Earth-Centered Models of the Solar System

REPRODUCIBLE 106 EARTH-CENTERED MODELS OF THE SOLAR SYSTEM

Saturn ARISTOTLE’S Jupiter MODEL Mars

Sun us Ven Me rc n u oo ry Strength of Model: M Able to explain why the sun and planets seem to move across the sky EARTH

Weakness of Model: Not able to explain why the planets seem to backtrack at times

PTOLEMY’S Ptolemy’s epicycles showed that MODEL planets orbited in small circles as they revolved around the Earth.

Jupiter Strength of Model: Able to explain why the sun and planets seem to move across the sky AND his Sun us idea of epicycles explained why the Ven Me rc planets seem to backtrack at times n u oo ry M

EARTH Weakness of Model: Very complicated; goes against the notion that simple is usually accurate

Mars

Saturn

Strength of Model: Jupiter Although his model included epicycles to explain predictions for planet Moon Earth positions, the model did not rely on Venus Me epicycles to explain why planets seem to rcu ry backtrack at times. Explained that planets seem to backtrack because Earth was also revolving! Earth wasn’t the

Weakness of Model: Mars Model still argued that planets revolved

in a perfectly circular path. Also included Saturn epicycles.

GALILEO’S In 1610, Galileo used a telescope to observe that moons orbited Jupiter. He realized that if all objects orbited Earth, MODEL then this couldn’t be true. But he believed in what he observed. This observation was part of the evidence that helped him decide to support Copernicus’ sun-centered model of the solar system.

OTHER BREAKTHROUGHS • In 1609 Johannes Kepler argued that planets moved in an elliptical (oval-shaped) orbit, not a circular one. This allowed scientists to better predict planet positions.

• In 1684 Isaac Newton combined the ideas of Copernicus, Galileo, and Kepler, and explained that a force called gravity caused planets to move in an elliptical orbit around the sun.

Copyright 2012, Five Ponds Press. All Rights Reserved REPRODUCIBLE 108 EARTH PATTERNS, CYCLES, AND CHANGE STUDY GUIDE EARTH, MOON, SUN EARTH MOON SUN Position and • Earth rotates (spins) on • The moon revolves • The sun is the center of Movements its axis once every 24 hours. around Earth once every 28 our solar system. Earth and This gives us day and night. days (about one month). the other planets revolve • Earth revolves around around it. the sun once every 365¼ days (one year).

• Large amount of water • Rocky with craters • Extremely hot gaseous Surface • Diversity of organisms • Temperature extremes plasma Conditions • Oxygen-rich • No atmosphere or life • 5500 °C atmosphere • Very little water • Mostly made of hydrogen and helium

• Average-sized yellow Other • About four moons star Facts could fit across the • 110 times the diameter diameter of Earth of Earth • About 4.6 billion years old SEASONS

May April Earth is tilted on an imaginary Virginia March June Northern Spring axis as it revolves around the sun. July Southern Autumn August Virginia This is called axial tilt. It is the Northern Winter reason for the seasons. Southern Summer SUN Virginia Northern Summer When the sun’s rays hit one Southern Winter February hemisphere of Earth more directly, January that hemisphere has summer and Northern Autumn December the other hemisphere has winter. September Southern Spring Virginia October November In spring and autumn, the sun’s rays aren’t hitting either axial tilt hemisphere directly, so temperatures are milder for us.

Copyright 2012, Five Ponds Press. All Rights Reserved REPRODUCIBLE 109 PHASES As the moon revolves around Earth, sunlight reflects off of it. The phases of the moon are the parts of the moon we see that reflect sunlight at different positions as OF THE MOON the moon orbits Earth.

Waxing First Waxing Waning Third Waning New Full Crescent Quarter Gibbous Gibbous Quarter Crescent New

MOON EXPLORATION

NASA astronauts explored the moon during the Apollo missions and made the following discoveries: • No living organisms live on the moon. • The moon is made of igneous rocks. • No evidence of water has been found on the moon. • The moon has layers. • The surface of the moon is covered with a powdery substance. • Evidence was found to date the moon to be about 4.6 million years old.

OUR SOLAR SYSTEM Aristotle and Ptolemy believed that all of the planets and the sun revolved around Earth. HISTORICAL Copernicus challenged that idea and argued that all of the planets, including Earth, revolve around the sun. CONTRIBUTIONS Galileo, the first scientist to use a telescope to study space. He used the telescope to observe that planets revolved around the sun.

THE PLANETS: SEQUENCE AND SIZE

The first four planets (Mercury, Venus, Earth, The last four planets (Jupiter, Saturn, Uranus, and and Mars) are called terrestrial planets Neptune) are called gas giants because they are made of because they are rocky planets. mostly gases. They are also the four largest planets. The planets in order from biggest to smallest are: Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars, Mercury.