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Tahsiri: Lecture notes :

Kenealy: Read chapters (1-6).

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* The civilization of Greece and Rome began to decline shortlyafter the time of Ptolemy. Fortunately, the discoveries of theancient astronomers were preserved by the Arabic astronomers,who found them and translated them into Arabic.

* Astronomical knowledge was gradually reacquired in Western Europe. By the fifteenth century, the level of knowledge matched or exceeded that at the time of Ptolemy.

* The geocentric model of Ptolemy was almost universally accepted as the correct description of the solar system.

* In the early sixteenth century, Copernicus proposed that the Sun rather than the Earth is the center of the solar system.

* In the heliocentric model, the daily and annual patterns of celestial motion are explained by the rotation and revolution of the Earth.

* Retrograde motion of the planets occurs whenever the Earth passes or is passed by another planet.

* In the model of Copernicus the orbital distances of the planets can be found through observations and geometry. In contrast, the geocentric model makes no specific predictions about the relative distances of the planets.

* Through his care in building and using astronomical instruments, Tycho Brahe was able to make observations of unparalleled accuracy.

* His regular observations of the Sun, Moon, and planets covered many years. His data replaced the ancient observations that earlier theorists had been using for centuries.

* Tycho was unable to detect stellar parallax and thus rejected the model of Copernicus. Tycho proposed a model in which the Earth was orbited by the Sun and Moon but all of the other planets moved about the Sun.

* Using Tycho's data, Kepler was able to discover the laws of planetary motion.

* His first law says that the planets move on elliptical paths with the Sun at one focus.

* The second law says that a planet moves so that a line drawn between the planet and the Sun sweeps out equal areas in equal amounts of time. This means that the product of speed and distance from the Sun remains constant as a planet moves about the Sun. The planet moves fastest when it is nearest the Sun.

* Kepler's third law says that the square of the sidereal period of a planet is proportional to the cube of its average distance from the Sun. The third law implies that there is a common principle that governs the orbital motions of the planets.

* Galileo's telescopic observations provided strong support for the heliocentric model. In particular, his observations that Venus shows all the phases from new to full could not be explained by Ptolemy's model of the solar system.

* Galileo summarized his arguments for the heliocentric model in his book, Dialogue Concerning the Two Chief World Systems. The book put Galileo in conflict with church authorities and resulted in his persecution.

a) Illustrations(1) The Ptolemy Project (2) Nicolaus Copernicus (3) Retrograde motion (4) Kepler's Third law (5) Johannes Kepler (6) Galileo's Pendulum Experiments (7) Galileo's Acceleration Experiments (8) Brief History of Astronomy 9) History of Astronomy (10) History of Astronomy

1. Which of the following was a consequence of Tycho's failure to detect parallaxes of stars? it convinced him that the earth was stationary
2. Which of the following is one of Kepler's Laws of Planetary Motion planets move on elliptical orbits with the Sun at one focus
3. Suppose a planet has an elliptical orbit. The speed of the planet is 20 kms when it is at its average distance from the sun. Which of the following is most likely to be the planet's speed when it is nearest the sun? 25 kms
4. A hypothetical planet orbits the sun a distance of 3 AU. What is its orbital period? 5.2 years
5. It has been suggested that there are very remote planets in the solar system, with periods of about ten million years. Approximately how far from the Sun would such a planet be? 50000 astronomical units
6. In which of the following models of the solar system is it possible for stars to show parallaxes? Copernicus' model
7. When does retrograde motion of Jupiter occur in the heliocentric model of the solar system? when the earth passes Jupiter
8. A shift in the direction of an object caused by a change in the position of an observer is called parallax
9. A planet has a synodic period of 3 years. What is the sidereal (orbital) period of the planet? 1.5 years
10. What was the significance of Galileo's discovery that Venus shows all phases from new to full? in the geocentric model, only some phases are possible

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