The Sun and The Origins Of The Solar System the cloud collapsed so much that it became dense enough and hot enough for nuclear reactions to begin and the Sun was born Meanwhile away from the center the gas and dust in the spinning disk cooled Solid grains of silicates and other minerals the basis of rocks condensed out of the gaseous material in the disk Farther from the center where temperatures temperatures were lower ices of water methane ammonia and other gases began to form The spinning material in the disk collided and began to stick together forming larger and larger objects Ultimately some of the clumped together objects grew huge and developed into planets The inner planets formed mostly from chunks of silicate silicate rock and metal while the outer planets developed mainly from ices Smaller chunks of matter and debris that did not get incorporated into the planets became asteroids in the inner part of the solar nebula and comet nuclei in the outer part of the nebula At some point after the matter in the nebula had condensed and clumped into objects the intensity of the solar wind suddenly increased This blew much of the rest of the gas and dust off into space This general formation process is thought not to be unique to the solar system but rather to be how stars and planets throughout the universe develop Astronomers have detected disks of matter surrounding newly formed stars 8
Introduction The future of the solar system depends on the behavior of the Sun If current theories of stellar evolution are correct correct the Sun will have much the same size and temperature for about 5 billion more years By then all of the hydrogen in its core will have been used up Other nuclear reactions will begin in a shell around the core Then the Sun will grow much brighter and larger turning into a red giant and expanding beyond the orbit of Venus perhaps even engulfing Earth Much later when all its nuclear energy sources are exhausted the Sun will cool down evolving into a white dwarf star Around it will orbit the remaining planets They will have turned into frozen chunks orbiting their shrunken star 9
CHAPTER 1 Understanding the sUn Although the Sun is a rather ordinary star it is the source of virtually all Earth’s energy It provides the heat and light that make life on Earth possible Yet Earth receives only about half a billionth of the energy that leaves the Sun The telescope has been used in solar studies since 1610 The solar tower telescope was later invented for use in solar studies Its long focal length can give very large images of the Sun The coronagraph another special telescope is used to examine the Sun’s outer atmosphere The instrument blocks the direct light from the Sun’s disk allowing the much dimmer corona to be viewed The Italian scientist Galileo Galilei and the German mathematician Christoph Scheiner were among the first to make telescopic observations of sunspots Scheiner’s drawings in the Rosa Ursina are of almost modern quality and there was little improvement in solar imaging until 1905 In the 1670s the British astronomer John Flamsteed 10
The sunset over Joshua Tree National Park in California and the French astronomer Gian Domenico Cassini calculated calculated the distance to the Sun Sir Isaac Newton set forth the role of the Sun as the centre of attraction of the known planetary system The sunspot cycle a huge effect was not discovered until 1843 by Samuel Heinrich Schwabe The German amateur astronomer was looking for a planet inside the orbit of Mercury and made careful daily drawings to track its passage across the face of the Sun Instead he found that the number of sunspots varied with a regular period The Swiss astronomer Rudolf Wolf confirmed Schwabe’s discovery by searching through previous reports of sunspots 11
