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 possessive form for the noun moonlight (an uncountable noun) is moonlight's.example: The moonlight's illumination was enough to easily see the path.
moonlight's
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.
Moonlight is a silvery cloak draping the earth in ethereal glow.
"moonlight" has two syllables.
The moonlight was bright
It is not moonlight it is the moon reflecting the sun's light
"Light" is the base word in "moonlight."
Moonlight Agony was created in 1999.
Dancing in the Moonlight was created in 1972.
Portraits in Moonlight was created in 1964.