Phys141 Principles of Physical Science Chapter 15 The Solar System Instructor: Li Ma Office: NBC 126 Phone: (713) Webpage: Department of Computer Science & Physics Texas Southern University, Houston Nov. 8, 2004

Topics To Be Discussed An Overview The Planet Earth The Terrestrial Planets The Jovian Planets and Pluto Skip §15.5 – §15.7

The Solar System The universe is the totality of all matter, energy, space and time Astronomy is the study of the universe Solar system is a complex system of moving masses All these moving masses are held together by gravitational forces Sun: a star at the center of solar system, the dominant mass

The Solar System (cont) Objects revolving around the Sun: –9 rotating planets –over 70 satellites (moons) –thousands of asteroids –comets, meteoroids, interplanetary dust particles, gases, and solar wind composed of charged particles

The Model of Solar System Geocentric model: Earth-centered model Heliocentric model: Sun-centered model Kepler’s first law: law of elliptical paths –All planets move in elliptical paths around the Sun at one focus of the ellipse Kepler’s second law: law of equal areas –An imaginary line (radial vector) joining a planet to the Sun sweeps out equal area in equal periods of time

The Model of Solar System (cont) Kepler’s third law: harmonic law –The square of the sidereal period of a planet is proportional to the cube of its semimajor axis (one half the major axis) (period) 2 ∞ (semimajor axis) 3 T 2 = kR 3 –Sidereal period (T): time of one revolution with respect to a star, the orbital period with respect to the stars – the true period of revolution

The Model of Solar System (cont) For the Earth, time of one revolution with respect to the Sun is one year (T = 1 y) Astronomical Unit (AU): average distance between the Earth and the Sun –1 AU = 1.5 x 10 8 km So, k = 1 y 2 /AU 3, and same for all planets Table 15.1 on page 384 e.g. R = 1.52 AU, T = ?

Planets in Solar System Terrestrial planets: inner planets –Mercury, Venus, Earth, and Mars Jovian planets: outer planets –Jupiter, Saturn, Uranus, and Neptune Pluto: does not resemble the Earth or Jupiter, has the smallest diameter Prograde motion: west-to-east revolution Retrograde motion: east-to-west revolution

The Planet Earth The Earth is a solid, spherical, rocky body with oceans and an atmosphere. In our solar system, the Earth is the only planet with large amounts of surface water, an atmosphere that contains oxygen, a temperate climate, and living organisms The Earth is an oblate spheroid, fattened at the poles and bulging at the equator

The Planet Earth (cont) The Earth is undergoing several motions simultaneously –The daily rotation on its axis –The annual revolution around the Sun –Procession Rotation: spinning on an inter axis Revolution: the movement of one mass around another

The Planet Earth (cont) The Earth rotates eastward around a central internal axis that is tilted 23.5° from the line perpendicular to its orbital plane –The Foucault pendulum is an experimental proof of the Earth’s rotation on its axis The Earth revolves eastward around the Sun –The observation of parallax –The telescope observation of systematic change in position of stars annually

The Planet Earth (cont) The 23.5° tilt of the axis and the revolution of the Earth around the Sun are the reason for the four seasons we experience annually

The Terrestrial Planets Mercury, Venus, Earth, and Mars Relatively small in size and mass Composed of rocky material and metals Relatively dense and have solid surface and weak magnetic fields Relatively close to the Sun None has a ring system

The Terrestrial Planets (cont) Only the Earth and Mars have moons Only the Earth has surface water and an atmosphere that is 21% oxygen, others have no free oxygen in their atmosphere Mercury: the closest planet to the Sun, has the shortest period of revolution, is the fast- moving planet

The Terrestrial Planets (cont) Venus: our closest planetary neighbor, third brightest object in the sky, exceeded only by the Sun and our Moon Mars: has a reddish color when viewed from the Earth, is the planet that most closely resembles the Earth; unmanned spacecrafts have been sent to Mars, a manned landing may be sent in future

The Jovian Planets & Pluto Jupiter, Saturn, Uranus, and Neptune large in size compared with the terrestrial planets gaseous, no solid surface, composed mainly of hydrogen and helium All have a very low density and have strong magnetic fields have many rings and moons Very distant from the Sun with orbits far apart

The Jovian Planets & Pluto (cont) Jupiter: the largest planet of the solar system, in both volume and mass, has many moons Saturn: has three prominent rings, three spacecrafts have visited it, another is on its way Uranus: has a ring system that is very thin, has over 20 moons

The Jovian Planets & Pluto (cont) Neptune: regarded as a twin to Uranus due to their similarity in size, composition of their atmospheres and internal structure Pluto: the most distant planet from the Sun, the only planet that has not been visited by a space probe

Assignment Homework Assignment –Review Questions (page 412 – 413): 1,3,9,11,13,25,42 –Exercises (page 414): 2,4 –It’s due Monday, 11/22/04 Reading Assignment –Chapter 16