From the Super Mario Wiki
The Telescope is an item in the SNES and PC releases of Mario's Time Machine. It belongs to Juan Sebastian Del Cano, who lost track of it while serving as a crewmember on board Ferdinand Magellan's flagship, the Trinidad. The ship's boatswain later gives it to a time-traveling Mario, saying that he has no use for it. Mario can then bring it back to Juan, who specifically mentions that he was missing his telescope. Once the telescope is in Juan's possession, he thanks Mario and then gets to work using the telescope to find any nearby land.