An Ancient Science A stronomy is one of the oldest sciences in the world Thousands of years ago there were no calendars or clocks People kept track of time by watching the sun and the stars It was important for them to know the time in order to plant their crops and gather their harvests These people were the first astronomers The study of astronomy involves all of the objects outside Earth’s atmosphere These include the sun moon An astronomer’s job involves identifying objects in space such as the stars and clouds of gas and dust in this image 4
This astronomer is looking through a large telescope Astronomers spend a lot of their time observing the sky VOCAB U LARY Matter is anything in the universe that takes up space planets stars galaxies and all other matter in the universe An astronomer’s job is to observe measure and interpret the data they collect about these objects This knowledge helps us understand what happens in space and how it affects us here on Earth 5
What’s Up There T he closest star to planet Earth is our sun It is the center of the solar system The solar system consists of the sun and everything that orbits or travels around the sun This includes the eight planets and their moons dwarf planets and countless This diagram compares the sizes of the planets in the solar system It shows them closer together than they actually are asteroids comets and other small icy objects However even with all these things most of the solar system is empty space The solar system itself is only a small part of a huge system of stars and other 6
A comet is a small chunk of dust and ice that orbits the sun Comet West seen here was named after the astronomer who discovered it Richard West objects called the Milky Way galaxy Just as the planets in the solar system revolve around the sun the stars in the Milky Way revolve around its nucleus or center It takes the sun about 200 million years to travel around the nucleus of the Milky Way VOCAB U LARY A galaxy is a group of stars clouds of gas and dust particles that move together through the universe 7
