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
Our solar system includes the Sun eight planets five dwarf planets and many moons comets asteroids and meteoroids Planets dwarf planets comets asteroids and meteoroids orbit the Sun This means they travel in a path around the Sun They do so because of the Sun’s powerful gravitational pull A moon orbits a planet because of the planet’s gravitational pull Each planet dwarf planet and moon also spins or rotates on its own invisible axis while orbiting Earth is the third planet from Earth is the third planet from the Sun in our solar system the Sun in our solar system Sun Earth 8
There are many good reasons to explore our solar system and the space beyond it Exploring our solar system helps scientists discover our place in the vast universe By studying other planets we learn more about Earth and what makes it unique Galaxies are grouped by the shape they form M81 is a spiral galaxy Other galaxy shapes are elliptical or irregular 9
