Via Arnold he met his second wife Maria Margaretha Winkelmann (1670–1720), who had learnt astronomy from self-study and from Arnold. While jointly observing the comet of 1702, they discovered the globular cluster M 5 (5 May 1702).
Arnold's second wife, Maria Margaretha Winkelmann (1670–1720), was an astronomer who learned astronomy through self-study and with Arnold's guidance. They observed a comet in 1702 and discovered the globular cluster M 5 on May 5th of that year.