SC.5.E.5.1 Galaxies
SC.5.E.5.1: Recognize that a galaxy consists of gas, dust, and many stars, including any objects orbiting the stars. Identify our home galaxy as the Milky Way.
What Are Galaxies Made Of?
A galaxy is a cloud of gas, dust, stars and any objects orbiting the star. When you look up at the sky at night, you can see many stars in the sky. Each star that you see is like our Sun. The Sun is a star: it is a huge body in space that produces energy, some of it in the form of light. Every star you see is so far away that you don’t see the shape of the star like you can the Sun. You can only see a twinkling point of light in the sky. We only see one star during the day: the Sun. The Sun is so bright that it makes it impossible to see the other stars in the sky, even though they are there.
Just like the Sun, many other stars have planets orbiting them. Planets do not produce their own light. Planets reflect the light of the star they orbit. When a planet orbits a star, it moves in a path around that star. The gravity of a star is so powerful that it pulls the planet toward it: otherwise, the planet would just spin off into space! As each planet revolves, or travels in its orbit around a star, it is also spinning on its axis. The rotation of a planet or moon on its axis causes the cycles of day and night.
The Solar System. The Sun is the star at the center of our solar system. There are eight planets in our solar system. Between Mars and Jupiter is a belt of rocky objects known as asteroids. Around the edge of the solar system are the comets.
What is the Milky Way?
When you look at a cloud in the sky, you are looking at a collection of billions of floating droplets of water. Just like a cloud, a galaxy is a collection of hundreds of billions of stars floating in space together. There are clouds of gas and dust floating between the stars. From Earth, this cloud of gas, dust, many stars and all the objects orbiting the stars looks like a glowing path across the night sky. Some ancient people though that this was a path of spilled milk, and so the gave it the name “Milky Way.” The name of our galaxy is the Milky Way. There are many billions of galaxies in the entire universe: the Milky Way is just one of many.
The universe is all of space and time. The universe is made up of hundreds of billions of galaxies like the Milky Way. Each galaxy is made up of gas, dust, many stars and any objects orbiting the stars. Objects that orbit stars include planets, moons, asteroids, and comets. The star at the center of the Solar System is one of about four hundred billion stars in the Milky Way galaxy. Many other planets in other solar systems around other stars have been discovered but are too far away to visit.
