The Sun was actually the Son in the Book of Malachi 4:2

Malachi 4:2 (KJV)

2 But unto you that fear my name shall the SUN of righteousness arise with healing in his wings; and ye shall go forth, and grow up as calves of the stall.

Hebrews 1:3 (NIV)

3 The SON is the radiance of God’s glory and the exact representation of his being, sustaining all things by his powerful word. After he had provided purification for sins, he sat down at the right hand of the Majesty in heaven.

Since Jesus as the SON is the RADIANCE of God’s glory, He can rightly be also called the SUN of Righteousness. So what Malachi was talking about was actually JESUS!!