Our Solar System. Lesson 5. Distances Between the Sun and the Planets

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1 Our Solar System Lesson 5 T he Solar System consists of the Sun, the Moon, planets, dwarf planets, asteroids, comets, meteors and other celestial bodies. All these celestial bodies are bound to the Sun by gravity. Scientists often divide the Solar System into three different parts. The inner zone of the Solar System includes Mercury, Venus, Earth, Mars and the asteroid belt. The middle zone consists of the gas giants, Jupiter, Saturn, Uranus and Neptune. The outer zone of the Solar System includes everything in the region beyond Neptune that is bound to the Sun by its gravity. This region includes the dwarf planet Pluto found in the Kuiper Belt. The average distance to the Sun is about 93 million miles (149,597,870 kilometers). Scientists use the astronomical unit when discussing distances within the Solar System. The astronomical unit is based on the average distance from the Sun to the Earth. Earth is one astronomical unit (AU) from the Sun. Planets Distances Between the Sun and the Planets Astronomical Units Millions of Kilometers Millions of Miles Mercury Venus Earth Mars Asteroid Belt * Jupiter Saturn 9.5 1, Uranus , Neptune , * The asteroid belt is an area between Mars and Jupiter filled with solid rocky bodies orbiting the Sun that range in size from a few meters to hundreds of meters across. The chief component of our Solar System is the Sun. It is so large it can sustain nuclear fusion and constantly produces nuclear energy. The nuclear energy produced in the core is transmitted to the surface where enormous amounts of energy are constantly being emitted. The Sun is a main sequence star classified as a moderately large yellow dwarf. The Sun is slowly growing brighter. Our Sun is a population I star that contains hydrogen and helium plus a higher percentage of heavy elements than population II stars. The high percentage of heavier metallic elements in the Sun is thought to be crucial in the development of planets.

2 The inner Solar System is the traditional name for the region where terrestrial planets and most asteroids are found. The planets all have dense, rocky compositions with few or no moons. They are mainly composed of minerals with a high melting point. Venus, Earth and Mars all have substantial atmospheres. All four of the terrestrial planets have tectonic surfaces containing features like rift valleys and volcanoes. All four of the planets have impact craters on their surface. Mercury and Venus are sometimes referred to as inferior planets because their orbits are within the orbit of the Earth. NASA Planets (starting at far left going down) Mercury Venus Earth Mars (space between Mars and Jupiter contains the asteroid belt) Jupiter Saturn Uranus Neptune The main asteroid belt lies between Mars and Jupiter. Scientists believe that the asteroids are the remnants of a failed planet. They think that the gravitational pull of Jupiter kept a planet from forming. Instead the asteroid belt contains tens of thousands of rocky objects that are orbiting the Sun about 2.8 AU from the Sun. The middle region of the Solar System contains the gas giants and their moons. Jupiter, Saturn, Uranus and Neptune contain a higher proportion of water, ammonia and methane than the terrestrial planets. The four planets contain 99% of the mass of material that circles the Sun. The planets are so cold that astronomers have suggested they be classified as ice giants. All four of the planets have rings but only Saturn s rings are easily observed from Earth. Icy-like comets that orbit in the region between Jupiter and Neptune are called Centaurs. The first Centaur discovered was 2060 Chiron. The Centaur has since then been reclassified as a comet because it

3 developed a coma, which is a spherical cloud of material surrounding the head of a comet, during its orbit around the Sun. The outer region of the Solar System has been largely unexplored. The Kuiper belt is a region where small icy bodies reside. The entire mass of all the various objects in the belt is estimated to be between 1/10 and 1/100 of the mass of the Earth. Pluto, a dwarf planet, is one the largest known object in the Kuiper belt. It was discovered in 1930 and classified as a planet. Since then several larger objects have been discovered. In 2006 when a formal definition of a planet was adopted Pluto was reclassified as a dwarf planet. Three asteroids NASA The point where the Solar System ends and interstellar space begins is not precisely known. The boundary is a place where the solar wind and the Sun s gravity do not affect interstellar space. The solar wind s influence is thought to end about four times Pluto s distance from the Sun. The Sun s gravitational influence continues much further into outer space. Lesson summary Solar System consists of the Sun, planets, dwarf planets, asteroids, comets, meteors and other celestial bodies. The Sun is a main sequence star classified as a moderately large yellow dwarf. The inner Solar System is the traditional name for the region where terrestrial planets and most asteroids are found. The middle region of the Solar System contains the Jupiter, Saturn, Uranus, Neptune and their moons. The outer region of the Solar System has been largely unexplored.

4 Table of Contents Lesson 1 Introduction...2 Quiz 1 Space Pretest...5 Star Gazing...6 Lesson 2 Early Astronomers...9 Quiz Finding Constellations...13 Lesson 3 Telescopes...16 Quiz Moon Gazing...20 Lesson 4 The Spectrum...23 Quiz Light Waves...28 Lesson 5 Our Solar System...31 Quiz D Solar System...35 Lesson 6 Terrestrial Planets...38 Quiz Astrolabe...42 Lesson 7 Jovian Planets...45 Quiz Create Your Own Planet...50 Lesson 8 The Moon...53 Quiz Moon Walking...57

5 Lesson 9 Small Bodies in Space...60 Quiz Impact Craters...65 Lesson 10 The Sun...68 Quiz Solar Oven...72 Lesson 11 Life Cycles of Stars...75 Quiz H-R Diagram...79 Lesson 12 Galaxies...83 Quiz Galactic Mobile...87 Lesson 13 The Space Age...91 Quiz Designing a Space Station...95 Lesson 14 Hubble Space Telescope...98 Quiz Hubble Photo Album Lesson 15 Space Probes Quiz Robot Puzzle Lesson 16 Space Theories Quiz Space Bingo Answer Key Glossary Bibliography Books by Myrna Martin...127