CONTENTS What Is a Planet Types of Planets Formation of Planets Evolution of Planets Orbits of Planets I2 14 16 Rotations of Planets 18 Days Years and Seasons The Inner Planets The Outer Planets 20 22 Other Planets 26 28 A Sky Full of Planets Glossary For More Information 30 31 Index 32
WHAT IS A PLANET The word planet comes from the Greek word planetes which means wanderer Planets are large natural objects that orbit or travel around stars Eight planets orbit the star called the Sun In order from the closest to Sun 865 000 mi 1 392 000 km Jupiter 89 000 mi 143 000 km Saturn 74 900 mi 120 600 km Neptune 31 000 mi 50 000 km Venus Mars 7 500 mi 4 200 mi 12 100 km 6 800 km 3 Mercury Earth 3 000 mi7 940 mi 4 900 km 12 780 km Uranus 32 000 mi 51 000 km Sizes given are the approximate diameter of each body A The eight planets in the solar system have very different
the Sun these planets are Mercury Venus Earth Mars Jupiter Saturn Uranus and Neptune The solar system is the collection of the Sun and the objects that orbit around it including the eight planets Planets differ from other objects such as comets asteroids and meteors In general planets are the largest objects in the solar system after the Sun Most of them orbit the Sun in a path shaped nearly like a circle Many also have a layer of gas surrounding them Most of the planets have at least one moon Jupiter has more than 60 moons CoMPARE AND CONTRAST There are different objects orbiting the Sun Compare and contrast planets comets and meteors lo a moon of Jupiter has an active volcano like ones on
