Understanding Our Sun

Understanding Our Sun — page 1 — CHAPTER 1 Our Amazing Sun Our Solar System is our home in the universe As well as Earth it comprises seven other planets dozens of dwarf planets and moons and millions of asteroids and comets flying around At the center of everything is the Sun It makes up 99 8 percent of all the mass of our Solar System Its gravity keeps Earth and the other objects in predictable orbits which are regular paths around the Sun The surface of the Sun is around 9,932 Fahrenheit 5,500 C and its energy gives us light and heat At the Center Our Sun is a star like one of about 250 billion others in the galaxy Each star is surrounded by its own solar system of planets and other objects Along with the Moon the Sun is one of the easiest celestial objects or objects in the sky to see from Earth It is only in the past couple of centuries however that people have looked at the Sun in a scientific way They ask questions about the Sun’s physical qualities How was it created Why is it so hot Has it changed Will it continue to change Earth’s atmosphere is an envelope of gases that surround the planet The atmosphere distorts the Sun’s light making it look as though it has rays 4

Understanding Our Sun — page 2 — MISSION Space Science Our Sun is 1 astronomical unit AU from Earth An AU is a unit of length used by astronomers to measure distances in space It is defined as the average distance between Earth and the Sun This is about 93 million miles 149,668,992 km At its widest the diameter of the Sun is about 865,000 miles 1 4 million km The volume of the Sun is huge it is so large that 1 3 million Earths could fit inside it Scientists darken bright images of the Sun to reveal details of the activity on its surface It is impossible to send spacecraft to the Sun It is too hot for anything to approach without being destroyed But by studying the Sun with different scientific instruments people have come to know a lot about it We know what it is made of We know that it is 4 603 billion years old which is more than 60 million years older than Earth Many questions still remain however Scientists are just beginning to unravel the secrets of the Sun New Discoveries Careful observation and advanced technology reveal new information about the Sun Astronomers are scientists who study space Using the Hinode spacecraft they found that the Sun’s surface bristles with jets of X-rays These jets fire blobs of energy off the surface at about 1 9 million miles per hour 3 2 million kph Even after centuries of watching the Sun our star continues to surprise us 5

Understanding Our Sun — page 3 — The All Important Sun All life on Earth exists because of the Sun The Sun gives out energy in the form of light and heat This energy supports all life on Earth It warms the oceans and the atmosphere Green plants convert sunlight into food for themselves and for animals The Sun's gravity also holds Earth in its regular orbit If Earth drifted out of its orbit and off into space the planet would become bitterly cold and all life would end As gas and dust clumped together at the center of this cloud it formed a star As the star attracted more material its gravity grew stronger This gravity made the cloud around it spin More clumps of matter became planets and dwarf planets They were made from the same materials as the Sun itself The Sun generates a huge amount of energy and magnetism Magnetism is a force that attracts or repels other objects The Sun's magnetism forms the heliosheath This is a magnetic field that extends beyond our Solar System This acts as a shield to protect our Solar System from harmful cosmic radiation from deep space The Center of It All More than 4 6 billion years ago our Solar System did not yet exist There was nothing but a cloud of gas and dust This interstellar dust occurs throughout our galaxy The Sun's magnetic field may protect our whole Solar System as it orbits the center of the Milky Way Galaxy Saturn Uranus Neptune 6 Sun Mercury Venus Earth Mars Jupiter

Understanding Our Sun — page 4 — About 10 percent of the stars in our Milky Way galaxy are yellow dwarfs like our Sun Dwarfs and Giants The Sun is a G-type main sequence star also known as a yellow dwarf This is a type of star that is a little more than a million times larger than Earth More than 70 percent of the Sun is made up of hydrogen which acts as the fuel for the star Most of the rest is helium with small amounts of other elements Yellow dwarfs can keep burning their hydrogen for up to 10 billion years Many stars in the universe are bigger and burn brighter than yellow dwarfs These stars called giants supergiants and hypergiants only last for a few million years before they run out of fuel Other stars called red dwarfs last much longer but do not burn as brightly By providing a lot of energy but also burning for billions of years the Sun may be an ideal star for supporting life on the planets that orbit around it 7

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