The Sun and Stars

The Sun and Stars — page 1 — 4 In this book we’re leaving Earth to travel past the Sun across our galaxy and ﬁnally out into the universe looking at the countless different types of stars and other objects that ﬁll the cosmos Twinkle Twinkle This book will take you on a journey around the cosmos ﬁrst to the Sun our nearest star and then through a whole range of objects that reveal the life story of a typical star Finally we’ll take a look at our star-city or galaxy and venture many light years 1 light year is about 5 9 trillion miles or 9 5 trillion kilometers into the cosmos to look at the different types of galaxies that are out there Stars are dense balls of gas that shine because of nuclear reactions in their central cores While most objects in space including planets such as Earth and satellites such as the Moon shine only by reﬂecting light or sometimes by absorbing and re-emitting it stars create their own energy and light Stars come in a huge range of sizes Some are barely the size of the solar system’s largest planet Jupiter while others are so big they would engulf Jupiter’s entire orbit around the Sun Their brightness also varies greatly from brilliant giants 100,000 times brighter than the Sun to weak dwarf stars see page 19 100,000 times fainter A star’s color is determined by its surface temperature running through the whole rainbow from cool red and orange to scorching blue and violet BEYOND THE SUN WHAT IS A STAR

The Sun and Stars — page 2 — 5 ANTARES RIGEL SIRIUS A THE SUN NEED TO KNOW Earth is one of eight planets in the solar system a collection of astronomical bodies in orbit around our star the Sun Taking a look at the stars closest to the solar system reveals just some of the huge variety of stars in the universe THE SUN Our own star is yellow-white with a pretty average size and temperature PROXIMA CENTAURI It might be the closest star to the Sun at just 4 2 light years but Proxima Centauri is a feeble red dwarf star that is so faint you can only see its reddish light through a telescope RIGEL With a mass some 17 times that of the Sun this blue supergiant is the sixth brightest star in the sky Located in the constellation of Orion Rigel is also 40,000 times brighter than our star ANTARES A massive red supergiant star Antares is 800 times wider than the Sun SIRIUS A The brightest star in the sky it lies 8 6 light years from Earth Sirius A is brilliant white with a surface almost twice as hot as the Sun and it is twice the mass of the Sun SIRIUS B This tiny white dwarf star orbits Sirius A every 50 years It is hard to see its white light because of the brighter star’s glare It is all that is left of a star that was once much heavier hotter and brighter than even Sirius A

The Sun and Stars — page 3 — The Sun The nearest star the Sun is 93 million miles 150 million km from Earth This huge ball of exploding gas measuring 870,000 miles 1 4 million km across produces a blaze of heat and light that enables life to survive on our planet But while it’s essential to us the Sun is really just an average star BLAZING FIREBALL The Sun is too bright to look at directly but special ﬁlters can help to show off some of its surface features This reveals that the Sun has a surprisingly sharp edge a layer called the photosphere where the burning gas suddenly becomes transparent Light is created at the center of the Sun but the interior is foggy and stops the light from getting out The photosphere layer with a temperature of around 9,930 F 5,500 C is where the fog lifts and light escapes allowing the Sun’s surface features to become visible 6

The Sun and Stars — page 4 — SOLAR INFLUENCE The Sun has a huge inﬂuence over the space around it It pumps out more energy in a second than all of Earth’s power plants would produce in 750,000 years This energy spreads out as heat and light keeping space within the inner solar system out to around the orbit of Mars fairly warm The Sun’s gravity trails off far more gradually than its energy It traps planets and smaller objects in orbit out to about 1 light year away a distance from which the Sun looks like just another star Huge jets of hydrogen gas shoot out at regular intervals from the Sun’s surface 7 Light is not the only thing escaping from the solar surface In addition a blizzard of tiny electrically charged particles constantly blows away from the photosphere and out across the solar system This solar wind is mostly invisible and can be harmful to space travelers Some of its particles travel so fast that they will pass straight through an unshielded spaceship and through you Planets with strong magnetic ﬁelds such as Earth and Jupiter trap solar wind particles The ﬁelds funnel the particles toward the planet’s north and south poles Here the particles collide with gases in the atmosphere creating beautiful glowing patterns called aurorae or the northern and southern lights But watch out there’s a dangerous side to all this beauty in the form of deadly radiation belts that are also trapped by the magnetism THE SOLAR WIND Solar wind particles collide with Earth’s magnetic ﬁeld above the North Pole creating swirling patterns of light The Sun’s rays warm Earth sustaining life here Plants convert the star’s energy into food and the Sun’s heating effect on Earth’s air and oceans drives our planet’s climate and weather

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