Sun in ninth house is in the house of his friend Jupiter. Sun does well in the ninth house provided there are no major afflictions. Sun is radiant, illuminating and elevates the soul to the higher conscious. Ninth house is the house of spiritual divination, higher knowledge, mysticism and long distance travels. It is a great combination to have Sun in the ninth house if the goal is to achieve spiritual progress or for a travelling wanderer set out to unravel the mysteries of life and search for truth. 

      According to B. V. Raman, an afflicted Sun in the ninth house may turn a native to change his religion, have hostile feelings towards his elders, father, gurus and place where he grew up. But if Sun is not afflicted then the native would be a dutiful son and would have high regards for his heritage. If Sun combines with Moon then there could be eye problems according to B. V. Raman. With Venus could give sickness. What has been observed is native is bereft of patriarchal inheritance. Sun is hot and fiery and can destroy all the matters related to the concerned house both good and bad. Ninth house is the house of fortune and good luck. So chances of a difficult life may increase especially if Sun is in a fiery sign along with malefics. Also native may have to travel a lot due to various circumstances. Sun is the significator of soul and ninth house is the house of religion and spirituality. There is no better place then the ninth house for Sun which allows soul to connect with higher self via means of religion and spirituality. There are chances of ego problems with siblings as Sun aspects the third house from his placement in the ninth house. 

     Sun in ninth house makes for a travelling wanderer, one who takes a likening to mysticism, one who may despise his/her heritage and religious pratices along with disrespecting his forefathers and teachers/gurus won't be liked by one and all. As long as the native stays away from bashing and self loathing of heritage any road he takes to self realisation is more then welcome. 

     Sun is good in the ninth house as long as there are no malefics associated with it. If there is a bad placement of Sun in ninth house and if the native has to wander aimlessly, often bashes his heritage and gets into arguments with father and gurus then he must try to go into abode of Lord Vishnu especially his avatar Lord Ram. Ram is the most ideal God for those with Sun in the ninth house. 

References:

Raman, Bangalore Venkata. How to Judge a Horoscope. Delhi: Motilal Banarsidass, 2014. Print.