You are probably referring to the "Moonlight Sonata" which is the popular name of Piano Sonata No. 14 composed by Ludwig van Beethoven and is one of the most well-recognised classical pieces.
The singular possessive of "moonlight" is "moonlight's."
moonlight's
she danced gracefully in the moonlight
In Moonlight was created in 1904.
The clouds obscured the moonlight. The moonlight allowed me to walk home without a flashlight. Bright moonlight means it is harder to see the stars.
Dancing in the Moonlight was created in 1972.
In the Chapel in the Moonlight was created in 1936.
Mandolins in the Moonlight was created in 1958.
It is not moonlight it is the moon reflecting the sun's light
Moonlight Whispers was created in 1999.
Moonlight on Water was created in 1989.
Box of Moonlight was created in 1996.