Rain in a dream often signals emotional release -- tears you haven't let yourself cry, or tension finally finding an outlet. A gentle rain can feel cleansing, washing away something you've been carrying, while a relentless downpour may point to sadness that's asking for more attention than you've given it.
Make the Sun, or any of the superiors to signify princes and great persons. Scribes and rusticks, [are shown by] the inferior planets, and chiefly the Moon. - William Lilly (1602.-1681.)