Beethoven Piano Sonata No. 14
The Piano Sonata No. 14 in C-sharp minor "Quasi una fantasia" , Op. 27, No. 2, by Ludwig van Beethoven , is popularly known as the "Moonlight" Sonata . The work was completed in 1801  and dedicated to his pupil, 17-year-old Countess Giulietta Guicciardi ,  with whom Beethoven was, or had been in love.  The name "Moonlight" Sonata derives from a 1832 description of the first movement by poet Ludwig Rellstab , who compared it to moonlight shining upon Lake Lucerne .   Beethoven included the phrase "Quasi una fantasia" ( Italian : Like a fantasy ) in the title because the sonata does not follow the traditional sonata pattern where the first movement is in regular sonata form and where the movements are arranged in a fast-slow-fast sequence
The sonata has three movements:
- Adagio sostenuto
- Presto agitato
The first movement is written in a kind of truncated sonata form . A melody that Hector Berlioz called a "lamentation" is played (mostly by the right hand) against an accompanying ostinato triplet rhythm. The movement is also played pianissimo or "very quietly", and the loudest it gets is mezzo-forte or "moderately loud". The movement has made a powerful impression on many listeners; for instance, Berlioz wrote that it "is one of those poems that human language does not know how to qualify." The work was very popular in Beethoven's day, to the point of exasperating the composer, who remarked to Czerny "Surely I've written better things." 
The second movement is a relatively conventional minuet and trio ; a moment of relative calm written in D-flat major . This key signature is enharmonically equivalent to C-sharp major , that is, the tonic major for the work as a whole. The slightly odd sound of the first eight bars seems to be the result of the minuet starting in the "wrong" key; i.e. the dominant key of A-flat major . The music settles into D-flat only in the second phrase, bars 5-10.
The stormy final movement, in sonata form, is the weightiest of the three, reflecting an experiment of Beethoven's (also carried out in the companion sonata, Opus 27 no. 1 and later on in Opus 101 ) placement of the most important movement of the sonata last. The writing has many fast arpeggios and strongly accented notes, and an effective performance demands flamboyant and skilful playing.
Of the final movement, Charles Rosen has written "it is the most unbridled in its representation of emotion. Even today, two hundred years later, its ferocity is astonishing."
The musical dynamic that predominates in the third movement is in fact piano . It seems that Beethoven's heavy use of sforzando notes, together with just a few strategically located fortissimo passages, creates the sense of a very powerful sound in spite of the overall dynamic.
For more detail : http://en.wikipedia.org/wiki/Piano_Sonata_No._14_%28Beethoven%29