This is the parallel minor of G major scale and Bb is its relative major key.
G minor harmonic scale.
About G minor key
Let the teacher, as in the previous lessons; explain the difference between D and G minor scale. G minor was the most appropriate key to express tragedy and melancholy according to Mozart: for example, Amadeus composed his well known Symphony Number 40 in this key. Chopin’s piano Ballade Number 1 is in G minor.
Piano Minuet in G minor key : Handel
This is a selection from Handel’s Opera “Almira”. The Minuet is a dance, which originated in France and was first dance at Versailles during the reign of King Luis XIV. It is a slow dance always written in 3-4 time. Observe the change of fingering, also the double dot in the fifth measure.