In Jyotisham, Sun represents “Soul” and the exact word for soul is “sol” which in roman means Sun God. And, The sanskrit word for Sun is “Surya” which means the “Prana brought in action” which is the absolute meaning through the vedic varnamala. Now, the Surya is the prana travelling through the various lokas and it takes up body to experience the plane of existence. This pranic energy carries the past experiences of many lives on various planes of existence and an impression is carried to the next consecutive birth in the form of “sanskaar” which is the behavior and personality put together formed through the karma performed in the previous life, which reflects in this current life as Prarabdha (the challenging experiences) and Sanchit (the pleasure based experiences). The results of which are wholly dependent upon the Kriyaman karma performed in the presented situation in the current life matrix. The functioning of the rest of the gruhas depend upon the placement of Surya.
E.g. if the Sun is carrying the imprint of universal knowledge from the past life then this will enhance the functioning of mercury in this life as well.
So, Sun is the memory chip carrying all impressions end to end.