Lily Moon

"‘Moon’ … ‘Nott’ … ‘Parkinson’ … then a pair of twin girls, ‘Patil’ and ‘Patil’ … then ‘Perks, Sally-Anne’ … and then, at last –"

—Harry waiting for his name to be called.^[src]

Lily Moon (c. 1979-1980) was a witch who began attending Hogwarts School of Witchcraft and Wizardry in 1991. She was in the same year as Harry Potter and was Sorted into either Gryffindor, Hufflepuff, or Slytherin.^[3]

Behind the scenes

Only Lily's surname was revealed during the Sorting ceremony in Harry Potter and the Philosopher's Stone, but on the student list shown on Harry Potter and Me, the first three letters of her first name could be made out as either "Lil-" or "Lib-". Her full first name was finally revealed by J. K. Rowling as supplementary content on the Pottermore website.^[4] According to Rowling, this character was named before she settled on the name of Harry Potter's mother, and was the "first intimation of Luna Lovegood," giving her the idea for a "fey, dreamy girl."^[4]
During a practical examination, for their O.W.L.s, Lily was not called to take her test. She would usually appear after Draco Malfoy but before Theodore Nott. This could just be a mistake of J. K. Rowling's, or Lily may have been unable to attend her test. It is possible that she had failed her exams at a point between first and fourth year, forcing her to repeat the year.

↑ Lily has to have been born during these dates, otherwise she would be too old, if born before, or too young, if born after, to be starting Hogwarts in 1991.
↑ "World Exclusive Interview with J K Rowling," South West News Service, 8 July 2000 - "Hogwarts just serves Britain and Ireland."
↑ ^3.0 ^3.1 J. K. Rowling's original list of forty students contains five males and five females from each house. As all five Ravenclaw females are known, the remaining females whose houses are unknown must be in one of the other three houses.
↑ ^4.0 ^4.1 Pottermore (transcription available here)