简介:Likepeople,starsareborn.Theywillalsogrowoldanddie.Theirbirthplacesarehuge,coldcloudsofgasanddust,knownas“1)nebulas.”ThemostfamousoftheseistheOrionNebula.Itisjust2)visiblewiththeunaidedeye.Thesecloudsstartto3)shrinkundertheirown4)gravity.Asthecloudgetssmaller,itbreaksinto5)clumps.Eachclumpeventuallybecomessohotand6)densethatnuclearreactionsbegin.Whenthetemperaturereaches10milliondegreesCelsius,theclumpbecomesanewstar.