▁and ▁Spain ) ▁had ▁joined ▁the ▁Union , ▁bringing ▁the ▁total ▁membership ▁to ▁ 1 9 ▁countries . ▁Although ▁the ▁Union ▁was ▁officially ▁formed ▁eight ▁months ▁after ▁the ▁end ▁of ▁World ▁War ▁I , ▁international ▁collaboration ▁in ▁astronom y ▁had ▁been ▁strong ▁in ▁the ▁pre - war ▁era ▁( e . g ., ▁the ▁Astronom ische ▁Gesellschaft ▁K atalog ▁projects ▁since ▁ 1 8 6 8 , ▁the ▁Ast ro graph ic ▁Catalogue ▁since ▁ 1 8 8 7 , ▁and ▁the ▁International ▁Union ▁for ▁Sol ar ▁research ▁since ▁ 1 9 0 4 ). ▁ ▁The ▁first ▁ 5 0 ▁years ▁of ▁the ▁Union ' s ▁history ▁are ▁well ▁documented . ▁Sub sequ ent ▁history ▁is ▁recorded ▁in ▁the ▁form ▁of ▁rem in isc ences ▁of ▁past ▁I AU ▁Pres idents ▁and ▁General ▁Secret aries . ▁Tw elve ▁of ▁the ▁four teen ▁past ▁General ▁Secret aries ▁in ▁the ▁period ▁ 1 9 6 4 - 2 0 0 6 ▁contributed ▁their ▁re collections ▁of ▁the ▁Union ' s ▁history ▁in ▁I AU ▁Information ▁Bul letin ▁No . ▁ 1 0 0 . ▁Six ▁past ▁I AU ▁Pres idents ▁in ▁the ▁period ▁ 1 9 7 6 – 2 0 0 3 ▁also ▁contributed ▁their ▁re collections ▁in ▁I AU ▁Information ▁Bul letin ▁No . ▁ 1 0 4 . ▁ ▁Com position ▁▁ ▁As ▁of ▁ 1 ▁August ▁ 2 0 1 9 , ▁the ▁I AU ▁includes ▁a ▁total ▁of ▁ 1 3 , 7 0 1 ▁individual ▁members , ▁who