Hi Vettius! The 9th house in traditional astrology deals with dreams, notably of a prophetic nature, which is how the ancients understood meaningful dreams, anyhow.
If your can get hold of a copy of Francesca Rochberg, The Heavenly Writing: Divination, Horoscopy, and Astronomy in Mesopotamian Culture, see pages 80-86. (You can ask your local public library to get this book for you via Inter-Library Loan.) The Babylonians saw dreams as omens, and had spells for dis-spelling the negative ones. The sun as both luminary and god (Shamash or Samas) was supposed to enlighten dreamers and dream interpreters as to what a dream portended.)
Possibly for this reason, the sun joys in the 9th house, in traditional western astrology. Apollo was the early god of prophecy in ancient Greece, and he was later assimilated to the sun (previously Phoebos, Helios.)