Final answer:
The opening of the first movement of Eine kleine Nachtmusik contains a 'rocket theme,' which describes a musical figure that rapidly rises in pitch, similar to a rocket's launch.
Step-by-step explanation:
The opening of the first movement of Eine kleine Nachtmusik begins with a marchlike theme that rapidly ascends to its peak, a "rocket theme," then turns downward at the same rate. The term "rocket" is a musical figure that quickly ascends in pitch over a short duration, much like a rocket launching into the sky, and then often mirroring this action with a similar rapid descent. This kind of theme was commonly used in the Classical era to create a dramatic and energetic opening to a piece. Wolfgang Amadeus Mozart, the composer of Eine kleine Nachtmusik, was known for his masterful employment of such motifs to evoke strong emotions and set scenes through his music.