] 2 5 ▁October ▁ 1 7 8 6 ) ▁was ▁an ▁English ▁astronom er ▁who ▁made ▁significant ▁contributions ▁to ▁ 1 8 th - century ▁science ▁and ▁American ▁history , ▁particularly ▁through ▁his ▁invol vement ▁with ▁the ▁survey ▁of ▁the ▁Mason – D ixon ▁line , ▁which ▁came ▁to ▁mark ▁the ▁border ▁between ▁Maryland ▁and ▁Pennsylvania ▁( 1 7 6 4 – 1 7 6 8 ). ▁The ▁border ▁between ▁Del aware ▁and ▁Maryland ▁is ▁also ▁defined ▁by ▁a ▁part ▁of ▁the ▁Mason – D ixon ▁line . ▁ ▁Early ▁career ▁Mason ' s ▁early ▁career ▁was ▁spent ▁at ▁the ▁Royal ▁Green wich ▁Observ atory ▁near ▁London . ▁ ▁He ▁served ▁as ▁assistant ▁astronom er ▁from ▁ 1 7 5 6 ▁to ▁ 1 7 6 0 ▁under ▁the ▁Re ver end ▁James ▁Brad ley , ▁the ▁Astronom er ▁Royal . ▁ ▁While ▁employed ▁at ▁the ▁Green wich ▁Observ atory , ▁Mason ▁became ▁familiar ▁with ▁Professor ▁Tob ias ▁May er ' s ▁T ables ▁of ▁the ▁Moon . ▁ ▁The ▁L un ar ▁T ables ▁were ▁designed ▁to ▁solve ▁the ▁problem ▁of ▁determ ining ▁longitude ▁at ▁sea , ▁a ▁challenge ▁that ▁fr ustr ated ▁scient ists ▁and ▁navig ators ▁for ▁dec ades . ▁ ▁Mason ▁worked ▁throughout ▁his ▁life ▁to ▁perfect ▁the ▁L un ar ▁T ables ▁as ▁a ▁method ▁of ▁impro ving ▁navigation ▁at ▁sea . ▁ ▁In ▁ 1 7 8 7 , ▁Mason ▁was ▁awarded ▁£ 7 5 0 ▁by ▁the ▁Board ▁of ▁Long itude ▁for ▁his ▁work ▁on