 Introduction. Only about five hundred people have left Earth behind to explore the wonders of outer space. Now you too can voyage through space and time and enjoy an experience that is out of this world. As you turn the pages of this lavishly illustrated encyclopedia, you will learn about how rockets and telescopes work, discover what it is like to work and live in space and unravel the mysteries of the final frontier. You will travel from our small blue planet to strange worlds with poisonous atmospheres, hidden oceans and huge volcanoes. Then head out into the milky way to discover the multicolored clouds, stars and galaxies that lie scattered throughout the universe. Full of amazing facts, this encyclopedia is invaluable as a reference book for researching projects or perfect for just dipping into. For anyone who has ever stared up at the night sky and wondered what the universe is really like, this book is an essential read. Peter Bond. Observing the universe. We live on one tiny planet in the vast universe. Finding out what else is out there has been one of our biggest challenges and it started with people simply staring at the sky. What is space? We live on a small blue planet called Earth. It has a surface of liquid water and rock and is surrounded by a blanket of air called the atmosphere. Space begins at the top of the atmosphere. It is an unimaginably vast, silent and largely empty place, but it has many amazing properties. Even in places far from stars and planets, space contains scattered particles of dust or a few hydrogen atoms, the edge of space. Earth's atmosphere does not end suddenly. It gets gradually thinner and thinner as you travel up from the ground. Most experts agree that outer space starts at a height of 100 kilometers, 62 miles. Yet even above this height, there is a layer of very thin air called the exosphere. Hydrogen and other light gases are slowly escaping into space from this outermost part of Earth's atmosphere. Sample complete. Ready to continue?