Night Skies Variables, Expressions, and Equations Dawn McMillan
Table of Contents A Visit to the Planetarium 4 Our Solar System 6 The Inner Planets 8 The Outer Planets 16 Making a Model 21 Problem-Solving Activity 28 Glossary 30 Index 31 Answer Key 32
A Visit to the Planetarium Last night, Dad and I visited the planetarium (planuh-tair-ee-uhm). A planetarium is like a theater with a big domed ceiling. People learn about the stars and the planets there. A special projector shows images of the night sky on the roof above. Dad and I took our seats. Suddenly it was dark and we were on a tour of the night sky. We learned that all of the stars we see in the night sky are part of our galaxy. Our galaxy is called the Milky Way. Our solar system is part of the Milky Way. It can be found toward the Milky Way s edge. The show lasted 35 minutes. But, there was also a bonus feature after the show. That was a fun surprise. 4
The Milky Way galaxy I enjoyed seeing the stars in the Milky Way at the planetarium. But what interested me most was our solar system. An astronomer (uh-stron-uh-mer) at the planetarium told me more about it. Variables (VAIR-ee-uh-buhls) are letters or symbols that can be used to represent numbers. An expression is a group of symbols or numbers that can stand for a number or quantity. It does not have an equal sign. An expression can be written to show the total number of minutes spent watching the presentation in the planetarium. Here is the expression: 35 + x a. What does the 35 represent? b. What does the x represent? 5
Our Solar System At the planetarium, I learned that the main part of our solar system consists of the sun and 8 planets. The planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. There are at least 3 dwarf planets and over 150 moons in our solar system as well. There are also many other things such as asteroids, meteoroids, and comets. Not a Planet! In 1930, scientists thought they had discovered a new planet. They named this planet Pluto. But in 2006, it was decided that Pluto is a dwarf planet. It is not big enough to be called a planet. sun Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune The sun and 8 planets in our solar system 6
The Sun The sun is an enormous star that is at least 4.6 billion years old. It is the center of our solar system. The sun s gravity is very powerful. This means each planet is pulled toward the sun. At the same time, each planet s motion moves it away from the sun. The balance between the sun s pull and a planet s motion makes the planet orbit the sun. Giver of Life The energy from the sun gives Earth both light and heat. Without the sun, there would be no life on Earth! 7
The Inner Planets Our solar system consists of 4 inner planets and 4 outer planets. The inner planets are Mercury, Venus, Earth, and Mars. The outer planets are Jupiter, Saturn, Uranus, and Neptune. The inner planets are rocky, with solid surfaces. They are often hit by asteroids. This creates many large craters on their surfaces. The inner planets of our solar system sun Mercury Venus Earth Mars In one month, astronomers recorded that 8 asteroids hit Mars. The next month, some more asteroids hit Mars. Write an expression to show how many asteroids hit Mars in the 2-month time span. 8
Mercury Mercury is the closest planet to the sun. It is just over 1 / 3 of the size of Earth. A year on any planet is the time it takes the planet to make 1 orbit around the sun. Mercury orbits quickly around the sun. It only takes 88 Earth days for Mercury to orbit the sun. A day on any planet is the time it takes to make 1 rotation (row-tay-shuhn) on its axis. Mercury rotates very slowly. One day on Mercury is equal to 176 Earth days. That means you would have to stay up for 176 days on Earth to experience one day on Mercury! sun Mercury Hot and Cold Temperatures on Mercury can get as high as 860ºF (460ºC) and as low as 356ºF ( 180 C). 9
Space Discovery Astronomers have just discovered a new solar system in a distant galaxy. It has six planets orbiting around a sun. Some of the planets are about the size of Earth. Others are much larger. And this new solar system has a combined total of 30 moons! The table below is missing some of the current information astronomers have learned about this new solar system. Name of Planet Planets in New Solar System Approximate Diameter (miles) Number of Moons Zenner z 1 Xenox 3,000 x Axiom a 2 Centaur 75,000 c Yukka 36,000 17 Solve It! For each question below, write mathematical equations using variables to help you figure out the answers. a. Xenox has 15 fewer moons than Yukka. How many moons does Xenox have? 28