 Molyneux 's celestial globe was virtually a copy of Gerardus Mercator 's globe of 1551 , which itself was based on a globe of 1537 by Gemma Frisius that Mercator had helped to construct . To the constellations featured on Mercator 's globe , Molyneux added the Southern Cross and Southern Triangle , though somewhat to the west of their true positions . His source appears to have been Andrea Corsali 's diagram of the Antarctic sky published in 1550 . 
