For questions specific to Beethoven's Sonata Op. 27 No.2, popularly known as the "Moonlight" sonata. Questions may related to analysis, history, interpretation, technical details such as fingering, or other aspects of performance and/or theory. Additional tags related to the area of interest should be included. Do not use this tag for questions in which the sonata is only used as an example in a broader query.
Beethoven's Sonata quasi una fantasia in C sharp minor, op. 27 no. 2 ("Moonlight"), sometimes referred to as sonata #14, was published by Giovanni Cappi on March 3, 1802.1
It quickly became popular, and the first movement is one of the most celebrated in all Beethoven's works.2
The nickname "moonlight" derives from the 1824 novel Theodor, by Ludwig Rellstab, in which a character describes the sonata's first movement as portraying moonlight reflecting on a lake. The nickname became popular in the 1850s.3
1Barry Cooper, "Commentaries" in Beethoven: The 35 Piano Sonatas, Volume 2 (2007, ABRSM), page 20.