Chapter 25. 1: Exploring the Solar System & 25 Chapter 25.1: Exploring the Solar System & 25.5 The Origin of the Solar System

GeoCentric vs. Heliocentric Model Geo = “Earth” Centric =“in or at the Center” Most Ancient Greeks thought that the EARTH was the center of the Universe. *In a GEOCENTRIC Model, Earth is stationary while other objects in the sky move around it. Helio = “pertaining to the Sun” Aristarchus developed a heliocentric model--- In this model, Earth and the other planets revolve around the SUN. In the 1500s, with evidence supported by Copernicus and Galileo, this Heliocentric Model was proven Correct!

Heliocentric Evidence… The apparent motions of the sun, moon, and stars result from Earth’s daily rotation on its axis.

*Isaac Newton realized that the Sun Planetary Orbits What keeps the planets in their orbital paths? *Isaac Newton realized that the Sun Exerts a Gravitational Force on the planets that keeps them in orbit. Otherwise, the planets’ Inertia would cause them to fly off into space* GRAVITY and INERTIA combine to keep the planets in orbit around the SUN!

25.5 The Origin of the Solar System This is the generally accepted explanation for the formation of the Solar System. *The Nebular Theory states that the solar system formed from a rotating cloud of dust and gas. A large, thin cloud of dust and gas like the one that formed our solar system is called a Solar Nebula. The Nebular Theory

Nebular Image

Nebular Theory Continued…. According to the Nebular Theory, the solar nebula formed from the material expelled by previous stars. Nearly all of the mass of the solar nebula, about 99.9% became concentrated near the center –where the SUN would form in this region. 10 million years after this solar nebula formed, Nuclear reactions began and OUR SUN was born!

Additional Points about the Nebular Theory It also explains how the planets could have formed--- Balls of dust collided and grew larger & larger and eventually these asteroid-like bodies combined to form planets! The theory provides an explanation for the Current motions of the Sun, Planets, and most Moons.