What Is Light Light is everywhere Every morning sunlight fills the sky and at night we switch on the electric lights in our homes Light shines from our cell phones and TVs and from our streets and our cities Light for Life Humans plants and animals all need light to live Without it we wouldn’t be able to see Even worse we wouldn’t have any food and there would be no life on Earth 쑼 Early morning sunlight streams through the trees in a park in central India The Sun is our main source of natural light 4
DAY AND NIGHT The place where you live cannot be in daylight all of the time because Earth spins When your part of the world is turned away from the Sun it is nighttime See for yourself how night and day happen You will need a ball or globe a sticker a flashlight or small lamp 1 Place the sticker on the ball to mark where you live 2 Darken the room as much as you can Shine the light at the ball to act as the Sun 3 Slowly spin the ball around Your home moves into the light daytime then away from the light nighttime 1 2 3 쑿 Divers use flashlights to explore a flooded cave system in Mexico Light Energy Light is a strange and amazing form of energy like heat electricity and sound What is light exactly and where does it come from How far and how fast does light travel How do our eyes see it and how do animals and plants use it You’ll find the answers to all these questions in this book 5
Where Does Light Come From Light is a kind of energy Energy is the power to do work or to make things happen There are many forms of energy and one form can change into another Making Light Light glows from objects when another kind of energy changes into light that we can see For example a candle contains chemicals that store energy When you light it the chemicals burn and some of the chemical energy turns into light energy Light Sources Something that gives out light is called a light source Candles electric lights and stars are all light sources There are even some animals that produce their own light 쑼 Even birthday candles are a light source though they do not last for long 6
씱A traditional lightbulb containing a tungsten filament that glows when electricity flows through it The Sun Most of the light in our world comes from the Sun our nearest star It’s a giant ball of gases that are constantly changing into other gases This process gives out light and heat energy The Sun is so huge and powerful that it can light up the earth from 93 million miles 149 million kilometers away If an average lightbulb were the Sun the earth would be the size of a pinhead and 164 feet 50 meters away Lightbulbs turn electrical energy into light energy In an old-fashioned HOW LIGHTBULBS WORK lightbulb electricity runs through a thin wire inside the bulb called a filament The filament heats up and glows white-hot In a modern energy-saving bulb electricity flows through gases inside a glass tube making them give out light 쑼 A photograph of the Sun taken using a telescope showing its churning burning hot surface 7
