The Solar System Chapter 20 Updated May 2012

Section 1 Through the early history of civilization, people made observations about the night sky, sun, and moon. They tried to explain what they were observing with stories and folklore. They believed that the sun and stars revolved around the Earth.

The Greeks came up with the idea of a geocentric universe. Meaning they thought everything revolved around the Earth. A Greek astronomer named Ptolemy (1400 CE) designed a model of the universe which put the Earth at the center and had the planets moving on small circles which moved on larger circles.

Copernicus Copernicus (1543)- Made observations which led him to believe that the geocentric model was not accurate. His observations put the sun at the center and the planets revolved around it in perfect circles. In a heliocentric model the sun is placed in the center and the planets revolve around it.

Planetary Motion Galileo (1610) Galileo used the newly invented “spyglass” to make observations of the night sky. He discovered that Jupiter had moons that orbited it. This led him to the conclusion that not all objects revolved around earth. While looking at Venus he noted that it always stayed near the sun. He discovered that Venus goes through a series of phases similar to the Earth’s moon. Venus would not have a full set of phases if it circled the Earth. Therefore the geocentric model is incorrect.

Tycho Brahe Copernicus and Galileo correctly placed the sun at the center of the planets but incorrectly stated that the planets moved in perfect circles. Brahe continued his observations for another 20 years accurately recording the positions of the planets with out a telescope! Tycho Brahe died in His assistant named Johannes Kepler continued TB’s work by analyzing the planets’ orbits and mapped Mar’s orbit. He thought the orbit was round but his calculations did not match up. He discovered that the orbit must not be circular but an ellipse.

Since Galileos’s time our knowledge of the solar system has increased dramatically. In Galileo’s time only the planets Mercury, Venus, Earth, Mars, Jupiter and Saturn were known. Since then we have discovered three more planets as well as asteroids and comets.

The Sun (Our Enemy)

Interior pg. 706 Core- where the energy from the sun is produced through nuclear fusion. Hydrogen atoms come together to form Helium releasing energy. Radiation zone- energy produced in the core moves outward through this middle layer. It consists of tightly packed gas. Energy takes more than 100,000 years to move through this layer because it is so dense. Convection zone- outermost layer. Hot gases rise as cooler gases sink forming loops of energy.

The Sun’s Atmosphere Photosphere- the sphere that gives off light. When you look at the sun this is what you see (surface). Chromosphere- the “color sphere” middle layer visible during a solar eclipse. (reddish glow) Corona- Outer layer which extends into space for millions of kilometers. An even fainter layer visible during a solar eclipse.

Features of the Sun Sunspots- darker areas of gas on the sun that are cooler than the gases around them.

Prominences- Reddish loops of gas that link different parts of sunspot regions

Solar Flares- sudden release of energy that occurs when prominences link together