▁in ▁cold , ▁diff use ▁clouds ▁or ▁in ▁dense ▁regions ▁ill umin ated ▁with ▁ult rav io let ▁light . ▁Poly cyc lic ▁a rom atic ▁hydro car b ons ▁such ▁as ▁ac et yl ene ▁( C 2 H 2 ) ▁generally ▁group ▁together ▁to ▁form ▁graph ites ▁or ▁other ▁so oty ▁material , ▁but ▁other ▁organ ic ▁mole cules ▁such ▁as ▁ac et one ▁(( CH 3 ) 2 CO ) ▁and ▁bu ck min ster full eren es ▁( C 6 0 ▁and ▁C 7 0 ) ▁have ▁been ▁discovered . ▁ ▁Mot ion ▁in ▁the ▁universe ▁ ▁Stars ▁and ▁inter stell ar ▁gas ▁are ▁bound ▁by ▁gravity ▁to ▁form ▁galaxies , ▁and ▁groups ▁of ▁galaxies ▁can ▁be ▁bound ▁by ▁gravity ▁in ▁galax y ▁clusters . ▁With ▁the ▁exception ▁of ▁stars ▁in ▁the ▁Mil ky ▁Way ▁and ▁the ▁galaxies ▁in ▁the ▁Local ▁Group , ▁almost ▁all ▁galaxies ▁are ▁moving ▁away ▁from ▁us ▁due ▁to ▁the ▁expansion ▁of ▁the ▁universe . ▁ ▁Do pp ler ▁effect ▁and ▁red shift ▁The ▁motion ▁of ▁stell ar ▁objects ▁can ▁be ▁determined ▁by ▁looking ▁at ▁their ▁spectrum . ▁Because ▁of ▁the ▁Do pp ler ▁effect , ▁objects ▁moving ▁towards ▁us ▁are ▁bl ues h ift ed , ▁and ▁objects ▁moving ▁away ▁are ▁red shift ed . ▁The ▁w avel ength ▁of ▁red shift ed ▁light ▁is ▁longer , ▁appearing ▁red der ▁than ▁the ▁source . ▁ ▁Con vers ely , ▁the ▁w avel ength ▁of ▁bl ues h ift ed ▁light ▁is ▁shorter , ▁appearing