The Early History of Astronomy The ancient people

The Early History of Astronomy The ancient people saw seven celestial bodies moving through the stars; Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn.

l Five of these objects appeared to “wander” through the constellations. These objects were considered to be special stars, which they called planets.

Retrograde Motion l The planets move eastward and then loop back briefly, then continue moving eastward.

Ptolemy (100 -200 AD) l l Determined the positions of about 1, 000 bright stars. Summarized the geocentric model of the universe, which stated that the Earth is motionless and everything revolves around it.

l In the Earth-centred model, planets orbit on epicycles – wheels whose centers – are attached to the planets’ celestial sphere. (placing epicycles upon epicycles. )

Aristarchus 310 -230 BC l He proposed that all of the planets, including Earth revolved around the Sun, and that the Earth rotates on its axis once a day. This is the heliocentric model.

Aristotle 384 BC l Developed the concept of celestial sphere, stating that the universe is a perfect circle.

Galileo Galilei l Was the first to use the telescope to observe the sky. Galileo asserted, but never proved, that the Earth moves.

Johannes Kepler l Suggested the elliptical orbits of planets, and developed his Laws of Planetary Motion.

Isaac Newton l Developed the Law of Universal Gravitation.

Edwin Hubble 1920 s l Realized that the Milky Way is just one of the millions of Galaxies and discovered the expansion of the Universe.

Video Link for Retrograde Motion l http: //honolulu. hawaii. edu/distance/sci 122/ Sci. Lab/L 2/Mars. Retro. Many. html