by Giles Sparrow THE SUN AND STARS SPACE TRAVEL GUIDES
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
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
