people to accurately predict the date, time and location that certain celestial bodies would rise and set But….. Each new phenomenon required more and more additions to the geocentric model – the model became so complex that it contained 55 interior spheres, epicycles and many ‘rules’ ….it simply became too complex. Next… the Renaissance (XIV to XVII centuries) Exploration and scientific investigations became more and more popular in the west. Navigation and the calculation of time improved due to increasingly precise astronomical observations. Copernicus 1473-1543 • Copernicus studied mathematics and astronomy • During Copernicus’s time, Ptolemy’s geocentric model was no longer able to explain all of the astronomical phenomena that were being observed. • In response to the inadequacies of the geocentric model, Copernicus devised a HELIOCENTRIC model of the solar system placing the sun at the centre of the solar system. The heliocentric model also had the correct order of the planets. • Heliocentric = SUN centered The Heliocentric Model Tycho Brahe (1546-1601) Tycho Brahe was a danish astronomer most know for his incredibly precise and very thorough observations. Tycho Brahe was wealthy and eccentric. He used his money to build many pieces of astronomical equipment which he designed. Johannes Kepler(1571-1630) • Kepler worked with Tycho Brahe’s observational data • Using Brahe’s data, Kepler made very precise calculations about the orbits of the planets • Kepler developed 3 rules related to planetary motion • One of these rules explains that the planets travel in ELLIPTICAL paths – not circular ones An ellipse is an ELONGATED circle Instead of a center, an ellipse has two FOCI Galileo Galilei (1564-1642) Using homemade telescopes, Galileo made several discoveries in support of the heliocentric model of the solar System • Sun spots • Craters on the moon • The moons of Jupiter • The rings of Saturn • The phases of Venus • Galileo’s observations led him to the conclusion that the heliocentric model (of Copernicus)was superior to the geocentric model establish by Aristotle The development of the heliocentric model: heliocentric = SUN centered 1. In response to the inadequacies of the geocentric model, Copernicus devised a HELIOCENTRIC model. 2. Kepler explained that the planets travel in ELLIPTICAL paths – not circular ones 3. Galileo developed the telescope and made observations that led him to the conclusion that the heliocentric model was superior. . Today • The planets orbit the Sun • The planetary orbits are ellipses (elongated circles) • There are 8 classical planets (and three dwarf planets including Pluto)
"histroy of astonomy"