Chapter 1 SPACE EXPLORATION have gazed at the night sky for thousands of years Ancient peoples used the positions of the stars and People People planets in the sky to tell the passing of time Ancient Greeks grouped the stars into constellations In 1610 Galileo Galilei constructed a telescope to see far into the night sky With his telescope Galileo discovered more about the universe than anyone had before Space exploration has come a long way since Galileo’s discoveries Many spacecraft have been launched into the solar system to photograph and gather information People have even walked on the Moon All of the stars that can be seen in the night sky are part of the Milky Way 4
DID YOU KNOW In 1968 U S astronauts orbited the Moon for the first time on the Apollo 8 mission On July 20 1969 Neil Armstrong became the first person to step foot on the Moon on the Apollo 11 mission He was followed by crewmate Buzz Aldrin Scientists who go into space are called astronauts Scientists who study space from Earth are called astronomers Astronauts and astronomers work together to gather information about our universe Astronomers use many types of math and a science called physics Physics is the study of how the world works Physicists observe and identify laws of motion and gravity Gravity is what keeps us on Earth It pulls us down Galileo Galilei lived from 1564 to 1642 5
Astronomers use the principles of math and physics to learn about the nature of the universe Because the universe is so large astronomers have to use what they know about math and physics to create theories about what is difficult to observe For instance physicists know that light travels at 186,282 miles 299,792 kilometers per second They can use this figure to determine the distance between planets Using math and physics astronomers can figure out how long it would take to travel to a distant planet or star using light-years A light-year is the distance light travels in one year Let’s Calculate How Far Light Travels in a Year 186,282 miles 299,792 kilometers speed of light Use the speed of light to figure out how far light travels in one year First you need to know there are about 31,536,000 seconds in one year one second Next use the speed of light to figure out how far light travels in one year 31,536,000 seconds 186,282 miles 299,792 kilometers x 5 9 trillion miles 9 5 trillion kilometers One light-year is equal to about 5 9 trillion miles 9 5 trillion kilometers one second one year one year 6
DID YOU KNOW Scientists estimate the Sun to be about four and a half billion years old The Sun is expected to burn much like it does today for another five billion years The universe is vast Huge telescopes can see into other galaxies that are billions of light-years away A galaxy is a large system of dust gas and millions to trillions of stars A solar system is a group of objects such as planets that orbit around a star The Milky Way galaxy is home to our solar system Earth is part of this system Other solar systems exist in the Milky Way galaxy The Milky Way has hundreds of billions of stars one of which is the Sun Any star that can be seen in the night sky is in the Milky Way galaxy 7
