Chapter 15 Learning Objectives

 

After reading, studying, and discussing the chapter, students should be able to:

 

·        Briefly discuss the contributions of the Greek philosophers and Ptolemy to ancient astronomy.

·        Explain the contributions of Copernicus, Brahe, Kepler, Galileo, and Newton to modern astronomy.

·        Understand the differences between the terrestrial and Jovian planets.

·        Discuss the origin of the solar system.

 

Chapter 15 Outline

 

    I.  Early history of astronomy

       A.  Ancient Greeks

            1.  Used philosophical arguments

            2.  Some observational data

            3.  Held geocentric view

                 a.  "Earth-centered"

                      1.  Earth center of universe

                      2.  Stars on the celestial sphere that traveled daily around Earth

                 b.  Seven wanderers (planetai)

                      1.  Changed position in sky

                      2.  Included

                           a.  Sun

                           b.  Moon

                           c.  Mercury through Saturn (excluding Earth)

                 c.  Planets show apparent westward drift

                      1.  Called retrograde motion

                      2.  From planet's & Earth's motions

            4.  Ptolemaic system

                 a.  A.D. 141

                 b.  Geocentric model

                 c.  To explain retrograde motion, Ptolemy had planets moving in

                      1.  Deferents (large circles), and

                      2.  Epicycles (small circles)

 

       B.  Birth of modern astronomy

            1.  1500s and 1600s

            2.  Five noted scientists

 

                 a.  Nicolaus Copernicus (1473-1543)

                      1.  Model put Sun at center

                      2.  Circular orbits for planets

                      3.  Ushered out old astronomy

 

                 b.  Tycho Brahe (1546-1601)

                      1.  Precise observer

                      2.  Tried to find stellar parallax

                           a.  Shift in a star's position

                           b.  Due to revolution of Earth

                    3.  Did not accept Copernican system

                         (unable to see stellar parallax)

 

                c.  Johannes Kepler (1571-1630)

                      1.  Ushered in new astronomy

                      2.  Planets revolve around Sun

                      3.  Three laws of planetary motion

                           a.  Planet's orbits are elliptical

                           b.  Revolve at varying speed

                           c.  Proportional relation between

                               1.  Planet's orbital period and

                               2.  Its distance in to the Sun in AUs (Astronomical unit)

 

                 d.  Galileo Galilei (1564-1642)

                      1.  Supported Copernican theory

                      2.  Used experimental data

                      3.  Built astronomical telescope

                      4.  Discoveries using telescope

                           a.  Four large moons of Jupiter

                           b.  Planets appeared as disks

                           c.  Phases of Venus

                           d.  Features on Moon

                           e.  Sunspots

                      5.  Tried and convicted by Inquisition

 

                 e.  Sir Isaac Newton (1642-1727)

                      1.  Law of universal gravitation

                      2.  Explained planetary motion

 

   II.  Solar system

       A.  Overview

            1.  Solar system includes

                 a.  Sun

                 b.  Eight planets and their satellites

                 c.  Asteroids

                 d.  Comets

                 e.  Meteoroids

            2.  Planet's orbits lie in the orbital plane

            3.  Solar system composed of

                 a.  Gases–hydrogen and helium

                 b.  Rock

                      1.  Silicate minerals

                      2.  Metallic iron

                 c.  Ices

                      1.  Ammonia

                      2.  Methane

                      3.  Carbon dioxide

                      4.  Water

            4.  Two groups of planets

                 a.  Terrestrial (Earthlike) planets

                      1.  Mercury through Mars

                      2.  Small, dense, rocky

                      3.  Low escape velocities

                 b.  Jovian (Jupiter-like) planets

                      1.  Jupiter through Neptune

                      2.  Large, low density, gaseous

                      3.  High escape velocities

                 c.  Pluto not included in either group

       B.  Origin

            1.  Nebular hypothesis

                 a.  Planets formed at same time about 5 billion years ago

                 b.  Large cloud of dust and gas

                      1.  Called nebula

                           a.  80% hydrogen

                           b.  15% helium

                           c.  All other heavier elements

                 c.  Nebula contracted and began rotating

                 d.  Protosun forms

                 e.  Protoplanets form