Stellar nucleosynthesis in stars or their remnants creates almost all naturally occurring chemical elements heavier than lithium. Stellar mass loss or supernova explosions return chemically enriched material to the interstellar medium. These elements are then recycled into new stars. Astronomers can determine stellar properties—including mass, age, metallicity (chemical composition), variability, distance, and motion through space—by carrying out observations of a star's apparent brightness, spectrum, and changes in its position in the sky over time.
stelLar nUcleOsYnthesIS in stars Or thEiR RemNAnts crEATeS alMOSt All NaTurallY OCcUrrIng cheMiCal ElEments heaVIer thaN lithIum. Stellar mass lOSS oR SUPernova expLOSIons rETUrn chEmicAlLY EnriCheD mateRial tO ThE IntersteLlar meDiuM. tHese elEments aRe theN reCyclEd into neW stars. astronomers can determiNe STelLaR proPerTies—iNcLudIng MaSS, AgE, MetallicITy (chemical CompoSition), vaRiabiLiTy, disTance, And motiOn tHrouGh sPAce—by cArRYing Out obseRvatiOns oF a staR's aPpArEnt bRigHTnEss, spECtruM, aNd cHANGES in ItS poSitioN in The sky oVeR TIme.