- Joseph Baker (1767–1817) was an officer in the Royal Navy, best known for his role in the mapping of the Pacific Northwest Coast of America during the Vancouver Expedition of 1791–1795. Mount Baker is named after him.
- Jordanus (constellation)
Jordanus (the Jordan River) was a constellation introduced in 1612 (or 1613) on a globe by Petrus Plancius and first shown in print by Jakob Bartsch in his book Usus Astronomicus Planisphaerii Stellati (1624). One end lay in the present-day Canes Venatici and then it flowed through the areas now occupied by Leo Minor and Lynx, ending near Camelopardalis. This constellation was not adopted in the atlases of Johann Bode and fell into disuse.