18 September is the 261st day of the year (262nd in leap years). There are 104 days remaining until the end of the year.
- 1743: Gideon Flatworthy is crushed to death beneath cattle and haystacks, after Summoning an entire farm to the cave in which he was living in, in Pembrokeshire.
- 1991: The Gryffindor first years have an Astronomy Class at midnight, on the top of the Astronomy Tower.
Behind the scenes
- 1929: Elizabeth Spriggs, who played the Fat Lady in the film adaptation of Harry Potter and the Philosopher's Stone, is born.