Rose Johnson - Discoveries in Earth and Space Science That Changed the World

Published in 2015 by The Rosen Publishing Group, Inc.

29 East 21st Street, New York, NY 10010

2015 Brown Bear Books Ltd

First Edition

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written consent in writing from the publisher.

Library of Congress Cataloging-in-Publication Data

Johnson, Rose, 1981-author.

Discoveries in Earth and space science that changed the world / Rose Johnson. -- First edition.

pages cm. -- (Scientific breakthroughs)

Audience: Grades 5 to 8.

Includes bibliographical references and index.

ISBN 978-1-4777-8609-3 (library bound)

1. Earth sciences--History--Juvenile literature. 2. Space sciences--History--Juvenile literature. 3. Discoveries in science--Juvenile literature. I. Title.

QE29.J64 2015

520.9--dc23

2014027727

Editor and Text: Rose Johnson

Editorial Director: Lindsey Lowe

Childrens Publisher: Anne ODaly

Design Manager: Keith Davis

Designers: Lynne Lennon

Picture Researcher: Clare Newman

Picture Manager: Sophie Mortimer

Brown Bear Books has made every attempt to contact the copyright holder. If anyone has any information please contact:

All artwork: Brown Bear Books

Picture Credits

t=top, c=center, b=bottom, l=left, r=right.

FC, Ammit Jack/Shutterstock; , Walter Myer/Stocktrek Images/Alamy.

Contents

Introduction

Understanding how Earth works is the first step in understanding space. The same scientific laws control them both.

E arth and space could not be more different, from the human point of view. Earth is in constant change, but when we look out into space it always appears to stay the same.

The first science

Astronomy, the study of stars and other heavenly bodies, is perhaps the first science. Scholars in China and Babylon (modern Iraq) were recording the movements of the stars and planets 4,000 years ago.

The ancient people who built Stonehenge in England knew about the movement of the Sun through the year. The stones show where the Sun rises and sets in the shortest and longest day of the year.

There are 80 billion galaxies in the Universe. Our planet orbits just one star in a galaxy containing 100 billion others.

The Babylonians used these observations to calculate that the year lasted 365 days. (The accurate measurement is 364.25 days.) Other cultures used the motion of the Sun, Moon, and stars to keep track of the changes in the seasons.

Finding patterns

Earths seasons were important to the first civilizations, who needed to know when to plant crops and bring in the harvest. The predictable motion of the stars was the best way to keep track of time. However, not all lights in the sky followed the same rules. Some moved around by themselves. The Greeks called them wanderers, or planets.

Finding patterns

The study of planets would eventually help us understand the structure of outer space. Today we know that Earth is just one of many billions of planets in the Universe.

Eclipses

The first scientific breakthrough ever recorded was in the 6th century BCE, when a Greek philosopher predicted a solar eclipse.

T hales of Miletus (624546 BCE) is said to be the first scientist. He was an ancient Greek philosopher, although his hometown, Miletus, was in what is now Turkey. Thales was the first person to use the evidence of what he could observe to explain natural processes. He got a lot of things wrong, but he appears to have been able to predict eclipses.

Good omen

The story goes that Thales predicted that the Sun would be eclipsed at sunset on May 28, 585 BCE (although he would have used a different dating system). On that day, two armies were fighting nearby, and when the eclipse occurred, the soldiers saw it as a sign that they should make peace with each other.

Thales predicted that an eclipse would happen at sunset on May 28, 585 BCE, in the middle of a battle between Greeks and Persians.

People must wear special glasses to observe an eclipse. Looking directly at the Sun, even during an eclipse, damages the eyes.

FACTS

There are between two and five full solar eclipses every year.

A solar eclipse can only be seen from a narrow band of Earths surface. It is never visible from everywhere on Earth all at once.

During a solar eclipse, you can see the atmosphere of hot gas surrounding the Sun.

Blocked by the moon

No one knows how Thales predicted this eclipse (some think the story is untrue). Today, we understand that a solar eclipse is caused by the Moon moving between Earth and the Sun so that it blocks out the light for just a few minutes.

During a solar eclipse, the moon casts a shadow on Earth. Anyone under that full shadow will see the Sun disappear.

Measuring Earth

The first accurate measurement of the size of Earth was made by a Greek mathematician using the angles of shadows cast by the Sun.

A t midday, every day, wherever you are on Earth, the Sun reaches its highest point in the sky.

In the 3rd century BCE, Eratosthenes, a Greek scientist living in Alexandria, Egypt, heard about a well in the city of Aswan where the Sun cast no shadow at noon. Sunlight shone straight to the bottom of the well.

Ancient people saw that Earth always cast a round shadow on the Moon during a lunar eclipse. That meant that the world was a sphere.

The well used by Eratosthenes in his calculations still exists in Aswan, Egypt.

ERATOSTHENES

Born in Cyrene, a Greek city in what is now Libya, in 276 BCE, Eratosthenes is known as the founder of geography. His map of the world had Britain in the west, the Sahara Desert in the south, and went as far east as India. Eratosthenes also developed a system for finding prime numbers. It is still used by mathematicians today.

Different location

On the same day in Alexandria, the sunlight cast a short shadow at noon. Eratosthenes reasoned that the Sun was directly overhead Aswan but at a slight angle at Alexandria. He realized he could use this difference to calculate the circumference of Earththe distance all the way around the planet.

Using angles

Eratosthenes set up a pillar in Alexandria and measured the length of the shadow it produced at noon. He imagined the pillar and the shadow were two sides of a trianglethe third side was made by a ray of light coming from the Sun.