ab , ▁prov is ional ▁design ation ▁, ▁is ▁a ▁dark ▁background ▁astero id ▁and ▁a ▁potentially ▁slow ▁rot ator ▁from ▁the ▁central ▁regions ▁of ▁the ▁astero id ▁bel t , ▁approximately ▁ ▁in ▁diameter . ▁It ▁was ▁discovered ▁on ▁ 2 2 ▁August ▁ 1 9 4 9 , ▁by ▁South ▁African ▁astronom er ▁Ernest ▁Leonard ▁Johnson ▁at ▁the ▁Union ▁Observ atory ▁in ▁Johannes burg . ▁The ▁likely ▁C - type ▁astero id ▁could ▁have ▁a ▁long ▁rotation ▁period ▁of ▁ 2 7 5 ▁hours . ▁It ▁was ▁named ▁after ▁Aust rian ▁amateur ▁astronom er ▁and ▁software ▁engineer ▁Herbert ▁Ra ab . ▁ ▁Or bit ▁and ▁classification ▁▁ ▁Ra ab ▁is ▁a ▁non - family ▁astero id ▁from ▁the ▁main ▁bel t ' s ▁background ▁population . ▁It ▁or bits ▁the ▁Sun ▁in ▁the ▁central ▁main - b elt ▁at ▁a ▁distance ▁of ▁ 2 . 0 – 3 . 4   AU ▁once ▁every ▁ 4 ▁years ▁and ▁ 4 ▁months ▁( 1 , 5 9 3 ▁days ; ▁semi - major ▁axis ▁of ▁ 2 . 6 7   AU ). ▁Its ▁orbit ▁has ▁an ▁ecc ent ric ity ▁of ▁ 0 . 2 6 ▁and ▁an ▁incl ination ▁of ▁ 8 ° ▁with ▁respect ▁to ▁the ▁e cli ptic . ▁The ▁body ' s ▁observation ▁arc ▁begins ▁with ▁its ▁official ▁discovery ▁observation ▁at ▁Johannes burg ▁in ▁August ▁ 1 9 4 9 . ▁ ▁Phys ical ▁characteristics ▁▁ ▁This ▁astero id ' s ▁spectral ▁type ▁is ▁unknown . ▁Based