Many years ago people thought the earth was flat. They believed that the sky __61__ a big upside-down bowl and that the sun, moon, and stars were lamps hanging from the top of the bowl. Later, people __62__ better. They found out that the earth __63__ round.
We call the study of the skies and the planets astronomy, __64__ we call the watchers of the skies astronomer. Early astronomers thought the earth was the center of __65__. They thought the heavens spun __66__ the earth. Later, they changed their __67__. They knew the earth was not the center. They believed that the earth and the __68__ planets spin around the sun. Today we know this is true.
Ancient scientists studied the skies __69__ simple instruments. The first person __70__ a telescope was named Galileo. In 1610 __71__ four moons around the planet Jupiter. Today __72__ use more complex equipment. Some of these measure the brightness of light. __73__ break lights up into different colors. Radio telescopes make
stars and planets __74__ far closer than Galileo’s telescope could.
Early astronomers __75__ five planets in the sky. Besides Earth, they knew about mercury, Venus, Mars, Jupiter, and Saturn. In 1781 a seventh one was discovered and named Uranus. Years later, astronomers found another planet and called it Neptune. The ninth planet to be found is called Pluto. It was not __76__ until 1930.
Today scientists can __77__ almost anywhere. They have reached the heavens with their spacecraft, in 1959, a spacecraft __78__ took pictures of the dark side of the moon. Ten years later a spacecraft landed two Americans on the moon. Other important journeys into space __79__. Who knows Maybe __80__ human beings will live on
another planet. Maybe you will be one of them.